i am just about to start the first floor of my rear extension. i have one question that i am concerned about.
i am fixing the brick and blockwork skins of the extension to the existing cavity wall using the usual wall starter kits. once the rear extension is built i will be knocking through the whole width of the existing rear of the house to create a larger bedroom.
in my opinion i need to put a vertical dpc inbetween the new cavity wall where the skins are attached to the existing brickwork.
however, by cutting a 3mm vertical strip and placing a vertical 100mm dpc this will weaken the part of the wall that the blockwork is attached to via wall started kit, therefore when i knock through, the blockwork will have the wall starter basically attached to a 100mm "pier".
i hope this makes sense, i know normally when putting an extension on the back of a house requires a vertical dpc but in this case it seems it would be weakening the wall and causing possibly more problems. this is a first floor bedroom extension and so i am not anticipating a huge amount of driving rain against the adjoining areas.
any help/advice would be appreciated.