Condensation on Roofing Felt in Attic

CBYR1983

What's the best way to tackle this - roof line is normally leaky as a sieve in terms of air intrusion (not water thankfully) but noticing more condensation on felt in this weather. Any solutions?

antiskeptic

CBYR1983 wrote: »

What's the best way to tackle this - roof line is normally leaky as a sieve in terms of air intrusion (not water thankfully) but noticing more condensation on felt in this weather. Any solutions?

Have you an expansion/feed tank in the attic that services the central heating. If so, cover it to prevent moisture loss.

Or an expansion/vent from the hot water tank. If so, you could extend the pipe so that it vents to outside.

CBYR1983

antiskeptic wrote: »

Have you an expansion/feed tank in the attic that services the central heating. If so, cover it to prevent moisture loss.

Or an expansion/vent from the hot water tank. If so, you could extend the pipe so that it vents to outside.

I do indeed, I just insulated the feed and expansion tank the other day. I didn't insulate the vent pipe as I thought it would just be hot water going through it anyway but I see now it could be causing condensation.

House is quite old, with sloping roofline down to eaves. I fear eaves are not perfectly clear but there are definitely some parts that have no insulation at all. Just not accessible, obviously never considered when the house was being built (1930s).

I've tried to reduce heat escaping up to the roof. I'll think about insulating the top of the feed and expansion tank, at the moment I only have some fairly ill fitting polystyrene on top (100mm fibreglass wrapped around it though) and expansion pipe is not lagged.

Cause is definitely warmer air/moisture getting into the cold attic then???

Praying for the cold snap to end as snow flurries down on Dublin 8!

antiskeptic

CBYR1983 wrote: »

I do indeed, I just insulated the feed and expansion tank the other day. I didn't insulate the vent pipe as I thought it would just be hot water going through it anyway but I see now it could be causing condensation.

It's not so much insulation that's needed for the tank as covering it. A board of stiff plastic (a serving tray?) would be ideal. Leave the cover uninsulated. The water that evaporates (moreso because it's warm) in the feed tank will now condense against the cold surface of the lid - and drip back into the tank - instead of escaping from the currently open tank and condensing on your roof felt.

Similarily, it's the water vapor escaping from the hot water vent pipe that condenses on your roof. Leave it uninsulated as a cold pipe will better condense vapour within which will drain back to the hot water tank.

I'd imagine the problem to be largely to do with the open feed tank so try covering it first.

House is quite old, with sloping roofline down to eaves. I fear eaves are not perfectly clear but there are definitely some parts that have no insulation at all. Just not accessible, obviously never considered when the house was being built (1930s).

I've tried to reduce heat escaping up to the roof. I'll think about insulating the top of the feed and expansion tank, at the moment I only have some fairly ill fitting polystyrene on top (100mm fibreglass wrapped around it though) and expansion pipe is not lagged.

Cause is definitely warmer air/moisture getting into the cold attic then???

Praying for the cold snap to end as snow flurries down on Dublin 8!

An insulated feed tank lid won't condense water and, because it's currently ill fitting, the vapour will escape easily (albeit not as rapidly) from the tank. Leave the lid uninsulated.

A last check would be to ensure the condensing water on the lid doesn't seep to outside the tank and drip onto your ceiling. A way to ensure this is to place a heavy object in the centre of the lid when in place to cause the lid to bulge downwards ever so slightly in the middle. Water condensing on the underside will run from the edges towards the middle of the lid before dripping off.