Advice on DPM Partial Garage Conversion

[PhilT1989]

Hi all,

Wondering if anyone can advise please. I've attached a photo of our kitchen as it is now. The dark area round the far wall and right hand wall used to be part of the garage, which has just been filled with concrete. I have some queries/concerns with how things have been done but I don't want to annoy the builders by 'meddling'.

I'm concerned that they have built the stud walls from the garage floor level, including OSB on the internal face which the concrete has been poured against, I have a worry that the moisture will damage the OSB.
The builders did put a DPM in under the stud walls and left it trailing out, into the kitchen, my understanding was that the concrete would be poured on top of this, but a separate builder came in to pour the concrete and cut this DPM right at the base of the stud wall. As far as I'm concerned the existing garage had no DPM and I could visibly see damp areas on the surface of the garage floor, now I'm worried that could soak up through the new concrete.

I'm also concerned the plaster is touching or even embedded in the concrete at points, is this a problem?

Am I right to be worried? Could they somehow have sealed the floor and walls before pouring? As I said I don't want to appear to be meddling but I don't want to install tiles and a new kitchen if I could face potential problems in the future.

Cheers

 

[^woody^]

What do the approved design drawings specify?

 

[PhilT1989]

What do the approved design drawings specify?

We were told as it's just a partial garage conversion we didn't need anything like that... is that right if we've not changed the exterior of the house and still have a garage? We did ensure with them that the stud walls adhere to the correct fire ratings but that's about it.

 

[Ivor Windybottom]

Stop being a pushover and ask them where the DPC is.

I'm pretty sure there should be insulation under the floor too, but I've no idea how this works where you're not making a new room but just extending an existing one that isn't insulated.

No planning permission needed, but I think I'm right in saying a garage conversion should involve Building Control, your builder should know this and probably does.

OSB should be water-resistant enough to stand a concrete pour, it's often used as formwork.

 

[PhilT1989]

Stop being a pushover and ask them where the DPC is.

I'm pretty sure there should be insulation under the floor too, but I've no idea how this works where you're not making a new room but just extending an existing one that isn't insulated.

No planning permission needed, but I think I'm right in saying a garage conversion should involve Building Control, your builder should know this and probably does.

OSB should be water-resistant enough to stand a concrete pour, it's often used as formwork.

Haha I will, I'm hoping not a mix up in communication as the builders got the plasterer to lay the floor to help move things along. Will double check on building control too. Can a DPM be laid over the concrete before tiles go down?

Insulation I have no idea, again I don't know if they put anything down under the concrete. They've definitely insulated stud walls and ceilings to the correct specs but this extension is an extension of an existing extension. You can see the original wall of the house to the right of the pic then previous owner extended into the garage.

That's good on the OSB but would it withstand prolonged periods of damp if it were to come to that?

 

[^woody^]

You don't need drawings, but you do need building regulation approval - which relies on the builder doing things right and the inspector then checking and approving things at certain stages.

The inspector would have needed to check the floor damp prevention methods and insulation before proceeding or covering them up.

That new stud wall would need to be built to external wall standards in terms of thermal and sound insulation and fire resistance.

Any DPM/DPC should be continuous.

The design should prevent cold bridging at the base and sides.

Plaster board or plaster should not touch concrete floors.

You should check whether you needed planning permission - losing a garage parking space may be an issue with some homes or original planning conditions.

 

[PhilT1989]

You don't need drawings, but you do need building regulation approval - which relies on the builder doing things right and the inspector then checking and approving things at certain stages.

The inspector would have needed to check the floor damp prevention methods and insulation before proceeding or covering them up.

That new stud wall would need to be built to external wall standards in terms of thermal and sound insulation and fire resistance.

Any DPM/DPC should be continuous.

The design should prevent cold bridging at the base and sides.

Plaster board or plaster should not touch concrete floors.

You should check whether you needed planning permission - losing a garage parking space may be an issue with some homes or original planning conditions.

Thanks for the detailed response.

Builders have confirmed they used a liquid DPM and SBR polymer in concrete, hopefully that will suffice, apparently was the only way to bridge between the DMP they installed under stud wall and the existing DPM that is buried in the existing concrete. We can chip away bottom of the plaster easily enough. We already checked there's no issue on planning re: parking spaces. Thermal bridging, sound, fire all taken into account in the stud wall but yeah sounds like I need to check building regs then. Can checks be done retrospectively somehow given all insulation and damp proofing is now covered?

Cheers

 

[Ivor Windybottom]

I doubt there's any DPM or SBR but what can you do about it?

If you're happy with it all and haven't involved BR so far then it may make life simpler to not involve them now. It depends on whether you want to start again or not.

If nobody checks it for 2 years then they're not allowed to retrospectively demand you do anything.

