Hi, Sorry if this is a question that has been asked a thousand times. I have read lots of posts about the best way of doing insulating garages but they are all slightly different to mine and the posts are quite old so i was hoping for a bit of advice. The garage is approx 16 ft x 16 ft built out of single skin brick with a pitched tiled roof. I am going to keep the garage doors but seal them with silicone and bolt shut (so they can be used if we ever come to sell the property) and build a stud wall in front. The garage floor is a concrete slab and i can see a DPM that is 2 bricks above floor level. I think i am going to build a wooden frame out of treated wood, insulate and then board with something like Kingspan K18. Do i need to build the stud wall in-front of the garage door first before the floor? Do i need to lay DPM over the concrete floor if it already has it or can i just put insulation straight over it and then board. If i do then do i run the DPM up the walls and garage door then build the stud wall over it? I was going to leave a gap between the baton and the brick wall but how big does the gap need to be? Can i paint the brick walls with liquid DPM or do some of the newer types of plasterboard have these on them or can this trap moisture between the brick wall and new wall? I am sure i have missed something but the more i read the more confused i am getting Thanks, Lee
Hi Devil's, No there will be no building control with this, although I would like to do it as close to the guidelines they use as possible dependant on cost because we may convert it properly when the kids are older in about 10 years. It will be used as a golf simulator/cinema room. Thanks, Lee
Hi, I think i have got this correct now but if someone could point out if i've missed anything that would be a great help. 1. Seal the garage doors shut with waterproof sealant 2. Lay DPM on the concrete slab up the brick walls to above the DPC and up the inside of the garage door. 3. Lay a wooden frame on the floor over the DPM at 600mm intervals and level out with wooden shims near garage door to fix the slope leaving a gap for expansion. Not sure what size gap to leave? 4. Install Celotex insulation between the wooden battens and tape where they meet. Not sure what insulation to use yet, any recommendations? 5. Lay T&G chipboard flooring. 6. Leave a gap between brick wall and new stud wall. Not sure what size gap to leave? 7. Construct wooden frame for the stud walls and insulate and board over with foil back PB so no vapor barrier will be needed. Do i need a membrane on the back of the stud walls if i leave a cavity? Thanks, Lee
Hi.That sounds pretty good. I've done this myself - convert an attached, single-skin garage to a multipurpose room (where I'm currently sitting). 1) I guess sealing the garage door makes sense, to prevent rain coming in if anything. Not sure quite how necessary it is, tho', as the room you're building inside will be well insulated and shouldn't be affected by a draught around the garage door. I wonder if even a good tape - like the kind used to join vapour-barrier/insulation sheets - will be enough? I wouldn;t like to have to remove the silicone in the future... But, your call on this. 2) Anyhoo, a further DPM makes sense to be sure to be sure. Take it up the walls as you say. I think, on the external wall, I'd be tempted to take it pretty much all the way up chust in case there's any rain penetration in the future. You could always line this wall separately from the floor DPM of course, making sure the floor sheet goes over the wall sheet. 3) The frame idea is good. I did similar to this, but just bedded the joists down on lines of concrete (on top of the DPM) and tamped them down until they were level. These joists aren't going to expand and contract much, so you can take them as close to the walls as you like, although you don;t want the edges to damage the DPM - so a half-inch gap is actually ok. 4) Ok, a tiny proportion of the room's heat will be lost through the floor - most is via the walls, windows and ceiling. So the floor really doesn't need much - I used 25mm Jablite sheets which I cut to fit snugly, and then layered them on top of eachother to fill the sloping space (mine went from around 40mm to about 150mm as I recall...) 5) Yup. 6) No need. 7) Ok, I didn't bother with leaving a gap betwixt the brick wall and the new stud frame. What I did was to plug and screw treated 2x1 (roofing battens) direct to the walls at 600 centres, fill in between them with 1" Jablite (cheap exp-polystyrene insulation) and then screw the thinnest Kingspan K18-type board I could find, which was 35mm overall thickness (around 25mm polyurethane insulation). Total thickness was therefore 60mm (plus plaster skim) and the room is genuinely the cosiest in the whole house.
Hi Devil, Thanks for the detailed reply. I have had the garage roof finished now so am looking to get this started now. I am going to go with your suggestions above as it seems easier and cheaper than what i was going to do. I have just a couple of hopefully final questions if that's ok Can i paint the walls and floor with liquid DPM instead of the sheets then i can just paint the whole of the walls seems easier? If i go with the liquid DPM can i lay the floor last or is it best to do this first? If i plug and screw battens straight to the walls will this affect the DPM? Thanks for all you help really appreciate it
Hi Lee. I'm not an expert on this stuff, but I have converted my own attached garage and have had no issues. For the floor, I don't see why you'd want to go any other way than 'membrane' as it's simply easier. Your garage floor almost certainly has one anyways, but it's always worth a second one to be sure to be sure. Could you go 'liquid' DMP instead? I don't see why not, and I can see your reasoning - especially for the walls. Modern liquid DPMs/tanking products are cracking stuff, so sound ideal for what you say. I understand that cementous 'slurries' are the best, but worth checking this out first. Yes, plugs and screws will penetrate any membrane going up t'walls, but in practice this isn't important for such small points. It's really just an 'in case' feature, and if your walls were so bad that they were pishing in water then you'd be nuts to convert that anyway without addressing this issue. I think - now you've mentioned it - what I would do is 'plastic' DPM for the floor, going a couple of feet up the walls, and a liquid DPM for the walls as this will be easier to do. Sounds good to me
Thanks for the response Sorry i've just thought of a couple more questions if that's ok Did you tape the joins where the insulation buts up to the wooden flooring frame? When i lay the DPM sheets down i need to overlap 2 sheets, how much do i overlap and do i tape this join? if so what sort of tape? Where the DPM goes up the wall do i tape this to the wall? Thanks again, sorry nearly there. I have just ordered the materials to lay the floor
Hi Lee. Hmm, mine was all a single DPM sheet which covered the floor and went a few feet up the wall. What overlap is required - or whether tape is needed - should all be info easily available on t'net. Certainly, when you are trying to 'seal' walls from penetration (usually to stop interior moisture getting through to a cold space and condensing out) it is usually to tape/seal all joints perfectly. However, if you are fitting TLB to the insides, then this in itself will do that job. So to prevent any moisture coming in through from the outside would, I'd have thought, only require an overlap - with the upper sheets overlapping the lower ones. But, I don't know for sure. I didn't tape my DPM to the wall as the strapping secured it in place. As for fixing your T&G boards, you choice is to nail/screw them down (as normal) or else glue them together to make a floating floor that sits on top of the joists. I don't think I'd glue and screw them as they could split when they expand and contract. I kept my boards exposed - stained light oak - so nailed them down as I like the 'authentic' look of nailed boards.
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