HELP!! wet roof timber

[dougiem]

Hi

Long explanation but want to try to give all factors to help find solution, have read the sticky on condensation, but want to make sure it is not something else

Story
200 year old cottage, used only for holidays, but have basic heating 1 hour morning , 2 hours at night, while not there to stop freezing and dampness, had roof reslated in July and a breathable membrane fitted(previously no felt), insulated between ceiling and attic floor with rockwool and floored loft, have flame retardant EPS to fit between roof joist but had not got round to doing it was planning on it after christmas holidays, after a 8 day holiday where the house was well heated I noticed all the sarking and all the roof joist were soaking with water dripping from the nail points, is this def condensation or can there be any other problems ?

Facts
Tumble dryer outside house in brick built lean too, so no effect on problem
Bathroom has extractor fan, used always when showering
Do not dry washing on radiators
House probably over heated 18 to 22 degrees (wife feels the cold in Scotland)
Oil fuelled boiler feeding standard water filled radiators in every room
Small multi burning stove in living room, but not used much
Single glazed sash and case windows, problem with condensation on them
Probably don't open windows enough
Think rockwool is pushed too far into eaves,must check
Attic hatch not insulated, ramsey ladder fitted to top of it

Questions
1/ Drying the roof, will a dehumidifier dry it enough or will I also need to heat it ?
2/ How do I insulate the hatch ?
3/ How do I know how much to pull back insulation from eaves?
4/ Will opening the windows regularly solve the problem or do I need to do something else (will also drop the temp to 16 18 max in winter)

Important questions
A/ Do you think the contractor that done the slating on the roof, could have done anything to cause this problem ? I don't think so but want to ask

B/ Anything else I should be doing to help eliminate this problem, suggestions are very welcome?

C/ Should I be doing anything else when I am not there that could relive or help the problem ?

Thanks in advance for any help

Regular reader of the forum, but not enough experience to help with other peoples problem, maybe in the future

Dougie

 

[dougiem]

I have just been told that my breathable membranes are not waterproof and the membrane must have got wet during installation, is this correct and what is the point if it is not waterproof ??

 

[big-all]

you need through ventilation eather via the eaves or roof vents

breathable membrane would dry within days with enough ventilation

where does the bathroom extractor exit the property!!!

 

[datarebal]

breathable membranes are water resistant dont bank on waterproof.
when exposed to the elements for a period of time they can and do become saturated and let in .. a little.

 

[dougiem]

Hello

my post was moved from lofts and stairs to roofs and guttering (no complaints) but there was a couple of replies which I know can't see
can anybody help ?

 

[dougiem]

ignore last post can see them now

 

[dougiem]

The rockwool may be pushed too far into eaves I need to check, but the membrane sarking and roof timbers are soaking and have not dryed in a few days, I now have a dehumidifier in the loft to try to help
Bathroom is an extenstion and extracts to outside wall

 

[dougiem]

The manufacturer of the membrane Fakro is saying that the membrane must have been exposed to rain when during fitting(house in Scotland so this is about 100% chance of being correct) and that like all breathable membranes they are not waterproof, but on their website it says they are, it is not exposed to the elements now, but is soaking and is not drying out, not sure what to do

 

[big-all]

you either have a leak or lack of ventilation

your loft should feel draughty and cold like your outside but a bit sheltered

and dont forget iff your lacking ventilation every time you open the loft hatch you are introducing hot warm air that will make the situation worse
do not worry about a dehumidifier proper ventilation will clear up the problem in a few days

the roof timbers will not be further harmed by a few weeks being wet

happy xmass

 

[RedHerring]

I haven't got any solutions, just comments.
Surely if the roof was reslated in July the membrane should be dry by now, even if it did get wet.
Last year I re-roofed my house in France, Finished the membrane (Facro) 1 week before Xmas last year and left it like that until May this year, when we returned to complete the job. The membrane was still acting as it should and dryed within hours after rain.

The membrane only acts as a temporary barrier against rain. Once the slates are on, it becomes more or less redundant, doesn't it?

