Wet roof question.

[Harpo]

I have just finished putting extra loft insulation in place and my mate noticed some water drops on the inside of the roof, on the fabric membrane around where it is nailed to the roof wood.
Being cold, some was frozen so it was noticeable as it was white on a dark background.
Whilst it wasn't like Niagara , I was surprised that it wasn't totally 100% dry.

The flat was built about 8 years ago. The original insulation looks okay, but who ever fitted it was a bit slack.
In places it looks like the roll ran out a few feet before the wall/eaves and they couldn't be bothered to cut a piece for there and just left it bare.
I have put some in there and then put a second layer throughout the loft.
Around the spotlights there was an excessive amount missing. Now covered, using the flowerpot trick.

So I don't know if warm moist air was escaping from the flat and then condensing on the cold roof or if it is anything else?
The eaves appear not to be blocked by insulation and the ventilation is good up there. Can it be too cold?
The 10 year guarantee has 18 months to go, so I have that to fall back on.
I would appreciate some helpful advice guys. Cheers!

By the way, B&Q ran out of the £3 rolls, so the next best I found in a hurry was at Wickes. Buy 1 at £30, get 3 free.

[deeps]

There needs to be an air flow through the loft or condensation forms, plastic felt is the worst for that. Eaves are vented through the soffit or on top of the fasia boards if no soffit. Some modern houses now have a vented ridge too.

Breathable felt is supposed to prevent condensation, but whether it does I don't know. I've been in some modern lofts that were saturated with condensation.

So in your case, you have air flow to the eaves and breathable felt?

[mk1fan]

It's now all three venting elements, breathable felt, eaves vents and ridge vents.

Firstly, the current conditions are a bit extreme. I would keep an eye on it to see what the 'normal' conditions are. If the condensation remains during the spring and autumn then you should check the external ventilation to the loft and check to see if there's any leakage of warm air from the flat into the loft.

For example, it's not unknown for people to vent bathroom extractors into the loft space. Of for recessed lights not to be sealed off.

[deeps]

mk1fan said:

For example, it's not unknown for people to vent bathroom extractors into the loft space.

Lol very true. It's also very common for the flexible ducting to have dropped free from the vent tile, as it's sometimes just bodged on with a bit of tape.

[eliot]

Ive been venting my bathroom extractor into the loft, although admittedly stuffed down towards the eves without any problems. Having said that, my loft is very drafty.

[Globs]

eliot said:

Ive been venting my bathroom extractor into the loft, although admittedly stuffed down towards the eves without any problems. Having said that, my loft is very drafty.

You are a brave man, roofs are a rail pain to replace

[Harpo]

Thanks guys.
I'll check on the bathroom fan ducting. It is that cheap looking plastic stuff no doubt held in place with old masking tape!
Pretty confident that the ventilation is good but I have no idea if the felt is breathable. I will inspect it again once this cold weather has moved on.

[Deva Link]

mk1fan said:

Firstly, the current conditions are a bit extreme.

Not only is it very cold, but where we are we've had several very still days - so all the ventilation in the world isn't going to work if there's no air movement.

[mk1fan]

It's still been windy round here - no sniggering please.

It is not very often in the UK that there's such a tempreture between outside and inside.

[jeff m]

The builders were not remiss in stopping the insulation short of the eaves.
With a vented loft the insulation should only reach and insulate up to the point where the wall meets the ceiling.
Theory behind this is to keep the inner and outer of the roof at similar temperature by allowing airflow in at the eaves, out at either a ridge vent or end vent.
Thus avoiding the cold lager in a warm bar effect.

ETA think of the purpose of the insulation not only to keep your house warm but also to stop heat getting into your loft.

Edited by jeff m on Friday 3rd December 13:54

[andy43]

If you've been up there sweating and swearing laying insulation, and have had the loft hatch open for more than a few minutes, that's where the water has come from. Leave the hatch shut for a few days, then sneak up there really quick to have a look. Bet the felt's dry

[RICHBRO]

I have wet marks on my ceilings that follow the joists in the loft. Apparently, according to the builder, during the very cold weather ( minus 10 on one occasion)a slight frost would have formed on the inside of the roof. When warmed up again the frost would form droplets and fall onto the insulation and was drawn down by the wooden joists. The property is about five years old and conforms to latest building regs. The builder states additional vents wont help and all that can be done is to drop the trap door every now and again to help dry out and to do the same if we get very cold weather again. This doesn't seem right to me but looking at other forums it does seem a difficult problem to resolve. To me it seems as if there is too much insulation but would welcome any advice.

[Flintstone]

Harpo said:

I have just finished putting extra loft insulation in place and my mate noticed some water drops on the inside of the roof, on the fabric membrane around where it is nailed to the roof wood.
Being cold, some was frozen so it was noticeable as it was white on a dark background.
Whilst it wasn't like Niagara , I was surprised that it wasn't totally 100% dry.

The flat was built about 8 years ago. The original insulation looks okay, but who ever fitted it was a bit slack.
In places it looks like the roll ran out a few feet before the wall/eaves and they couldn't be bothered to cut a piece for there and just left it bare.

New build, there's a surprise

When I moved back to the UK we needed a place in a bit of a hurry and frankly couldn't afford to be choosy so ended up with a small place about seven years old. What a pile of wk. During our brief ownership I found any amount of ill fitting mouldings, timber, trim, roof valleys (cut too short so instead of discharging into the gutter all the rain discharged onto the soffit), poor wiring and poor plumbing. I'd never buy a modern house again.

[Deva Link]

RICHBRO said:

I have wet marks on my ceilings that follow the joists in the loft.

Burning candles can leave the same marks.

It would surely take a ton of condensation to soak into the joists and then through the ceiling?

[andy43]

RICHBRO said:

The builder states additional vents wont help and all that can be done is to drop the trap door every now and again to help dry out and to do the same if we get very cold weather again.

I'm guessing sending warmer moist air up there will just make things worse.

[Globs]

andy43 said:

RICHBRO said:

The builder states additional vents wont help and all that can be done is to drop the trap door every now and again to help dry out and to do the same if we get very cold weather again.

I'm guessing sending warmer moist air up there will just make things worse.

+1

considerably worse I would think!

[mk1fan]

RICHBRO said:

The builder states additional vents wont help and all that can be done is to drop the trap door every now and again to help dry out and to do the same if we get very cold weather again.

+2 with making it worse.

There's plenty that can be done but the builder doesn't want to spend the time & money or doesn't understand the issues involved.

Sounds like you could do with an independant assessment of what's there.

[RICHBRO]

Thanks for the comments. The property is still under the 10year build guarantee, so I am placing it in their hands.

[mk1fan]

I very much doubt that you'll get this ressolved under the 10year guarantee. I'd be looking at getting the problem independantly assessed by a Professional - not a tradesman with a vested interest.