Another loft condensation post

[Alfie25]

Another person here with condensation in the loft – wet rafters and water droplets dripping off the roof felt. I know there’s many many historic posts talking about this problem as I’ve read most of them but am thinkng of removing the new insulation…

I moved into my house last spring. The existing loft insulation was just loose fill, which ranged in depths depending on how it had been scattered – between 20mm and 70mm on the whole. In summer I had new 300mm loft insulation laid on top of it by Carillion (free grant). They re-lagged the pipes and put new jackets round the water tanks as well (both have lids). I noticed some condensation in the loft in November when we first had freezing conditions, read all the advice on here and made sure the insulation wasn’t blocking the eaves vents and that they were clear. The vents were clear and loft insulation wasn’t tucked in but I moved the insulation back a little more to hopefully increase airflow. When standing in the loft you can certainly see daylight from both of the eaves (house is detached, built late 1980’s). Other relevant info is there are no ridge vents, there is a vapour barrier fitted to the loft floor over the bathroom only. I have no bathroom extractor but always open the window when taking a bath (I rarely use the shower) and leave the window open a while afterwards. I live on my own so shouldn’t generate too much moisture (!) – its not as if I’m a big family having multiple baths or doing loads of cooking.

I don’t know if this happenned last year as I wasn’t living there then. All I know is it’s happenning now, and incidentally my house is the only 1 in the street whose roof is still fully covered in snow. The insulation is obviously doing its job but is it doing it too well!? Haven’t measured the temp in the loft but its bl00dy cold! I’m seriously considering removing the new insulation in an attempt to alleviate the problem! I’d rather lose a bit of heat from the house into the loft and have a dry loft/roof. What do you reckon?

 

[stem]

The problem is caused by moist air that is warmer than the roof ambient temperature getting into the loft space somehow and the moisture condensing out of it as it meets the cold surfaces up there.

Even if you were to remove the insulation (not recommended BTW) the roof surface would probably still be cold enough to allow condensation to form. Just as condensation can still form on the inside of windows in a heated room.

The question is. Where is the moist air coming from?

Is the water in your storage tanks hot or cold? It shouldn't be hot unless there is a problem with your heating system, but if it is, moisture may escape as the lids often don't fit too well.

Does the loft hatch fit tightly especially if it is in the bathroom ceiling?

Is there any sort of pipe / vent / duct passing through the loft that is allowing air to get up there.

Can fumes containing moisture from a gas boiler be blown into the loft through the gap in the eaves?

 

[joe-90]

Downlighters are the usual culprits.

 

[Alfie25]

I have no downlighters so they cant be the culprits.

The cold water storage tank is cold. The feed and expansion tank can get a little warm but I believe it's normal to warm up a bit as the water expands.

Loft hatch is on the landing and is very heavy. Seems a good fit to me but I could add some sealing tape round the edges. The back of the hatch is polystyrene backed.

The soil stack in the corner of the house exits through the loft and out of the roof (about 6 inches is visible in the loft). In the bathroom below, the stack is boxed in behind the bath. Where it enters the loft, there's a bit of space around the pipe if you see what I mean. I suppose warm air from under the bath could be travelling around the outside of the soil stack (in the boxing) and then into the loft.

Gas boiler is on the ground floor. Depending on where the wind blows I suppose the fumes could rise up and into the eaves vents but they aren't directly above the wall where the boiler flue is.

The roof is pitched east/west. The condensation so far is only occurring on the northern half of the roof.

 

[joe-90]

If the main problem area is near the soil pipe - then I think you may have sussed the culprit.

 

[foxhole]

Expansion tank should not be warm, unless its getting hot water in it therefor lots of moisture in the loft, must be a problem there, make sure the vent cannot touch water surface or it will syphon. Happened to me once when the string [yes string] holding the overflow up rotted and snapped.

 

[Alfie25]

There's no vent pipe over the feed and expansion tank so I presume it's a combined feed and vent?

 

[algas]

You will probably need additional roof vents.

 

[easyas123Viessmann]

tank should not be warm convert to a pressurised system if possible and see if the condensation goes away.

 

[stem]

The water in most heating system F&E tanks I've encountered are slightly warmish (as opposed to hot) due to the expansion of the hot water from the heating system, or conduction via the pipe, so I believe that is fairly normal.

Installing a pressurised system, seems a bit of an expensive suggestion just to "see if the condensation goes away"

 

[easyas123Viessmann]

Shouldn't cost very much. Has many other benefits. May cure or help your problem. Tank shouldn't be warm.