New walls meeting existing detailing.

williamglossop · 2 Apr 2021

I'm having a 2 storey side extension. Where the new walls meet the existing corner of the house, is this an acceptable way to join the two together......

Screenshot_20210402-220219_Adobe Acrobat.jpg

If it is, what width would the vertical cut normally be and is there a particular product that is used as an insulated dpc? The new walls are block, the existing are brick. The exterior is being rendered.

^woody^ · 2 Apr 2021

Surely the air in a slot is both a thermal break and DPC?

AKA a cavity.

williamglossop · 2 Apr 2021

That pic was from LABC website..... I wasn't sure (for the reason u just gave), hence me asking here. I've never done one before, so was just trying to find out what's acceptable

Once did it on a porch, and just ground a 50mm slot in the house wall.... it worked fine, but no building inspector

Notch7 · 2 Apr 2021

williamglossop said:
If it is, what width would the vertical cut normally be

I've generally seen builders do a 50mm slot.

And firfix wall starters on both inner and outer leaf (at least on Single storey)

^woody^ · 2 Apr 2021

Normally, you'd just run the disc saw up the wall and slide some DPC in and either wedge it with folded dpc or a bit of mastic. No need for insulated dpc.

But in reality most people don't bother, and the chance of moisture moving over 300mm sideways to reach the new inner wall is nil.

kingandy2nd · 3 Apr 2021

^woody^ said:
Normally, you'd just run the disc saw up the wall and slide some DPC in and either wedge it with folded dpc or a bit of mastic. No need for insulated dpc.

That’s what I’ve done.

Laggy · 6 Apr 2021

I asked my BC about this as my DIY books said I need to do it.. BC said no need for any cut or anything ..

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New walls meeting existing detailing.

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