Insulating roof to use grenier space

[Laggan]

Hello all,

We have a roof that is in perfect condition (seems completely watertight over a 2.5 year period). We want to use the space up there (and insulate the house) and I am rather at the mercy of anyone who comes in and does the job. We have an English acquaintance who is all set to come in and put Kingspan up prior to plasterboard. Although in perfect condition, this is a typical French attic space (you can see daylight through the tiles in places). Consensus seems to be you just bang up the Kingspan (already available) and then the plasterboard. But I am nervous - this is a big family investment (family making savings available). Someone else suggested a semi-permeable membrane needs to go in first (including perfectly watertight roof being removed). I know this is a regular kind of query here (have spent hours looking at old posts). But any thoughts? He is due to come and start in the next few days (has sourced Kingspan himself), hence nerves! Possibly of interest - it's a 19th century barn/attic space built around the 16th century centre of the house. Only the 19th century roof (believed renovated recently) will be insulated, but there is the old stone building (including rising damp and ancient fosse septique) in the centre/to one side.

[idun]

Roof space to do what exactly?

 I only ask as we were clearly told that if we wanted to use our roof space, no planning permission would be granted as our terrace used up the last of our available m² in relation to the size of our land.

[Laggan]

I don't quite understand the question? No one is 'allocated' a maximum space for use in France? Our house already covers the square meterage that it covers. If you are talking about how much tax we pay then, yes, it is possible that we would pay more after the renovation. The idea is to renovate/use a side of the house which currently already has two bedrooms in the midst of an otherwise unliveable garage/attic (the bedroom/s are already counted in our Taxe Fonciere). As far as I am aware you don't need permission to insulate your attic (which is what this is, on paper). The additional space would be 'happy' living areas (library in the attic/summer living room) to join the existing bedrooms up to the rest of the house. A difficult situation to describe. But we are definitely not adding bedrooms, just trying to use a massive part of the house that is not currently used (garage/attic).

[idun]

Insulating is one thing, if they think that you are going to 'use' it as a room then it is becomes what is called part of the COS 'coefficient d'occupation des sols'. 

And that can include a terrace and also roof space and they can say no.

Some departments actually go and visit properties and check up.

I have been through this, heck we actually had a terrace M² refused, we had to make it smaller than we wanted and they were quite clear, do not use your loft for anything, our COS was all used up!

[Laggan]

Ok - but has anyone got any helpful thoughts on the subject of my original question?

[Chancer]

The only problem you will have is if a tile cracks or lifts in the future or blown snow, if you have cupped floorboards in the grenier then that is an indication of snow ingress in the past.

I was faced with a similar dilemma, I used polystyrene cut tight to the rafters but arranged them overlapping each other like internal roof tiles, I then fixed the reflective multicouche insulation across the inside of the rafters held down by screws through battens, most ingress of water would hopefully run down the polystryrene or the foil and egress through the eaves but the rafters would get wet and there would probably be ingress where the purlins support the rafters and around the veluxes etc.

I took the risk and its still all dry on the inside after several winters, last one was very severe and virtually my whole cellar filled up with snow but no problems in the roof space.

If you want to be 100% sure then its a complete re-roof, tiles off battens ripped off, ecran sous toiture then new battens and the old tiles, a lot of money, its your call [8-)]

[Laggan]

Thanks for that - very helpful. I'm finding it difficult to be comfortable with the idea of not stripping the roof, hence question (I'm a worrier!). We had a good builder give advice and he said he was happy to strip the roof if we wanted, but general opinion (from him and from the guys who would put in the Kingspan afterwards) was that it was not essential (and, as you say, would add considerably to the cost). But they did not tell us (for obvious reasons) that everything would be fine without stripping the roof. It has to be our educated decision (and gamble). I was of the mind that, given there are no existing problems with the roof, it would be better to pay someone to go up and check the roof once a year in early autumn?

[ericd]

As stated, nobody can tell you if your roof is going to remain waterproof for years to come. "ideally" you would stip the tiles, fit the breathable membrane (called Pare-Pluie) and then re-tile. Then no problem with Kinspan as you mention. If money is an issue, put the kinspan and keep an eye out for any misplaced tiles. The tile stripping exercise can be done at a later date without damaging the kinspan/Plasterboard..

[Laggan]

Thanks so much for that - I think that was the kind of reassurance I was looking for! If we can strip the roof and put the membrane in at a later date without destroying the investment we are trying to make at the moment, it's as near a guarantee as I'm going to get. I'll have a chat when he arrives to start work tomorrow.

[woolybanana]

Laggan, if you have decent quality interlocking tiles, there should be no problem; roman tiles with flats underneath should be ok too, but the very traditional roman on top an bottom would need checking.

But then, you probably check regularly anyway. I know I do.

This being siad, many houses have little leaks which simply flow away without being seen or being a problem; mice and other creatures probably cause more damage to insulation.

[ericd]

[quote user="woolybanana"]  ......... but the very traditional roman on top an bottom would need checking. ....[/quote]

Those are called "Tuiles Canal" and some were made (so the story goes) ..... by modelling the clay on the undressed thighs of local Nuns. Good luck with the project.