Understairs cupboard floor - need DPM?

[DIYC]

Hi,

I'm trying to make use of the space under my stairs by turning it into a cupboard.

I've made a whole in the plasterboard big enough to crawl inside and now I'm in I've found a few things that raise some questions.

The stairs are open on one side and join an internal wall that has the garage on the other side. Obviously this wall is block work, not a stud wall.

My garage floor is several inches lower than the rest of the house, which is pretty normal I think.
My lounge floor is the same height as the rest of the ground floor.

The floor space under my stairs is somewhere in between the two.

The plasterboard wall I've broken through was simply a stud wall.
It had a top and bottom rail and 3 vertical studs.

When I look at the bottom it looks like the DPM for the lounge floor stops there.

What do I do in my new cupboard under the stairs?

I'm not putting anything particularly precious under there, do I need to do anything?

I'm thinking I could simply seal the concrete and paint it with some garage floor paint (that's all I did in the garage).

Alternatively, I could batten the floor, put some loft boards on it and then tack some carpet on top. If I do this, do I need a DPM? It's starting to sound like an expensive project for something that was supposed to be a quick 'knock a door through a plasterboard wall' job!


Thanks,

C.

 

[RedHerring2]

If there is no dpm, you'll need one.

 

[DIYC]

So surfing around the usual shops it seems like I can get a big enough DPM for the cupboard from ToolStation for a tenner.

What do I do?

Put the DPM on the concrete base.
Make a timber frame, lay that on the DPM.
Put some 25mm polystyrene insulation in the frame.
Screw some plywood on the frame.

Is that it?
What do I do with the edges of the DPM?

Obviously I then need to plasterboard the walls and under the stairs.
Do I do the floor first or last?

Thanks again,

C.

 

[RedHerring2]

If the existing surface is smooth and won't puncture the dpm, then, yes lay the dpm on the existing surface. Alternatively, blind the existing surface with building sand to provide a smooth surface. Often 50mm thick layer is used on compacted hardcore. You'll have to assess what/if it's needed.

The dpm should be allowed to lap up the walls past the existing dpc. Tape in place if needed. Or the upstand insulation may hold it in place sufficiently. I use the base insulation to hold the upstand insulation in place. The dpm can be trimmed later, but allowed to run up behind the pb a little.

I wouldn't use timber joists/frame or floorboards 'cos there's no ventilation. I'd lay some concrete in there, over the insulation. Don't forget to allow for a screed.
You'll also need to prevent the water from the concrete finding its way down any joins in the insulation.

Lay the floor, then the pb on the walls. Don't allow pb to rest on the floor, raise it slightly, say with a 25mm batten underneath which can be removed after fixing. This gap will be covered by skirting.

 

[^woody^]

If there is no dampness in there now, then I can't see why a DPM would be needed

 

[RedHerring2]

I'm tempted to agree, Woody.
I thought that there might be a possibility of ventilation dispersing any dampness in there currently, thereby masking its presence.
And for the cost of a bit of dpm, why not install it?

If there is already any dpm, another can't do any harm.