Damp on Concrete Ceiling Roof (Ed.)

[oliviamorris664@gmai]

Hi there,

We moved into our new house last winter and noticed water on the ceiling of a small extension to our kitchen. At first, we thought the roof was leaking, so we replaced the felt roof. However, we now realize it's due to condensation.

I want to fix this before winter, but I'm unsure of the best approach.

Can we insulate from the outside without removing the felt roof? If so, would we need a vapour barrier?

Alternatively, should we insulate from the inside using spray foam? Would a vapour barrier be needed in this case?

I'm not sure where to start. Thank you for your help in advance!

 

[freddiemercurystwin]

What is the existing roof construction from the plasterboard through to the felt? You might need to do a trial hole in the plasterboard to find out. Got some photos (externally of the roof and how it joins the house? How do you know the room doesn't just need better ventilation?

 

[oliviamorris664@gmai]

I'll grab a picture when I get back to the house but there is no plasterboard (just concrete) on the ceiling and no insulation inside. From an external perspective, there is no insulation on the roof either, just the felting layer. It seems like the flat roof is just a concrete slab (the house was built in the 50's/60's). At the time of replacing the roof, we weren't aware that we needed an insulation/vapour layer as we're very new to DIY and home improvement.

If it comes to ventilation, what would be the best way to do this without losing too much heat during the winter?

Thanks for your reply!