water droplets in attic ques

cubix

Can anyone advise me why this may be happening.

This is an attic space with a low apex type roof that ends and goes into a flat type roof. The layers seem to be there is ploythene tacked to the underside of the roof beams then normal plaster slab screwed and ceiling skimed. Above all this in the attic space there is fibre insulation layed between the joists. The roof is lined with the old type non breathable under felt with normal concrete tiles on top. IF you can make out from the pictures there is water droplets forming on the attic side of the underfelt. I am putting this down to a layer of snow on the outside but can not say for sure as I have not been up top and cannot see this part of the roof from the ground. Not sure if this is only happening now or also happens when it rains but will check when weather improves and snow melts.
So am hoping if anyone can tell me if they have this setup and have had
similar water droplets forming and if so do they know why.

I have seen mould etc forming on the underside of the plaster slab (living room side) due to no insulation in the attic. As hot air was going through the slab and getting trapped between the polythene and slab and turning back to water. But never seen water droplets forming on the underside of the felt.

Thanks

steamengine

Yes, sounds familiar! I had this problem last year, a lot of condensation formed on the inside of the roof - also shallow apex. It was widespread and due to snow on the roof. The rafters were also quite damp also. Just wait until this cold snap ends and check again.

cubix

Cheers SE, did you try and rectifiy or just let snow melt. Also any idea if it only affects low apex's, if so why. Anyone know if I change out the old underfelt with new Tyvex that it would stop this problem?

Thanks

Slick50

You should get some insulation, and cover the rest of the attic, unless there is some reason that this patch has been left bare. It will also prevent further mould building up on the ceiling.

cubix

Insulation only pulled back for purpose of photo, attic completely insulated. Ref regarding mould was made to another propety I seen with out insulation.

steamengine

cubix wrote: »

Cheers SE, did you try and rectifiy or just let snow melt. Also any idea if it only affects low apex's, if so why. Anyone know if I change out the old underfelt with new Tyvex that it would stop this problem?

Thanks

No - it's a normal attic well insulated, well ventilated at the eaves. Snow whilst at 0 degrees or below forms an insulation barrier of its own on the roof. There hasn't been a lot of wind with this current cold spell and clearly what is happening the moisture content of the air inside the attic is high and just condensing on the cold underfelt. If the roof tiles were free of snow the attic heat would transfer through the tiles and the inside surface temperature of the tiles would be higher, and there would be little if any condensation. In my case last year I let it be and it rectified itself after a week or so. Changing the underfelt would not rectify it in my opinion.

You could put a de-humidifier in the attic temporarily if you wished to remove the moisture.

Slick50

steamengine wrote: »

No - it's a normal attic well insulated, well ventilated at the eaves.

That could be another factor, ventilation is very important. Roofs should be vented at the apex as well as the eaves.