DPM options for new garage on slab foundation

I wasn't suggesting that you actually employ a builder for your slab, just that it is more challenging than a strip found & therefore time consuming. I really don't think that you can or should rush at a job like this, the entire build depends on its accuracy. The whole point of diy is that time isn't of the essence surely?
What does your local building control suggest, or aren't you bothering them?
If floor insulation is a must then why not float a floor over the slab. It would make the initial build a bit easier, albeit still a challenging shutter but if you have the materials to hand, then your half way there.
 
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I totally agree with you. It's just that the work to put the slab in was already done before i posted the original question. I left all that out in the first post as i didn't want to bore everyone with detail. Hence, already commited to a slab. :)

I checked to see if BC wanted to see the works. They didn't. Not spoken to them since. Can't imagine they'd be too keen on helping out for free?

Re "floating a floor over the slab". How would that be different to a screed over the polystyrene, done after casting the slab found?
 
Ignoring the slab versus strip method (logic) and the fact that the screed might well crack and the pointless insulation blahdy blah, unless I've lost the plot, this is how the dpm can be made to work.


 
Thanks for that.

Of course the screed could crack, any suggestions as to why you think it would? I could always throw some mesh in.

Why do you think the insulation is pointless? Surely it wouldn't be as cold as the slab itself if sitting on it with your arse???
 
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You or the next owner driving a car over it will apply massive point loads that a 50mm screed is simply not designed to take. 50mm polystyrene insulation is a bit pointless as its a cr*p insulator, you should think about having around 100mm Celotex or Kingspan for effective insulation. If you plan to use it as a den you may aswell fit cavity insulation at the same time too.
 
Aye fair point.

i'll either raise the internal floor level to allow decent insulation and thicker/screed, or just put the DPM under the slab rather than under the screed.

Cheers.
 
Yes but you can't stick your dpm under the slab or you won't be able to lap it into the wall other than externally where it will be incredibly vulnerable.
 
A bodge, it won't last forever.
Just get a small digger in and dig the strips, failing that get a couple of labourers in for a day.
and a skip.

If you insulate and want to drive about on it, min 80mm celo'span and 100mm concrete on top with lapped A142.

Have you considered timber frame internally? Better for insulation spec and you can build it off of 3 courses of brick with the dpm lapped over this. Then you could insulate and pour crete on top and come in just below the top of the brickwork. You will need a ramp outside though.
 
Hi guys,

Drains laid this weekend. Thought the muddy work after the foundations was done, but a mornings of rain, meant a lot more mud.

Any advice on how to tie the new dpc into the existing. This is not a solid slab extension, I'll have suspended timber floor with Oversite. My question here is simply the dpc on each skin of the walls into the existing dpc. Do I try to remove some mortar under the existing and push the new under the existing?

Out of interest, do you genrally keep the dpc at the same level, or is it acceptable to drop it by a coarse or two?

Thanks

Mac
 

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