# Insulating garage floor



## RichD1 (14 Feb 2015)

I want to insulate my garage floor as I want to use it as a workshop but still want to be able to park cars.

I'm thinking about laying 100 x 50 treated timbers at 400mm centres over a layer of DPM. The joists will be topped with 25mm ply with insulation between.

Do you think this will be strong enough to support a car?

Richard


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## blackrodd (14 Feb 2015)

I would think that over a period of time the ply will bend and buckle.
Could you mark the area where the wheels are going to be and solid the floor up, just at those areas.
Even marking the finished floor, stripes etc?
You could lessen the cost by using a 19mm flooring grade ply over all.
HTH Regards Rodders


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## Alexam (14 Feb 2015)

The whole floor of the garage or the part you will be working on?

I have some heavy duty golf range driving mats across my double garage, Really thick, but leaves areas other than where I work as the normal painted concrete. This allows easy movement of equipment across them. If you have a timber floor, the damp may have an adverse effect, but this is not the case with the matting. It could be over the whole area, but the extra cost is not really worth it.


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## RichD1 (14 Feb 2015)

Thinking of insulating the whole floor.

Yes good idea, I could work out roughly where the car wheels are likely to be and then ensure that there are joists in that area. I intend to fit the joists from front to back so would work OK with the line of the wheels of the cars. Also thinking that there would be noggins separating the main joists so this will reduce the area of ply which is unsupported. I'm hoping that I can make the insulation between the timbers come level with the top of the joists and this should also provide a bit of support. 

Originally I had a simple t&g chipboard flooring floated over some 50mm polystyrene and this lasted about 5 years before the rainwater penetration caused the poly and chipboard to fail. Didn't fit a DPM then either. 

Surely 19mm ply is going to be weaker than 25mm ply.

Current garage floor is very dry apart from when it rains and water gets through the wall floor joint on one side. I intend to apply tanking slurry on the outside and also seal this joint along the inside wall. Hopefully with this and the DPM lapped up the walls will keep the floor dry.


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## artie (14 Feb 2015)

I would make sure it was dry before doing anything else.


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## RichD1 (14 Feb 2015)

artie":36nt2xns said:


> I would make sure it was dry before doing anything else.



Yes, that's my first priority. Just having the front wall rebuilt and a new insulated roll door fitted. Once that's done then I can start to seal the wall/floor joins on the one side where the rainwater comes in.

Richard


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## blackrodd (14 Feb 2015)

quote" surely 19mm ply is going to be weaker than 25mm ply" unquote 
I would have thought if the car parking area was taken care of by almost solid timber work,under the flooring, then you just needed a workshop floor, so 19mm on 400 centres would suffice.
Bang in a few bicuits between the joisting, even.
Unless, of course, you have intentions of moving cast iron type machinery into place, in which case you ought to bring the floor level up to at least 6" concrete for both potential requirements. 
meaning that if you have 4"" of concrete now, add on another 2", at least, taking care to prime the old concrete to accept the new layer. Regards Rodders


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## finneyb (14 Feb 2015)

Alexam":1hoi4gur said:


> The whole floor of the garage or the part you will be working on?
> 
> I have some heavy duty golf range driving mats across my double garage, Really thick, but leaves areas other than where I work as the normal painted concrete. This allows easy movement of equipment across them. If you have a timber floor, the damp may have an adverse effect, but this is not the case with the matting. It could be over the whole area, but the extra cost is not really worth it.



+1 , it's quicker, better and probably cheaper than ply IMHO

Brian


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## AES (15 Feb 2015)

I'm not in the trade at all, and this may not help any, but about a year ago when I was regularly visiting Outpatients at my local hospital. They were refurbishing the area where the ambulances park when delivering patients to A&E (right next to the Outpatients entrance).

I was very surprised to see that they excavated the asphalt & concrete down to about a foot/eighteen inches deep, then laid a new concrete base about 6 inches deep. When dry they then took sheets of a very rigid foam plastic about 6 inches thick and cut the sheets up to fill the whole area. I saw then cutting the stuff and they just used normal hand saws. After that they then just laid tarmac on top(? - see below).

I'm sorry, I've no idea what the foam was called, it had no names on it, but it was a cream colour and, IF I remember correctly, was silver on one side (aluminium?). As said, it was very rigid (I could hardly pinch my thumb and forefinger together on a bit of off cut I found).

That was about a year ago and Ambulances are now parked on it regularly (Mercedes Sprinter based vehicles mainly) and when they are not present one can't see any sign of deformation on the upper surface where the vehicles have been standing. The area is big enough for 2 such vehicles to stand side by side.

Unfortunately I did not see if they laid anything on top of the plastic before laying the tarmac - one week it was still all plastic foam, next week it was all tarmac!

As said that was about a year ago now, no sign of any deterioration since, and apart from an overhanging roof and wall to one side, the rest of the area is open to the elements, like a car port. Summer temps can be 30+ deg C, winter down to -15 deg, sometimes snow covered, and like UK, it "sometimes" rains in Switzerland!!

Sorry I have no idea of the name of that foam but perhaps there's enough info above for you to ask some Qs at a builders merchant?

FWIW
AES


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## RobinBHM (15 Feb 2015)

I wonder if you could cover the whole area with celetex type pir insulation board then 2 layers of 18mm plywood all three layers with joints offset. There would be no joists that could rot in an unvented space and there would be no thermal bridging, as there would be with joists. It would probably depend on how flat the existing slab is.


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## RichD1 (15 Feb 2015)

The existing concrete floor has been laid for over 25 years and is still sound with no cracks or movement. It's not dead flat but pretty close so the 100 x 50 joists will be virtually fully supported. Not sure whether I need to fix the joists down with concrete bolts. With the potential weight on the floor and that the ply will be screwed every 300mm I don't think it will be going anywhere. I guess a little float for expansion is a good thing?


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