Damp proof membrane for New Build garage floor.

[Mavan1984]

Hi everyone,

Our house is a 10 year old new build. We have a garage which is attached to the side of the house and we recently had it converted so that we could use it as a small cosy or study.

Me and my DH are very inexperienced when it comes to building work and we blindly trusted our builder who frankly hasn't done a great job.

The garage originally had a concrete floor and the builder skimmed over it but I'm not sure if he has layed any damp proofing down. I also dont know if the house builders had put any in. I have recently read online that this is a necessary step to avoid damp issues.

Ive had the room painted and had skirting boards put in. I will be getting carpets put down and the last thing I want is mold or damp issues. Is there anything I can do to prevent such issues? We've tried to get in touch with the builder several times to ask if he's damp proofed but we can't get through to him.

Any suggestions on what I can do please?

Thanks.

You need a DPM. It’s not up
to habitable standard without one.

Thanks for your reply. What's the best way to put one in at this late stage?

Any flooring people can do it. My hallway didn't have one as my dad did my initial flooring when we moved in 16 years ago. Once I had flooring people in they said I would need it and were surprised it wasn't done. Didn't have any problems previously but think it's better to have it

Thanks, do you know what they put down? I've read that you can get a plastic membrane put in.

@Mavan1984 Did it get signed off for building regs?

What exactly did you see when he did the works? Garage floors are usually lower than the house so they have to raise it, sometimes this is a sheet of membrane (your damp proofing) then Kingspan thermal flooring on top (giant sheets of silver backed foam boards) then sometimes concrete on top of that or just sheet floorboards, I have had both kinds as one was a kitchen extension and one a garage conversion. Alternatively they install joists depending on the height difference. Most go for Kingspan as it is quicker.

If you want to see what I mean, The Restoration Couple on Youtube and their "INSULATING A CONCRETE SLAB - DIY Garage Conversion Floating Floor" video.

Unfortunately we didn't apply for building regs because it an integral garage and we don't plan to move from here any time soon. In hindsight we should have applied for it for piece of mind more than animating else.

Both times I've had it done - kitchen extension and then hallway - it's been like a black rubbery liquid which is applied and then left to dry for 24 hours

m.youtube.com/watch?v=rtTNsLFCLkQ

https://www.amazon.co.uk/Drybase-Liquid-Damp-Proof-Membrane/dp/B008KMCWNI?crid=1J6XBRXCFOUI7&keywords=drybase&qid=1673880989&sprefix=drybase,aps,65&sr=8-14&th=1&linkCode=sl1&tag=ragnbonebrown-21&linkId=b9966a63401c5601f7b5789a466b9ad3&language=enGB&reff=asliiss_tl

Thanks for your reply. Did this go over the concrete? Also once that's down would I be OK to put a thick underlay over it and then carpet? I'm not too fussed about putting any insulation in. Thanks.

Do you have any photos of the garage floor before the conversion? Usually there is a membrane already under the concrete, and it’s usually visible at the edge of the floor where it meets the wall.
At only 10 years old, yours will have a membrane under the concrete, 99.9% sure.
what were the external walls finished with? Did you have the single skin exterior wall plasterboarded on a frame or battens? And where is the finished floor height in relation to the DPC? Usually the top of the concrete floor is about 2 courses of bricks below the DPC ( black plastic usually clearly visible ).

As above , if your house is only ten years old then it will have a dpm under the concrete in the garage , same as the rest of the house . It probably wont have any insulation under the concrete floor ? But will have damp proof.

Lack of a building regs certificate could come back to bite you on the arse when you do go to sell further down the line as you were living in the house when the work was done. You see it on here all the time. It also ensures a level of competence by the builder which you are now questioning yourselves. My builder arranged the building regs people from the council to check his work. This is now registered with the council and is available to view online.

Did you also check planning because it is considered a "change of use" to a "habitable room" and impacts parking even if you didn't park your car in there. New build estates have to consider off road parking and on my estate which is slightly older we don't have permitted development, everything has to go through planning permission but it is free because of this. This included my integral garage conversion.

Did you take photos as the work progressed? Applying retrospectively for building regs can have issues if they need to look at the underlying structure. If you have photos it might show the work the builder carried out in terms of insulation in the walls etc.

Thanks for your reply. Did this go over the concrete? Also once that's down would I be OK to put a thick underlay over it and then carpet? I'm not too fussed about putting any insulation in. Thanks.*

Yes it went over the concrete and Yes that would be fine I think*