New garage - DPC level?

[Ivor Windybottom]

I'm about to build a new garage. It's detached from the main house, alongside an existing garage.

I'd like to match the old garage floor level, which is 2 courses below the DPC. The garage floor is at ground level at the front, at the back the ground rises very slightly to be about 30mm above the floor. In the old garage, the DPC is 2 courses up from the floor. The bricks below this are definitely damp, they look darker and have white salts on them.

As we're starting from scratch with the new garage, is there a better way? It's being built with a cavity wall, so I do have the freedom to have different levels for the inner and outer DPCs. Or there can be trays across the cavity if this is a way of doing it.

Is there a better way than just matching the existing and accepting that there will be two damp courses at the bottom of the wall? I suppose what I'm looking for really is how habitable rooms would be built in this scenario?

 

[Ivor Windybottom]

My best effort so far...

The floor DPM is completely normal. DPM(1) is the DPC. DPM(2) is just to catch any possible cavity condensation and push it towards the outer skin as otherwise DPM(1) would guide it towards the inner skin.

Issues or other ideas gratefully received!

 

[Ivor Windybottom]

Talking to myself!

Today's simpler idea is as follows...

Any other ideas or comments appreciated.

 

[Ivor Windybottom]

I think I'll go with the second doodle idea. But with an additional second inside DPC, two bricks up from the first at the same height as the outside one. Just in case there's a massive flood and the cavity fills with water. Very unlikely but it won't do any harm.

All unless anyone else has any better ideas.

 

[cdbe]

I did this on n my extension:

Inside floor is lower than external ground level but completely dry. I think I chucked in a dpc level with the acco on the outside and on top of the dpm where it was folded back over the inner skin.

Just a lot of polythene flapping around to manage and look after till it's all safe inside the wall.

 

[Ivor Windybottom]

Thank you, that looks like a really excellent idea. Then there are no joints between the floor and the higher DPC level, it's a sealed tray within the building.

I will absolutely steal your idea, as it's better than all mine!

 

[stuart45]

When the ground level is too high, especially in solid walls, there's a solution such as the eco Tiffin air drain.