# Forum Home Renovation Heating & Cooling  Insulating shed with polystyrene

## beer is good

I have a 5m x 4m x 2.7m colourbond shed which gets as hot as hell in summer. I am thinking about fixing polystyrene sheets to the underneath of the roof - no ceiling. Has anyone done this and is it likely to help.

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## dazzler

Why not just use batts.  Unless of course you have an huge supply of poly lying around.  :Tongue:

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## elkangorito

> I have a 5m x 4m x 2.7m colourbond shed which gets as hot as hell in summer. I am thinking about fixing polystyrene sheets to the underneath of the roof - no ceiling. Has anyone done this and is it likely to help.

  Sounds like a bloody good idea to me.
And yes...it will help.

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## Eastwing

Yeah it works well, I use it in Factories, order the length to fit between the Truss/Rafters. sheets are 1200mm wide by whatever thickness and length you want (up to about 5.4m) you want.

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## Kaptan

> Has anyone done this and is it likely to help.

  I lined the ceiling and unprotected western wall of my 6x5 Colorbond shed with Foil-Board, and after last summer, I am so glad I did.
Stops any radiant heat coming through, the difference is remarkable.
Foil-Board is foil bonded to both sides of polystyrene sheets. It comes in various thickness's and lengths.
One side is shiny, the other has a coloured printing. (See the off-cut piece next to the window that I use to cover the window in the afternoon!).
I sandwiched the boards between the Colorbond sheets and the rafters/purlins when I built the shed. There is no space between except for the flutes in the iron.
There would be no reason that you couldn't just glue polystyrene boards to the underside of your Colorbond, and seal the edges off with thin aluminium flashing tape.
Not too sure about the look though, maybe you could find those stick-on polystyrene ceiling tiles that were the rage in the 70's? 
I say go for it. :Luck:

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## watson

Looks good Kaptan,
But you're up for a Code Violation.....your shed's too bloody neat!!   :No:   :No:   :No:

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## Frankmc

Thats what i was thinking also Watson....;-) ..Im sitting here drooling looking at that pic.. 
Any more pics of that shed  Kaptan .. ;-) 
Frank

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## BRADFORD

It's impossible to produce any thing from an area so neat.
By that measure my shed is super productive. (I wish)

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## tricky4000

Yes Kaptain that is a mighty neat looking shed.  
Beer, if you already have the polystyrene by all means use them but note, gluing them directly to your ceiling is not the ideal way, you should always leave an air barrier between them in your ceiling for best insulation result.  Something else to note too is that polystyrene might be a bit of a fire hazard.  If you're thinking of going out to buy them...get yourself some batts instead but if you already have them...then just keep the fire hazard issue in mind.  They will make a huge difference in summer for sure!

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## exotiic

Tricky, 
I note that you said to leave an air barrier between the roof and the insulation. Ive noticed many posts stating the same thing. If you had the time could you tell me what the importance of the air barrier is and why its much more effective? Thank you!

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## tricky4000

Hi exotiic
I'm not an thermal engineer but I believe the air barrier will move the heat/cold back and forth so it won't penetrate so much to the next barrier - the insulation.  I think if the insulation is pressed hard up against the outer surface, the heat/cold will penetrate...because the two barriers are touching.  
Can anyone else out there answer this question better than me?

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## GraemeCook

Hi BiG 
I am not a thermal engineer either but I believe that the recommended minimum gap of 25mm is largely to act as a vapour barrier - to stop moisture getting into the insulation and to allow any that does get in to escape.   It is generally recommended that the most cost effective means of stopping radiant heat from the inside of iron roofs/walls is reflective foil insulant then some bulk insulation.   Have a look at, especially W11, W6 and W5: www.timberbuilding.arch.utas.edu.au/publications/PDF/R-values Part 3 - Wall elements Ed 1.1.pdf 
There are plenty of commercial buildings and steel boats with spray in foam insulation - this binds well to the exterior surface and there is no space for vapour to get between them. 
Why do you plan to use foam sheets - cheap supply?   Batts and blankets are usually cheaper and easier to handle. 
Cheers 
Graeme

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## Kaptan

> Any more pics of that shed  Kaptan .. ;-)

  So I don't hijack this thread, I will post over in The Garden Shed. 
And that picture was taken when I was still setting things up, there's dust on everything now.   :Anoyd:

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## elkangorito

> Hi BiG 
> I am not a thermal engineer either but I believe that the recommended minimum gap of 25mm is largely to act as a vapour barrier - to stop moisture getting into the insulation and to allow any that does get in to escape.

  I agree with Graeme. In a shed like yours, I wouldn't be worrying about vapour barriers unless your shed it pretty tightly sealed against air movement. 
I would put the sheets directly against the metal roofing.

