UPVC porch

[ray bush]

I did sort of ask this question a while back .

I've recently built a UPVC framed porch with 20mm heat reflective double glazing , PolyCarbonate pitched roof on a concrete base. I'm finding that i get what seems like condesation on the glazing inside the porch .
The porch was a kit type of construction and was not vented. I've seen a few porches of a similar build none of which are vented,but all of which have a flat felt roof ,could this have something to do with it ???.
Any help would be great.

Cheers Ray

[buildersmate]

Two points really - where is the water vapour coming from and why is it not getting out!
1) Did you put a DPM down under the concrete to prevent moisture in the ground getting through the concrete? If not , that's where the source of the moisture is coming from.
2) Once in, it can't get out. Flat roofs aren't particularly permeable to water vapour either, but polycarbonate certainly aren't. Could you allow for a vent to be constructed where the polycarbonate crosses over the top of the UPVC window frame, to allow air in? If not, a ridge vent, perhaps?

[ray bush]

Thanks for the reply.

When i laid the base i installed a DPC membrain approx 50mm below the surface of the finished screed. The only vent that i might be able to install would be a very narrow one in one of the rails above the windows,if that would make any difference ?.

[KARL]

One possible source of the condensation is if/when air from the warmer/heated house proper enters an adjacent closed and unheated 'room'. The air cools down, the humidity rises and when it gets close to the the glass it further cools down below dew point - condensation forms on the glass. Possible solutions are venting as suggested (ensuring the 'room' has replacement of air and in the process is even colder), heating the 'room', using a dehumidifier, or ( just possibly) forcing circulation over the glass using a fan or fans.