Old Roof and Building Control Concerns

[RobertG]

 

Hi,

I've just had a conversation with my architect and he's informed me that Building Control with most likely not allow me to keep my existing roof structure as the rafters and joists won't meet modern BC regs. 

 

To say it's a setback is an understatement as my budget won't stretch to a new roof and I'm at a loss how to proceed. 

 

It's a 200 y.o. cottage and I was hoping to renovate it sympathetically to allow the stone walls to breathe again and I'm now concerned that other building elements like the floor joists will also have to be replaced to meet current regs. 

 

Has anyone any experience of this sort of problem that they could maybe advise me how to progress? Thanks.

 

Robert

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Mike]

No, it's never a problem that I've come across when the timbers are in good order. If everything had to comply with the latest Regs then you'd be demolishing the lot!

 

It just needs to be safe and, if there's any doubt about that, then you'd need a Structural Engineer's involvement.

[RobertG]

4 minutes ago, Mike said:

No, it's never a problem that I've come across when the timbers are in good order. If everything had to comply with the latest Regs then you'd be demolishing the lot!

 

It just needs to be safe and, if there's any doubt about that, then you'd need a Structural Engineer's involvement.

Thanks Mike. 
 

I know it’s safe as it was holding double the weight that the new insulation will weigh but the SE says that they aren’t structurally meeting the requirements. 
 

it was a lath and plater ceiling which is usually about 50kg / sq m and the new insulation is about 17kg / sq m. Apparently these timbers won’t support it? 
 
I’d like to get some way of knowing how to approach it regarding BC that’ll satisfy them. My architect says he’ll just remove any roof aspects from his submissions. 
 

Thanks for your help. 
 

Robert
 

 

[Mike]

It looks in good condition & you have 200 years of evidence that it's adequate. What has changed over the years is that current standards require the timber to flex (sag) much less under load than would have been acceptable in the past; that's normally more a risk of cracks along plasterboard joints, rather than one of structural stability.

 

I doubt the the BCO will raise it as an issue, but if they do, then you'll need that SE. If I were drawing the plans they'd just have a note saying something like "existing lath & plaster removed & replaced with plasterboard". And something similar if you're planning to replace the tiles externally / add additional insulation, etc.

[Temp]

Did the Architect say why he doesn't think it will meet Building Regs? Is it a structural issue or an insulation issue or ?

 

If the roofing felt is old it might not be vapour permeable like modern membranes. That may mean a 50mm ventilated void is required between the felt and insulation. That might not leave enough depth for insulation ?

 

If that's the issue there are likely to be ways around it. Perhaps by putting more insulation elsewhere.

 

Ask him what he thinks the issue is.

 

Edit: Ah I see your SE thinks it's not strong enough.

 

 

Edited April 7 by Temp

[Temp]

Thinking aloud... See what the BCO says first but If structural changes are needed

perhaps you could reinforce what you have rather than replace. Sistering joists is common. Perhaps add another purlin if the rafters need it? Don't offer to make changes unless the BCO questions it.

[nod]

Your probably going to need to engage a SE So I’d get a survey done before speaking to BC So that you can tell him what remedial measure If any you will take 

Your Architect will air on the side of caution As will BC 

[RobertG]

1 hour ago, nod said:

Your probably going to need to engage a SE So I’d get a survey done before speaking to BC So that you can tell him what remedial measure If any you will take 

Your Architect will air on the side of caution As will BC 

Thanks Nod,

 

That seems to be the stance the architect is taking but is advising that remedial work will probably cost the same as a replacement roof. He's omitting his roof detail from his drawings to see how the BC application progresses. 

 

Hypothetically - The BCO insists on a new roof and I'm not in the financial position to replace it. What happens? No work at all can start?

 

Robert

[Mr Punter]

I don't understand why this has come about.  Normally, existing structure is considered OK unless there are obvious defects.

[Temp]

13 hours ago, RobertG said:

Thanks Mike. 
 

I know it’s safe as it was holding double the weight that the new insulation will weigh but the SE says that they aren’t structurally meeting the requirements. 
 

it was a lath and plater ceiling which is usually about 50kg / sq m and the new insulation is about 17kg / sq m. Apparently these timbers won’t support it? 
 
I’d like to get some way of knowing how to approach it regarding BC that’ll satisfy them. My architect says he’ll just remove any roof aspects from his submissions. 
 

Thanks for your help. 
 

Robert
 

 

 

Google says the weight of plasterboard and skim is around 8.5kg/sqm. The insulation you estimate at 17kg/sqm making a total around 25.5kg/sqm. 

Google say lath and plaster is 30-40kg/sqm.

 

I would suggest the architect add a note to the drawings that says the new design therefore reduces the load on the roof which has stood for 200 years and is in excellent condition. 

 

Most BCO will work with you unless you mess them around. 

[Wil]

Looks significantly better than my roof! Fortunately I’m married to the SE and a quick site meeting was enough to decide to crack on without full replacement.

 

I’d agree with the above- architect notes that existing load on roof being reduced and roof improved with breatheable materials.

 

 

[RobertG]

8 hours ago, Temp said:

Most BCO will work with you unless you mess them around. 

 

I hope so Temp. It's a worry and an uncertainty that'll be hanging over me until the BC Application has been processed. Fingers crossed

[Redbeard]

I want to add Larsen Trusses and 250mm+ of mainly flexi wood-fibre to my Victorian roof. 75mm rafters, 270mm purlins. He wrote me as report stating that given the reductions in weight by removal of exg ceilings etc and the commensurate increase by insulating would result in some net gain. However while he said that such timbers would not be approved in a new-build he is satisfied that it will take all built loads and the worst-case snow load. That will keep BCO happy. It sounds like you already have the 'ammunition' you need.

[RobertG]

Thanks all for the input. My architect is going to submit my BC Application pointing out the removal of lath and plaster and the replacement with plasterboard. We'll have to make the case, if required, that we're significantly reducing the loads on the roof which is still in good condition and has been fine for many decades. I suppose it will all come down to the BCO. Not a great situation as I wait for my application to be processed but it's my only option to try and avoid an expense I can't afford. Fingers crossed. Thanks again. 

 

Robert