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## Haveago1

Comment moved to Shed Thread....

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## Bleedin Thumb

Besides the fire hazard issue I wouldn't use straight polystyrene because it puts off  extremely toxic fumes when it burns and it is not a readily recyclable material, and if it ends in landfill it is basically non biodegradable.....  
I know it may seem a bit hippie dippie but these should be considerations when choosing your materials ...Cradle to Grave.......

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## beer is good

G'day and thanks to those who replied,
I am fairly keen on the polystyrene if it can be glued in place. My understanding is that with the foil insulation it needs at least 20mm between the roof and the foil to stop the heat from the roof from transferring to the foil and then into the shed. Needing a gap makes the installation much harder.  
I really wish I had insulated properly when I had it built, as there is a lot of stuff in the shed now which will need moving as I think I might as well insulate  the wall that cops all the sun.  
Hindsight is a wonderful thing.

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## beer is good

Over the Christmas break I put polystyrene in the roof. I used Zero Nails glue from Bostik (cheaper than Liquid Nails) to glue the sheets to the underside of the roof. The sheets were 40mm thick by 1metre square. This was a good size to handle as I did it on my own. Cutting the sheets to fit between purlins was very easy. You can use a hand saw but because the poly is so soft it is very easy to stray off a 90 degree cut. The poly just doesn't resist like wood. So I found the best way was a jigsaw on the lowest speed - like a knife through butter. 
I think it keeps the shed a bit cooler as it stops the radiated heat from above, and as I am 6'6" tall my head is a bit close to the roof which is 2.7metres high in the middle. I think that to get the temperature down by 10 degrees or so I would have to all the walls as well, but there are two sliding doors on the front which I normally leave open to let the light in. But, of course, doing that lets in hot air if the outside is hotter than inside, so full insulation of the walls might not make a big difference. There is no gap between the roof and the poly. To have a gap would have complicated the project as I would have to put in purlins or a suspended ceiling, and the guys at the government energy advice office said that a gap would not help. Poly works by just preventing the heat from travelling from the roof to the inside. Foil though does need a gap of at least 25mm. It works because the aluminium doesn't transmit or radiate heat the way that steel does. 
There is some wild creeper growing on the western side of the shed so I will encourage that to grow up the wall and maybe shieding that wall from direct sun might help.  
The poly is easy to work with but dents very easily. I'm happy to give more tips to anyone contemplating the same.

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## Moondog55

Been following the thread, just re-read the website for "Foil-board"
The mention using what they call a fold back.
I assume they cut almost through the sheet on each edge and then fold over , this would give a double thickness on the edges and an air gap that is the thickness of the board, I imagine that the air gap would give a better R rating  
We are going to be using reflective foil faced polystyrene when we do the West wall of the house here in Geelong, hopefully before it gets too cold.
We are removing the WB as they are too far gone to patch and paint, so taking the opportunity to insulate properly

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## Bloss

Air gap issues seems to be a confusion - it is needed when using foil insulation but not when using styrofoam or boards with the foil the inside and not batts (but note that air gaps in veneered walls need suitable material).

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## Moondog55

G'Day Bloss
I understand what you are saying, but on the website the manufacturers give different advice, they do say that the product works better when the reflective face works in conjunction with an air gap between roof and the foil face.
As an aside; for many years the big department stores have used bead-board for advertising, you can still get it for free in 15 and 20mm thickness if you make friends with the people at Myers for example, it ends up in the rubbish tins after a short use, I insulated a steel garage in Melbourne with old advertising hoardings from Myer; double layer of 20mm board, quite effective and very cheap, I used construction adhesive and offcuts of the foam-board to make double layer panels with an air-gap, then glued them to the roof.
the stuff is very easy to work with if you use instant grip construction adhesive that is water based.

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## Bloss

> G'Day Bloss
> I understand what you are saying, but on the website the manufacturers give different advice, they do say that the product works better when the reflective face works in conjunction with an air gap between roof and the foil face.

  Yep it would - but I said when the foil faces the inside ie: the inside of the shed. If the foam has foil on just one side and the foil side faces inwards (which is what I'd do) then the foam contacting the roof is a non-issue. If the board has foil both sides (which some do then an air-gap would give some improvement and help with condensation issues. If you wanted the foil to face the roof then an air gap would be the go. The way you face it varies according to your climatic zone. 
BTW _ You idea of suing s?H styrofoam is a good one. I know a house that has a double layer of styrofoam fruit boxes as underfloor insulation and it works very well. The styrofoam has no fire retardent as does the building boards, but for this use that's hardly an issue IMO. Cost the owner some time, some staples and the foam was free.

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## Moondog55

OK, my fog dissipates, more than one way to skin a shed roof then

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