Spray Foam Insulation

[DerekJ]

Hi All,

 

I have a single skin box profile roof on the garage. In the winter the condensation rains down as if the roof was not there.

 

Thinking of coating the inside with THIS STUFF in the spring, anyone tried it or have any better ideas of stopping the condensation?

 

Cheers

DerekJ

[Welly Jen]

Spray foam is used on the roof and walls on a lot of modern narrowboats. The foam goes on the steel work and there is a gap then to the wooden lining. Very effective at preventing condensation in what is essentially a steel box. Not sure about its use for waterproofing a porous roof. I suspect the moisture would just track between the roof and the foam and reappear somewhere else inside, but for a basically sound roof it should be good.

 

Jen

[Wile E. Coyote]

If you're getting condensation, do you also need to look at ventilation?

 

I'm part way through insulating the roof of my garage with Celotex type products (rigid foam panels - ignore the Wickes/B&Q prices as they're massively cheaper at a builder's merchant if you're buying a few packs) and was advised to make sure there were plenty of soffit vents installed to stop moisture build up in the uninsulated void above.  If it's single skin/flat, I suspect there's no reason you couldn't use the same panels to put in a suspended ceiling if you vent in between the layers.

[Mooch]

You must be heating the garage if you are getting condensation. I'm not a fan of spray foam insulation and wouldn't touch it with a bargepole in a loft space. Some use it to compensate for a knackered roof with leaking tiles but water will always track through and you will never find where it is coming from. By spraying this gunk on the inside of your garage, you will be creating a 'cold roof' so warm air hitting it will still condense on the cold side and cause problems because there will be inadequate ventilation by which the moisture can escape.

I think Wile E coyote has the right idea. Foil backed foam insulation boards and a ventilated air gap above to stop moisture build up. Fixing the boards to wooden battens should give the gap you need. Tape the joints on the boards for the best effect.

[DerekJ]

Thaks Guys.

 

I'd looked at Celotex etc. but I don't have the head room to create a suspended ceiling. I've seen some small packs on sale and think that I'll get one to test it to see if it works.

 

DJ

[Wile E. Coyote]

You'd be surprised how effective Celotex is.  From memory it's 3x the effectiveness as rockwool type insulation.

 

I reckon a bit of a gap, 50mm Celotex (which with big washers you can screw directly through to the joists) and you'd notice the difference.

 

You could probably do it losing less than 6"...

 

Word of warning though: when you cut it (which you can do with an old wood saw) do wear a dust mask.

[Mark (smokey mow)]

If you're getting condensation, do you also need to look at ventilation?

I'm part way through insulating the roof of my garage with Celotex type products (rigid foam panels - ignore the Wickes/B&Q prices as they're massively cheaper at a builder's merchant if you're buying a few packs) and was advised to make sure there were plenty of soffit vents installed to stop moisture build up in the uninsulated void above. If it's single skin/flat, I suspect there's no reason you couldn't use the same panels to put in a suspended ceiling if you vent in between the layers.

this ^^^^^ is the best way to do it IMO. The key to avoiding condensation is to ensure there is good ventilation with airflow openings on opposing sides of the roof so as to allow for the removal of moisture laden air and to prevent the build up of condensation on the underside of the roofing.

I have a personal hatred for spray foam insulation products, but that's IMO. thermally though even 25mm thickness of Celotex or PIR insulation will perform better than the spray foam and the installation is completely reversible should you wish to remove it again in the future.

The best way to cut Celotex and PIR insulations is with a sharp knife such as a bread knife. Using a saw creates a lot of dust, which is very unpleasant stuff to inhale.