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This frequently asked questions deals with the roof, its maintenance, its insulation, the cleaning of the tiles...

The maintenance of the roof of his house in 11 questions

Is the roof underlay screen mandatory?

I remake the roof of my house located at 1400 m altitude. The roofer tells me that the under-roof screen is mandatory. Is this really the case?
DTUs make it mandatory to install an under-roof screen "for protection against powder snow" which seems necessary when you are in the middle mountains. For my part, I recommend the under-roof screen in all places.

Roof isolated from the outside

There are two techniques for insulating roof panels from the outside: sarking and seasoned boxes. What is the most effective?

The insulation of a roof from the outside is always superior to that from the inside. The effectiveness of both solutions is equivalent.
The sarking consists of placing panels on the frame. The insulation is placed on these panels. Chevrons and battens are reported on the set to receive the cover. This is the ideal technique if you want to keep an apparent framework in the attic.
The seasoned boxes are self-supporting panels consisting of a layer of insulation between two rafters, which replace the original rafters. We gain much in thickness.

Gel on the roof witnessing good insulation

snow-covered roof and insulation

Why does the roof of our neighbors' house stay frozen longer than ours?

White frost or snow melt all the faster as the temperature of the roof is high. In other words, the faster the blanket heats up, the faster the frost or snow melt. This is the case when Roof is insufficiently insulated. In this case, the calories escape through the blanket (by heating it on the underside) instead of remaining confined in the attic or in the rooms of the house if the attic is lost. You would therefore have any interest in reinforcing the insulation of your roof (from inside or outside) or the floor of your attic.

Treat and waterproof porous tiles

A company offers me the renovation of my roof (which dates from 1974). This is a low pressure cleaning, plus an antifoam in the day and then six weeks after, water repellent using a resin of their composition. What do you think?

In itself, the proposed method is not bad (including the use of the bass and not the high pressure), but it is justified only if your tiles are porous. If your roof is waterproof and if its appearance is still correct, why embark on an expensive renovation operation that will bring nothing more?

Breton flat tiles

We are in Brittany and would like to replace the slates of our house with flat tiles. What do you think ? Is there an authorization?

The renovation of an identical roof only requires a prior declaration of work. On the other hand, the replacement of the roofing material imposes an application for a building permit.
First, find out about the local urban planning constraints (PLU or POS *) that may exclude (and probably even) the use of such or such materials (it is likely, for you, that only the slate be allowed). If your home is near a listed building or within an Urban and Landscape Architectural Heritage Protection Zone (ZPPAUP), you will need to have notice or permission from the architect of the buildings of France (ABF).

* Local urban plan or land use plan.

Can we clean tiles with a wire brush?

I removed the mosses and white marks on my tiles with a squeegee and a wire brush attached to a drill. Did not I make the tiles more porous? However, I intend to pass a waterproofing product. Is this a good method?

Your question reveals that you have some doubts about the method... The white traces are not saltpetre but probably lichens. Like foams, they are eliminated with a commercial product that rinses under the effect of rain or a low pressure jet. I do not recommend the use of a pressure washer: your stripping with the rotating wire brush is even more violent! Even applying a waterproofing product, this method may indeed decrease your tiles and make them permeable.

Clean concrete tiles

Can a pressure washer be used to defoil concrete tiles?

I do not recommend using a pressure washer whatever the nature of your tiles. The jet, very powerful, can "decouter" and make them porous. In addition, it may damage the seals and promote the subsequent implementation of foams. Opt for an anti-foam spray. Rain rinsing.

How to remove the foam from a roof?

Our tile roof is overgrown with moss. How to eliminate it permanently? Is a copper wire taut at the ridge effective?

  • Foam should not be removed by overly aggressive means. Not recommended in particular: the high-pressure cleaner which may dechilate the tiles and especially remove them.
  • Instead, use a biodegradable antifoam that has no effect on the environment. Apply with a telescopic lance that avoids having to climb on the roof.
  • As for the copper wire stretched at the top of the ridge, it is not only without efficiency, but it also risks attracting lightning!

Sealing of a concrete terrace

Above our house is an uncovered concrete terrace. It is no longer waterproof. How to cure it?

In apartment buildings, the terrace is a common part of which maintenance and repair is the responsibility of the building manager.

There is no miracle solution to re-seal "at a lower cost".
If it is an occasional access deck, first remove the gravel that (usually) lines it to identify the source of the leaks.
These are often cracks, holes in the waterproofing coating and / or bearings of the latter at the level of chimney stumps and acroteria (border walls).
Then place repair parts and strips on the roof.
It is also possible to apply on the entire terrace a semi-pasty acrylic sealing coating, with a roller.

Bleach and roof foam

Is 12° diluted with 50% water bleach effective at removing foam from a roof?

I formally advise against this method which, if it actually destroys the mosses, is not without consequences on the roof as on the environment.

Bleach whitens some materials, such as fiber slates or concrete tiles.
In addition, it is very harmful for the environment and for your shrubs or other plants around the house.
Opt instead for a commercial antifoam, easier to use and especially biodegradable.


Video Instruction: 8 Questions you should be asking before replacing your roof - 2: Colorbond or Zincalume?