for People with a Passion for Period Property
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Stephen Boniface - Stephen Boniface specialises in building conservation providing multi-disciplinary consulting services. He is Chairman of the Building Surveying Faculty and member of the Residential faculty. He serves on the RICS Building Conservation Forum Board and is the 'Agony Uncle' on the Period Property UK website (

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Our experts are all specialists in matters directly involved with older properties. So, if you have a problem with an older building - or if you think you might have a problem - ask an Agony Uncle...

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Our stone window surrounds are leaking
Andrew Douglas

We've recently moved into a Grade II listed property with sandstone window surrounds and mullions. During persistent wet weather, the upstairs south-west facing window lets in a lot of water, particularly if there is a strong wind driving the rain into the window recess. The window frames look sound and well sealed - the water appears to be soaking through the stone rather than leaking in round the edge of the frames.

There's lots of conflicting advice over the use of silicone based sealants to waterproof porous stone - a lot of experts suggest it can cause more problems than it solves as it prevents the stone from "breathing" naturally. There are products out there which claim to be water repellant yet don\'t block the pores in the stone allowing it to breath - what\'s your experience with these products and what are our options regarding the leaky mullions - is it something we\'re just going to have to live with?

Andrew Ferguson

Without seeing the problem for myself I cannot provide a specific solution, but offer some suggestions to assist you in assessing the matter.

Please see my other answer regarding sealing gaps between frames and the masonry reveals. However, I am not convinced that sealing the perimeter of a window frame with a modern silicone sealant will lead to problems relating to lack of breathability because the area involved is so small. This is not the same as sealing the stone generally, which I will comment on below.

I suggest you have the problem properly investigated and that every possible point of water entry is considered so that it can be included or excluded as needing attention.

You need to assess whether there is water ingress around the frame perimeter, in which case sealing the junction should resolve the problem. However, if the problem is porous stone allowing water penetration the problem is more difficult to resolve. I would not advise using a modern sealant on an historic building. I am aware that some of the modern sealants are potentially less damaging, but I do not believe that the most recent products have been in use for enough time to assess whether such products will cause problems. I have used modern sealants on modern stone and as yet have not seen adverse issues, but would be very reluctant to use them on an historic building.

You should also consider whether there is a problem with additional water hitting this area, e.g. from a gutter or roof area? If so is there a way of reducing the amount of rain that hits this part of the building?

I would be surprised if this building is the only one suffering such a problem in the area. I therefore suggest looking at other buildings of similar age and construction with a similar orientation. What have they done to combat such a problem? Some may have a lime render finish, or simply limewash. In some regions a cladding such as tile or slate might be used.

I do not think it is something you should live with and unless evidence in the property suggests otherwise I doubt if it has always suffered a problem. In fact you should consider what may have been changed that could have resulted in a weakness that is now allowing this problem to occur. If you can identify a change it may be possible to reverse it and remedy the problem.

This is something that you perhaps ought to discuss with the Conservation Officer in case a change is required to deal with this e.g. rendering or cladding the elevation. It could also be the case that the CO has seen a similar problem elsewhere in the region and can offer a solution.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at The Whitworth Co-Partnership for responding to this question.
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Builder claims roof tiles have become porous
Tessa Holland

My mother has a property in Berwick upon Tweed with red clay pantiles on the roof. I am not sure how old the roof is (perhaps original?) though the building is eighteenth century. The wooden structure supporting the roof is failing and we are wondering how to assess whether the tiles themselves need to be replaced, or whether some can be salvaged and re-used. A local builder told us that they have become 'porous' and need replacing, but I am unsure how authoritative this opinion is.

Could you give us any advice either on the likely lifespan of such tiles and how to assess the integrity of the surviving tiles, or how to locate any reliable contractors in the area who could give us an informed opinion?

Tessa Holland

If the roof slope is quite low the pantiles might have suffered frost damage over the years and this could have made them difficult to salvage. However, assuming a standard roof pitch I doubt that too many will have been affected by this. I would normally expect to be able to re-use from about 50% to 70% of the tiles. However, a reputable and trustworthy roofer should be able to assess them.

It is of course possible that these tiles have deteriorated such that they cannot realistically be re-used. However, you should bear in mind that an untrustworthy roofer might say they are unusable and then take care when stripping them because he will then sell them on!

You mention that this work is being undertaken because of failure to the roof structure, but I would start by questioning whether the structure is so badly damaged that the roof does need to be stripped, repaired and re-covered? Who has said that such extensive work is required?

Unless there has been a serious problem of leakage, etc over the years I am surprised that a roof on an C18th building needs such major work. With historic pantiles it is difficult to say what lifespan they might have as many I see are still sound and could yet have many years (unquantifiable) life left.

I would strongly suggest that you seek independent professional advice. A building surveyor experienced in dealing with older properties should be able to fully assess what work needs doing and also advise on suitable contractors in the area.

Finding reliable contractors is always problematic, but speaking to people locally who have had similar work undertaken may help. You could also ask the conservation officer whether there are a few contractors they know are experienced in roofing this age of property that could be approached.

Period Property UK would like to thank Stephen Boniface, Tony Redman and other partners at The Whitworth Co-Partnership for responding to this question.