Roof Insulation

Roof Insulation: Which Technique to Choose

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Roof Insulation: Which Technique to Choose


Whether for new construction or a complete re-roofing, roof insulation is important because it is where 20 to 30% of the heat in the house escapes. When a roof leak causes saturated insulation, you must always replace that insulation. Let’s see closer below.

Insulating your roof from the outside has several advantages:

no need to empty the rooms under the attic;

no reduction in living space;

limitation of thermal bridges.

There are different techniques to insulate your roof from the outside. Here is an overview of their advantages and limitations.

Insulating your roof with sarking

The principle of sarking is to superimpose different elements, from below to above:

the decking: rigid panels allowing to have a flat base to put the other parts, it will be the ceiling of the attic;

the vapour barrier: a porous film that will allow vapours from the inside to gradually escape to the outside;

the insulation: to be laid continuously over the entire roof;

the under-roof screen: only if your insulation is not airtight;

the counter-battening: to create an air space between the insulation and the roofing material;

the battens: which will support the roofing;

the roofing: this is what will give the final appearance of your roof (tiles, slate, etc.).

Please note: sarking is reserved for sloping roofs.

Simple solutions for roof insulation

Roof Insulation

Sarking is effective but time-consuming. There are much simpler ways to insulate your roof from the outside.

Herringbone Boxes

The characteristics of herringbone caissons are as follows:

As the name suggests, they are caissons (long lengths) that can be up to 2.40 m wide and 6.80 m long.

They are made of plates with an insulator enclosed inside by expanded or extruded polystyrene, or polyurethane foam, known for their outstanding insulating capabilities.

Their back face is worked to act as a ceiling in your attic.

The significant advantage of the chevron boxes is that they are straightforward to install:

they are self-supporting: no need to fix them;

they are “all-in-one”: they include the decking, the vapour barrier, the insulation and the counter-battens;

their installation is therefore speedy and much more straightforward than sarking.

Sandwich panels

Another solution if you prefer simplicity: sandwich panels.

They are very similar to chevron boxes, with a few notable differences:

Sandwich panels interlock with each other, which helps prevent thermal bridges.

They can be equipped with a counter-battening for even faster installation: you can place the roof covering on top of the panels.

The methods must evolve accordingly to the loss of surface area (loss of thickness with an interior insulation technique) and living space. Thermal insulation from the outside will gradually become the norm. In this respect, solutions already exist, particularly for roofs.

Fundamentals of sandwich panels

Sandwich panels are panels that integrate the entire insulating structure: the underside or interior facing, the insulation and the waterproof exterior facing under the roof.

Sandwich panel: advantages

Their constitution is made of a single piece, an “all in one” quick to implement (up to 100m²/day).

The “made to measure” is possible.

Factory manufacturing considerably reduces the risks of waterproofing defects and increases the duration of the finished product.

The disadvantages are:

Three people are needed to handle the panels, and a lifting system is essential in most cases.

Moreover, it is necessary to foresee the thickness of the panels upstream (on the construction plan), which slightly increases the height under the ridge because of their “external” positioning.

The current “traditional” insulation consists in placing the insulation inside the building. The inertia due to work habits is always long to abolish!

Note: You may have to check with the local authority to make a work request for the renovation.


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