In the days before roofing felt, torching or lime mortar was used on the underside of tiles or slates to keep them in place and to prevent strong winds from getting under the tiles and lifting them. Over the years this torching can crumble and break, normally falling with a thud on the floor of the roof space during the middle of the night! Whilst this may be alarming, unless there are subsequent leaks then missing torching is a little like torn roof felt – not a problem in itself but it may contribute to other problems with a roof.
Whilst torching may be seen as a little old-fashioned it is still used today in heritage properties, as an alternative to modern breathable membrane. The torching on heritage roofs contributed to securing the clay tiles on roof, in the days before nibs were added to hold them on the wooden battens.
When a roof is being renewed for other reasons then torching is often replaced with breathable membrane not least because most roofers do not have the skills to do torching and current building regulations direct them towards other methods.
Renewing torching is a specialist task. Roofers who can do this are normally to be found working on heritage properties. A mix of lime mortar mixed with horse hair is often used for this task.
Note: torching on pitched roofs is not to be confused with torch on felt used for flat roof construction.
I just had a homebuyers survey completed and the surveyor highlighted a defect within the roof structure. Namely, the timber had damp and was deteriorating and the torching is in bad condition, daylight can be seen through some slates and there are signs of condensation.
Any advice on how much this would cost?
I’ve just purchased a property that has torch mortar. It’s mostly in a good condition, but some areas need repairing. Would it be recommended to have the entire roof upgraded to modern methods or seek patch repairs. I want to future proof and improve insulation up there too.
Hi Craig,
It would mainly depend what your longer term aims are. If the roof “works” then patch repairs make sense. The torching is to help keep out wind blown rain and snow and helps to keep the tiles in place. If you are looking to add insulation then it would depend where you are looking to add it. If it is added to the loft floor to insulate ceilings then the loft area will get colder (cold roof), which increases the risk of condensation. With your type of roof with good ventilation this is unlikely to be a problem. If you insulate between the rafters (warm roof) then this is usually linked to converting the loft into a useable space and then a rethink would be required.
Hope this helps
Kind regards
Jon
is there a substitute to torching to patch roof
Hi William,
If refurbishing the whole roof then a breathable membrane could be used….although on a heritage property torching would be preferable. For smaller areas then torching may well be the most cost effective.
Hope this helps.
Kind regards
Jon
No most roofers do have the skills which are rather easy, they do not have the time and the customers don’t have the money plus membranes work better
I am looking for a traditional torching mortar mix for repairing the inside of my very old slate roof. Have you any idea what materials went into such mixes ?
Thanks
David – in Caernarfon North Wales
Hi David, I have the same issue on our Grade II listed building and we get all of our Lime mortar from Mike Wye and associates – http://www.mikewye.co.uk. They sell a lime mortar which also includes horse hair. Give them a ring and they will be able to help you out.
All the best.
M