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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Tiny House
Insulation That
Fits Thin Walls

What fits in 2×3, 2×4 and 2×6 walls, trailer floors and loft roofs, with the code and certification numbers, condensation math, weight and cost, from the people who make ArmorFoam.
Tiny House Quotes

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Tell us what you're building (on wheels or on a foundation), the size, and where it will live. We'll connect you with an ArmorThane-certified spray foam applicator who will quote foam type, thickness and R-value in writing, surface by surface.

  • Tiny houses on wheels and on foundations
  • Walls, loft roof and trailer floor in one visit
  • Foam type, thickness and R-value in writing
  • Builders: ask about ArmorFoam and spray rigs
Rather talk now? Call (417) 831-5090
Step 1 of 3
400 sq ft
The code’s tiny house limit
IRC Appendix Q / AQ, lofts excluded
102 in.
Max road width: each inch of wall costs two
23 CFR 658.15
R-11.8
What an R-13 2x4 wall really delivers
Our whole-wall math, 25% framing
≈$330/yr
To heat a 24-ft tiny house in Chicago
Our model, heat pump, 2x4 R-13 walls

Tiny house insulation is ordinary insulation with three extra problems: the walls are thin, the house may ride down a highway, and two people breathing, cooking and showering in 200 square feet make a lot of water. Get those right and a tiny house is cheap to heat. Get them wrong and you get a cold floor, fogged windows and damp insulation.

Quick answer

Closed-cell spray foam fits the most R-value into thin walls, but it isn’t the only good answer. In a 2x4 wall, closed-cell is R-22.8 as labeled; mineral wool is R-15 and fiberglass R-13. Studs cut all of them, and an inch of exterior foam over batts beats full-cavity foam on whole-wall R-value. Foam the trailer floor or secure batts so they can’t fall out, give the loft roof the deepest rafters you can, ventilate on purpose, and match the rules to your build: the IRC and energy code on a foundation, a certifier’s standard on wheels. Run the wall planner or price your shell.

Most articles on this topic are a list of materials and a sales pitch for one of them. That skips the questions tiny house builders actually argue about on forums: what fits in a 2x4 once the studs are counted, how much width you lose, whether foam is too heavy for the trailer, if poly is needed, and what the heating bill really is.

We make ArmorFoam spray foam in Springfield, Missouri, and have been supporting applicators for 35 years. So here’s the version we’d give a builder: code and certification numbers first, the math shown, and straight talk about where foam is worth it and where a roll of mineral wool and a good air seal will do.

What’s in this guide
  1. 1Best insulation for a tiny house, compared
  2. 2On wheels vs. on a foundation: which rules apply
  3. 3What fits in 2x3, 2x4 and 2x6 walls (planner)
  4. 4Roof and loft insulation
  5. 5Insulating a tiny house floor on a trailer
  6. 6Road vibration, weight and the trailer
  7. 7What it costs and weighs (estimator)
  8. 8Condensation, vapor retarders and ventilation (check)
  9. 9Heat loss and heating cost (calculator)
  10. 10Spray foam in a tiny house: pros and cons
  11. 11How to insulate a tiny house, step by step
  12. 12Common mistakes
  13. 13Tiny house insulation FAQ
Materials

What is the best insulation for a tiny house?

The best insulation for a tiny house is the one that gets the most R-value into shallow framing while controlling air and moisture. Closed-cell spray foam does all three in one layer. Mineral wool, fiberglass and sheep’s wool batts cost less and work well when you air-seal carefully and add the right vapor retarder. Exterior rigid foam is the most underused upgrade.

MaterialR-value2x4 wall: label → whole-wallAir and vaporWeight (lb/ft³)DIY?Cost basisWatch out for
Closed-cell spray foamR-6.5/in. aged (ArmorFoam)R-22.8 → R-15.2Air barrier at 1 in.; Class II vapor retarder (0.83 perm at 1 in.)1.9Kits to 2 in.; full depth is a pro job$1.00–$2.12/bf installed (2026)Thermal barrier over it; hard to rewire later
Open-cell spray foamR-13.6 at 3½ in. (ArmorFoam 0.5)R-13.6 → R-12.1Seals air; vapor-open0.5Pro$0.44–$0.73/bf installed (2026)Needs a vapor retarder in cold zones; job minimums
Mineral wool battsR-15 at 3½ in.; R-23 at 5½ in. (ROCKWOOL)R-15 → R-12.7Air-permeable; 42 perm at 3½ in.1.8+Easy$1.00–$2.50/sq ft, materialNeeds a separate air and vapor plan; dusty cuts
Fiberglass battsR-13 at 3½ in.; R-21 at 5½ in. (high density)R-13 → R-11.8Air-permeable; kraft facing is Class IINot verifiedEasy$0.30–$1.30/sq ft, materialGaps, compression, sagging in floors and ceilings
Sheep’s wool battsR-14 at 3½ in. (Havelock PRO)R-14 → R-12.3Air-permeable≈1.5 (our estimate)Easy$2.56/sq ft (Sept. 2026 list)Price; maker’s health claims not verified by us
XPS board, cut and sealedR-5/in. (DuPont Styrofoam)R-17.5 → R-13.6Air barrier only with sealed edgesNot verifiedTedious$0.25–$0.70/bf, materialEvery edge needs canned foam or caulk
Polyiso board, foil-facedR-5.0–5.6/in.; about R-4.5 on a cold dayR-19.6 → R-14.3Foil is close to vapor-closed; seal edgesNot verifiedTediousVaries by boardCold-weather R-value drop
Bubble foil (radiant)Needs an air space to work (DOE)Not a cavity insulationVapor-closed sheetLightEasy$0.30–$2.00/sq ft installedLittle help in cold climates
R-values: ArmorThane (ASTM C518), ROCKWOOL Comfortbatt data sheet, Havelock Wool, DuPont and the Colorado Energy R-value table. Polyiso cold-weather drop: GreenBuildingAdvisor. Costs: HomeGuide (Dec. 2025) for materials and reflective, our spray foam insulation cost guide for installed foam. Whole-wall values are our parallel-path math: 25% framing, ½ in. sheathing, siding and drywall.

Closed-cell spray foam

The most R-value per inch you can spray into a cavity. ArmorFoam closed-cell tests at R-6.5 per inch aged, stops air at 1 in. (ASTM E2178) and measures 0.83 perm there, a Class II vapor retarder. At 1.9 pounds per cubic foot it bonds to studs, sheathing and trailer steel, so nothing sags. Tiny Home Builders uses it in most of its houses and hires the spraying out, which matches our view: full-depth closed-cell is a rig job. The catch is a thermal barrier over it and the fact that wiring behind it is effectively permanent. Our closed-cell spray foam guide covers the chemistry.

Open-cell spray foam

Cheaper per board foot and quieter, but only R-3.9 per inch (ArmorFoam 0.5), so a 2x4 tops out near R-13.6, about what fiberglass gets. It’s vapor-open, which means a warm-side vapor retarder in cold climates. We’d use it in a foundation tiny house in zones 1–4 with 2x6 walls, not in a thin THOW wall. The open-cell spray foam guide goes deeper.

