Insulation around RSJs

16 Oct 2014
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United Kingdom
We have a pitched roof at the front of our semi detached house. We took the ceiling down and now have exposed joists and RSJs. With the weather being as it is, the wind blows into the pitched roof and through the gap between the RSJs into the front room. So as the ceiling is not going back up in a rush, I need to insulate the ceiling area somehow.

The pic shows the void in the pic roof. The space on the left has been filled with Celotex Insulation board. There is a 1 inch gap between the wooden joist and the 1st RSJ & a 1 inch gap between the 1st and 2nd RSJ. The wind blows through the two gaps, what's the best way to fill the gaps?

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Can we use expanding (fire retardant foam) to fill the gaps between the RSJs? Will this cause any damp/condensation issues when i put the ceiling back up? What's the building reqs regarding this?

The gap is too small to put anything up there except for rockwall or something similar. So if I can't use expanding foam, can i use rockwall or is there a better product?
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Before you fitted your Celotex you should have shoved a load of Rockwool or similar up in the gap to encapsulate it. Though what are the two steels supporting exactly? The two skins of the cavity wall above? And what is that on the far right? A concrete lintel supporting the innner skin maybe? As per the (tonyesque) sketch)

Is there a gap above them?

Or you could just bring a continuous layer of Celotex beneath them.

I would still be looking to insulate their 'exposed' side though ie inside the void.

Thanks for replying! The 1st steel (Left Hand Side) does not have anything resting on it, it just spans the void. The 2nd steel (Right Hand Side) has the external front wall of the house. To the far right (only visible at the bottom of the picture) is the joist for the floor above.

I did wonder about putting rockwall up there before the Celotex but was concerned this might cause condensation to form on top of the Celotex or on the ceiling below.

The picture is very Tony Art !! :D

I can look at removing the Celotex and laying Rockwall up there (covering over the areas of steel but I won't be able to cover the entire void as there is a further 15ft from the bottom of the picture to the corner of the house. From the top of the picture, it there's another 5ft and then the neighbours void. Not to mention the fact I will struggle to get up there due to eating too many doughnuts! And drinking too much beer :D

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