Metal shed - Roof condensation problem

Status
Not open for further replies.

TimMatrix

TimMatrix

TimMatrix

Associate
Joined
21 Jan 2010
Posts
181
Location
UK
I am fed up of condensation on the inside of a metal shed, especially the roof, dripping water onto items in the shed, causing a bad mouldy smell.

How do one recommend to "insulate" the roof and what with, in order to keep out the condensation problem? I do not care how cold the shed might be, but I do want condensation to go away, thus keeping the contents nice and dry.

Any ideas? If there is a website showing some advice, or how to install something to keep condensaton at bay, I'd like to hear from you.


Many thanks. :)
 
I think they are all like that aren't they?
But yes, spray the lower corrugations and push the polystyrene onto it.
Make sure the contact surface is cleaned with something like white spirit first.

Ideally you would use spray foam, but that is ridiculously expensive.
 
Last edited:
bitslice said:
I think they are all like that aren't they?
But yes, spray the lower corrugations and push the polystyrene onto it.

Ideally you would use spray foam, but that is ridiculously expensive.
Click to expand...

Hmmm, thanks.

I will give a trial with a small segment covered with polystrene foam tiles and 3M glue spray.

If no condensation arises from that segment, then I will do the rest!! :D
 
This is unlikely to work, basically put condensation arises when moisture laden air contacts a cold surface. Insulating the underside of the roof won't work because what you are trying to do is prevent the metal from becoming cold. You would need to insulate the outside otherwise your dew point will still be inside the shed and condensation will simply form between the insulation and the metal. You can make it work internally but you need a externally ventilated air gap between the insulation and the deck.

Assuming the space is unheated your best solution is to add ventilation so that warm air isn't trapped in there in the first place.
 
Applied foam is excellent, we've specified it / used it for years for refurbishment jobs especially on profiled metal decking because it bonds directly to deck. The issue is though is, to do so its applied hot, the delivery system heats it before its applied and I very much doubt you could "can" apply it. The problem is therefore cost, it needs applying properly and its not cheap which comes back to the point of why insulate an unheated garden shed when you can achieve the same solution by just ventilating it.
 
LOAM said:
This is unlikely to work
Click to expand...
As you can see from MP's links, internal insulation does work as it's used in commercial buildings. You can get DIY two part foam kits but they are really expensive, polystyrene sheet is just a cheaper alternative.
Have a google, other people have tried this solution too.

LOAM said:
Insulating the underside of the roof won't work because what you are trying to do is prevent the metal from becoming cold.
Click to expand...
I think the principle is the opposite? Keeping the warm internal air from condensing on the colder metal.
Yes ventilation will do the same, but so will removing all four walls, it's a compromise.
 
Last edited:
bitslice said:
As you can see from MP's links, internal insulation does work as it's used in commercial buildings. You can get DIY two part foam kits but they are really expensive, polystyrene sheet is just a cheaper alternative.
Have a google, other people have tried this solution too..
Click to expand...

I didn't say spray applied foam wouldn't work, we use it all the time. I said its costly to undertake and needs to be applied properly. I did however say gluing polystyrene to the underside wouldn't work in my opinion.

bitslice said:
I think the principle is the opposite? Keeping the warm internal air from condensing on the colder metal.
Yes ventilation will do the same, but so will removing all four walls, it's a compromise.
Click to expand...

Warm deck / cold deck roofing, look it up under Part C of the building regs. Warm deck roof (insulation on the outside) in the case of a single ply roof requires no ventilation as the deck is kept warm, cold deck (insulation on the underside) requires ventilation as the deck is exposed to cold air.

Gluing polystyrene sheets to the underside will not stop condensation, all that will happen is that air trapped behind it will still condense, you just might not see it. In a timber construction this would result in rotten woodwork and if it was in a heated, habitable home it would fail building regs.

The point of ventilating an area that is not heated as oppose to insulating it is that you are dealing with the problem directly, which is that of trapped warmer air. You could at considerable cost insulate it and prevent it condensing but you need a good application that will cost considerably more than drilling several holes in the shed. Its completely insane to insulate a non heated space to cure a ventilation issue.
 
Last edited:
LOAM said:
cold deck (insulation on the underside) requires ventilation as the deck is exposed to cold air.
Click to expand...
As I stated in my post?

Gluing polystyrene sheets to the underside will not stop condensation, all that will happen is that air trapped behind it will still condense, you just might not see it. In a timber construction this would result in rotten woodwork and if it was in a heated, habitable home it would fail building regs.
Click to expand...
And in a spaceship it would explode in a ball of flame!!!... Nobody mentioned housing :p
The air behind the sheet would be roughly at the same temp as the roof and should not condense to any great degree I reckon.

The downside of ventilation to this degree is that the humidity increases to the level of the outside and your stuff rusts anyway, that's why there is a halfway house of insulation and ventilation.
I'm not suggesting anything oddball here, plenty of people have done the same thing without issue, I'm just passing on the consensus.
 
Air trapped behind the insulation in the voids of the profile deck (as well as air that can leak into this space from below) will behave in exactly the same way as air would in an uninsulated space, IE a perpetual cycle of condense and evaporate. Unless you can get a full bond that follows the profile you will have air pockets that will condense as the deck cools over night. Its no different to how an unventilated loft behaves.

I'm sad so i've drawn it :P

sectionEE-Model.jpg


Also, unless you can achieve some degree of air tightness then warmed air will rise through the joints and still condense on the cold deck.
 
Last edited:
LOAM said:
Unless you can get a full bond that follows the profile you will have air pockets that will condense as the deck cools over night.
Click to expand...
Or if the end channel were sealed with a profile section the air would just sit there, isolated from the warmer internal air by the insulation. I recognise this isn't perfect compared to full bond, but going from other people's findings it apparently works.

(random first link (tiles under the roof):
http://www.bikechatforums.com/viewtopic.php?p=2689704
...actually I didn't believe tiles would work and suggested sheets instead, but apparently they do anyway :o)


I'm not disagreeing with you, applying house ventilation theory to a similar problem is valid, I'm just pointing out that other methods appear to work too and may be preferable to just letting cold air in.
 
I'd put expanding foam in the voids and use that to glue the poly sheet. Would need to wedge the sheets in place with timbers to stop the foam pushing it away. Heat the can in some warm water before use and give it a good shake and it's surprising how far it will go.
 
Me too (also considering a metal shed), although I did wonder if it would actually be possible to stop the foam from pushing back. I was considering doing this on a flat surface and then just scraping the excess off, before then attaching the polystyrene.
The gluing effect of the foam is a big bonus though, the stuff takes forever to get off your hands.
 
If you were starting a metal shed from scratch, then the best solution is an anticon fleece that was applied before the sheets are profiled. Cost over and above a single skin profiled steel sheet is minimal.

www.dripstop.net
 
Anyone who has used expanding foam will know you squirt then deal with the consequences, can't see how you are going to squirt upside down without ending up with most of it on you and the floor.

It's not cheap either.
 
maccapacca said:
Anyone who has used expanding foam will know you squirt then deal with the consequences, can't see how you are going to squirt upside down without ending up with most of it on you and the floor.
Click to expand...
This.

Companies apply spray foam to the inside of newly built narrowboats for exactly this reason but I doubt it would be cheap to have a shed done.
 
Status
Not open for further replies.
Back
Top Bottom