Insulating a tiny house: thickness, materials and winter

In a conventional house, you judge the insulation by the heating bill. In a tiny house, you feel it within a few hours. It is the technical item that makes the difference between a home that is comfortable all year round and a house that is pleasant six months a year. This guide explains what really matters, and what to check before you sign.

Why does insulation matter more in a tiny house?

Because of the ratio between the surface area of the walls, roof and floor and the interior volume. A 100 m² house has a lot of volume behind each square metre of wall. A tiny house of 20 to 30 m² has almost as much envelope per occupant, for a volume five times smaller. Every flaw in the insulation therefore shows up immediately, as cold in winter and overheating in summer.

There is one more particularity: the floor is exposed to the outside air. On a trailer, there is no solid ground floor or crawl space to moderate heat exchange. A poorly insulated floor is enough to make a tiny house uncomfortable, even with flawless walls.

Finally, the small volume makes even one cold wall noticeable: you can feel a poorly insulated wall from a metre away, which does not happen in a large living room.

Which thermal regulations apply to a tiny house?

None, in the most common case. The RE2020 (French environmental regulation for new buildings) applies to the construction of new buildings that require planning authorisation (articles R172-1 et seq. of the Code de la construction et de l’habitation, French construction and housing code). A tiny house on wheels, which is legally treated as a caravan, falls outside this scope.

This has an important consequence for buyers: no minimum performance is imposed on the builder. Two houses of the same floor area, at the same advertised price, can have completely different insulation. It is up to you to ask for the thicknesses and materials, item by item, and to have them written on the quote.

A tiny house set on foundations and subject to planning permission (permis de construire), on the other hand, falls under ordinary construction law. The different regimes are explained in our guide on tiny house regulations.

What insulation thickness should you aim for?

The performance of a wall is measured by its thermal resistance R, which increases with thickness and decreases with the conductivity of the material. In a tiny house, thickness is constrained by two practical limits: the overall width allowed on the road, and the gross vehicle weight of the trailer.

This is the central trade-off in the design: every extra centimetre of insulation is taken from the living area and from the payload. Hence the value of knowing the figures actually used rather than general promises.

On our models, the insulation is rock wool, with a minimum thickness of 10 cm in the walls. On the Skywood and the Sharewood, the floor is insulated with 14 cm: it is the most exposed surface, so it gets the thickest treatment.

Which insulation material should you choose?

There is no single best insulation material: each has its qualities, and the choice comes down to three criteria — conductivity, behaviour with moisture, and phase shift, that is, the time it takes for summer heat to pass through the wall.

• Rock wool: a mineral insulation that is non-combustible, stable over time and good for sound. It is the choice made for our houses, for year-round use.
• Wood fibre: good phase shift, and therefore a real advantage for summer comfort, but heavier for the same performance — a sensitive point on a trailer.
• Cellulose wadding: recycled and inexpensive, provided it is installed in a perfectly sealed cavity to prevent settling.
• Synthetic foams: very effective at low thickness, but sensitive to fire and not very permeable to water vapour, which calls for rigorous design.

The right approach is not to choose a material on principle, but to ask the builder what thickness of which material, on which surface, and to compare quotes on that basis.

How do you avoid condensation and thermal bridges?

High-performance insulation that is badly installed is useless. Three points make the difference in a tiny house:

1. Continuous insulation. The junctions between wall and floor, wall and roof, and around windows are where the insulation is interrupted. These are thermal bridges, and they create the cold spots where moisture settles.
2. Airtightness. A wall that lets air through also lets water vapour through, which condenses on cold areas. ADEME (the French ecological transition agency) stresses this point: without airtightness work, an insulation material does not reach its stated performance.
3. Managing water vapour. A continuous vapour control layer on the inside stops moisture produced in the home from migrating into the insulation. It is essential in a small volume where cooking, showering and breathing concentrate a lot of vapour.

Insulation and ventilation go hand in hand: the better insulated and more airtight a house is, the more it needs controlled air renewal. Our houses are fitted with MVHR (balanced ventilation with heat recovery, VMC double flux) and an air purifier; the subject is covered in detail in our guide on ventilation and humidity.

And summer comfort?

Overheating in summer is the weak point of small, heavily glazed volumes. There are four levers, in order of effectiveness: shading the glazing that faces south and west, the thermal mass and phase shift of the walls, night-time ventilation, and only then air conditioning.

The orientation of the house on its plot, which costs nothing, is often more effective than any equipment. It is something to decide when choosing the location, not after delivery.

Our houses are pre-equipped for reversible air conditioning, which also serves as back-up heating: see our guide on heating a tiny house.

Does sound insulation matter too?

Yes, for two reasons specific to this type of home. First, rain on the roof, which is very audible when you sleep in the mezzanine (sleeping loft) under the sloping ceiling. Second, living together in an open volume: without treatment, a conversation carries through the whole house.

Dense insulation materials such as rock wool improve acoustics as well as thermal performance. The cladding also plays a part: on our houses, larch is fitted at 22 mm on the outside and 16 mm on the inside.

Questions to ask before you sign

1. Which insulation, and what thickness in the walls, the roof and the floor?
2. How are the thermal bridges at the floor and around the openings dealt with?
3. Is there a continuous vapour control layer, and how is airtightness achieved?
4. Which doors and windows: glazing, frame material, quality of fitting?
5. Which ventilation system, and what maintenance does it need?
6. Are these details on the quote, or only in the brochure?

These answers say more about the quality of a tiny house than any interior photo. They also explain some of the price differences between builders: see our guide on the price of a tiny house.

Key points

• A lot of envelope for very little volume: you feel the insulation straight away.
• On a trailer, the floor is the most exposed surface, and the one most often neglected.
• No thermal regulations apply to a tiny house on wheels: insist on the figures.
• Thermal bridges, airtightness and the vapour control layer matter as much as thickness.
• Insulation and ventilation are designed together, otherwise damp sets in.