Comparison of the insulation inside or outside

Comparative isolation techniques from inside and outside.

Comparative outer VS interior insulation on the forum
insulation and heating Forum


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 methods of thermal insulation: 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

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

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- 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, etc.)
- 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
- Finishing protection (plaster) or siding required = 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 opening can be problematic
- Can distort a facade (stone from the country for example)

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

Comparative outer VS interior insulation on the forum
insulation and heating Forum

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