cliftyhanger
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| posted on 11/1/21 at 09:02 AM |
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Car Port condensation, what insulation?
As an update to my thread a while ago, my car port is built. 8x2 joists with spans from 4.8m to 5.8m with a metal roof. I used 200mm barge boards
around the edges, and teh neighbours have been pleasantly surprised (a relief)
However, it gets terrible condensation. I spoke to a few people who all thought it would be OK as 2 sides are totally open so very well ventilated.
However, not so.
If I had realised I would have used some for of insulation before screwing the roofing on. I suppose I could take the roof off and do that, but what a
ballache.
Other ideas so far:
DIY spray foam insulation. I can get a kit that would give about 3/4" thickness, but it could be a steep/messy/expensive learning curve.
Buy 2"thick polystyrene boards and cut to a tight fit, stick up onto the roof boards
Use foil/bubble insulation Would need sticking to the roof again.
Anybody got any insights?
I wish I had done the behind my garage first (currently plastic corrugated roofing). That is next on the list, I already have the roofing sheets. I am
wondering if a layer of 11mm OSB may be adequate to stop the issue?? Or would proper insulation be a better option?
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roadrunner
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| posted on 11/1/21 at 09:09 AM |
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Is your roof pitched or flat.
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cliftyhanger
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| posted on 11/1/21 at 09:29 AM |
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Almost flat (just enough to let rain flow off, a bit more than the minimum recommended fall)
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roadrunner
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| posted on 11/1/21 at 09:38 AM |
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That means having a membrane under the metal roof won't make any difference.
I'm afraid to say, but you have used the wrong materials for the roof.
It's good that you have plenty of ventilation but that air needs to be moving on the underside of the roof.
Is it possible to lower your fascias at each end to create an air gap under the roof.
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40inches
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| posted on 11/1/21 at 09:38 AM |
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I had the same problem with my metal roofed garage, 6m x 6 m.
I stopped the condensation, more like rain inside  by sticking 25mm polystyrene insulation to the metal panels and sealing any gaps.
Now dry and toasty 
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roadrunner
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| posted on 11/1/21 at 09:41 AM |
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Corrugated bitumen is one of the best products to use.
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40inches
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| posted on 11/1/21 at 09:49 AM |
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quote:
Originally posted by roadrunner
Corrugated bitumen is one of the best products to use.
Anything but steel
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rufus357
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| posted on 11/1/21 at 10:32 AM |
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sorry to state the obvious but you have to both insulate and stop all the warm wet air getting past the insulation to the roof. Spray foam works well
for that (Pro might be cheaper than DIY?) or PIR (eg Celotex) push for a tight fit and sealed around the edges with expanding foam gun. You could then
also cover over with waterproof membrane which might neaten the appearance.
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Slater
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| posted on 11/1/21 at 01:28 PM |
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Do you have a gas boiler flue intake/exhaust under your car port?
I had one under my car port which is closed off with house on 1 side, garage door on the front and wall 90% up the other side and only fully open at
the back. The boiler flue exhaust caused huge condensation under the roof, but I cured it by fitting an extension to the exhaust flue up through the
car port roof.
Why do they call Port Harcourt "The Garden City"?...... Becauase they can't spell Stramash.
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cliftyhanger
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| posted on 11/1/21 at 02:06 PM |
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No boiler flue.
Steel is used for many buildings, and I understand the concept of warm air meeting cold surface etc, but I am amazed that in such an open structure
there is a temp difference at all above and below the roof.
Interestingly, I have used "clear" fibreglass in one section, nd despite fibreglass being a better insulator than steel, it appears to
suffer more. Not sure what I can do with that though.
And for the record, I think corrugated bitumen is sh!t. Looks terrible, no rigidity and so on. fine if it can't be seen. I used it before for a
customers shed, at their
Looks like I will buy some insulation boards and glue up to the roof. I doubt I will need to foam any gaps, maybe caulk. As I said, if I had known
before, I could have put the boards in a continuous layer under the roof, but now I will be sawing a dozen or so 8x4 sheets up. Ho hum. Think I will
wait for warmer weather.
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ianhurley20
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| posted on 12/1/21 at 09:34 AM |
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Seconds and co are often good prices for insulation, they are an outlet for Kingspan. I used 100mm insulation board for my extension I built recently
and they were seconds because they were 105mm thick!
https://www.secondsandco.co.uk/
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cliftyhanger
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| posted on 12/1/21 at 10:08 AM |
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quote:
Originally posted by ianhurley20
Seconds and co are often good prices for insulation, they are an outlet for Kingspan. I used 100mm insulation board for my extension I built recently
and they were seconds because they were 105mm thick!
https://www.secondsandco.co.uk/
Thanks, but minimum order is £350.
I can buy 50mm polystyrene 8x4 £120 for 10 sheets delivered off fleabay. They will be adequate, and rigid enough
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coyoteboy
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| posted on 13/1/21 at 04:26 PM |
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I don't really understand why everyone says "ventilation is the solution to condensation" in garages. It's barely applicable,
and a car port explains why.
You can have all the ventilation in the world (my sectional garage is like a colander) but if you have a cold surface that is colder than the dew
point of the air moving through, you'll get condensation. In a house, where the house is warm and full of breathed air (or combustion
byproducts) then it's more applicable - flushing the damp air out keeps it from condensing on the walls, but in a cold garage there's
chuff all you can do to stop it unless you can warm the garage or make it of materials that have much lower thermal mass and better insulation.
All the heavy metal objects in my garage are drenched in condensation, and the wind whistles through that like there's no walls. The only way to
fix that is to insulate and heat, or not put metal objects in it.
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