Mineral wool, fiberglass and sheep’s wool batts

All three are air-permeable, so the air barrier has to come from somewhere else: taped sheathing, an airtight interior finish and sealed penetrations. Mineral wool rates R-15 in a 2x4 and has flame-spread and smoke-developed indexes of 0 (ROCKWOOL). Fiberglass is the cheapest per square foot. Havelock’s wool batt rates R-14 at 3½ in. and lists at $2.56 per sq ft, above HomeGuide’s $1.00–$2.50 range for mineral wool. One builder’s Maine log shows the batt route: ROCKWOOL R-15 in 2x4 walls, R-23 in a 2x6 ceiling, canned foam at every gap, and poly on the warm side.

Rigid foam, cut and cobbled or outside the studs

Boards cut to fit between studs work (Tiny Home Builders cuts XPS about an inch small and fills the gap with canned foam), but it’s slow, and every edge has to be sealed or it’s just insulation, not an air barrier. The better use of foam board is outside the sheathing as continuous insulation: it covers the studs, which carry more than 40% of the heat loss in a batt-filled 2x4 wall by our math. DOE puts it plainly: rigid board “can block thermal short circuits when installed continuously.”

Reflective bubble foil

Several sellers pitch foil as a thin substitute for insulation. DOE says a radiant barrier only works when the reflective face looks at an air space, works best in hot climates (5–10% cooling savings in warm, sunny ones) and doesn’t slow conduction like real insulation. In a cold climate, DOE says more insulation is usually the better buy. Foil under a roof deck in Texas, alongside real insulation, can help. As the only insulation in a Minnesota wall, it won’t.

What about SIPs?Structural insulated panels give continuous foam with few studs, and DOE credits SIP homes with 12–14% energy savings over conventional framing. In a tiny house the trade-off is plumbing: Tiny Home Builders notes pipes can’t run through SIPs, and chases eat interior width.
Code and certification

Tiny house on wheels vs. on a foundation: which insulation rules apply?

On a permanent foundation, a tiny house is a house. The IRC’s tiny house appendix relaxes ceiling heights, lofts and stairs for dwellings of 400 sq ft or less, but it says tiny houses “shall comply with this code except as otherwise stated,” and it says nothing about insulation. So the full energy code applies. On wheels, the house usually follows a certification standard instead.

On a foundation: IRC appendix plus the energy code

The tiny house appendix was Appendix Q in the 2018 IRC, AQ in 2021, and Appendix BB in codes based on the 2024 edition, such as California’s 2025 residential code. It defines a tiny house as a dwelling of 400 sq ft or less excluding lofts, allows 6 ft 8 in. ceilings in habitable space, and sets loft minimums (35 sq ft, 5 ft in any direction). Some states adopt it in the body of their code; Kentucky’s version applies to tiny houses “set on a permanent foundation.” Insulation follows the IECC table for your climate zone, and any foam needs the IRC thermal barrier.

On wheels: certification standards

Tiny houses on wheels (THOWs) are usually built to a recreational vehicle or tiny-house standard and inspected by a third party. NOAH RDI inspects to its own standard plus NFPA 1192, ANSI A119.5 and the NEC. It’s also blunt that ANSI A119.5 was written for recreational use and “may be inadequate for long-term residential use” on thermal performance, which is why its dwelling standard sets its own insulation minimums. Your lender, insurer or tiny house community may require one of these certifications, so pick it before you frame.

RulebookWallsFloorRoof / ceilingWindows
NOAH+ (THOW quick reference)R-13R-13R-19Double pane
NOAH Dwelling, warm zoneR-13R-13R-19U-0.40 recommended
NOAH Dwelling, moderate zoneR-13R-19R-30U-0.35 recommended
NOAH Dwelling, cold zoneR-15R-19R-30U-0.32 (U-0.30 severe cold)
2021 IECC, zones 1–2R-13 or 0+10ciR-13R-30 (zone 1), R-49 (2)Per IECC table
2021 IECC, zone 3R-20, 13+5ci or 0+15ciR-19R-49Per IECC table
2021 IECC, zones 4–5R-30, 20+5ci, 13+10ci or 0+20ciR-19 (4), R-30 (5, Marine 4)R-60Per IECC table
2021 IECC, zones 6–8Same as zones 4–5R-30 (6), R-38 (7–8; IRC R-30)R-60Per IECC table
NOAH RDI standards (quick reference and Dwelling Standard chapter 13); single-pane glass is prohibited in the Dwelling Standard. IECC values from the DOE/PNNL summary of 2021 IECC Table R402.1.3. “13+5ci” means R-13 in the cavity plus R-5 continuous insulation. Many counties still use older IECC editions with lower numbers; ask which one applies.

Look at the gap. A foundation tiny house in zone 5 is asked for R-60 overhead and R-30-class walls, the same as a 3,000 sq ft house. Nobody fits R-60 into 2x6 rafters. The IECC’s R-30 allowance for ceilings without attics is capped at 500 sq ft or 20% of the ceiling area, whichever is less, so in a tiny house it covers only a small patch. In practice, foundation tiny houses get there with foam above the roof deck, deeper rafters, or a whole-house trade-off calculation your building department accepts.

If your house will moveA THOW can be sold and towed to a colder state; Tiny Home Builders makes the same point about buying used. Build to the coldest zone you might plausibly live in, and pick a vapor strategy that works in both the North and the South (see vapor retarders).
Interactive tool 1 of 4

How much R-value fits in tiny house walls?

In a 2x4 wall: R-13 to R-15 with batts, R-13.6 with open-cell and R-22.8 with closed-cell, as labeled. The studs take a big bite. At 25% framing our math puts an R-13 wall at about R-11.8 whole-wall and a closed-cell wall at R-15.2. An inch of exterior polyiso over R-13 batts lands near R-18, better than either, and costs 2 in. of interior width.

Assembly planner

What R-value, thickness and interior width will this assembly give?

Pick the surface, framing and fill. The planner works out label and whole-assembly R-value, thickness, width inside a 102 in. shell, and checks it against the IECC or the NOAH standard, the vapor rules and the thermal-barrier rule.

Walls: over the sheathing. Roofs: above the deck. Floors: under the joists.
Our default; measure yours
R-13.0
Label R (cavity + continuous)
R-11.8
Whole-assembly R
5.25 in.
Wall thickness, siding to finish
91.5 in.
Interior width at 102 in. outside (7′ 7½″)

Label R is what the code tables compare: cavity R-13.0. Whole-assembly R adds air films, sheathing, finish, siding and the framing at 25%.

Works, with changesWall · fiberglass batts · 3½ in. framing
Target

Below NOAH Dwelling, cold zone

  • NOAH Dwelling, cold zone minimum for the wall: R-15 (NOAH RDI). Your wall: R-13.0.
  • Mineral wool (R-15), closed-cell or flash-and-batt in a 2x4 gets there; so does an inch of exterior foam.
Moisture

Vapor control looks right

  • Zone 5: the model code wants a Class I or II vapor retarder on the warm side (poly, kraft facing or vapor-retarder paint). On a house that could move to zones 1–4, where interior poly isn’t permitted, choose Class II.
  • Batts and open-cell are air-permeable: an airtight finish and sealed penetrations do the air-barrier job.
Fire

No foam, no barrier rule

  • Kraft or foil facings must be covered or in substantial contact with the finish (flame spread ≤25, smoke ≤450, IRC R302.10.1).
Fit

Space, framing and install

  • Interior width 91.5 in. (7′ 7½″), the same as a 2x4 wall with drywall and no exterior foam. Every inch of wall costs two inches of room at the 102 in. legal width (23 CFR 658.15).
  • Studs and plates carry 43% of the heat loss at 25% framing (our assumption), so the label R-13.0 works like R-11.8.

