My garage

[m_c]

Thanks for that. I've tried googling for those figures/calcs in the past, and always given up due to finding totally irrelevant or overly techincal stuff that just makes my head hurt, but those pages simplify things well!

[irving2008]

Thanks for that. I've tried googling for those figures/calcs in the past, and always given up due to finding totally irrelevant or overly techincal stuff that just makes my head hurt, but those pages simplify things well!

Yes i found it useful as well

Sample calcs...

For a 5m x 2.5m concrete panel garage, 2m high. corrugated steel roof

Wall area = (5 + 5 + 2.5) * 2 = 25sq m. heat loss = U x A x dT . U = 1/R for concrete ~ .08/25mm so a 50mm panel R=0.16, U = 6.3, loss = 6.3 x 25 x (20 - 0) = 3150W
Up n over door = 2.5 x 2m = 5sq m. U of metal door = 6.8 Heat loss = 6.8 x 5 x (20 - 0) = 743W
Roof = 5m x 2.5m = 12.5sq m. U of corrugated metal = 8.5 Heat loss = 8.5 x 12.5 x (20 - 0) = 2125W
Concrete slab = 5 x 2.5 = 12.5sq m. Assume 150mm thick, so U = 1/((150/25)*.08) = 2. Also assume undersoil temp = 12degC Heat loss = 2 * 12.5 * (20-12) = 200W


Total loss = 3150 + 743 + 2125 + 200 = 6218W so something in excess of 4kW heating will be needed to maintain a comfortable working temperature.

insulating the roof (R=.12) with 100mm of polyurethane foam (R=1.2 per 25mm) and 18mm of OSB (R = .25) gives a U factor of 1/( .12 + 4.8 + .25) = 0.2 and therefore a loss of 0.2 x 12.5 x (20-0) = 50W, a big improvement.

Similarly the walls, but say 50mm poly and 11mm OSB, U = 1/( .16 + 2.4 +.15) = 0.37, therefore loss .37 x 25 x(20-0) = 185W

Not much you can do about the slab (except put some carpet down :) ), but even now the losses are 185 + 743 + 50 + 200 = 1178W.. a four-fold+ reduction in heating needed...

I'd do something about the door, simply to avoid a temperature gradient inside, it'll feel colder that end!

Caveat... Its really hard to find accurate U and R factors for the actual materials used, so this is at best an approximation, however it shows why insulation is a good thing! Also doesnt account for air circulation and interchange - so you will lose heat through ventilation as well...