Cavity wall insulation - wall plate

[John Smith Esq.]

Thanks.

Builder has returned with the plastic roll tray stuff and it is a joke. Extremely flimsy. So the rood insulation is just going to push it up to the felt and probably close all the gaps.

 

[Deluks]

Not necessarily, the insulation goes where you want it to go, once the roll has fully expanded, it doesn't magically get bigger later on.

 

[John Smith Esq.]

But what I mean is, the roll tray stuff is not even 1mm thick. So the idea that it will hold the insulation down over the wall plate and maintain a gap to the felt above seems fanciful. There is no rigidity. Interesting that the roofers merchant asked "what do you want that stuff for, nobody uses it any more"

 

[Deluks]

You've got the cheap and nasty one then. Thicker ones are available, or just make your own with a strip of ply and some battens.

 

[John Smith Esq.]

You've got the cheap and nasty one then. Thicker ones are available, or just make your own with a strip of ply and some battens.

Can your ply idea be done from the inside or do we need to go over the rafters near the eaves like the cheap nasty trays?

 

[noseall]

How does that maintain an air gap down to the eaves? Unless that's a different type of roof.

In those images you will see some rigid insulation (with a gap on top) and glass-wool slab, which will be folded down snug beneath the eaves vent trays.
Air admittance via OFV's seen here...

trap1.jpg

• noseall
• 11 Nov 2024

 

[John Smith Esq.]

So will the air flow in your case be over the ply boards you've put in? Presumably can't get under them if the roof insulation is touching the ply.

 

[noseall]

But what I mean is, the roll tray stuff is not even 1mm thick. So the idea that it will hold the insulation down over the wall plate and maintain a gap to the felt above seems fanciful. There is no rigidity. Interesting that the roofers merchant asked "what do you want that stuff for, nobody uses it any more"

It works. It'll be fine.

 

[robinbanks]

The ventilation is to remove moist air, but how much moisture escapes into the loft from the living space isn't really something we can quantify as strangers on the internet.. Lot of variables, and probably only really a direct measure will answer that particular question. If you find your loft needs more ventilation post, you can get replacement tiles and ridges that will increase ventilation to the space