Shed Insulation

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!

17 Responses

  1. What about if you made a frame and used 2 sheets of laserlite, like double glazing?

  2. Stu, I lined the whole shed with 75mm Anticon Blanket and lined the walls with 15mm ply, see my thread on WWF here showing it
    Another thing to take into account is the effects of sunlight/UV fading finishes on finished items, peculiarly when the whole thing isn’t exposed to the light from skylight, just ask Robbo about a high value item that had to be redone due to this.

  3. Another thing to take into account is the effects of sunlight/UV on finished projects that have only been partly exposed, just ask Robbo about a high value item that had to be refinished due to this, another reason why I don’t have skylights in my shed.
    I fully lined mine with 75mm Anticon Blankes and also lined the walls with 15mm ply. A link to my shed build on WWF showing blanket and ply lining,

  4. The bloke/ business that built and lined my shed (and constructs many) approximates insulation costs at 8% of shed cost. He does not recommend sky light as it breaks insulation and therefore may cause condensation issues… in comes a whirly bird? ?

  5. Your figure of 2700w heater does not compute with the formula you gave: if 2 = 54 x 10 / x, then x would be 270w, not 2700w (2 =540/270). Either there is a constant missing from the formula, or something else is going on – my thought is that 270w is much too low a figure to maintain a 10 degree difference in a 6x3x2m shed. ((270w is only a little over 2 people (240w) and no matter what they are doing to each other, I am fairly certain the temperature would not rise 10 degrees))

    • Hmm – not sure what has happened there. Let me crawl over it for a while, see if I can figure out how I got there!

    • Ok, so I rechecked the formula, and worked examples including worked examples on Wikipedia, and the formula is correct. Yes, I did manage to stuff up by adding a zero!

      When the shed has a 10 degree difference, in a perfectly insulated shed (no gaps etc), maintaining that difference only requires 270W.

      However, this is not the size heater required to raise the temperature to produce that difference. That is a completely different calculation! So no matter what the activity in the shed (!), you are right- it would not raise the temperature by 10 degrees! However, once there was that temperature difference, it would be sufficient to maintain it!

  6. Id be more worried about keeping the heat out in summer than the heat in in winter. 25ºC day and the shed can become unbearable if uninsulated.

    Id also go with laserlite, the natural light is amazing – much nicer than fluros. Also allows you to walk in just to grab something.

  7. Roller doors often have a gap at the top. Stuff in a lump of carpet.

  8. Hi Stu
    Good to see that things are progressing for you. Just a few thoughts on the topic of your post based on my recent shed build.
    I second the comments above that as convenient as they are, skylight panels are not a great idea from an insulation perspective – you’ll end up having to do a lot more to the rest of your structure to compensate for the heat loss through those panels. I was very keen on them, but abandoned them when I determined the insulation consequences of using them. They would also have made installation of the Foilboard insulation that I used on my ceiling far more complicated.
    As small and piddly as my shed is, I hope that my drum kit will one live in it.So to that end, I had to do a fair bit of workk insulating the walls. The solution that I came up with was earthwool thin batts in the walls, held in place with second-hand 12mm strucutral ply that I bought on eBay from old construction site hoardings. Gave them a blast on the lawn with 40 grit on the orbital to get rid of the cement spatter and other crap on them, screwed them in place, filled up the joins and then threw on a $20 can of Dulux on them from the mis-match reject bin at Bunnings. I was toying with the idea of buying some of the non-strucutral ply that some people are drop-shipping out of China (also on eBay) and then throwing poly varnish on the walls, but concluded that it would be too much hassle and would probably look a bit wanky for good measure.
    All the best

  9. Stu,

    Thanks for starting this thread – it was very timely. I’m just planning to install insulation in an existing steel roofed garage before the hot weather hits. I had almost settled on the AirCell product when I found your post. Does anyone have any experience installing the Anticon underneath an existing steel roof that doesn’t have any sarking installed ?

    Any idea how much air gap between the Anticon and the steel roof is enough? Is this material meant to have a ceiling under it, or can a layer of “chicken wire mesh” be sufficient to support the Anticon ?


    • The reason I looked this product up was one of the other readers (and active member of the Woodworking Forums) mentioned he has it in his shed. The Anticon is designed to go directly under the metal of the roof – it doesn’t rely on an air gap to create an insulation effect. It uses a more traditional method – glass fibres (batts) that traps a lot of air to provide that insulation layer, and as such can be in direct contact with the metal of the roof.

      I don’t think it needs any extra support – not that I can see in the photos. It doesn’t need a ceiling under it (any ceiling would improve the insulation, irrespective of the product), but is designed to be the last layer before the roof struts, and then the interior of the shed itself.

      If going under an existing roof, they might have a different product that would be more suitable? No idea – worth ringing the manufacturer (they were very obliging when I rang them last week).

  10. You may get away with not using roof mesh but it is easier to install the insulation by using it, it also stops sagging and the mesh is an important safety feature in case a workman falls while installing the sheeting or removing it at a later date. The product is 1800mm wide by 50 meters long with 300 x 150 x 2mm apertures and costs about $95 a roll, (about 95c a m2 so not very costly). Most places like Bunnings stock it. It is installed by drilling 3mm holes in the top of the purlins at each side of the roof then threading the wires thro and twisting them back on themselves, every second wire is enough to secure the mesh. I would definitely use the 75mm anticon blanket.

  11. Hi Stu,
    The house I am owner building is all steel, frames and cladding. I have used aircell for insulation. Frame – aircel 65 – 22mm top hat – corry cladding. first winter and summer – snow to 40 deg heat – never hot or cold inside. I then added R2.7 batts to walls and R6 in ceiling prior to cladding inside needless to say things just more comfortable. Aircell is tough stuff my rafters (more steel) are at 900 centres and can walk on the arecell – not recommended but. I am also next to a wind farm and it all stayed on in the months it took me to hang all the iron and it was dry inside. Great stuff really I would use it again.

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