Comparative interior insulation ITI and external ITE

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Comparative interior insulation ITI and external ITE

by Christophe » 02/07/12, 09:08

Summary note that I wrote to compare interior and exterior insulation techniques: advantages and disadvantages of each method. To be completed if necessary.

Comparison of interior and exterior insulation techniques.


Insulation is the best method to save energy: the heating bill for buildings represents around 40% of the overall energy bill in a country, the potential for gain is significant. Insulation (and hunting for air leaks) is the only solution available.

There are 2 thermal insulation methods: inside (ITI) or outside (ITE). Let's see the advantages and disadvantages of each method. Advantages or disadvantages which will also depend on the choice of insulating material (breathable or not).

A) From the inside

- Fairly "light" site can generally be carried out by the owner
- Work that can be done progressively (piece by piece) according to its means
- Less expensive
- Low thermal inertia (rapid heating of rooms: for example bathroom)

- Depending on the configuration, does not solve the problem of thermal bridges (floors for example)
- Low thermal inertia and almost zero phase shift: lower comfort than in ITE
- Unprotected exterior wall (frost, infiltration ...)
- Depending on the material, risk of condensation in the insulation: the steam must be properly installed.
- If using an insulation with a high resistance to water vapor: requires ventilation

B) From the outside

- Heat accumulation in the walls: good inertia and phase shift increasing comfort
- Eliminates thermal bridges (if done well)
- Protection of the existing wall against rain, frost, temperature ...

- More expensive
- Quite heavy site
- Generally: requires scaffolding and construction by a professional
- Requires the addition of ventilation if performed with vapor-tight material
- Protection of finish (plaster) or cladding necessary = additional cost and can be administrative file (type of facade / region)
- Increases the thickness of the exterior walls: can reduce the light in the house and cause connection problems at the roof level (over thickness)
- Finishing at the sashes can be problematic
- Can distort a facade (local stone for example)


Each method of thermal insulation has its advantages and disadvantages.
We can think of an intermediate solution which would be a compromise between the 2 on a case-by-case basis since each site is unique. It is advisable to use the solution and especially the most suitable materials. For example, nothing prevents you from having exterior insulation or insulating constructive walls (Ytong) and from "over-insulating" your bathroom from the inside with styrodur provided there is adequate ventilation (the use of multipor, breathable, may dispense or greatly reduce the use of CMV).

ps: the corresponding article ... -4417.html
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