Thread: Shed insulation

Originally Posted by Dougal

That stuff only gets to about an R value of 1.

I am sure that now have a rate of RT2.1 but in any case it was approved as insulation under Queensland Building Laws.
Take note that there are several types of Air-Cell and some of them are only for sheds and commercial applications and others for residential purpose.

Originally Posted by Chucaro

I am sure that now have a rate of RT2.1 but in any case it was approved as insulation under Queensland Building Laws.
Take note that there are several types of Air-Cell and some of them are only for sheds and commercial applications and others for residential purpose.

Some of the shed insulation products have a rating that is "installed", meaning it's not the rating of the actual product, but the rating of the building construction with that product inside it.

For high R values the installed rating is actually lower as studs, purlins etc conduct heat/cold through (thermal bridges).
For low R value products the installed rating is higher as it gains a small amount from each air-gap and the conduction of thermal bridges isn't as significant because you have more heat coming in from everywhere else.

Keep in mind I'm not in Queensland. But the shed I plan to build will have at least R4 in the roof and at least R2.8 in the walls. Building code be damned, I'm insulating for my own comfort and long term cost reduction.

The office I'm sitting in right how has a black tile roof (can hit 80C in the sun) and originally had just building paper and 10mm boards in the ceiling. It was intolerable in full sun and you could feel the heat coming through. Even with all the windows open it was an oven that on a 30C day would be at ~37C inside.

Just over a year ago I fully lined it with R3.2 batts and a layer of Gib. Now it has no problem keeping at the outside ambient temperature under full sun.
You would be amazed how many people told me it would be hotter in summer with the insulation.

Originally Posted by Dougal

Numbers like that mean it's almost a waste of time. A sheet of building paper to create an airgap will give an R value of 0.2

A R value of 0.2 means with a temp of 60C on one side (roof in the sun) and 20C inside you'll be gaining heat at the rate of 200 watts per square metre.
Every 10 square meters is like having a fan heater inside.

If you can get R3 insulation into the roof you'll drop that to 13 watts per square metre.

Thermotec themselves are claiming a summer rating of 2.5 & winter of 1.4 for 5mm (pitched metal roof, no ventilation: Etherm for Thermal Performance | Thermotec ).
There's virtually no difference between 5mm & 8mm. I guess that means the air gap is more important than the material.

Originally Posted by Basil135

Is there a particular reason you are thinking of putting the slab down first?

The shed frame is bolted to the slab. My current shed is on piers into the ground & I laid the slab last. This shed appears to be designed to be bolted onto the slab.

Originally Posted by VladTepes

Where you blokes get such big bloody sheds? Or room for em ? Ya buggers !

Living out in the sticks has to have some plusses .

Umm, yes.
The sticks does help.
My other shed is 7.5x14.5.
Sorry Vlad
Steve

Originally Posted by Scouse

Thermotec themselves are claiming a summer rating of 2.5 & winter of 1.4 for 5mm (pitched metal roof, no ventilation: Etherm for Thermal Performance | Thermotec ).
There's virtually no difference between 5mm & 8mm. I guess that means the air gap is more important than the material.

Indeed.
It also means that the insulation isn't the part in the building offering the most resistance to heat transfer.

I was doing a lot of work last year on heat transfer to the air through stainless vs PVC piping. I was surprised to find virtually no difference.
In that situation the bottleneck (greatest resistance to heat transfer) was actually air against the outside of the pipes. The thickness or even material of the pipe was such a small contributor that it was irrelevant.

It was a serious WTF moment, but it did all eventually make sense.

The upshot is, there is a minimum thickness of insulation before it can make any difference. Below that minimum thickness, a single sheet of paper is just as effective as the air-gap is your insulation.

Like double glazed windows. Glass isn't the insulator. The air-gap is.

In the 2 steel homes that I have built the roof have a 15 cm air gap between the insulation and the inside face of the plaster board (15 cm purlins) and the walls have 10 cm gap. Because the insulation material was against the colorbond roof and the steel cladding I guess that was a big part why Air-Cell was so effective.

Figures shmigures!
I know what I've got & it works!!!

Originally Posted by Saitch

Figures shmigures!
I know what I've got & it works!!!

Bingo saitch, as I said I have the air cell on my shed, (roof and walls) the other day it was 32 degrees here, 21 in the shed