Quick and easy garage insulation?

[R P McMurphey]

I have a garage that id like to turn into a heated workshop...its single brick thick with a tiled roof and no insulation. any products recommended?

Steve

[Christian McArdle]

recommended?

First you need to insulate. Don't worry about the single brick walls, they're fine.

I'd recommend using 50mm of Celotex/Kingspan (not polystyrene!) solid insulation on the walls. Then line with plywood, screwed to the walls through the insulation into the brick. This gives something to hang stuff off (and attach tall shelving/racking units to), and ensures no cold bridging through studs or battens. Either paint or plasterboard the plywood. I'd be inclined to plasterboard for fire safety.

The roof should also be insulated. You must ensure that there is sufficient ventilation above the insulation. You can probably provide this using air bricks or tile vents. The exact form of insulation will depend on what you have. However, 100mm of Celotex/Kingspan would do here, lined with plasterboard. Ensure there is vapour check on either the insulation or plasterboard and that it is taped.

Now, a quick heat loss calculation (these may not be very accurate, as I'm guessing u-Values a bit), assuming a single garage gives me:

Air Changes: 450W Walls: 225W Ceiling: 70W Floor 585W Access door: 155W (single PVC) Garage door: 650W

As you can see, the floor and garage door are the real culprits here. You will serious improve matters by loading the garage door with Celotex and draft proofing it. You may need to adjust balance weights or springs to allow for the extra weight.

The floor is less easy to solve. If you no longer wish to park the car in there, then even 25mm of Jablite will drop the heating requirement massively, although you need to decide what you need above, either lots of concrete, or a suspended or floating wooden floor.

As for heating, if you aren't intending to heat constantly, then electric heating should be fine. If the floor and garage door can be brought down to reasonable values, then you are talking a peak loss of just under 2kW. A

2.5kW electric convector with fan boost, thermostat and timer would be indicated. Alternatively, if the house central heating circuit passes nearby and can be conveniently tapped into, then a 2.5kW radiator or fan convector would be easily enough. If I didn't intend heating all the time, I would be inclined to put a programmable room stat and zone valve in there. If the system isn't suitable for subzoning, you can still install them, but they would operate as a glorified timed TRV. As you are likely to want the timing to be less than that of the house, this would not be too bad.

Christian.

[The Natural Philosopher]

Wood, foil backed plasterboards and rockwool for the walls, or celotex if space but not cash is limited.

build false ceiling and rockwoool it for teh roof.

[Andy Hall]

I've done exactly this with the same kind of building using 50mm Celotex sheet.

The roof is a fairly standard trussed type of construction.

The first job was to board over most of what in a house would form the loft so that I had easy access to walk about and get to the sloping roof.

It's important to have ventilation behind the insulation on the cold side, so I fitted soffit vents between each rafter section. For the roof I then cut and fitted Celotex sheets on the surface of each rafter, attaching with long drywall screws with washers to spread the pressure. THis is a very lightweight material, but it's good to fix it firmly. Cutting and fitting the roof pieces was easy, if a bit time consuming. I then taped the joints of the Celotex using a metallised tape to seal against draughts.

For the walls, I built studding using pressure treated timber, 75mm x

50mm with short side facing the wall. This was stepped off by about 25mm from the wall and the frames attached to the floor and to the joists above, not to the wall. Air bricks were put into each wall. The Celotex sheet was then cut and friction fitted into the spaces in the studding and taped. The framing was then clad in 18mm WBP ply which means that I can fit virtually anything to virtually anywhere on the wall.

I have up-and-over doors and these certainly needed insulation as well. I created a wooden frame on the insides in fairly light timber and attached Celotex into that as well. Some draught strips were added to the doors as well.

I decided not to go to the upheaval of digging up and insulating the floor. It worked out by calculation not to be the largest loss of heat anyway. I could have put in a false wooden floor and insulated that I suppose, but I didn't want the loss of height or the ramp from the outside.

The result is well worthwhile. Previously the garage was for workshop purposes too cold to use for the winter months. I would run two 3kW fan heaters and it hardly made an impression. I calculated that uninsulated, it would have taken 12-15kW to achieve 18 degrees or so inside when it's zero outside.

With the insulation, I calculated that 3-4kW would be required, and this has proved to be the case. For heating, I fitted a heat exchanger to the central heating system to create a separate circuit and run the pipework insulated through ducting buried between the house and the workshop. Conventional panel radiators in the workshop provide the heating from that and of course it is configured as a separate heating zone with its own thermostat and timer.

If you are going to embark on a project like this, it is worth doing a complete materials list and going along to a timber and materials merchant like Jewsons and asking them to quote for the whole thing. I did that and got very good pricing.

To give you an idea, Celotex in 50mm costs about £15-18 for a

2440x1220 sheet.

.andy

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[Andy Hall]

This is basically what I did, Christian, although in speaking to both Celotex and Kingspan technical departments they recommended using studded framing fixed top and bottom and ventilation behind. This also makes for easier fixings. I felt that ply was more suitable than plasterboard again for strength reasons and less likely to get dinged in a workshop. Regarding fire, the main risks are solvents and in a woodworking environment not clearing up the debris properly, so I've taken care of those.

I debated the various ways of doing the insulation including putting some between and some on top of the rafters, all on top etc. The rafters are only about 75mm or so and I didn't want to have 100mm of Celotex on top - it cuts into the space too much. Frankly, the cutting and fitting was lengthy, so in the end I elected for using the same 50mm as on the walls. Doing the sums there is very little overall difference to the building. In my roof construction, soffit vents (round ones fitting into a hole cut with a hole cutter) worked.

I found that by boarding at ceiling level that the overall heat loss upwards is reduced. It ends up that the space above achieves a temperature of about 5-7 degrees on average below that of the space below, so it reduces the loss through the Celotex anyway. Since I want to use the top space for storage anyway, I don't really want it at outside temperatures. The arrangement works well.

The door is certainly a big culprit. With a fairly light wooden frame and Celotex, the extra weight did not seem to be a problem. I may go back and add heavier sound deadening material later, and that would impact the

I have a larger garage and as a proportion, the heat loss was not as bad though the floor although it is now the largest part. I felt that digging up the floor and redoing with Jablite was not a practical proposition and I didn't want to raise the height of the floor, a) because I need the headroom to the ceiling for various equipment and b) I didn't want a ramp to outside. If the building were taller, it would have been interesting to have a raised floor to run ducting for air extraction for woodworking, but that would need 150mm or so and that's much too much for whatg I have.

I did the heating as a separate zone from the CH and via a heat exchanger. This is the cheapest way to heat. I used conventional radiators because I don't want fan heaters etc. blowing wood dust all over the place....

.andy

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[Christian McArdle]

It probably depends what you want to hang off the walls. A few light shelves and stabilising connections to floor standing shelving/racking should be OK to plywood screwed regularly to the wall through 50mm of solid insulation (and supported properly at the bottom for vertical loads). However, I'd be worried about connecting kitchen wall units or heavy shelving directly.

My personal preference is to use both. Plywood, then plasterboard screwed directly to it. I have a thing about spiders and find plasterboard easier to keep clear of the little bastards than plywood, which has nooks and crannies in the surface that attract cobwebs. It is also far more flame proof. It is still easy to screw stuff to the wall as the thin layer of plasterboard has plenty of compressive strength when screwed tightly to the plywood, so long screws go through the plasterboard, screw nicely into the plywood and have the insulation behind to make screw length not significant. I'm not talking about attaching with dabs here.

You're probably right. With 100mm I was calculating only 70W through the ceiling. 50mm is probably just fine.

Christian.