Garage Conversion - Joist Mounting below DPC

[terminator999]

Need your help!. We are planning on converting our integrated garage into a kitchen. Just for some back ground info, a bathroom sits on top of the garage for its full length and width, the outside wall is double cavity.

Problem i have is the floor of the garage is 8 brick courses below the Damp course. To maintain the level and avoid steps from the existing kitchen (single door to be cut into garage back wall for entrance/exit point to proposed new kitchen) i need to put in a timber floor (width of garage 2.4mtrs) and joists will fall BELOW the current Damp course. Not possible to lower the damp course by chemical means etc as there is a paved walkway that runs down the side of the garage.

Option i'm thinking off is using joist hangers bolted to the wall. Is this permissible or do i need to seal off at the back of the hanger plates where they contacts the wall (below DPC) and also where the bolts enter the wall, and i presume i need to seal off the joist ends.

Any advice would be welcomed as i'm fairly good at DIY but don't particularly want to be caught out with the BCO should they arrive unannounced and i have to rip out the whole lot.

Thanks for taking the time to read and appreciate all feedback.....

I don't want to get into building stub walls to support the joists as i prefer to maximise the area beneath the joists for storage of ladders and timber lengths (5mtrsx2.4mtrs x 6 course high)

cheers

T999

 

[RichTeaBiscuits]

Not sure I can answer the specific question regarding installing the joists but the following may help - I converted my garage last year with BCO involvement and approval.

1. The BCO will probably want insulation installed beneath the floor, which is likely to impede your storage of ladders. I got away with 50mm celotex for mine, but that may have been because the garage floor was higher than the house floor (not sure how the original builders got away with that one....)
2. I suggest using a liquid DPM, lapped up the bottoms of the walls, in order to provide damp proofing. BCO was happy with that, as long as it overlapped the DPC in the walls.
3. I installed a floating floor, with no joists. Fortunately I could build straight on top of the concrete (or at least on top of the celotex.

If you can fix the joist hangers to the walls above the DPC then you should have no problems. Any contact with the walls below DPC will be covered by the liquid DPM. If you needed to fix the hangers through the liquid DPM then you may have more of a problem. An option could be to install the hangers and then coat them in with the liquid DPM too.

I suggest also that you involve the BCO - it will mean the conversion will add value to your house come sale time, plus you can be confident that you're not going to have any problems with damp.

 

[^woody^]

You can do what you propose with the joist hangers, but run some DPM polythene up the wall behind them.

An easier way would be to fix a timber to the wall (this will be nice and level) and fit timber hangers to this