attaching stud wall to exterior wall - damp course question

26 Sep 2012
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United Kingdom
Hi, I have an attached garage that I have recently knocked a doorway into via the cavity wall in the kitchen to create a utility/storage room. Now I want to plasterboard the walls in the garage to create a nice finish to my new utility room and hide all the surface mounted pipework etc. however...

the garage floor is 1 course lower than the damp course of the house/garage wall. If I fix studwork to this wall what do I need to be careful of ? I assume that i cannot fix or have any studs touching the wall below the DPC, so do I just fix a sole plate to the floor (leaving a gap between that and the existing wall) on top of some new DPC ? Is there a minimum/maximum width of cavity between the exsting wall and the stud wall ? is there a minimum height above the DPC of the house that I can start fixing studs to ? Is there anything else I should be worried about ?
Appreciate if anyone has any advice on this.

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You should have a DPC between any timber and brick wall or concrete floor. In the timber frame industry when nails are shot-fired through the timber and DPC it would form a self sealing gasket but I presume you wont have specialist gear like this so I would put plenty of silicone between the timber and DPC where you are going to fix. Lap the DPC around the timbers before fixing plasterboard.
Either screed the garage floor with min 50mm, pref 100mm screed to level it (typically garage floors have a run off slope) and put a membrane DPC under running it up the walls to the existing DPC level and then tying it in to the existing DPC with mastic/bitumen paint, use liquid DPC (bitumen paint) to paint the garage floor and walls to the DPC level then screed or lay solid insulated floor covering. Technically this is change of use for the garage and you should check with building control/planning.
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thanks for the replies, I don't want to raise the floor as I want to retain the ability to convert it back to garage easily if necessary.

I think Matty's suggestion of just putting DPC between all the timber and concrete/brick and sealing all the punctures with silicone is probably the easiest, thanks.

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