Jumped onto DJ’s suggestion, and contacted Bradford’s local supplier to get some pricings (and other details).
Oh, and just a side comment (and not targeting any specific company) – I’m always fascinated how many try to baffle you with bullshit. Companies contradicting each other, and themselves. You’d think that this was magic and not science, or a simple engineering issue. Just once, I wish that if someone doesn’t know the answer they’d say “I’m not sure, let me find out”. Happens in all industries, and perhaps I am too skeptical for my own good, but I (hopefully often will) quickly pick up when someone is leading me down the garden path.
To start, the product that every shed manufacturer seems to promote is called AirCell. That is all they tell you. Turns out there are about 8 different types of AirCell
One is called Insulshed, and from talking with Kingspan (the manufacturers), it is really only for sheds used for storage, not for workshops. It has an R-value of R0.9, but in any case noone seems to want to claim it has any thermal rating at all. Wonder why you’d use it then, even though their website claims “indoor temperatures that are significantly cooler in summer and warmer in winter”
They recommended a different product of theirs called Insulbreak, for commercial properties, which has an R-value of 0.9 (out), and 1.9 (in). The difference is apparently because the material is relying on the air gap between it and the metal roof. I guess that indicates a simple sheet of foil creating the same air gap would achieve about R1.0 in and R0.0 out, which makes sense as that is the science behind a Thermos Flask. Of course you are not going to be able to achieve a vacuum between the surfaces, or be able to fill them with a thin gas (and expect it to hang around!)
So I contacted a shed supplier (the one from yesterday) to see what they use. “Dunno – it is Air Cell” Ok, cool. Which one? “Uh – let me put you through to head office” Well at least they didn’t spin me a line. Turns out they supply another AirCell product – Glareshield. Not sure what the glare part of the name is, but it is another thermal-reflecting product. That one has an R-value of 1.0 These values have been determined in-situ, in other words relying on the installation of the product in a structure, and gleaning the thermal benefits from that structure. The R-value of the material itself is around R0.15, which is the only one I will use when comparing it to other materials (which would also benefit from the structure it is installed in to achieve a final real-world R-value.
To cover the entire structure in that would cost $2000.
Poor thermal rating, no noise retardation, about the only thing it would probably achieve is to stop it raining on my tools (condensation).
Before I go further, some further information about the whole R-value thing.
The R-value is (and I am only going to use the SI version, rather than imperial measurements) m²ΔK/W
So how does that help us? The answer is heaps!
m² – how many square meters of area is allowing heat out of the shed (there will be more for ceiling rather than wall, but we’ll let that go through to the keeper).
ΔK – This is the difference in temperature between the inside and the outside in Kelvin. Conveniently, Kelvin and oC are the same scale, just with different starting points. K starts at absolute zero, and oC starts at the freezing point of water at 1 atmosphere.
W – watts – how much heat is passing through
To put it all into perspective, if the shed is 6mx3m, 2m high with a flat roof, it is 54 m². The outside temperature is 8 oC, and inside we want to have at least 18 oC. The walls and ceiling are insulated with R2.0. What size heater is required to maintain the temperature? (Note, this is not the size heater required to raise the shed to that temperature!)
2 = 54 x 10 / x
x=270W A human body produces an average of 120W, so combined with a few machines running, it appears this is sufficient to maintain the temperature. (Thanks to Derek for pointing out a glaring error!) Better not have the dust extraction running outside the shed though – it will be sucking out the 18 oC air and drawing in the 8oC air!
This doesn’t calculate how long it takes to warm up the interior to that temperature – that is a factor of the thermal load of the air and the contents, and the internal volume plays a big part in that. And the reverse of that – if the outside is 10oC, and there is no heater, the inside will slowly drop in temperature until it matches the outside, but again it comes down to the thermal load and how much heat is contained to know how long it takes to cool down.
Back to insulation then. As I mentioned at the start, I researched DJ’s solution, from CSR Bradford.
They have a number of insulating materials.
For the roof, they suggested Anticon – stands for anti-condensation. Has a thermal rating of R1.5 and has some noise reducing properties. Cost for the roof alone would be $270. Compared to $600 for AirCell for the roof (only), it is a good start.
For the walls, R2.0 glass wool ($793) Total shed cost $1063, but I’d need to line all the walls to cover up the batts, so there is an additional cost in that.
The other material they sell is Acousticon, but it wasn’t being pushed. It has R1.9 and is 80mm rather than 60mm for additional sound absorption (and insulation). It is Anticon with more thickness. For the roof, it would cost $495, for the walls $1155. The whole shed therefore would be $1650
The other option is to go with the Anticon all round, which would cost $900. It is a lot easier to manage than the batts (needing wall linings), and quite a bit cheaper than the Acousticon, which doesn’t have a much higher R-value in any case.
Sounds like a good option to me.
The only disappointing thing in all this, is you don’t seem to be able to have thermal insulation of the shed, and natural light.
Laserlite has a U value of 7.2 and U=1/R, which gives it a R-value of 0.14 Guess that really works as a huge hole in the insulation. No matter how well insulated the rest of the structure, heat gets sucked straight out the laserlite – like leaving a door open!
So I’ll feed all this into my design concepts, and see how it all plays out. If it comes down to a choice between outside light and inside warmth (or coolness in summer), thermal comfort will win – installing and running lights is a lot cheaper than air conditioning!!!!
***Update*** Following on from the amendment after Derek found a mistake I’d made in a calculation (now corrected), I thought I’d work out how much energy would be required to maintain a 10 oC difference between the inside and the outside of the planned shed, using R1.5 Anticon.
Energy (W) = ΔK x m²/R
W = 10 x 180/1.5
Now if I manage to wield my calculator correctly this time(!), this means I need a 1200W heater to maintain that temperature difference. And that is without skylights. Achieving that temperature difference would be a mission – hate to think what the thermal load would be! My (secret) plan to install a Coonara fireplace (and/or) a potbelly looks to be the only way I could hope to heat the place up sufficiently.
Interestingly, if I went to the extra expense to install R2.0, it would drop the maintenance heat input from 1200W to 900W.
If this was a residential house, where you’d (hopefully) find R4.0 insulation, this would make the maintenance heater size to 450W – about 3.5 humans worth!