Another point may be worth investigating is that the op mentioned sarking. Is the membrane laid directly on the sarking? Should it be or should there be an airgap?

 

[dougiem]

<I don't think it is a leak, because every part of the roof is wet, not just in areas, the loft is much colder than in the house but I think the rockwool may be pushed to far into eaves, will be there in a couple of days so will pull back the rockwool and hope it helps, very happy to hear that there should not be permenant damage to the roof, that was the biggest worry

thanks for your feedback will update you after the new year

 

[dougiem]

(Surely if the roof was reslated in July the membrane should be dry by now, even if it did get wet. )

that is what I would think, but is not the case

(Last year I re-roofed my house in France, Finished the membrane (Facro) 1 week before Xmas last year and left it like that until May this year, when we returned to complete the job. The membrane was still acting as it should and dryed within hours after rain. )

maybe my roofers did not wait till it dryed before slating, but I don't know, also the guy from Fakro told me that breather membranes are not waterproof, even though it states they are on their website


(Another point may be worth investigating is that the op mentioned sarking. Is the membrane laid directly on the sarking? Should it be or should there be an airgap?)
I beleive that the membrane is on top of the sarking no room for battens and in a conservation area, so can't change much from the original, but I believe it is fitted correctly

 

[dougiem]

The guy from Fakro has now told me the sarking must have got wet during installation and is too wet to dry out via the membrane, he told me to heat the loft for a couple of days and this would resolve the problem

had three fan heaters and a dehumidifier running for 5 days, seemed to dry the timber out when I stopped heating, wetness returned within a day

checked rockwool insulation and pulled it back out of the eaves, but still no better, anything else I shuld try ?

Ps, I don't dry washing on radiators, shower has an electric extractor to outside wall, tumble dryer in lean too outside house, oil filled boiler again vents to back wall of house, no water tanks in loft, is it possible that the breathable membrane is not breathing ?

 

[Bryntony]

Hi Dougie,

It sounds from your description you're going to have to treat your roof as a conventionally ventilated cold roof system.

You need to achieve at low level ie eaves, the introduction of at least 10,000mm2 per linear metre, allowing the airflow to pass into the roofspace. The use of soffit vents, overfacia vents, or as a last resort slate vents should be used to achieve this. There are plenty of proprietry systems on the market. Add to this some high level ventilation. The only way would be slate vents positioned within a couple of courses of the ridge and again gaining an airpath out of the roofspace. These would need to be centred to achieve the equivalent of 5000mm2 per linear metre. For example, a vent with a free air capacity of 10,000mm2, one per 2 metre centres would suffice. At eaves, one per 1 metre centre. Having high and low level ventilation produces a stack effect i.e constant air movement, no matter the external weather conditions.

To use a breathable membrane and expect it to work on a refurb is a tall order. To comply with any certification and therefore any guarantee, the roof structure needs to be treated as a separate unit to the house. Vapour checks need to be installed, any penetration through ceilings need to be vapour tight and any penetrations through the membrane need to be vapour tight. Not easy.

I've looked up the use of breathables direct on to sarking boards and securing the slates directly through the membrane into the sarking. No problem. I would be concerned about the lack of airgap to allow the membrane to breathe and release the moisture without becoming trapped and forcing back into the roofspace.

Good luck.

Bryntony

 

[dougiem]

Hi

thanks for the information, not sure I understood it all but I think what you are saying is if I put vents in at the eaves and at the top this should solve the problem ?
Under the eaves should not be a problem, but I cannot have any vents in the roff itself because it is in a conservation area, I believe the top ridge is already vented, but will need to check

It is at the moment a cold roof system with rockwool between beams and then chipboard loft panels, I also have EPS insulation to put between rafters on the roof timbers but I am waiting till I am sure the problem is solved

I really did not understand the vapour checks info, sorry

To update everybody on the problem, all over the christmas holidays the roof was still wet (also very cold temp outside, upto -18 at night), after the house had been empty for a couple of weeks the roof seems to have dried out, seems the problem might only be while we are using the house(holiday home)

Is there any device you can buy or hire to check the level of moisture inside the timber, just incase it is only the surface that is drying out ?