Government loft insulation oversight

[Uncle Peter]

[Cash]

Interstitial condensation caused by poor ventilation of the roof space - a common problem and known since the year dot, particularly since the introduction and common use of underfelt on the roof.

It appeared in my property after having installed loft insulation (not unexpectedly) and it used to run down the underside of the roofing felt and out at the eaves. This was caused by poor ventilation - even though there was sufficient space left between the wallplates at eaves level and the edge of the insulation - which allowed condensation droplets to form on the underside of the felt, probably from residual heat passing through the loft insulation and internal and external temperature differences of the roof structure itself.

This was eventually cured when I had a very old roof refelted with Tyvek underfelt and new tiles, with the loft space properly vented at just above eaves level and vented ridge tiles allowing a very good air flow.

Please do not reply with the invective that you use in your response to 'sailor' at it will be ignored - and show your lack of knowledge of the subject.

Thank you

Cash

[Uncle Peter]

My loft is very well ventilated, but it happens to me. I don't actually have the new thick insulation, but I have it floored and there's so much junk up there it may as well be.

I don't know who sailor is, but he started it. I reply in kind.

[harryagain]

Bollix.

It is not interstitial condensation. That is caused by lack of a vapour barrier.

The problem in the article is probably caused by warm moist air from inside the building getting into the loft space. eg leakage round the loft trapdoor. Or even the exhaust plume from a boiler blowing IN through the eves ventilation.

[Uncle Peter]

What?

[Uncle Peter]

Explain why cars fog up outside at night. Oh that's right, the OUTSIDE air is damp. There's no warm moist air coming from somewhere, the moisture comes in through the eaves ventilation. Without warmth in the loft, this will not dry out.

[Cash]

And temperature differences between internal and external areas - amongst other factors of building construction old and new.

Harry, I was involved in this sort of problem when loft and cavity insulation were in their very early days and read many of the BRE digests on the subject, which included heavy condensation in the various rooms of newly insulated houses and njected foam cavity insulation disasters - so please don't teach "granddad how to suck eggs" especially as you seem search the net for many of your answers rather than having worked on the problems themselves. Stick to bragging about your FIT con!

Peter I'm replying to "Harry" via your post as I have him binned - please DO NOT respond.

Cash

[Fredxxx]

Condensation can happen anywhere where a surface is at a temperature lower than the dew point of local air.

A reduction of surface temperature such as a roof is likely on cloudless nights, where a surface temperature will drop more rapidly than air temperature. That can cause dew both inside and outside of the loft, irrespective of loft ventilation. It doesn't require any warm air through a ceiling or loft hatch, though that will exacerbate the problem, especially if the loft is poorly ventilated.

You have heard of dew, haven't you?

[Uncle Peter]

At last, a sensible reasoned post based on science.

[harryagain]

The outside air is cooling and reaches dew point (ie. 100% relative humidity) Water droplets start to fall out of the air and land everywhere (including the car).

You really are thick as shit aren't you?

[Uncle Peter]

No, you are. It's been explained to you by another poster. Exactly the same thing happens in the loft. The house could be vacated or anything, you have OUTSIDE air coming in through the eaves, just like it gets into the car. The roof is colder than the air, so the air reaches dew point and condenses on the underside.

[Uncle Peter]

I really don't understand how you can be that thick actually. You've just explained to me (correctly) why it happens in the car, yet you won't admit the EXACT SAME THING happens in the loft, nothing to do with the house being underneath it. It STOPS it happening when you have warm air from the house (poor insulation), as the air in the loft is heated and can hold more moisture before condensing.

[harryagain]

Read the posting shit fer brains. I was pointing out to our resdient half wit that the problem was NOT interstitial condensation.

[Uncle Peter]

Ah that explains why my car gets frosted on the right only. The left is next to the house - although the house has cavity wall insulation, and the only nearby window is a small double glazed bathroom window above the car). Mind you the boiler vent isn't far away.

[Uncle Peter]

You've been corrected by four people that I can see in the last few days. Just f*ck off and go somewhere where you have the slightest bit of knowledge.

[harryagain]

So how has condensation outside a car go tanything to do with condensation inside a roof space? I never mentioned inside the car shit fer brains.

[CB]

Irrespective of all the name calling, if we accept that this phenomena exists ( a thread on here before xmas probably suggests that it does) and increased ventilation wont fix it (it seems it wont if its to do with ambient air coming in through the roof ventilation and then condensing on a cold roof - as on a car windscreen).

Damp patches on the bedroom ceiling is less than ideal so what is the solution?

A series of drip trays in the loft to catch the drippings that will eventually dry out when the ambient conditions change? After all if it is a significant problem it should be easy to see where to position them.

[Tim Lamb]

I suppose if condensation is collecting on the rafters, trickling down and then dripping off the purlins, an evaporator/collector could be hung there. Narrow roll of fibre insulation hung strategically below the drip points?

>

[DICEGEORGE]

Modern super insulated houses have mechanical ventilation of so much per ho ur, but old houses and roofs depend on air passing through, which is a lot more on windy days. So how big the ventilation holes in roof are is a balan ce, I can accept a few days in maybe still and foggy conditions there will be condensation, which will dry out on the 99% or more normal weather days. Similarly after lots of rain from a certain direction theres rain inside m y attic, which will evaporate away when the weather changes. wood only rots when its been wet for many weeks. But ifg you have lots of showers, and ov erboil lots of cooking, and block up your house airvents (as some tenants d o) then there will be condensation everywhere, hose and attic. [g] PS STOP SWEARING - WHAT YOU SAY IS WHAT YOU ARE

[harryagain]

I have a super insulated house and never experience condensation. There is no mechanical ventilation. The roof space has ventilation holes that allow through ventilation.

If you are experiencing wet in your roof in windy conditions it's likely water is being driven "uphill" under the roof tiles. ie there is insufficient overlap for the "slope" of your roof.

Wood rots a lot easier than that. Once wet it might take weeks to dry out. Long enough for rot to set in. And if you get dry rot, then drying out won't help at all.