Steady-state parallel-path math with handbook layer values. Educational summary of model code and the NOAH RDI standard; your building official or certifier decides.

How we calculated this: parallel-path U = framing share ÷ R(through the stud) + (1 − framing share) ÷ R(through the cavity), with handbook layer values (inside film 0.68, outside 0.17, ½ in. sheathing 0.63, siding 0.61, softwood R-1.25 per inch). Batts are prorated per inch outside their rated thickness. Interior width = 102 in. − 2 × wall thickness. Estimates only; your building official or certifier decides.

What each wall gets you

WallLabel RWhole-wall RInterior width, 102 in. shell
2x3, fiberglass (no stock batt; prorated)R-9.3R-9.393½ in.
2x3, closed-cellR-16.3R-11.993½ in.
2x4, fiberglassR-13R-11.891½ in.
2x4, open-cellR-13.6R-12.191½ in.
2x4, mineral woolR-15R-12.791½ in.
2x4, 1½ in. closed-cell + fiberglassR-17.2R-13.591½ in.
2x4, closed-cellR-22.8R-15.291½ in.
2x4 fiberglass + 1 in. polyiso outsideR-13 + 5.6ciR-18.089½ in.
2x4 closed-cell + 1 in. polyiso outsideR-22.8 + 5.6ciR-22.689½ in.
2x6, fiberglassR-21R-17.187½ in.
2x6, closed-cellR-35.8R-21.787½ in.
Our calculation: 25% framing, ½ in. sheathing, ¾ in. siding and trim, ½ in. drywall. Polyiso at its rated R-5.6 per inch; on a cold day it may deliver closer to R-4.5 (GreenBuildingAdvisor).

The width and height squeeze

Federal rules set trailer width at 102 in. (23 CFR 658.15; wider loads need special permits), and most states cap height between 13 ft 6 in. and 14 ft (FHWA). The trailer deck eats 24–27 in. of that height on Tiny Home Builders’ trailers. So every layer of insulation competes with living space: an inch of exterior foam on both long walls costs 2 in. of width, and an extra inch of roof or floor costs headroom in the loft.

91½ in. inside (2x4) 93½ in. with 2x387½ in. with 2x6 loft 13′ 6″–14′ typical state height limit 24–27 in. trailer deck 102 in. (8′ 6″) legal width Walls: siding, sheathing,studs, finish ≈ 5¼ in. each Floor insulation betweenthe trailer and subfloor
End view, roughly to scale. Width limit: 23 CFR 658.15. Height: FHWA says most states set 13 ft 6 in. to 14 ft. Deck height: Tiny Home Builders’ trailer specs. Interior widths are our math with ¾ in. siding, ½ in. sheathing and ½ in. drywall.

Why exterior foam beats a fatter cavity

In a batt-filled 2x4 wall at 25% framing, the studs and plates carry about 43% of the heat loss by our math, because wood is only R-1.25 per inch. Filling the cavity with closed-cell raises the label from R-13 to R-22.8 but the whole wall only from R-11.8 to R-15.2, since the studs don’t change. An inch of polyiso over the sheathing covers the studs too and gets R-18.0 with plain batts. Go 2x6 instead and you get R-17.1 while giving up 4 in. of width. On a THOW, 2x4 plus exterior foam is usually the smarter trade; ArmorThane’s own guide calls flash-and-batt “badly underused” for the same reason.

2x3 walls

Framing with 2x3s to save weight and width? You gain 2 in. of room but there’s no stock 2½ in. batt, and even closed-cell only gets R-16.3 as labeled (R-11.9 whole-wall). If you frame 2x3, plan on exterior foam or accept a colder wall.

Applicator in a white protective suit and respirator spraying foam insulation between wood wall studs
Spray foam fills the cavity and seals it. The studs between the bays still conduct heat.
Overhead

Tiny house roof and loft insulation

A tiny house roof is a cathedral ceiling, usually over a sleeping loft, so it’s either vented (batts with a 1 in. air channel under the deck) or unvented (foam against the deck). In 2x6 rafters that means about R-16.7 with vented fiberglass, R-26 with 2 in. of closed-cell plus fiberglass, or R-35.8 with all closed-cell. Only the last meets a R-30 roof minimum in 2x6s.

Vented roofs

The IRC wants at least 1 in. between the insulation and the roof sheathing (R806.3), open from eave to ridge in every bay. In a 2x6 rafter that leaves 4½ in. for insulation. It’s cheap and forgiving, and it’s where most batt-built tiny houses fall short of an R-30 roof. Skylights and a ridge that stops at a gable wall make continuous venting hard, so plan the roof shape around it.

Unvented roofs

IRC R806.5 allows unvented rafter assemblies when air-impermeable insulation is in direct contact with the deck, with no Class I vapor retarder on the interior. All closed-cell qualifies. Flash-and-batt qualifies only when the foam meets the table for your zone: R-5 in zones 1–3, R-10 in 4C, R-15 in 4A/4B, R-20 in zone 5, R-25 in 6, R-30 in 7 and R-35 in 8. Two inches of closed-cell (R-13) covers zones 1–3 and Marine 4 and nothing colder. Open-cell against the deck needs a vapor-retarder coating in zones 5–8. Our cathedral ceiling insulation guide has the full rules.

Rebuilt RV roof with the decking removed, showing closed-cell spray foam filling the bays between wood roof framing
Closed-cell foam in the roof framing of an RV rebuild. A tiny house loft roof is the same shallow-cavity problem.
RaftersVented fiberglassVented mineral woolOpen-cell*2 in. closed-cell + batt*All closed-cell*
2x4 (3½ in.)R-9.3R-10.7R-13.6R-18.6R-22.8
2x6 (5½ in.)R-16.7R-19.3R-21.4R-26.0R-35.8
2x8 (7¼ in.)R-23.2R-26.8R-28.2R-32.5R-47.1
* Unvented, foam against the deck. Label R-values, our calculation. Vented bays lose 1 in. to the air channel; batts are prorated per inch. Green = meets the R-30 roof minimum in NOAH’s moderate and cold zones. None of these reaches the 2021 IECC’s R-49 (zones 2–3) or R-60 (zones 4–8) without foam above the deck.

Heat rises, but in a tiny house the roof isn’t the biggest loss. The walls are: there’s roughly three times as much wall as roof in a 24-ft THOW. In our Chicago model the roof is about 12% of the heat loss and the walls about 45%. What the roof does decide is loft comfort. A loft bed sits a couple of feet under the roof deck, so the roof sets how the loft feels in January and in July. That’s a reason to favor the unvented closed-cell roof even where the heating math is modest.

Down below

How to insulate a tiny house floor on a trailer

Fill the floor framing with rigid foam, closed-cell spray foam or mineral wool over a metal pan or flashing, secure it so road wind can’t pull it out, and get it inspected before the subfloor goes down. NOAH RDI’s FAQ says floor insulation “must be secured so it doesn’t blow out when transporting,” and its standard wants floors “secured against vibration/sagging.”

Why the floor matters more than you’d think

Under a THOW there’s moving outdoor air, road spray and a steel frame. Leave the floor uninsulated and in our Chicago model it becomes the largest single heat loss, about 45% of the total, and the heating bill climbs roughly 60%. A properly filled floor drops to about 11%. A cold floor also makes a small space feel colder than the thermostat says.

