Insulation - cold roof meets warm roof

Joined
21 Apr 2011
Messages
36
Reaction score
0
Location
Cornwall
Country
United Kingdom
Hello,

We had a larger flat roof dormer extension built a couple of years ago. The ceiling and roof is made up of plasterboard - timbers- celotex - osb - rubber. They key fact for this topic being that the celotex insulation is above the timbers making it a warm roof.

At the back of the dormer's flat roof it meets the old pitched roof, which is a cold roof with the insulation sitting between the joists on top of the ceiling plasterboard.

I was about to top up the old loft insulation when I noticed that the two roofs are open to each other. Because no insulation is above the plasterboard in the flat roof, cold air from the loft in the old cold roof area can just flow into the space above the new ceiling in the dormer, bypassing the celotex insulation. Diagram below.

What's the appropriate way to deal with this situation? I don't want to make a condensation problem by putting insulation in the wrong place.

Thanks in advance!

1659558050872.png
 
Last edited:
Sponsored Links
Joined
29 Jul 2011
Messages
5,312
Reaction score
863
Location
Lancashire
Country
United Kingdom
Sounds like the warm air can also leak into the attic from what I understand!
 
Joined
21 Apr 2011
Messages
36
Reaction score
0
Location
Cornwall
Country
United Kingdom
Well yes, it seems there's an open air path bypassing the insulation. I've added a diagram to my original message to try and make it clearer. I'm tempted to block the air path up, but that would mean restricting ventilation to the dormer roof timbers. I thought these warm roofs didn't need to be ventilated, but I don't know what I don't know and so I'm seeking advice :)

Thanks again
 
Joined
29 Jul 2011
Messages
5,312
Reaction score
863
Location
Lancashire
Country
United Kingdom
Yes need blocking off near your blue arrows, that will stop you loosing the heat from that room below.
 
Sponsored Links
Joined
21 Apr 2011
Messages
36
Reaction score
0
Location
Cornwall
Country
United Kingdom
Thanks for your advice. I'm just concerned about blocking it in case it was left open for a reason, likely relating to ventilation.
 

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

 
Top