Attic condensation

jezko

Have a 1940s built house with slate tiled original roof, No felt under tiles.

The attic has been insulated between the joists.

Finding lot's of Moisture on the inside of tiles.

What can I do to prevent reduce this

I Believe I can't foam Spray the tiles as this reduces ventilation?

mykillokneel

Looked at job before Xmas similar age house old slates no felt ,slates in poor condition lots of gaps/broken/cracked some had gone into attic and put expanding foam to cover the gaps but all they ending up pushing the ends of the slates up so lots were cooking up on the roof so don't do that!
You need vents high up and low down, ideally if you budget allowed you should be felting with breathable felt also but that means strip slate, you may be to re use if in good shape. II'd guess there sitting okay or else the draught would be your vent!!

Calibos

Our business premises is the same roof construction. The condensation is warm moist air getting into the attic from the habitable rooms below and condensing on the cold tiles. Unless there are holes or cracks in the ceilings then most if not all the air is getting into the attic via the attic door. You need to make the attic door airtight.

Macspower

Easy enough fix and a very common roof system in older houses.

BTW for those that don't know, I am in the insulation industry so as to disclose my interests.

The condensation is caused as mentioned by the warm air hitting the cold surface of the tiles.

My suggestion and one of the fixes for the problem is to fit a breathable rigid membrane to the rafter leaving a gap between it and the tile. Then to spray foam to the membrane with open cell breathable foam. This can only be done if there is room at the soffit area to carry the membrane over the wallplate.

This system would allow moist vapor to travel through the insulation and through the membrane and into the space left behind it and vented out through the soffit. This however will be greatly reduced and the temperature differential will not be as great.

If warm vapor still condensates on the tile it can then drip to the membrane and run out over the wallplate.

there are those that will suggest spraying directly to the tile with a closed cell foam but unless done correctly as mentioned this can move the tiles. Generally this is only done in certain circumstances where the method mentioned above is not suitable.

here is a diagram of my suggested method of resolving the problem.

MicktheMan

Macspower wrote: »

My suggestion and one of the fixes for the problem is to fit a breathable rigid membrane to the rafter leaving a gap between it and the tile. Then to spray foam to the membrane with open cell breathable foam. This can only be done if there is room at the soffit area to carry the membrane over the wallplate.

OPs attic is already insulated. His/her problem is now lack of sufficient ventilation of the roof space. Adding more insulation on the slope isn't going to address this.

@OP: you need to add adequate ventilation to your attic space.

madmaggie

I had a similar problem to OP's with a tiled roof. The tiles, approx 80 years old had become porous. I watched the rain seep through on wet days. If the timbers are good you might get away with felt and slates/new tiles. Any ventilation from the soffit?