What to put there

  • Rigid foam (XPS or foil-faced polyiso). Cut to fit between the floor framing, edges sealed. It doesn’t mind road spray, doesn’t sag, and 3½ in. of XPS is R-17.5.
  • Closed-cell spray foam. Sprayed onto the pan or flashing between the framing, it bonds to steel and wood, seals every gap around the trailer members and is R-22.8 at 3½ in. It also keeps any water that gets past the pan out of the floor.
  • Mineral wool or wool batts. Workable if they’re fully supported by the pan and can’t shift. We’d still put foam directly against the metal: batts on cold, vapor-closed steel give indoor moisture a surface to condense on, the same physics we cover in our van insulation guide.

Thermal bridges and the steel frame

Steel conducts heat far better than wood, and NOAH’s FAQ calls out metal trailers and steel framing for thermal bridging. Where the design allows, keep a layer of foam between the steel and the subfloor, or run continuous rigid foam under the floor framing. Seal where plumbing and wiring pass through the pan, too; those holes are where mice and cold air get in. And protect the trailer itself: road salt attacks the frame from below, which our undercoating guide covers.

Skirting

Once the house is parked for a season, skirting around the trailer stops wind from scrubbing the underside and helps protect pipes. It isn’t a substitute for floor insulation, and it has to leave room for any combustion vents or access NOAH’s standard requires. On a permanent foundation, treat the floor like any crawl space: our crawl space insulation guide covers vented versus sealed.

On the move

Road vibration, weight and the trailer

Insulation weight rarely decides anything in a tiny house. Closed-cell foam is 1.9 lb per cubic foot and mineral wool more than 1.8, so they weigh about the same for the same fill; open-cell is 0.5. By our math, closed-cell in every wall, the roof and the floor of a 24-ft THOW is about 540 lb, under 4% of a 14,000-lb GVW trailer. Vibration is the bigger question.

Stays put

Bonded or fastened

Spray foam adheres to the framing and sheathing; our closed-cell guide lists vans, RVs and trailers as a strong fit because it’s “self-adhering” with “no settling under vibration.” Rigid board glued and edge-sealed stays put too. Batts in walls, behind a fastened finish, are fine.

Can move

Friction-fit and loose-fill

Batts held only by friction can sag in floors and ceilings, which is why NOAH requires floors secured against vibration and blow-out. Skip loose-fill in a house that travels: DOE notes loose-fill’s settled density increases over time.

Don’t count on it

Foam isn’t structure

Closed-cell stiffens walls in racking tests, but no U.S. model code lets you count it as a shear-resisting element. Anchor the house to the trailer and sheathe it as if the foam weren’t there.

Budget it

Where the weight goes

Tiny Home Builders rates its trailers at 10,000 lb GVW (12–20 ft), 14,000 (24 ft) and 21,000 (longer). Insulation is a few percent of that. Siding, finishes, cabinets, water and appliances are where weight budgets get blown.

Interactive tool 2 of 4

How much does tiny house insulation cost and weigh?

HomeGuide puts tiny house insulation at $500–$3,000, or $0.80–$4.50 per sq ft (Jan. 2026). For a 24-ft THOW our math gives about $360–$1,320 in DIY materials for fiberglass walls and roof with a foam-board floor, and about $3,900–$8,300 to have closed-cell sprayed everywhere. Most builds land between, with foam where it matters most.

Shell estimator

Materials, cost and weight for walls, roof and floor

Enter the shell and pick a plan for each surface. The estimator deducts framing and openings, prices batts, boards, DIY kits and professional foam at published 2025–2026 rates, and adds up the weight it can verify.

Floor to eave
Batts and boards installed by
1,050 sq ft
852 sq ft of cavity after framing
$361–$1,319
Estimated cost
—
No spray foam in this plan
—
Insulation weight (fiberglass and boards not included)

Shell: 24 x 8.5 ft, 10 ft walls, gable roof at 6/12 (rise 2.1 ft). Walls 618 sq ft net of 50 sq ft of windows and doors, roof 228, floor 204. Cavity area deducts framing: 25% of walls, 10% of roof and floor (our assumption).

SurfaceCavity areaPlanLabel RCostWeight
Walls464 sq ft3½ in. fiberglass battsR-13.0$139–$603n/a
Roof205 sq ft4½ in. fiberglass batts, vented (1 in. air gap)R-16.7$62–$267n/a
Floor184 sq ft3½ in. XPS, cut and sealedR-17.5$161–$450n/a
Cost

Estimated total: $361–$1,319

  • Batts and boards, materials: $361–$1,319 (HomeGuide material prices, Dec. 2025; Havelock list price, Sept. 2026). Canned foam for board edges not included.
  • HomeGuide’s tiny house range is $500–$3,000 for insulation, or $0.80–$4.50 per sq ft (Jan. 2026).
Weight

Mostly unweighed materials

  • Fiberglass and foam boards aren’t in the total: we couldn’t confirm their densities from a manufacturer.
  • Densities: closed-cell 1.9 lb/ft³ (ArmorFoam), mineral wool 1.8+ (ROCKWOOL), sheep’s wool ≈1.5 (our estimate), open-cell 0.5. For the same fill, closed-cell and mineral wool weigh about the same.
Notes

Before you order

  • Roof: batts need a vented roof, so 5½ in. rafters hold 4½ in. of insulation.

How we calculated this: gable roof rise = width ÷ 2 × pitch ÷ 12; walls = 2 × (L + W) × H plus gable ends, minus openings; roof = L × W × √(1 + (pitch ÷ 12)²). Cavity area deducts 25% framing in walls and 10% in roof and floor. Professional foam: cavity area × depth × 1.15 at $1.00–$2.12 (closed-cell) or $0.44–$0.73 (open-cell) per board foot, with a $1,000–$2,000 minimum. Kits: 2 in. × area × 1.25, cheapest combination of five 2026 kits. Batt and board prices are HomeGuide material ranges (Dec. 2025) and Havelock’s list price.

Seven ways to insulate the same 24-ft tiny house

Plan (2x4 walls, 2x6 rafters, 3½ in. floor)Estimated costWalls / roof / floor, label RWeight we can verify
DIY fiberglass walls and vented roof, XPS floor$361–$1,319R-13 / R-16.7 / R-17.5n/a
Same, batts and boards hired out$532–$2,768R-13 / R-16.7 / R-17.5n/a
DIY mineral wool walls and roof, XPS floor$829–$2,122R-15 / R-19.3 / R-17.5≈380 lb + floor boards
Pro open-cell walls and roof, DIY XPS floor$1,553–$2,760R-13.6 / R-21.4 / R-17.5≈115 lb + floor boards
DIY sheep’s wool walls and roof, XPS floor$2,134–$2,423R-14 / R-18 / R-17.5≈320 lb + floor boards
Pro flash (1½ in.) walls, pro closed-cell roof and floor$2,976–$6,617R-17.2 / R-35.8 / R-22.8≈390 lb + fiberglass
DIY 2 in. kits + fiberglass walls and roof, 2 in. kit floor$3,157–$3,825R-18.6 / R-26.0 / R-13≈270 lb + fiberglass
Pro closed-cell everywhere$3,903–$8,275R-22.8 / R-35.8 / R-22.8≈540 lb
Our calculation for a 24 x 8.5 ft shell with 10 ft walls, a 6/12 gable and 50 sq ft of windows and doors. Excludes canned foam, tape, vapor retarders, drywall and protective gear. Kits exceed their 2 in. rating if you try to fill deeper in one application.

DIY kits or a pro?