Your builder should (would?) have known they were required to inspect, so you have to wonder why they didn't do it.

 

[^woody^]

If nobody checks it for 2 years then they're not allowed to retrospectively demand you do anything.

The issue is that rising damp or condensation damp will be at the surface long before 2 years, and no one will be interested in that except the OP.

 

[^woody^]

Builders have confirmed they used a liquid DPM and SBR polymer in concrete

Is there any indication of a liquid DPM layer?SBR does nothing as a damp proofer.

Anyway, DPM layers should be continuous.

Also, thermal bridging of a stud wall has not been taken account of unless there is an insulation layer on at least one face of the wall.

You need to involve building control. And be wary of any builder who undertakes controlled work without actually taking you that building regulations apply.

 

[PhilT1989]

I doubt there's any DPM or SBR but what can you do about it?

If you're happy with it all and haven't involved BR so far then it may make life simpler to not involve them now. It depends on whether you want to start again or not.

If nobody checks it for 2 years then they're not allowed to retrospectively demand you do anything.

Your builder should (would?) have known they were required to inspect, so you have to wonder why they didn't do it.

Is there any indication of a liquid DPM layer?SBR does nothing as a damp proofer.

Anyway, DPM layers should be continuous.

Also, thermal bridging of a stud wall has not been taken account of unless there is an insulation layer on at least one face of the wall.

You need to involve building control. And be wary of any builder who undertakes controlled work without actually taking you that building regulations apply.

Turns out I misread, they said SBR and poly went down before screed, I am assuming this means a poly dpm but confirm when I see him. There is definitely SBR as I can see a half used bottle of it. As far as I was aware there was an insulated board on garage side but could be wrong. Will have to double check everything again, easier face to face. Cheers again.

 

[Ivor Windybottom]

Thought you said they did put one there, but then their subcontractor stanley knifed it off. In which case they did put one in but it's not there any more.

Is there a DPM under the old floor anyway? You may be making a fuss about something that's not going to make the slightest difference to anything. Putting a DPM under the new bit might tick the box but wouldn't really achieve anything if the rest of the room doesn't have one, it won't if it's old.

You could just put an epoxy coating over the whole lot, seal it at floor level. E.g....

Epoxy Damp Proof Membrane 5kg

A two-component, solvent free, low odour liquid epoxy DPM that is tolerant of residual moisture in concrete floors. When dry it creates a new damp proof layer across the floor surface protecting the future covering from damp.

www.permagard.co.uk

 

[PhilT1989]

Thought you said they did put one there, but then their subcontractor stanley knifed it off. In which case they did put one in but it's not there any more.

Is there a DPM under the old floor anyway? You may be making a fuss about something that's not going to make the slightest difference to anything. Putting a DPM under the new bit might tick the box but wouldn't really achieve anything if the rest of the room doesn't have one, it won't if it's old.

You could just put an epoxy coating over the whole lot, seal it at floor level. E.g....

Epoxy Damp Proof Membrane 5kg

A two-component, solvent free, low odour liquid epoxy DPM that is tolerant of residual moisture in concrete floors. When dry it creates a new damp proof layer across the floor surface protecting the future covering from damp.

www.permagard.co.uk

Yeah a bit odd as they did leave the sheet trailing out from under the wall, I don't know if it wasn't big enough to cover the area or what but the plasterer cut it out and now builder saying poly and SBR went down before screed so who knows I don't know why they'd put a new one down or how they'd attach it to the old one anyway...
It's a 50s build with bitumen on the concrete floors elsewhere downstairs, although most of that has cracked and no issues elsewhere. Garage itself has never had damp, but the metre wide passage we extended the kitchen into did have the odd dark damp patch on the floor at base of the wall. That area is now covered by the new stud wall and insulation though so maybe it won't cause an issue.
They said they are going to seal the concrete before tiling, don't know if that means something similar to your recommendation will be going down.
I'm fussing because we have friends who are having to pull their floor up after similar works due to moisture on the surface of their tiles. Although my wife would tell you I'm too much of a worrier and a thinker regardless...

 

[Ivor Windybottom]

As it's 50s build it would have been completely pointless putting a DPC under the new bit, as the old bit will have nothing anyway. Problem solved, stopped worrying.

The dark patches were probably just because it was lower at those points. It's probably all damp to a greater or lesser degree, ours is also 50s built, it's just a fact of life. We sometimes see humidity rise after heavy rain. No mould or rising damp, just general airborne moisture. Possibly just from the air outside, but I suspect some vapourises from the floor despite the bitumen.

But I'd suggest now taking assertive control of the situation and ensuring that something genuinely waterproof goes on top of the concrete. A proper coating of an actual waterproof layer of plastic of some sort. I suspect that Bob the Builder is going to brush a £10 tub of SBR over it and declare job done.