Insulating my garage/workshop

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Good evening, I've got a detached workshop which I seem to be spending more and more time in, so I want to make it more comfortable for me (some warmth please) and make it a more suitable place for all my tools which I'm constantly adding to, next on the list is a small lathe, so I've got to get the place insulated, if only to stop the dreaded 'inside rain' that flows from the steel roofing and down the joists (this is the cause of their early demise) and onto everything!!!

Workshop dimensions are 5.5m wide by 6.5m long with a single sloping roof of box profile galvanized steel on timber joist. the walls are 100mm thick gp1 blocks rendered on the outside and un plastered but painted on the inside.

My plan for the roof is to remove the timber joists (end of life) and replace them with steel Z purlins.

http://www.steelroofsheets.co.uk/products.php?cat=14

On top of the Z purlins I plan to lay 80mm Celotex or Kingspan (the type with foil either side), tape the joints on both faces with aluminum tape then relay the box profile steel on top and give them a coat of paint while I'm there.Between the Z purlins and tight on the underside of the insulation I plan to fix plasterboards.

I'm fairly confident that this will work for the roof, I'm not so convinced on my ideas for the walls at present. I do not want to loose any floor space and want to minimize the flammable materials inside so I plan to insulate the outside.

Currently my plan for the walls is to lay 50mm Z purlins (mini Z's) horizontally and fix 50mm insulated steel composite panels to the mini Z's.

http://www.steelroofing.co.uk/composite-insulated-roofing-and-wall-cladding.html

Here are a few of the thing I like to get some feedback on.

1. The walls will have a 50mm air gap between them and the composite sheets, do I leave it like that, or do I need to line the wall with some sort of membrane before fixing the z's to it, or do I fill the cavity with 50mm Celotex or Kingspan foil backed insulation, or do I need to take a totally different approach.

2. Which paint would you recommend for the galvanized sheets - they have been in place about 15 years and the galvanizing has really stood up to the test of time - no rust - so I plan to extend their life as much as possible.

Your input would be most welcome.
 
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Why don't you use Kingspans insulated roofing panel?
Then you have a nice clean inner surface coloured white and looks good.

Corrugated galvanised tin is for the farm yard barns.

They also do a good range of architectural wall cladding panels too.

:idea:
 
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Hi Norcon.
Thank you for you reply, I plan to reuse the present roofing sheets which are in excellent condition (as previously stated they are not corrugated sheets but box profile - similar to the profiles of the kingspan composite sheets you mention) and I plan to paint them to extend their life as much as possible.
 
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I insulated my workshop roof from below using a mobile scaffold.
If I was going to strip off the tin then it would have been staying off and new sheets re-laid.

I used spray glue and glued loft insulation to the tin in between the timber purloins. That seems impossible but it does work.

It managed to defy gravity long enough to allow the fixing of a 25mm kingspan insulating sheet below which has one side white and textured for a finished appearance.

So there is about 150mm of insulation on the roof now.

Incidentally on an agricultural building treated timber will outlast Z purloins by many decades.
 
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Hi Norcon, as I said the galvanized box section sheets will be going back on the roof as they are almost like new, and by reusing them it is a considerable saving over purchasing new sheets, the only cost I will incur with them is the application of a suitable paint to their top surface for added protection so as to further extend their life. I find your comment regarding the longevity of z purlins interesting, I assume that you are referring to uninsulated open barn type buildings, z purlins are the defacto method of roof construction in almost all industrial steel buildings with a canted roof, but I will certainly investigate this further.
 
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Z purloins are OK where there is no livestock.
 
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That's not a problem then as I plan to be the only 'livestock' in there.
 
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