Any tips or experience insulating attic?

[Rosemouse]

Hello, I am a novice and am learning a lot from this forum. I finally have my own house! It is an old stone house in France that requires quite a lot of work, but it is liveable. I am working on structural and insulation problems first. I had the roof entirely replaced in May with terracotta tiles, and next i need to tackle insulating the attic floor/roof of this two storey house. The quotes I got were to lay two layers of wood batting fibre insulation at right angles to each other across the entire surface. The attic cannot be used as a room - the struts of the roof go right across the width of the attic at a height of about 50cm, so either a false floor would have to be built at that height, leaving not so much space, or the roof trusses would entirely have to be remodelled which would be a ridiculously expensive job - and anyway I don't need the space. So to avoid heating the entire large attic (100m square floorspace) we are going to just insulate the attic floor.
However as I started to learn about thermic bridges and suchlike I realised that I did not know what was underneath the floorboards of the attic. If the space was hollow, as i understand, it would be kind of a bit silly to just dump some insulation on top. Last night, we went up and pulled up some of the floorboards. Underneath we found cavities between the rafters, and those hollow red bricks that were often used here underneath plaster. The cavities were stuffed with newspapers and bits of cardboard (ugh) and dust (ugh ugh) dated to the 50's. The depth from the top of the rafters to the red-brick ceiling is 19cm - the width between the rafters is 43cm. From what I understand, the really best way to do this job properly would be to pull up all the floorboards, which are not in great condition after being underneath a leaking work for several decades, insulate between the rafters first, and then to lie another layer of wood fibre batting at right angles over the top. But should we put a vapour barrier all over and between the rafters first? How do we secure it properly? Does it need to go up the walls around the periphery? And how thick should the second layer of wood batting be?
I am slowly beginning to understand the principles of insulation, I am not very good at physics, but I thought I would pose this question because so many people on here have such great experience and I feel it never hurts to ask. And I don't want a ceiling stuffed with newspaper! Thank you!

 

[Matt Green]

Last night, we went up and pulled up some of the floorboards. Underneath we found cavities between the rafters, and those hollow red bricks that were often used here underneath plaster.

I think you mean joists? Rafters run from roof eaves to apex, joists are horizontal. It matters for your later question.

From what I understand, the really best way to do this job properly would be to pull up all the floorboards, which are not in great condition after being underneath a leaking work(roof?) for several decades, insulate between the joists first, and then to lie another layer of wood fibre batting at right angles over the top.

Sounds good- do that.

But should we put a vapour barrier all over and between the rafters first? How do we secure it properly? Does it need to go up the walls around the periphery? And how thick should the second layer of wood batting be?
I am slowly beginning to understand the principles of insulation, I am not very good at physics, but I thought I would pose this question because so many people on here have such great experience and I feel it never hurts to ask. And I don't want a ceiling stuffed with newspaper! Thank you!

You would if you were insulating the roof between rafters (internal to external); I think you are insulating an attic floor between joists (internal to internal), so you should be fine without a vapour barrier.


M.

 

[Rosemouse]

I think you mean joists? Rafters run from roof eaves to apex, joists are horizontal. It matters for your later question.

I did absolutely mean joists thank you! Most of my conversations about this are done in French, and I was thinking about them being the rafters of the roof below but thay are absolutely not, they are the joists of the floor above.

Sounds good- do that.

You would if you were insulating the roof between rafters (internal to external); I think you are insulating an attic floor between joists (internal to internal), so you should be fine without a vapour barrier.

M.

I am insulating an attic floor but I am going to remove the floor so the insulation will be open to the rest of the attic, which is not useable as a storage space. Above, the roof was recently redone and has a vapour barrier now underneath the tiles. Thank you so much for your response!

 

[Cubist]

Fortunately your home may be far enough North to escape the exigencies of termites but having had some problems with a leaking roof with a wooden plank attic floor below it maybe a good idea to be on the lookout for woodworm damage as you lift those boards and clear the rubbish from around the joists. Matt G possesses a considerable knowledge base concerning these wee beasties and can advise on how to detect, identify and treat the timbers to resist them.

 

[Rosemouse]

Fortunately your home may be far enough North to escape the exigencies of termites but having had some problems with a leaking roof with a wooden plank attic floor below it maybe a good idea to be on the lookout for woodworm damage as you lift those boards and clear the rubbish from around the joists. Matt G possesses a considerable knowledge base concerning these wee beasties and can advise on how to detect, identify and treat the timbers to resist them.

Yes this is the other reason I want to take up all the floorboards of the attic. They've been there a good long while and I need to make sure underneath is healthy. Sadly, the tiny area of the street i live in is one of only two places in the whole department where termites have been detected, although the mairie assures m it was 15 years ago and no outbreaks since. Still, the warmer and wetter everything gets, the further north they march.

 

[Cubist]

Well, if the mayor says its safe then... it's probably wise to think otherwise. Not that French politicians are any less credible than ours you understand.

 

[Rosemouse]

Well, if the mayor says its safe then... it's probably wise to think otherwise. Not that French politicians are any less credible than ours you understand.

Oh I utterly agree. The mayor thanked me for buying this house because the ex-owner was such a pain in the cul. But that still doesn't mean I believe anything he says