Old Roof Timbers with Moisture Content on Average 40%

Awakeatlast

Hi,

The roof timbers in my friends old home have a moisture reading of around 40%. It's an old slate roof on a traditional timber rafter and purlin construction. There are no slipped slates. There's no underfelt. The parging/torching was done with a lime mortar but has fallen off over 30% of the roof area. None of the timbers appear to be sagging or structuraly compromised. The house was built in the 1950's to 1960's and is an old council house.

The loft insulation has been laid without providing eaves ventilation so there is some salting to the timbers due to condensation.

There's no lead flashing around the chimney stack and the roof timbers in this area have the highest moisture content. I'm trying to find information about moisture in older roof timbers and the impact it may have already had on their structural integrity, if at all.

The two homes either side of this property, still remain in the local authorities possession and had had new concrete tiled roof's fitted about 10 years ago.

I know eaves ventilation needs to be installed and the chimney stack needs repointing and flashing and closing off from water at the top.

But if someone can point me towards information about the moisture content of the roof timbers I'd be grateful.

Thank you

grumpy_codger

But if someone can point me towards information about the moisture content of the roof timbers I'd be grateful.

https://www.google.com/search?q=moisture+content+of+the+roof+timbers

40% seems to be well above the norm

mta999

Which timbers are you talking about - the sloping ones that support the slates or the horizontal ones that support the ceilings inside

if it is the sloping ones that support the slates then I'm guessing water is getting in under the slates - maybe all the time or maybe only when it is raining and the wind is blowing in a certain direction

greyteam1959

What device are you using that gives you a supposedly moisture content of 40% ??

Awakeatlast

https://forums.moneysavingexpert.com/discussion/comment/81866802#Comment_81866802

A Draper mini moisture meter. It was set set to read wood. There is a large amount of pattern staining to the timbers which I would associate with water ingress. The staining is at the top of the rafters. There's nothing visible suggesting any rafters have structural problems. I've scraped one of the rafters with a chisel in a badly stained area with a high meter reading and it seemed ok. On of the highest readings was 50%. I took readings on all the rear rafters at the top and middle. I didn't take any at the foot as I couldn't clamber under the purlins and I knew they may be high due to the white condensation stains. I'm aware that the slates need to be removed and a breathable felt installed and a new roof covering of new tiles is needed. What I wanted to establish was is there any unseen damage to the roof timbers due to the high moisture content.

Thank you

Albermarle

 I'm aware that the slates need to be removed and a breathable felt installed and a new roof covering of new tiles is needed

Many houses, especially older ones have no felt at all , without any problems. It is more of a secondary defence against moisture ingress. So a nice to have rather than a must have.

Also why are you so sure that it needs new roof tiles? Are they obviously damaged ? There are still many slate roofs around that are a lot older than this one.

WIAWSNB

If the roof covering is not leaking, and if you restore the loft ventilation, then it should be fine.

You know the cause of the high moisture readings, and the cure is easy.

The felt layer is not essential - it has managed without it for donkey's - and its lack probably helps with ventilation under the current circumstances.

What's the actual problem? There doesn't appear to be any rot. Sort any leak, restore the missing ventilation, and jobbie jobbed. Probably.

Only go to the expense of a new covering when it's actually needed.

twopenny

Get the ventilation sorted by keeping the insulation away from the eves and let it dry out over summer. Flashing round the chimney would be good. The mortar too.

See what the levels are when it's dried out.

I wouldn't consider felting until you've done that. And it also depends what kind of tiles.

I spent decades in an old house and it was when the insulation went in that there were signs of damp because there is no heat getting into the loft below and when open fires, ditto. It's finding a balance but ventilation is essential. Once that's right it should improve.