Slate Roof Torching

[SteelCityResto]

Hi all,

I've just recently bough a large Victorian property that requires a little love. Overall, it's been maintained pretty well, and fairly sympathetically, the previous owner was an engineer or some type, and clearly knew the value in doing the job right first time.

The building has three main roofs, all of which are slate and have been well maintained over the years. The slates and battens are in relatively good condition; however, the torching has mostly come off. Given the fact that the roof is in good condition, I am looking to renew the torching with lime mortar.

I've carried out some research on lime torching and understand why it's the right material for the job; however, I can't seem to find much detail on the construction techniques. Because of the batten separation I think half torching is most appropriate, but I'd like to know more construction detail, e.g Mix type, whether or not to torch the perps, areas to, or not to torch e.t.c?

There is a book available for historic building roof maintenance, but it's pretty expensive, and I'm not sure what it's going to tell me. I have scoured Youtube and there doesn't seem to be much at all. My next step was to head to the city library and find out what information was available there.

Any advice would be greatly appreciated.

Thanks, Paul

 

[alexander]

your best bet is to leave well alone , if its the original roofs there is a very good chance it will have nail fatigue, by torching the battens there is a good chance you will disturb the tiles creating a problem were there was non, the reason the torching has perished is through lack of moisture i.e. no leaks it was designed to catch any drips getting under the slates & protected the wood work while allowing air flow into the attic space to prevent condensation building up, that job is done today by breathable membranes although a lot of breathable membranes on the market are not really up to the job & actually create condensation in your loft space,

 

[SteelCityResto]

Thanks Alexander,

I suppose your reply leads me to the option of reroofing the property. Another function of the torching was to keep the slates in-situ and avoid tile lift during high wind conditions. Without it, there is a further risk of the potentially fatigued nails failing and allow leaks. Certainly one to mull over!

Is there a properly breathable membrane you’d recommend?

 

[Cabinet]

This is a good blog post to read on the subject: https://www.theyorkshirelime.company/the-importance-of-lime-torching/

 

[SteelCityResto]

Thanks for that Cabinet, I’d actually previously read that article. I accept the fact that there is a risk of damaging some slates when re-torching, but repairing some slates is potentially more costs effective and period correct than re-roofing the whole property.

I wonder whether I could strip some areas of the roof and inspect the nails; the nails could even be examined my a Metallurgist for corrosion, #gettechnical lol.

 

[alexander]

Thanks Alexander,

I suppose your reply leads me to the option of reroofing the property. Another function of the torching was to keep the slates in-situ and avoid tile lift during high wind conditions. Without it, there is a further risk of the potentially fatigued nails failing and allow leaks. Certainly one to mull over!

Is there a properly breathable membrane you’d recommend?

you want an air permeable breathable membrane, some like klobar permo air or roofshield

 

[Stevers]

I'd heard of torching in the context of tiles particularly pantiles, but I've never heard of it in the context of slates before.