Extension detail query

[Ext2023]

Hi we are building a small extension at the rear of our house and I'm just wondering if I'm missing anything. It's blockwork cavity wall old and new. The existing external facade will become an internal face which we will dry line. Is there anything else that needs to be considered?

 

[Bonni]

Where you have the vertical insulated DPC installed, we just cut the fully cavity and slide the cavity insulation board up to the old inner leaf.

Foil backed plasterboard can't be dot and dabbed onto blockwork. The foil is a vapour barrier and really only needed on the ceilings under the loft, but still no harm using it elsewhere, just other than cost. Personally, just put 150mm in the cavity and not bother with insulated inside boards.

 

[Ext2023]

Thanks for the advice. Im using the the 110mm cavity insulation because I already have some. The plasterboard is one with 38mm insulation bonded to it with a vapour barrier. I'm fixing it with mechanical fixings. The reason I'm using that is extra insulation and also I can run heating pipes and electrical behind it and not have to chase walls or run plumbing under floors

 

[freddiemercurystwin]

A soft joint would be better between the existing and proposed walls instead of mortar as well as slip ties, otherwise there's a good chance the mortar will crack when the extension settles.

 

[Ext2023]

Thanks I will definitely be putting in control joints between existing and new blockwork and render