What ho one and all,

I do read many of the threads relating to EWI and although I do understand, I also don't understand.

I am not considering it as I have quite a lot of insulation in my t/f house. However, a neighbour is in the process of having it fitted. Naturally, I do understand the insulation benefits,

But !

My house has the insulated inner wall, the cavity and a block and render external. During building, I did consider changing the block and rend for some kind of external insulation and render but wa told by the BCO that as I was changing the specs, I would have to reapply for Building Control.

But he also told me, and this is what I don't understand about EWI, that since the cavity is ventilated, the outer wall is considered external as it has cold air on both sides and does not improve the insulation values.

So what am I missing?

Thanks

There's a good technical paper on avoiding thermal bypass, available here:

https://www.passivhaustrust.org.uk/guidance_detail.php?gId=55

Essentially you really want to avoid convective loops on the warm side of your insulation, especially if these are linked to outside air.

On a related note, I assume that most of the moisture risks in full-filling existing cavities that are mentioned in this paper would effectively be mitigated by the outer layer of EWI. Clearly you'd need to check this with your installer.

Posted By: RexI cannot see how a 2400 x 600 x 180 space filled with blown cellulose cannot slump

True - you have to put in things for the Warmcel to grip onto, at vertical intervals. For new studwork, weave light galv garden wire in/out of the studs @ 300 vertical c/cs, winding round a nail head, before blopwing it in. Easy, cheap.

Interesting that your Warmcel was retained by scrim, rather than e.g. the plasterboard - good practice that I've only seen in Americal instructions. The pressure can easily blow the plasterboard off its nails/screws. The scrim is stapled to the sides of the studs, a little way back from their room face. The scrim bulges when filled. You can easily roller back any xs bulges before fixing the pbd. With scrim you can also see visually that all nooks and crannies are filled.

With our Warmcel they used a mixture of scrim in some places and behind Panelvent in others. IIRC the stuff has glue or something to hold it together and prevent slumping? The pump measures the quantity supplied to guarantee that there aren't gaps, I believe. We have a certificate of the amount installed.