Two-part kits cost $1.22–$1.95 per board foot for material alone, close to a professional’s installed closed-cell price, and Froth-Pak’s evaluation report (ESR-3228) says to spray to a maximum of 2 in. So kits suit a flash layer and small jobs, not a full-depth house. Our DIY spray foam kits guide covers the respirator, ventilation and warm-up rules. A whole tiny house shell is only a few thousand board feet, and HomeGuide notes spray foam companies may charge minimums of $1,500–$2,000 or more, so ask an applicator to price it alongside other work on the same trip.

Interactive tool 3 of 4

Condensation, vapor retarders and ventilation in a tiny house

Two people living in 200-odd square feet release about 2.6 kg of water a day by our math: breathing, cooking and showering. In a house that small and tight, that moisture has nowhere to go but the windows and any cold surface indoor air can reach. Continuous ventilation, ducted bath and kitchen fans, the right vapor retarder and no unvented heaters fix it.

Where the water comes from

SourceWater releasedBasis
An adult at rest50 g per hour (1.2 kg a day, home 24 h)USDA Forest Products Lab (TenWolde and Pilon)
A cooked meal for fourAbout 240 g, food onlyUSDA FPL
A shower2.6 kg per hour of running shower; 110–230 g for five minutesIEA Annex 14 and Hite and Bray, via USDA FPL
Propane burner, 8,000 Btu/h for 20 minAbout 90 g of combustion waterOur stoichiometric math: ≈0.034 g per Btu
Unvented propane heater, 20,000 Btu/h for 8 hAbout 5.5 kgSame math; more than two people make all day
USDA FPL: TenWolde and Pilon, “The Effect of Indoor Humidity on Water Vapor Release in Homes” (2007).
Moisture and ventilation check

Will my tiny house run damp, and how much fresh air does it need?

A steady-state daily average: water released versus outdoor air coming in, the resulting indoor humidity, and the glass temperature on a cold night. Climate data: NOAA 1991–2020 normals.

Our assumption
For the volume
17 = IRC Equation 15-1 here
Our assumption for a tight build
2.6 kg/day
Water released (5.4 pints)
29%
Indoor humidity, average
34°F
Indoor dew point
57°F
Glass surface, cold night
People
1.40 kg
Cooking (food)
0.48 kg
Showers
0.69 kg

Chicago, IL: mean of the three coldest months 28.2°F at 70% RH outdoors (our assumption), 68°F inside, 2,244 cu ft. Daily averages from USDA FPL rates: 50 g/h per person at rest, 240 g per cooked meal (a meal for four, so conservative for two), 2.6 kg/h of shower time. Steady-state screening, not a hygrothermal model.

Humidity

On the dry side: 29% RH

  • Air exchange: 17 cfm of fan + 11 cfm of leakage at 0.30 ACH = 28 cfm. EPA says keep homes below 60% RH, ideally 30–50%.
  • To hold 45% RH at this moisture load you need about 12 cfm of total outdoor air.
  • IRC continuous minimum for 204 sq ft and 1 bedroom: 17.0 cfm by Equation 15-1, or 30 cfm from Table M1505.4.3(1). Bath fans: 50 cfm on demand or 20 continuous; kitchens 100 or 25.
Windows

Glass stays above the dew point

  • Inside glass surface on a 18.8°F night: 57°F with U-0.32 glass; room dew point 34°F. It stays dry. Frames and edges run colder than the glass center.
Notes

Fresh air and water sources

  • Heating 12 cfm of outdoor air without heat recovery costs about $39 a year here on a heat pump (COP 2.5, 17.3¢/kWh). An ERV or HRV recovers part of it.
  • Showers add 0.69 kg in bursts (2.6 kg/h, IEA data via USDA FPL). Run the bath fan during and 20 minutes after.

How we calculated this: saturation pressure by the Magnus formula (Alduchov–Eskridge); humidity ratio = 0.622 e ÷ (P − e); indoor humidity ratio = outdoor + daily water ÷ daily air mass (cfm × 1.699 m³/h × 1.2 kg/m³ × 24). Glass surface = indoor − (indoor − coldest-month mean low) × U × 0.68. Single-pane U-1.1 is our figure from handbook glass and air-film values. Screening math, not a hygrothermal model.

What the code asks for

  • Whole-house ventilation (IRC M1505.4.3): a continuous rate from Table M1505.4.3(1), 30 cfm for 0–1 bedrooms under 1,500 sq ft, or Equation 15-1: 0.01 cfm per sq ft plus 7.5 × (bedrooms + 1). For a 204 sq ft house with a sleeping loft that’s about 17 cfm.
  • Local exhaust (Table M1505.4.4): bathrooms 50 cfm on demand or 20 continuous; kitchens 100 on demand or 25 continuous. Duct both to the outdoors; NOAH’s standard says not into cavities or crawl spaces.
  • Heat: NOAH’s dwelling standard says unvented heaters shall not be the primary heat source and lists ERVs, HRVs, dehumidifiers and mini-split dry mode as moisture tools.

Vapor retarders: why poly is risky on wheels

Vapor retarders come in three classes: Class I (0.1 perm or less: poly sheeting, foil), Class II (0.1–1.0: kraft facing, vapor-retarder paint) and Class III (1–10: latex paint). The model code wants Class I or II on the warm side of framed walls in zones 5–8 and Marine 4, and it doesn’t permit Class I on the interior in zones 1–4 (2021 IBC 1404.3; the IRC’s R702.7 is the parallel residential section). A foundation house in Maine can use poly. A THOW built in Maine and sold to someone in Georgia now has poly where summer humidity drives inward. For a house that may move, a Class II layer is the safer middle: kraft-faced batts, vapor-retarder paint, or 1 in. or more of closed-cell foam, which is Class II on its own (ArmorFoam: 0.83 perm at 1 in.).

Keep the air barrier separate in your head from the vapor retarder. Batts need an airtight interior finish and sealed penetrations either way, because air leaks carry far more moisture into a wall than diffusion does.

Interactive tool 4 of 4

How warm will it stay? Tiny house heat loss and heating cost

Not much energy, whatever you choose. By our model a 24-ft THOW with R-13 2x4 walls, a vented 2x6 roof, a foam-board floor and good double-pane windows loses about 5,700 Btu/h on an average coldest-month night in Chicago and costs about $330 a year to heat with a heat pump. Upgrading the walls to closed-cell saves about $33 of that. Skipping floor insulation or using single-pane glass costs far more.

Heat loss and heating cost

How big a heater, and what will a winter cost?

Conduction through walls, roof, floor and glass plus air leakage, with NOAA 1991–2020 heating degree days and 2025 EIA prices. Change one thing at a time to see what actually moves the bill.

Our assumption; a blower door test tells you
Our assumption
Vented unit; our assumption
5,650 Btu/h
Heat loss, average cold night
1,656 W
The same in watts
$334/yr
Heat pump
$602/yr
Vented propane
Walls
45%
Air leakage
18%
Windows and doors
14%
Roof
12%
Floor
11%

Chicago, IL (zone 5A; verify your county): 5,974 heating degree days, coldest-month mean low 18.8°F. UA 114.8 Btu/h·°F for 618 sq ft of wall, 228 of roof, 204 of floor and 2,257 cu ft. Yearly heat 16.5 MMBtu: 1,930 kWh on a heat pump (COP 2.5), 4,826 kWh ($835) on electric resistance, or 225 gal of propane. No credit for sun, cooking or people, so real bills should come in lower. The load is for an average cold night, not a record low; size a heater with some margin.

