well, its getting colder. Its getting darker too, so im mindful of the approaching necessity of spending many cold hours in the garage /workshop. the roof is bare rafters and is gonna be tricky to insulate with rock wool type insulation. i have just priced up celotex and its £25 per 2sqm board! Even tri iso super 9 is £100 per 10sqm so that's not much cheaper either. There has got to be a more cost effective solution to insulating the garage. i will probably use a hot air and radiant heat source.
I went through this issue a couple of years ago. My 30m^2 garage was single brick wall with concrete floor and a pitched, felted tiled roof with access open from inside all the way up. There were up/over doors at the front (timber and ply construction with poor sealing around the edges).
I did the calculations for heat loss and to get the inside temperature up to a reasonable 18 degrees when it's around zero outside was in excess of 12kW. With electric heating, the implication would be a 50A supply and at 6p/kWh, a cost of 72p/hr to heat it. In practice, I could run two fan heaters and achieve about 10-12 degrees eventually but in a 3-4hour work session it really was hardly worth running the heating; plus for the 50A supply it would mean only
25A left for machinery which wasn't enough.
Therefore I did the calculations for using 50mm Celotex for the roof, walls and doors and nothing for the floor. This basically brought the heatloss down to about 3-4kW for 20 degrees inside and 0 outside.
I insulated against the rafters using Celotex attached with long drywall screws and flat washers, then joints taped with foil tape. I added soffit vents to allow ventilation behind the sheets.
For the walls I made a stud frame with a 25mm space behind for ventilation, infilled with Celotex and with 18mm ply over the top.
I improved sealing on the doors with special vinyl strips and again Celotex attached to the insides of the doors. It's light in weight.
FOr heating, I added a stainless steel plate heat echanger to the house CH system and added a secondary heating circuit for the garage so that the heat source is from gas rather than electricity. This results in a worst case cost of heating of about 5p per hour.
I used Celotex throughout because it provides good insulation for a given thickness and is light in weight and quick to fit. I was more concerned about space and running cost than capital cost.
To implement more cheaply, I would have kept with the Celotex for the roof and doors and used rockwool or fibreglass for the walls. I found it possible to get 50mm Celotex at £15-17 per 2440x1220 sheet by making a project including the timber and sheet materials and asking builders merchants to quote competitively for the lot.
The result is that I can use the workshop comfortably whenever I like and have adequate electrical supply for the machinery.
thanks all for the advice. if i can get celotex at that price i will do the roof with that. the walls i will probably do with thiner stuff because i cant realy lose the space. now the hunt is on for cheap celotex! if i cant get it that cheap, i will do the jablite thing.
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