Concrete floor in converted Garage

12 Apr 2011
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United Kingdom
Please can someone advise. I've recently bought a bungalow in which the integral garage was converted years ago to a bedroom. This room seems to get lots of condensation and can smell damp/musty. Upon further investigation, we took up the floor to find a timber floor had been put on top of original concrete floor to bring up to same level as rest of house.

But, the original concrete floor is damp so don't think this has a dpm under it and the first row of bricks is obviously damp up to DPC too. All the external walls (2) are cavity walls.
On the external skin of walls there are air bricks but nothing on the inside internal wall, so air bricks are just ventilating cavity.

So my question is do I paint something like Sinaprufe/Dry Base all over concrete floor and up bricks to DPC, to provide liquid DPM and then replace wooden floor? Or do I vent the internal wall opposite to where external air bricks are?
Or both?

Bearing in mind there's not a lot of space. There's literally the joist depth and say another inch before you hit to the original garage concrete floor. The joists are suspended from metal brackets attached to wall.
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sam1264, good evening.

How much time do you have?? and how old is the property???

If it were me?? I would remove the timber floor, and get some De-humidification going, not just a high De-hum something a lot, lot larger.

At the same time remove the brickwork internally so the air bricks externally do not vent only into the cavity, which by the way is a fairly large NO-NO cavity ventilation can and will reduce the thermal efficiency of the cavity.

Now for the time element?? once the concrete floor appears "dry" turn of the De-hum and see what happens to the floor? if the floor remains grey / appears dry then crack on and re-lay the floor +++++ between the joists Insulation.

How many external air bricks are there on each exposed elevation??

Hi thanks for your reply. To be honest, we wanted to get this done and finished with in the next couple of weeks. It was built in 1962. There a 2 air bricks in each external wall. The room is only about 2.5m X 3m.

I've also posted the same question on another forum and interestingly nobody has mentioned the air bricks. A floating floor has been mentioned, ie getting rid of joists altogether and another possibility was to put new DPM down, insulate then pour concrete over.

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