Retiling roof, concerned about purlin support and roof collapse

[Joe92]

Hi, I'm having half of my roof retiled due to some damage and leaks. The house is old, ~1890, and the roof has the typical purlin construction from that time.
Few concerns and questions:

- The roofer suggested replacing the existing man made slate tiles with concrete ones however I'm worried about the extra weight on the old wood. Should this be a concern? Would I need a structural engineer to work out weights? Assuming it's going to be easiest going like-for-like.

- Photos included for this. 1 of the purlins is supported by angled trusses anchored to strut and by being embedded in both the joining walls with neighbours. However the other is only supported by the trusses, one side is embedded into neighbours wall, the other side of it is the thick stone chimney breast and it hangs loose there. Is it possible to add a bracket for the purlin into the chimney breast for extra support or will it not have the integrity to take any weight?

- The truss on the unsupported side seems to be a cowboy job and it's just sitting on the strut rather than being anchored to it or the floor in any way. It has clearly slipped at some point or is slipping slowly and coming loose which is obviously a massive worry, especially with the possibility of extra weight. Will the roofer be able to replace this safely or does it need another trade?

Appreciate any help, thanks.

 

[wessex101]

I'm not sure they had artificial slates in the 1890's, I would have expected them to be natural slates from that era so if they are artificial it could well be that they are not the original roof covering. But I may well be wrong.

Reference replacing with concrete tiles. You will almost certainly need to strengthen the roof timbers to accommodate the extra deadweight of the concrete tiles. It is rather alarming that the "roofer" suggested the change without highlighting the likelihood of strengthening the roof. That would be a massive red flag for me and I would probably be looking elsewhere for a proper roofer.

I have to say the roof looks fairly dodgy already, with a very undersized purlin and rather suspect struts. Even if you replace the slates with modern artificial slates it would probably be worth getting someone to inspect the roof timbers to check their adequacy and potential repairs/strengthening.

 

[tony1851]

That has to be one of the smallest purlins i've ever seen in my 110 years of practice.
It won't collapse, but concrete tiles will turn that into a banana-shape.

 

[JohnD]

The problem of old slate roofs being overloaded by heavy concrete tiles has been known for many years.

Is your roofer ignorant because this is his first week in the job?

Or doesn't he care?

How did you find him?

 

[^woody^]

You'll need to apply for building regulations, so confirm with the inspector.