Change one thingHeat-pump costCold-night load
Walls to 2x4 closed-cell−$33/yr−566 Btu/h
Walls to 2x4 fiberglass + 1 in. polyiso−$52/yr−881 Btu/h
Roof to 2x6 unvented closed-cell−$18/yr−312 Btu/h
Floor to 3½ in. closed-cell−$6/yr−94 Btu/h
Windows to U-0.30−$3/yr−49 Btu/h
Air leakage to 0.3 ACH−$24/yr−400 Btu/h
Single-pane glass instead+$113/yr+1,919 Btu/h

How we calculated this: UA = Σ(U × area) for walls, roof and floor (whole-assembly U from the planner’s method) + window U × area + 0.018 × air changes × volume; cold-night load = UA × (indoor − coldest-month mean low); yearly heat = UA × 24 × heating degree days (base 65°F). Electricity 17.30¢/kWh is EIA’s 2025 residential average; propane $2.674/gal is EIA’s last weekly residential price of the 2025–26 season. 3,412 Btu per kWh and 91,452 Btu per gallon (EIA).

City (zone)Cold-night loadHeat pumpElectric resistanceVented propane
Houston (2A)2,790 Btu/h$71/yr$177/yr48 gal, $128
Atlanta (3A)3,720 Btu/h$141/yr$354/yr95 gal, $255
Portland, OR (4C)3,650 Btu/h$229/yr$574/yr155 gal, $413
Springfield, MO (4A)5,030 Btu/h$239/yr$598/yr161 gal, $431
Denver (5B)5,700 Btu/h$328/yr$819/yr221 gal, $591
Chicago (5A)5,650 Btu/h$334/yr$835/yr225 gal, $602
Minneapolis–St. Paul (6A)6,800 Btu/h$414/yr$1,034/yr279 gal, $745
Duluth (7)7,530 Btu/h$510/yr$1,274/yr343 gal, $918
Our calculation for the default 24-ft house (R-13 2x4 walls, vented 2x6 fiberglass roof, 3½ in. XPS floor, 50 sq ft of U-0.32 windows, 0.5 air changes per hour). No credit for sun, cooking or occupants, so real bills should be lower.

What the numbers say

In a tiny house the case for premium insulation is comfort, moisture and durability, not the heating bill. Take Chicago on a heat pump: closed-cell walls instead of fiberglass save about $33 a year; the same walls with an inch of exterior polyiso save about $52; an unvented closed-cell roof, about $18. Drafts and glass move it more: going from 0.5 to 1.0 air changes an hour adds about $59, and single-pane windows add about $113. An uninsulated floor adds roughly $205.

Heating options

A ductless mini-split heat pump is what NOAH’s dwelling standard calls preferred, and it dehumidifies too. Electric resistance is simple but costs about 2½ times as much to run at a COP of 2.5. Off-grid, a direct-vent propane heater keeps combustion water outside. A 1,500-watt space heater delivers 5,118 Btu/h, a little short of our Chicago default’s average coldest-month night, and NOAH says portable devices shouldn’t be the sole primary heat source.

Straight talk

Spray foam in a tiny house: the honest pros and cons

Closed-cell spray foam is the best-performing insulation for a tiny house on wheels: most R-value per inch, an air barrier and a vapor retarder in one layer, and nothing to sag on the road. It isn’t automatically the best value. For a batt-framed house in a mild climate, careful air sealing plus exterior foam often gets you more per dollar.

Why foam

Where it earns its price

  • Thin walls and roofs: R-22.8 in a 2x4 and R-35.8 in 2x6 rafters, the only way to meet an R-30 roof in 2x6s.
  • Trailer floors: bonds to the pan and framing, seals around steel, and doesn’t care about road spray.
  • A house that moves: Class II at 1 in., which works in cold and humid climates alike.
  • Air sealing: the gaps around fenders, wheel wells and window bucks get filled, not taped.
  • Weight: 1.9 lb/ft³, about the same as mineral wool.
Why not

Where something else wins

  • Budget: a full pro job runs about $3,900–$8,300 on a 24-ft shell by our math, against a few hundred dollars of batts.
  • Studs: full-cavity foam still leaves the studs; exterior foam over batts gets more whole-wall R.
  • Changes later: our own closed-cell guide lists walls you plan to open up soon as a poor fit. Run conduit or finalize wiring first.
  • Sound: in the comparison on our noise page, closed-cell brings an interior wall to STC 37, fiberglass and open-cell to 39, and ROCKWOOL to 45. For a quiet sleeping loft wall, mineral wool is better (see spray foam and sound).
  • The finish: foam needs a thermal barrier, so you can’t leave it behind bare pine.

The thermal barrier problem in tiny houses

IRC R316.4 requires foam plastic to be separated from the interior by ½ in. gypsum wallboard, 23/32 in. wood structural panel, or a material that passes NFPA 275 (R303.4 in the 2024 IRC). A wood structural panel means plywood, OSB or a composite panel; pine tongue-and-groove and ¼ in. plywood aren’t on the list. So a foamed tiny house with a board-paneled interior needs drywall or 23/32 in. plywood behind the boards, or a tested assembly. On a foundation that’s the law. On wheels, ask your certifier; we’d build it the same way.

Odor and re-entry

Correctly mixed foam cures and stops smelling. CPSC recommends people stay out for at least 24 hours after professional spray foam, and most manufacturers say the same. In a house this small, ventilate hard for the first few days. Foam that still smells a week later was usually sprayed off-ratio, which is why the installer matters more than the brand. More in our spray foam R-value guide and on our spray foam insulation page.

Step by step

How to insulate a tiny house, step by step

Pick the rulebook, design the assemblies, get the sheathing and windows airtight, finish rough-in, then insulate floor, walls and roof in that order, with an inspection before anything gets covered. Ventilation and the thermal barrier are part of the insulation job, not afterthoughts.

  1. Choose the rulebook and the climate

    Foundation: your county’s IRC and IECC editions. Wheels: the third-party certifier your lender, insurer or community accepts, such as NOAH RDI. Design for the coldest zone the house might live in.

  2. Design each assembly

    Run the planner for walls, roof and floor. Decide vented or unvented roof, exterior foam or not, and your vapor strategy before you buy framing.

  3. Build the floor over the trailer

    Pan or flashing, foam against the metal, framing, insulation secured, then the subfloor. Book the insulation inspection before the plywood goes down; NOAH’s FAQ says floor insulation is what it sees covered too early.

  4. Seal the shell

    Tape sheathing seams, flash and seal window and door rough openings, and add any exterior foam before siding. Air sealing is what makes every insulation type perform.

  5. Rough-in first

    Wiring, plumbing and vents go in before insulation, especially before foam. Put boxes and runs where you won’t need to cut into a foamed wall later.

  6. Insulate walls and roof

    Batts cut to fit without compression, split around wiring, and kept tight to the sheathing. Foam in 1½–2 in. lifts by a certified crew, or a kit flash layer of 2 in. or less. Keep the vent channel open in vented roofs.

  7. Vapor retarder, ventilation, finish

    Add the vapor retarder class your zone calls for, install ducted bath and kitchen fans and continuous ventilation, then the thermal barrier over any foam and your finish.

Spraying yourself in cold weather? Kits and rigs both need warm chemical and substrate; read applying spray foam insulation in cold weather first. Converting a shed or a shipping container instead? Our shed insulation and shipping container insulation guides cover those shells.

