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Raising an Existing Concrete Floor in a Garage

Postby AdamW85 » Sun Mar 07, 2021 4:26 pm

Good Afternoon, hope everyone is well.

I have a question about how best to go about raising the level of an existing concrete floor in my garage.

To give a bit of background, the property had a large side extension added to it ~20 years ago, long before we bought the property. There is a concrete floor in the garage, which is below the level of the main house, by approximately 100mm.

I would like to partition part of the garage to create a utility/walk in larder room, in doing so raising the level to match the adjacent kitchen.

2 external walls are cavity wall, brick outside and block inside.

The external ground level has a reasonable slope on it, and at the point where I would like to create the new room, the exisiting concrete floor level is ~6 bricks up from ground level (see external picture).

I do not know what is beneath the existing concrete floor. I could excavate part of it out, but not sure this is neccesary. Given I have ~100mm to add, I could add in some insulation.

1) What would be the best way to raise the level?
- Concrete or timber?
- Can I place insulation on top of the existing concrete floor, before pouring the slab?

2) I assume a vapour barrier is required, does this need to go up the internal block wall, and how far?

The 2 external cavity walls do have insulation in it, but I think I will take the opportunity to insulate the wall internally before plasterboarding. I am thinking of creating a stud timber frame attached to the blocks, with the insulation between it. Nothing too think, 50/60mm.

3) Would you poor the new floor slab, then add the wall insulation butting on top?
4) Or, insulate the wall then pour the slab?

Thanks in advance for any help and advice.

<a href=""><img src="" alt="20210307-141807" border="0" /></a>

<a href=""><img src="" alt="20210307-142249" border="0" /></a>
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Postby stoneyboy » Mon Mar 08, 2021 10:05 pm

Hi afamw85
Suggest you line walls with breathable vapour barrier, lay a DPM on the floor lapped up the walls. Insulate the walls, lay 75mm expanded polystyrene with 25mm chipboard on top, then board the walls.
Regards S
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