Insulation under frame

[pieroxy]

Hello,

I plan to insulate my attic under frame with rigid board wood fiber. This allows me to avoid all the metal reinforcement around non-rigid materials which creates thermal bridges. The idea is to attach the panels with 260mm "framing" screws directly into the rafters and extra large washers at the other end. So I can put 200mm of fiber under my rafters.

Does that make sense? I haven't seen this described anywhere, but from my point of view there's no reason it doesn't work ...

On the edges which are very low ceiling (roofing requires), I intended to put cellulose wadding or wood fiber in semi-rigid panel on the ground. The joint between the two sections would be vertical plywood and another 200mm of rigid fiber.

Wood fiber seems to be a good compromise today, which does not require you to redo everything in 20 years ...

Thank you for your insightful advice on this matter. NB: Where can we find rigid fiber? At merlin pinpin they do not ... I have this: http://www.actis-isolation.com/produitsactis.php?p=1&l=1&rub=54&vert=3 Is it worth something?

[Christophe]

The problem with your method is the vapor barrier and the finishes ... if it is integrated into the insulation and you do not want to finish it is ok, otherwise a counter lathing is necessary in my opinion and it will complicate the things in relation to a placement between rafters or the rafters would be the basis for fixing the finish ... but hey, I'm not a pro either ...

The sylvactis 55 fx won't do: it's too flexible to be fixed the way you describe it. I have placed a few m² (on thermal bridges) with us this year. We even made a subject on it: https://www.econologie.com/forums/sylvactis- ... t8944.html

The sylvactis 110 D could be suitable.

Otherwise I recently saw, not expensive at all (less than the equivalent R sylvactis), "rigid" cellulose panels at brico depot ... they do not appear on their site on the other hand (one shot?) And I don't know how stiff they had ...

[pieroxy]

The problem with your method is the vapor barrier and the finishes ... if it is integrated into the insulation and you do not want to finish it is ok, otherwise a counter lathing is necessary in my opinion and it will complicate the things in relation to a placement between rafters or the rafters would be the basis for fixing the finish ... but hey, I'm not a pro either ...

I thought that insulating between the rafters was bad because the rafters are thermal bridges? In addition, I have 8cm between my rafters and my battens, it is not really sufficient whatever the insulation.

For the vapor barrier, I had nothing planned ... Do you have to put it on the inside or outside?

For the finishes, I will use the attic as an attic, so no finishes.

The sylvactis 55 fx won't do: it's too flexible to be fixed the way you describe it. I have placed a few m² (on thermal bridges) with us this year. We even made a subject on it: https://www.econologie.com/forums/sylvactis- ... t8944.html

The sylvactis 110 D could be suitable.

Thanks for the info, I'll watch the 110D.

Otherwise I recently saw, not expensive at all (less than the equivalent R sylvactis), "rigid" cellulose panels at brico depot ... they do not appear on their site on the other hand (one shot?) And I don't know how stiff they had ...

I will continue to rummage on the ouèbe. Thank you.

[Christophe]

I thought that insulating between the rafters was bad because the rafters are thermal bridges? In addition, I have 8cm between my rafters and my battens, it is not really sufficient whatever the insulation.

Yes, but in 99% of cases it is wood, so the thermal bridge is very limited since wood is a good insulator by nature.

If you are only 8 cm deep, then you have to raise the rafter or better do it in 2 times: 8 cm between rafter and X cm later by placing them crossed with overlap ...

For the vapor barrier, I had nothing planned ... Do you have to put it on the inside or outside?

By steam = always between the "inhabitants" and the insulation therefore interior.
Also check the waterproofing of your roof and if necessary, put a rain screen between the insulation and the roof.

For the finishes, I will use the attic as an attic, so no finishes.

In this case if you find the panels rigid enough and you manage to fix the vapor barrier (or that it is integrated), it is ok you can fix with the 260 screws.

If you take some pictures for us, we will see it more clearly

[pieroxy]

A few months later and -5 ° outside and the project resumes a priority 1 at home ;-)

Here is a photo of my attic:


I bought some rigid wood fiber boards waiting for me in my dry garage. (I believe it is these: http://www.leroymerlin.fr/mpng2-front/p ... erall=on#5 )

The attic is dry, even after a good rain. The idea is to fix the panels directly under the rafters (left part at the top of the photo).

Edit: I just noticed that the panels are only 55kg / m3 ... Not really 110 ... In short, probably a fixing method to review.

Edit2: The link does not work: http://www.leroymerlin.fr/mpng2-front/p ... &myshop=55