Avoid these

Common tiny house insulation mistakes

  • Leaving the floor for last, or loose. Uninsulated, it’s the biggest heat loss; unsecured, it can blow out on the highway.
  • Batts against a cold metal pan. Put foam against the steel.
  • Poly on a house that may move south. Class II is the safer choice for a THOW.
  • Bare pine over spray foam. It isn’t a thermal barrier. Drywall or 23/32 in. plywood behind it, or a tested assembly.
  • Batts in an unvented roof. They need a vent channel or enough foam at the deck for your zone.
  • Counting only the label R-value. In a 2x4 wall the studs carry more than 40% of the heat loss with batts.
  • Bubble foil as the insulation. DOE says it needs an air space and does little in cold climates.
  • No planned ventilation. A tight tiny house with two people and no fan sits near 48% humidity in our Chicago example.
  • An unvented propane heater. About 5.5 kg of water a day at 20,000 Btu/h for 8 hours.
  • Single-pane windows. The inside glass runs near 31°F on a cold Chicago night; it will drip.
  • Full-depth kit foam. Kits are rated for 2 in.; thicker passes can overheat the core.
ArmorThane applicators

Spray foam for tiny houses from a certified applicator

If you’re building on a budget in a mild climate, batts, careful air sealing and a foam-board floor are a sound plan, and you don’t need us. If you want the most R-value in thin walls, a trailer floor that can’t sag or soak up road spray, or a roof that reaches R-30 in 2x6 rafters, an ArmorThane-certified applicator can spray ArmorFoam closed-cell to a stated thickness, or ArmorFoam 0.5 open-cell where it fits. Our closed-cell tests at R-6.5 per inch aged, passes as an air barrier at 1 in. and measures 0.83 perm there. Ask for foam type, thickness and R-value in writing, surface by surface.

Get a tiny house spray foam quote →Closed-cell spray foam guide
R-6.5 / in.

ArmorFoam closed-cell

Aged, ASTM C518. A 2x4 cavity is R-22.8; 2x6 rafters are R-35.8.

1.9 lb/ft³

Core density

ASTM D1622. About the same weight as mineral wool for the same fill.

≈5,000 bf

Per 55-gallon set

At ideal yield. A fully foamed 24-ft tiny house is well under one set.

For builders and contractors

Tiny house shells are small jobs. Line them up.

A fully foamed 24-ft shell is about 3,900 board feet with waste, well under the ≈5,000 a 55-gallon set yields. Partner with a tiny house builder who frames shells in batches and the jobs stack up, alongside crawl spaces, pole barns and polyurea work. We supply ArmorFoam, matched spray equipment and training at your location. Not a franchise: no franchise fee, no royalties. Startup packages start at $25,000.

Talk to us about a rig or startup packageStart a spray foam business

See the rigs: mobile spray foam rigs →

Straight answers

Tiny house insulation FAQ

What is the best insulation for a tiny house?

For most tiny houses, closed-cell spray foam puts the most R-value into thin walls: ArmorFoam is R-6.5 per inch aged, or R-22.8 in a 2x4, and it adds air and vapor control. On a budget, mineral wool batts (R-15 in a 2x4, per ROCKWOOL) or fiberglass (R-13) work if you air-seal carefully and use the right vapor retarder. In a 2x4 wall, an inch of exterior foam over batts beats full-cavity foam on whole-wall R-value, by our math.

Is spray foam good for a tiny house on wheels?

Closed-cell is. It bonds to the framing, can't slump in transit, shrugs off road spray under the floor, and is a Class II vapor retarder at 1 in. (0.83 perm for ArmorFoam), which suits a house that may move between climates. The trade-offs are cost, permanence (rewiring behind foam is hard) and the thermal barrier the code requires over foam in living space.

How much insulation does a tiny house need?

On a foundation, a tiny house has to meet your energy code like any other house. The 2021 IECC asks for R-13 to R-30 walls (with continuous-insulation options), R-30 to R-60 ceilings and R-13 to R-38 floors depending on climate zone (DOE/PNNL). Tiny houses on wheels usually follow a certifier's standard instead; NOAH's dwelling standard asks for R-13 to R-15 walls, R-13 to R-19 floors and R-19 to R-30 roofs by thermal zone.

What R-value can I get in 2x4 tiny house walls?

As labeled: about R-13 with fiberglass, R-15 with mineral wool, R-14 with Havelock wool and R-22.8 with 3½ in. of closed-cell foam. The studs pull that down. At 25% framing, our whole-wall math gives about R-11.8 for fiberglass and R-15.2 for closed-cell, and 1 in. of foil-faced polyiso outside a fiberglass wall gets about R-18, at the cost of 2 in. of interior width. The assembly planner runs your wall.

Do tiny houses need a vapor barrier?

Usually a vapor retarder, not necessarily poly. Model codes want a Class I or II retarder on the warm side in zones 5–8 and Marine 4, and don't permit Class I (poly sheeting) on the interior in zones 1–4 (2021 IBC 1404.3; IRC R702.7 is the parallel section). A tiny house that may move south is safer with a Class II layer: kraft facing, vapor-retarder paint, or 1 in. or more of closed-cell foam.

How do you insulate a tiny house floor on a trailer?

Fill the floor framing over a metal pan or flashing with rigid foam, closed-cell spray foam or mineral wool, and fasten it so it can't drop out on the road. NOAH's FAQ says floor insulation "must be secured so it doesn't blow out when transporting," and it should be inspected before the subfloor goes on. Foam also shrugs off road spray; break the steel frame's thermal bridge wherever the design allows.

Will insulation settle or fall out when I tow my tiny house?

Batts held only by friction can shift or sag in floors and ceilings, which is why NOAH's standard says floors must be "insulated and secured against vibration/sagging." Loose-fill is a poor pick for a moving house, since DOE notes its settled density rises over time. Spray foam bonds in place; batts behind a fastened finish or a secured pan stay put.

How much does it cost to insulate a tiny house?

HomeGuide puts insulation at $500–$3,000 for a tiny house, or $0.80–$4.50 per sq ft (Jan. 2026). By our math, a 24-ft tiny house on wheels has about 850 sq ft of insulated cavity; DIY fiberglass walls and roof plus a foam-board floor cost roughly $360–$1,320 in materials, while professionally sprayed closed-cell throughout runs about $3,900–$8,300 at 2026 rates. The estimator prices your build.

How much does tiny house insulation weigh?

Less than people fear. Closed-cell foam is about 1.9 lb per cubic foot and ROCKWOOL mineral wool more than 1.8, so for the same fill they weigh about the same; open-cell is 0.5. By our math, closed-cell in the walls, roof and floor of a 24-ft tiny house weighs roughly 540 lb, under 4% of a 14,000-lb GVW trailer.

Does spray foam need to be covered in a tiny house?

On a foundation, yes: IRC R316.4 requires a thermal barrier of ½ in. gypsum wallboard, 23/32 in. wood structural panel, or a material that passes NFPA 275 (R303.4 in the 2024 IRC). Pine tongue-and-groove and ¼ in. plywood don't qualify on their own. For a tiny house on wheels, ask your certifier and treat the IRC barrier as the safe default.

How do I stop condensation in my tiny house?

Control the moisture and keep air moving. Two people showering and cooking release about 2.6 kg (5.4 pints) of water a day by our math, so run bath and kitchen fans to the outdoors, provide continuous ventilation (the IRC formula is 0.01 cfm per sq ft plus 7.5 cfm per bedroom plus one), keep humidity at 30–50% (EPA), and don't heat with an unvented propane heater. Double-pane glass stays far warmer than single-pane.

