Hybrid shed build - Damp Proof Course

[morg]

Hi guys, looking for some guidance!

I plan to build a small hybrid shed (blockwork/timber frame) approx 2m x 3m

2 Courses of blockwork directly onto the 90mm concrete base, I know normally you would use DPC 150mm above ground but do you think it wil be ok 80-90mm above ground or shall I not bother at all with a DPC as its just a outbuilding storage shed.

Thank you

 

[^woody^]

You need to protect the frame from damp

 

[morg]

Ok thanks woody

The wooden frame starts on top of the 2nd course of brickwork, so are you suggesting the dpc is laid between brickwork and timber? And not use any dpc under first course of brickwork, cheers for any help

 

[^woody^]

Any DPC should lap onto any DPM for the floor. Depending on what you are doing, you may or may not be having a DPM or the floor level may or may not be level with the DPC/base of the frame.

Good practice requires the cladding (and hence the frame) to be at least 150mm above any external ground to protect against rot from damp and splashes, and likewise for any DPC in any wall. So normally the DPC protecting the frame is the same one preventing damp from entering the building.

You suggest placing a DPC under the first course of bricks, but it's not clear what height that means in context of the ground and floor levels. If its too low then you have a potential for damp to move across the wall above the DPC. If the floor level is below the DPC level, then you need to extend the DPM up the inner face of the wall to the DPC.

So hopefully that's clear and you can work on those principles.

 

[morg]

Thanks woody,

I haven't poured the base yet so trying to get it right before I do anything.

Plan was to pour a 90mm thick concrete base with a DPM underneath, this base would be approx 70mm above current ground level.
This base would also be the shed floor.

Then the blocks would be laid on top of this base. All timber would be 520mm above current ground level.

So in this image my DPC is laid 70mm above ground level.

If the floor level is below the DPC level, then you need to extend the DPM up the inner face of the wall to the DPC

I see what your saying there but I don't think that possible for this scenario, as the DPM is under the base and the sides of DPM would be trimmed level to the bottom of the base after the base sets, as the base is mostly above ground the base will be in full view.

Still unsure on where to put the DPC or if I even need to use it at all, I could perhaps tank (paint) the concrete floor and blocks instead.

Thanks for the help

 

[domdee]

i'm building the same set up when i finally can get round to it. Same as yours. dpm under slab. then was planning on putting dpc directly under the timber - the wider stuff like this https://www.screwfix.com/p/capital-valley-plastics-ltd-damp-proof-course-black-30m-x-225mm/85921 lipped downwards on the outside. that way any splashing upwards from the ground will be below the dpc/timber. Then waterproof breathable membrane over the framework. and then hang the outer skin down a few inch to cover the dpc. will watch to see what advice rolls in.

 

[domdee]

something to this effect

 

[morg]

Hi domdee, sounds like a good idea, thanks for the post!

Good idea with the DPC and breathable membrane, I will follow your plan too.

I don't think I'll bother with DPC underneath blockwork... If water ingress becomes an issue then I will just tank the floor and walls with 2k epoxy paint.
But I may beef up the base thickness to say 125mm.

 

[domdee]

I did post a thread on asking for advice before. They said 4” is more than enough concrete if it’s a shed with a good 4-6” of stone whacked down first.

 

[Ljc1980]

Does a course or 2 of engineering bricks on the slab with a DPC on them serve any benefit over blocks straight on the slab?

Asking due to a block garage I am planning