Insulating Web Joists in a flat cold roof

Joined
27 Sep 2020
Messages
17
Reaction score
0
Country
United Kingdom
Hi, we are building our flat roof extension with web joists. The structure is a cold roof with 150mm pir then a minimum of 50mm insulation with insulated plasterboard (25mm)under the joists.
The architect has said that pir should infill the gaps in the web joists as much as possible up to the level of the main insulation. Makes sense to me but our builder thinks not needed, I don't think they fancy the fiddle job it will be. He has suggested putting rockwall in there instead. Its not going to be perfect as there still going to be gaps for the thickness of the metal section but every bit of insulation counts with gas prices.
I don't think we want full fill as the web is going to give some cross-area ventilations.
Has anyone done similar or got any suggestions please? Any advice at all would be really appreciated.
 
Sponsored Links
You won't easily get PIR in the joist, it will be gappy.

I would fill with rock wool and PIR for outside the joist. (y)
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top