Floor in a converted garage - what do you think?

[JonnyMac2016]

Hi all,

Just bought a house (1981 build, uninsulated cavity walls, solid ground floors). The house originally had an integral garage which in the mid 2000s was converted into a living space.

This space has a very 'musky' feel/smell to it, and wondered if this might be to do with how they have put the floor together when doing the conversion. I've drawn a little picture 'side profile' which shows how it's put together.

The concrete slab (the original floor of the garage?) sits very slightly below the outside ground floor level. On top of this there are 3 inch deep wooden joists which run across the room with rock wool type insulation in between. On top of this there is a laminate flooring with a membrane underneath. All of this sits below where the DPC is on the external walls. As you can see in the external photos there is one brick depth below the DPC (and no air bricks).

Does this all seem very badly done? There is essentially a suspended floor in place with zero ventilation, beneath the level of the DPC, and stuffed full of rock woof insulation. To the idiot observer such as myself this seems like a recipe for damp.

Any thoughts if this is bad building work, and if so what should be done about it?

Thanks!

 

[Burnerman]

Unfortunately there's no guarantee that a damp proof membrane was laid below the garage floor concrete so there's every chance that moisture - although not visible - is wicking through.
Personally I'd strip back to the original floor and coat it with one of the Permagard products......its almost like its own rubber membrane when the stuff has cured after painting on, and its continued up to DPC level on the walls.
With mine (1960 built cottage) I allowed the Permagard to cure for a few weeks, and then laid a 3 x 2 timber frame with Kingspan insulation laid within. As the 3 x 2 was screwed down, where it pierced the Permagard I recoated with Evercryl before finally screwing down. After that it was 22mm waterproofed chipboard and then a MultiPanel flooring laminate.
I'm confident that in my situation the work has been a complete success - although it took 20 years before I got round to it!
No more musty smells at all.
John

 

[JonnyMac2016]

Thanks Burnerman!

I'm guessing yours didn't have rockwool insulation originally within the joists?

I also half wondered whether the bottom of the cavity is full of rubble and junk from the original build (given it was originally the garage) which might be allowing water penetration through into the floor void.

 

[JonnyMac2016]

Update!

I have pulled up the flooring and chipboard in one of the corners of the room (photo attached). There is a membrane on the bottom of the concrete floor slab, however the bottom of the wall is very damp and the insulation which was butted up against the wall is sodden. So I guess there is the problem.

I guess the solution would be in line with what Burnerman said and have a damp proof solution up to the level of the DPC in the wall? And then putting in the PIR insulation instead?

At what point does it become a better solution just to simply poor a load of concrete in and bring the floor level up to the rest of the house?

 

[Burnerman]

Whoever did the first work before me simply laid polythene sheet on top of the garage floor, and then laid timber on top of that - the timber wasn't fastened down and there was no underfloor insulation.
On top of that was 18mm chipboard. The room effectively became a bedroom after that.
Along I came and fitted a quality carpet with underlay.
As the years progressed the room always smelt musty and for example if you laid a book or whatever on the carpet for a day or so, when you removed it the smell was stronger.
I kept things at bay with the help of a dehumidifier for years afterwards.
So, when I stripped the room two years ago, I found what I described before....and lifting the polythene showed a slight condensation on the underside so some moisture was definitely getting through.
By tanking the property using the Permagard stuff, I'm convinced all is well now - and the only real alternative was to break the old concrete out, lay a DPM and then relay. That was too much work for me!
John

 

[Tigercubrider]

I helped a mate convert his detached 50's garage to a recording studio.

We tanked the floor and brought it up a foot on the walls, then added a polythene dpc before adding a very solid type of rockwool, and gluing chipboard into a solid floating floor which isn't attached to the walls. The walls sat on 1/2 thick neoprene so they were independant - for sound isolation.

We did this a good 15 years ago and his place is dry as a bone

I would think that your garage slab is getting very cold and condensation forms?

Hope this helps?