Is reflective or bubble foil insulation good for a tiny house?

Not as your main insulation. DOE says a radiant barrier only works facing an air space, is more effective in hot climates, and doesn't slow conduction the way insulation does; in cool climates more insulation is usually the better buy. Foil can help under a hot roof in the South, alongside real cavity insulation.

Is sheep's wool good insulation for a tiny house?

It's a reasonable batt. Havelock's PRO batt is R-14 at 3½ in., fits 2x4 framing at 16 in. on center, and listed at $2.56 per sq ft in September 2026. Like fiberglass and mineral wool it's air-permeable, so it needs careful air sealing and the right vapor retarder for your climate zone. We haven't verified the maker's moisture and air-quality claims.

What is the best way to heat a tiny house?

A ductless mini-split heat pump is the system NOAH's dwelling standard calls preferred, and it can dehumidify too. By our math, a well-built 24-ft tiny house in Chicago loses about 5,700 Btu/h on an average night in the coldest month and costs around $330 a year to heat with a heat pump. Vented propane works off-grid, but NOAH says unvented heaters shall not be the primary heat source.

AT
ArmorThane Technical Team · Springfield, Missouri
Written from code text, tiny house certification standards, manufacturer data sheets and 35+ years of making spray foam and training applicators. Last updated September 26, 2026.

Methodology and sources

Code text is summarized from the IRC tiny house appendix (Q, AQ and BB as adopted in Kentucky, Virginia and California), the 2021 IRC as adopted in Texas, and the DOE/PNNL summary of the 2021 IECC; THOW minimums are from NOAH RDI’s published standards. Climate data: NOAA 1991–2020 normals; climate zones from the 2018 IRC county table, so verify your county. Energy prices: EIA. Wall, roof, floor, cost, weight, moisture and heat figures marked “our math” are steady-state screening calculations, not a substitute for your building official, certifier or product literature.

  1. UpCodes, tiny house definition (California Residential Code 2025, Appendix BB): up.codes/s/tiny-house
  2. UpCodes, tiny houses (Virginia Residential Code 2021, R336 and Appendix AQ): up.codes/s/tiny-houses
  3. UpCodes, Kentucky Residential Code 2018, R328 tiny houses: up.codes/s/tiny-houses-general
  4. DOE/PNNL Building America Solution Center, 2009–2021 IECC and IRC insulation requirements: basc.pnnl.gov/information/2009-2021-iecc-and-irc-minimum-insulation-re
  5. 2021 IRC chapter 3, R316.4 thermal barrier (Texas adoption, UpCodes): up.codes/viewer/texas/irc-2021/chapter/3/building-planning
  6. 2021 IRC chapter 2, wood structural panel definition (UpCodes): up.codes/viewer/texas/irc-2021/chapter/2/definitions
  7. 2021 IRC chapter 15, M1505 ventilation and exhaust rates (UpCodes): up.codes/viewer/texas/irc-2021/chapter/15/exhaust-systems
  8. 2024 IRC M1505.4, whole-house mechanical ventilation (UpCodes): up.codes/s/whole-house-mechanical-ventilation-system
  9. IRC R806.3, vent and insulation clearance (UpCodes): up.codes/s/vent-and-insulation-clearance
  10. Unvented attic and enclosed rafter assemblies (UpCodes): up.codes/s/unvented-attic-and-unvented-enclosed-rafter-assemblies
  11. IECC ceilings without attics (UpCodes): up.codes/s/ceilings-without-attics
  12. Vapor retarder class definitions (UpCodes): up.codes/s/vapor-retarder-class
  13. IBC 1404.3 vapor retarders (UpCodes): up.codes/s/vapor-retarders
  14. Flame spread and smoke-developed index for insulation (UpCodes): up.codes/s/flame-spread-index-and-smoke-developed-index-for-insulation
  15. 2018 IRC climate zones by county (UpCodes): up.codes/s/climate-zones
  16. NOAH RDI, NOAH standards quick reference: noahcertified.org/noah-standard/
  17. NOAH RDI, NOAH Dwelling Standard (THOW): noahcertified.org/noah-standard/dwelling/
  18. NOAH RDI, FAQ: noahcertified.org/faq/
  19. 23 CFR 658.15, vehicle width (LII): law.cornell.edu/cfr/text/23/658.15
  20. FHWA, federal size regulations for commercial motor vehicles: ops.fhwa.dot.gov/freight/publications/size_regs_final_rpt/index.htm
  21. Tiny Home Builders, tiny house trailers (specs): tinyhomebuilders.com/tiny-house-trailers
  22. Tiny Home Builders, tiny house insulation: tinyhomebuilders.com/learn/insulating-your-tiny-house
  23. TinyHome.io, tiny house insulation build log (2023): tinyhome.io/insulation/
  24. HomeGuide, tiny house cost (Jan. 2026): homeguide.com/costs/tiny-house-cost
  25. HomeGuide, insulation cost (Dec. 2025): homeguide.com/costs/insulation-cost
  26. Colorado Energy, R-value table: coloradoenergy.org/procorner/stuff/r-values.htm
  27. ROCKWOOL Comfortbatt technical data sheet (PDF): brandportal.rockwool.com/original/gallery/39052/files/original/8e8b826
  28. ROCKWOOL, Comfortbatt: rockwool.com/north-america/products-and-applications/products/comfortb
  29. Havelock Wool, PRO batt R-14, 16 in. o.c.: havelockwool.com/products/r13-batt-insulation-16-o-c
  30. DuPont, Styrofoam Brand Square Edge XPS: dupont.com/products/styrofoam-brand-square-edge.html
  31. GreenBuildingAdvisor, cold-weather performance of polyisocyanurate: greenbuildingadvisor.com/article/cold-weather-performance-of-polyisocy
  32. U.S. DOE Energy Saver, radiant barriers: energy.gov/energysaver/radiant-barriers
  33. U.S. DOE Energy Saver, types of insulation: energy.gov/energysaver/types-insulation
  34. TenWolde and Pilon, indoor humidity and water vapor release in homes (USDA FPL, 2007, PDF): fpl.fs.usda.gov/documnts/pdf2007/fpl_2007_tenwolde001.pdf
  35. U.S. EPA, a brief guide to mold, moisture and your home: epa.gov/mold/brief-guide-mold-moisture-and-your-home
  36. NOAA NCEI 1991–2020 climate normals data service: ncei.noaa.gov/access/services/data/v1
  37. U.S. EIA, British thermal units: eia.gov/energyexplained/units-and-calculators/british-thermal-units.ph
  38. U.S. EIA, Electric Power Monthly table 5.3: eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_5_3
  39. U.S. EIA, heating oil and propane update: eia.gov/petroleum/heatingoilpropane/
  40. ICC-ES ESR-3228, Froth-Pak spray foam (PDF): icc-es.org/wp-content/uploads/report-directory/ESR-3228.pdf
  41. ArmorThane, closed-cell spray foam guide: armorthane.com/closed-cell-spray-foam/
  42. ArmorThane, ArmorFoam 0.5 open-cell spray foam: armorthane.com/products/armorfoam-products/open-cell-spray-foam/
  43. ArmorThane, spray foam insulation cost: armorthane.com/spray-foam-insulation-cost/
  44. ArmorThane, spray foam and noise (STC comparison): armorthane.com/does-spray-foam-insulation-reduce-noise/

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