Converted garage floor height/storm drain

[KatyMac]

I know I can and will ask a builder or possibly an architect but I kinda want to get my head around it now

Converting a double garage, the floor is about 10-12 cm below the house floor so there should be room for insulation

But in front of the garage is a storm drain so if we have a door will it need a proper ramp for wheelchair access or can we do something clever because of the storm drain as presumably the ramp can't block the drain

Show us a pic of this drain and the ground around it.

Is it a gutter gulley? Or a rainwater drain?

Looks most like this but with no grass just a brickweave drive, drain the garage door

Oh right.

That type is used to prevent rain running under a garage door when the floor is the same level as the ground outside. It is preferable to have a slight downward concrete slope outside, but the ground level might have been raised by paving being laid on top of it. If you're doing building work for a conversion, you can dig it out. It probably connects to a rainwater drain or a soakaway. I would hope that you are not on a slope where rainwater runs downhill towards your house walls. If you are, you would benefit from some kind of drainage system such as a French drain to intercept the water. Walls are OK to be damp below the DPC, but excessive water is undesirable and may make the concrete garage floor damp unless it has a DPM under it and lapped up the walls. This damp would affect your new floor.

BTW, integral garages have a floor that is lower than the house floor. One of the reasons is that in the (highly unlikely) event of a garage fire or petrol leak, flammable liquids will not run or spread into the house. I don't know if that is a current regulation.

But if we are converting the garage to liveable space with BR im assuming raising the floor (adding a dpc and insulation) will be a requirement

I see no problem with you raising the floor, as you are turning it into a habitable room.

I guess I just worry about putting/using a ramp over the drain

With a garage conversion I’d treat these as two separate details: the finished floor build-up and the drain at the doorway. Building Control will want a proper insulated floor build-up (DPM/DPC detailing, insulation and concrete or screed as designed), but the exact depth needs measuring against the existing damp-proof course and the external ground level. Don’t let the new floor bridge the DPC.

For the doorway, you wouldn’t normally solve it by covering a surface drain with a solid ramp. A builder or architect can set the threshold and use a linear/channel drain, or reconfigure the existing gully so water is collected before the door, while keeping the access gradients sensible. Get the levels checked first: house finished-floor level, garage floor, DPC, drive, drain invert and proposed outside level. Then show a simple sketch to Building Control before work starts. It should be a straightforward detail once those levels are known.