Weatherproofing Hamstone roof

[samspurgeon]

Hi,

I have a leaky roof on a single storey single room extension on my property. It was originally designed as a “strong room” and as such was constructed with a 4” thick hamstone roof.

The developer we bought the property from used blackjack to seal the roof (as you can see from the picture) but it’s now not doing the job.

I did have planning permission to construct a lead roof over the top of the hamstone (we cannot remove it due to historical significance) but this has proved prohibitive in terms of cost but also in terms of the maximum weight this roof can bear.

So I’m wondering if there is any way to better seal the hamstone against the elements? I don’t mind re-applying sealant when required but the blackjack used by the developers is not really fit for purpose.

Any advice appreciated!

Thanks

Sam

 

[a twig]

Would a fibreglass roof be an option? Or zinc as an alternative to lead?

 

[Kearn]

Would a fibreglass roof be an option? Or zinc as an alternative to lead?

Second that, we’re doing a small area of shallow roof connectng a pitched extension to an existing brewhouse. It will be done in zinc. Partly cost, but also weight and the fact that lead technically needs a physical break due to thermal bridging and condensation. Something we don’t have the head room for… jury still out on whether zinc would behave similarly in terms of temperature bridging.

 

[samspurgeon]

It’s listed so fibreglass might be a tricky one to get through planning. Zinc was a consideration but given the complicated nature of the lead roof design, swapping it out for zinc wouldn’t save enough to make it cost effective for a solution to basically fix a leaky roof.

 

[Flyfisher]

Would EDPM be an option? If so, would it even need planning? It's hardly visible and it would be a simple waterproofing addition to protect the existing structure and not not damaging to the existing fabric.

 

[Kearn]

It’s listed so fibreglass might be a tricky one to get through planning. Zinc was a consideration but given the complicated nature of the lead roof design, swapping it out for zinc wouldn’t save enough to make it cost effective for a solution to basically fix a leaky roof.

Zinc would be about 50% of the lead equivalent.

 

[samspurgeon]

Zinc would be about 50% of the lead equivalent.

Sure but there’s other fixed costs surrounding a covering roof build that are the same regardless of which material is used. These costs + material costs of lead or zinc (despite zinc being cheaper) means it’s prohibitive. So we’re looking at just sticking with our hamstone roof and I’m currently researching what kind of sealants are available and if there are any modern solutions that are superior to the bitumen/blackjack solution that the developers used. Any advice on this would be greatly appreciated!

 

[samspurgeon]

Would EDPM be an option? If so, would it even need planning? It's hardly visible and it would be a simple waterproofing addition to protect the existing structure and not not damaging to the existing fabric.

Yeah I did think think this would be a good route to go down. Have been advised that LBC may not be granted for EDPM but I’m tempted to put an application in and see. The only thing is it’s already been so long so part of me doesn’t want to risk another wait only to get turned down. Maybe if there are no good modern sealants I would go down this route thanks!

 

[Kearn]

Sure but there’s other fixed costs surrounding a covering roof build that are the same regardless of which material is used. These costs + material costs of lead or zinc (despite zinc being cheaper) means it’s prohibitive. So we’re looking at just sticking with our hamstone roof and I’m currently researching what kind of sealants are available and if there are any modern solutions that are superior to the bitumen/blackjack solution that the developers used. Any advice on this would be greatly appreciated!

The thing is, using modern sealants on relatively soft stone won’t solve a problem, as much as create more problems.

What’s actually the issue? Where’s the problem? And why?

Presumably this roof hasn’t always leaked. And had been there some time.

Blackjack will be doing the same as modern sealants, allowing water ingress through tiny gaps then trapping it. The stone will then delaminate and fail, making the gaps bigger.

How about stripping off the modern muck that doesn’t belong and lime point/fill the gaps as if it were a flagged floor.

I assume there is a fall to the roof to shed water, although the edges don’t look like they allow the water to run off as they seem stepped?

Does any other water discharge to this roof, or is it only rain directly falling on it?

 

[samspurgeon]

The actual issue is water ingress, I have attached a pic of the ceiling inside the room.

That’s certainly a suggestion - removing the blackjack entirely and lime pointing do you think this is worth exploring? Maybe my question should be what is the best way to remove blackjack.

The roof has an incline although not much. Between 1 and 2 degrees. There is a hole in the roof at the bottom of this slope that feeds a down pipe. Other than rainwater there’s no other runoff onto the roof.

Not sure how waterproof this roof has been through the ages although I do know that when the developers took the house on there was a tree growing in this room and I don’t think the room as a whole was weatherproof!

 

[samspurgeon]

Drainage hole pictured here. We’ll be widening this as part of the project

 

[Flyfisher]

Yeah I did think think this would be a good route to go down. Have been advised that LBC may not be granted for EDPM but I’m tempted to put an application in and see. The only thing is it’s already been so long so part of me doesn’t want to risk another wait only to get turned down. Maybe if there are no good modern sealants I would go down this route thanks!

The key thing here is the damage being done by the leaking roof, which will likely be irreversible and ultimately result in very invasive repair works and the loss of original fabric. I'd be inclined to think of EPDM as an emergency measure, a bit like putting a tarpaulin over a leaking roof (yes, been there, done that!) except that it will be more durable. Plus, if it's effectively invisible then it won't significantly affect the 'character' of the property, in which case I can't imagine it attracting any attention from the local council. And even if it did, would they really insist it be removed when you explain it's preventing damage to the building and you can't afford to make any further substantial repairs? More likely they'd just ignore it or, perhaps, issue respective LBC. But even if they do pursue you for a 'proper' solution, at least the property would be protected against further water damage while the details are all sorted out and you've saved enough to pay for their approved solution.

 

[samspurgeon]

This is great advice thank you. Sounds like a good course of action. Thanks