attic condensation

johnnyb6

Hi I have problem with weeping felt in attic. I converted attic few years ago and insulated room with rockwool between ceiling and felt. I have recently been told that this is wrong as I didnt leave 50mm gap. I got engeneer to look at it and he advised me to put in 10 vent tiles. This didnt solve problem so recently I pulled the rockwool from the attic ceiling. As the joices are 4 by 2, i will fit 50mm solid insulated board between them and with the vents , should I solve problem. I have attic slabbed and plastered and faced with tongue and grooved boards.

Grateful for any advice.

whizbang

If you use the foil backed insulation, fit it tight, seal any gaps between with tape, then this will act as sufficient vapour barrier. Also make sure the 50mm gap is maintained. ideally use spacers.

In your case it wasnt the lack of the gap that was the problem, its the lack of a vapour barrier.

johnnyb6

Thanks for your reply, but what do you mean by vapour barrier

whizbang

The condensation you are getting is water vapour from the house. People, Cooking, Showers etc.
This vapour passes easily thro plasterboard, and condenses where ever its cold enough. ie. on the felt.

A 'vapour barrier', or 'Vapour Control Layer', 'moisture control', 'air leakage membrane', etc, is a sheet of plastic that stops the air + moisture from getting thro the insulation. Always install on the warm inside.

Foil wall lining paper, and also vinyl wall coverings, all help do the same job. However most of the modern foil backed insulation does it too, without an extra layer.

johnnyb6

I used half inch foil back plaster slabs when i was doing attic ceiling. I have foil facing up.Is that a vapour barrier