Rotten window sill

[Padraig Clarke]

I am renovating an old cottage, 1890 or something. The wall under the window (internal) was slightly damp to touch, which drew me to the window sill. The window sill was clearly rotten as per the picture. As it happens I ripped it out today. It was MDF and was totally blown. Looking outside I can see no visible water entry points. Apart from maybe a few holes where tv cables went it. Although the slate window ledge outside is frayed. The house was not lived in for about 10 years and I have been finding the results of mass condensation left for years. Lots of rotten timber and damp plaster board.

Anyway, has anyone seen this before?
Can anyone see anything wrong with the window?
Is the slate window ledge a problem?
Is my theory on years of condensation a plausible one?

Many thanks.

 

[Gazman16]

I expect you are correct and a lot of it is years of no ventilation/heating. The old cable holes wont have helped either.
Slate in theory is non-porous so shouldn't be a problem but it is quite weathered so wouldn't hurt to paint it up.

I expect solid stone walls with no cavity wont help. But (and its hard to tell from the photos) has the external ground level been build up quite high against the house/render?

 

[Padraig Clarke]

Thanks Gazman.

I can fill in the wee holes with a bit of sealant.

Yep, as it’s so old there is no DPC. Drainage and guttering and roof has all been improved recently. Outside tarmac is high but has been done well as there is a good run away from the side of the house. Would this cause the wall under the window to be damp?

 

[Gazman16]

I'm no expert on solid walls/stone walls but I as with modern wall construction I can only assume high ground levels are a bad thing.

Modern builds they recommend ground level to be at least 150mm below DPC/floor level and 300mm away.
Could you cut the ground away a bit and install gravel or arrow drains to take water away from the walls?

Wouldn't hurt to post a photo here too of the ground levels/walls as others here may be more clued up on solid walls than I am.