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 8^oC 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 10^oC, 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 = 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!

A New Tab

At the top of the website, you will see a new tab has appeared – Shed Build. (It may take a little bit for it to appear – the site is quite heavily cached it seems!  Even mine is appearing and disappearing – idiosyncrasies of the web!)

I will use this to capture some of the specifics of the shed design and construction.  New content will still appear here as new blog entries, and then summarised and refined under that tab for prosperity.

So to start, I wanted to look at some of the lessons learned from the existing shed.

With the decommissioning of the current shed in approximately 30 days (a month seems so much shorter when you realise how many, or rather how few days there are, especially if you only count weekends!), I am going to document the process involved in setting up the new shed, at the new location.

The existing 8×4 shed was a great improvement when we built it, but it has been well and truly outgrown  in the past couple of years.  It was as large as I could justify on the existing block at the time.

Looking back through the website, I didn’t realise how long the existing shed had been around – time sure flies! (Built April 2008)

So what lessons have I learned from the existing one, that needs to be incorporated into the new design?

Size:

The current shed is 8m x 4m, with a 2.1m high ceiling (to the lower beams).  Shed width is a critical factor – not just the square metreage. 4m is ok, but 6m would be more desirable.  This allows machines to line the walls (those that suit that location), and still provide plenty of room between them for work, manipulation of stock etc.

Length then is as much as possible for maximum area – the more wall space the better too – I ran out a way back!

Height – 2m is a minimum, but I found I was regularly banging stock into the beams.  2.4 – 3m would have been better (as in total clearance).

Door:

The doors on this shed were a good size – about 2m across (when both were opened).  It would have been better if I hadn’t had to block one of the two for the bandsaw, and would have been preferable if I hadn’t had to consider out and through the doors as space for some of the tools outfeed!

Security:

She’s solid – no doubt about that, and with society as it is, nice to know things are locked away.  However, one point is lighting, which is the next category.

Lighting:

I ran 10x double fluorescent tubes in the workshop, and as there were no external windows or skylights, this was the only source.  These have been good, but more would have been better.  Daylight for example!  With the new shed going to be directly opposite the house, having some windows would be ideal, and the ability to open part of the side of the shed (roller door).  There is a limit of course – the more windows and doors, the less wall space.

Power:

I struggled along for quite a while with power being provided to the shed via an extension cord, but things really improved once I had a decent amount of power bought directly in.

2x 15A, plus 3x 10A circuits.  I made the mistake of using the ready-wired plugs from Bunnings for the 10A supply (wired into the supply by the electrician).  These had their own circuit breaker on each line that was forever tripping.  Running too much on the same circuit, and some being machines that needed the full 10A when under high load.  The circuit breakers on the GPOs tripped at 10A at best, if not before  Normally, circuit breakers do allow some overcurrent before tripping, but these seem to be right on the limit.

You can never have too much power.

Temperature control:

It was always either way too hot, or way too cold out there.  Insulation (and installed during construction) is mandatory!  Additional temperature control in the form of air con or heating would be a definite added bonus.  I tried a gas heater, but that posed a number of problems.  For cooling, I didn’t want to use evaporative – too much cast iron and too much timber to want to change the workshop moisture levels.  When I did give in, it was very ineffective (portable units don’t cut the mustard).  One way or the other, if it is not a comfortable environment, you can loose so much shed time by not wanting to be out there.  Shed time can be hard to come by, and you can’t afford to throw it away because the weather is too hot, or cold!

So that is a first pass – I’m sure there is much more that I can glean from the existing shed to build into the new design.