White Mold In Loft Rafters

[HenryFord]

Hi All, I own an 1840s stone cottage (with stone flag roof) which we are refurbishing to rent as a holiday cottage. Yesterday we had a new boiler (Vallant Combi) and had the header tanks removed from the old system (back boiler). Today we have been cleaning the loft out and I have noticed 2 things. Firstly a light covering of white mold on some of the roof rafters that wipes off easily (wood is still strong and not rotten) and secondly after uncovering the bottom of the loft some rot in a few ceiling rafters (wet rot I think). So 2 questions, firstly is the mold likely to disappear now the header tanks have gone and should I treat it, if so what with, and what is the best course of action to remove the 3 semi rotten ceiling joists and replace with new strong wood. Thanks again for your answers

[goodgoalie]

I have a similar property and replaced the stone tiles on the rear roof with terracota tiles with modern breathable roofing felt. The front is slate with that horrible bitumen roofing felt. I noticed some white 'bloom' (?) on some of the rafters, and would say that the most important thing - and this goes for ALL lofts - is to make sure that there is adequate ventilation. I put in two roof vents on the slate side, and all seems to be okay now, though I have had a lot of cluster flies from time to time!

[Goofy]

Someone has been reading too many American stories. Mould is spelt with a U in this country!

[The Builder]

Goofy and The Goalie are both correct ;o)

This is quite possibly "cellar fungus", Henry. Assuming no roof leaks, then the moisture is most likely coming from water vapour within the building condensing in the roofspace.

Ventilate, Henry. Let the vapour out. Fungus cannot then survive, and the timber stays dry.

Is there felt under your roof covering?
If so, does it look like it's old-type bitumen felt?

[HenryFord]

Hi Builder / Goofy, apologies for the Americanism (if I'm honest its just my poor spelling). The felt is 10 years old and the breathable variety. What is the best way to vent a roof, or do you mean vent the whole house with air bricks here and there? Thanks

[The Builder]

Well Henry... if you're sure it is a breathable felt, then I really am puzzled.
This is a bit of a long shot as I'm struggling here, but there are a lot of felts around that are a replacement for the old Type 1F bitumen felt. They look like modern breathables, but are not.

Or... and this is quite possible... the breathable felt is not enough to ventilate the space completely. There are a number of parameters:

Cold, exposed location.
Excessive amounts of water vapour rising from the habitable rooms
Semi-detached/terraced, where moisture is introduced from next door.
High levels of roofspace insulation. (Still a good thing of course, but will result in a much lower temperature above the insulation.)
Uninsulated stone gables (as in 1840 houses.)

If this really is breathable felt, then this simply means that the water vapour (hence condensation) is beating the ventilation.

So... retro-fitted vents needed.
A few of these on opposing roof slopes to create crossflow ventilation
http://www.roofingvents.co.uk/tile-and-slate-vents/002-00491.html?gclid=CNLv7JWkotQCFQEA0wodKrEKHQ

Have opposing gables? Simple terracotta masonry vents inserted in each gable is even more effective.

I have to say that I've been using "Tyvek" or "Protect" modern felts for years with absolutely no problem, even though the "expert", official advice is not to rely on them alone. Official expert opinion does tend to be a cover-all. They play safe, but maybe the climatic difference down here in Devon has something to do with it?

Look forward to you comments Henry.

[HenryFord]

Hi Builder, thanks for your comments. I am reliably informed that it is a breathable felt, fitted about 10 years ago (2006) and apparently the stone tiles were 'turned' at the same time....not sure what that means or why its done? I will wait and see a while, we have just had the header tanks removed and a combi boiler put in. The headers were not covered, and I suspect there had been leaks at some point, although the water was turned off when we bought the house. It was uninhabited for approx 6 months before we bought it. Also next door (semi) is a bitumen based felt...so not breathable, could this be the problem?

[The Builder]

Henry, yes, I would suspect that you are being overloaded by next door's water vapour. It has nowhere else to go!

I assume there is no firewall between you and next door (in the roofspace? Be prepared for Insurers to ask for this to be installed.