Re-Roofing dilema

[al4x]

Hi there my first post so treat me gently!

We've got a bit of a project house part of it has a lovely "fibre cement" roof. We're looking at options of changing this and have a few dilemas. Firstly the building is far from square and secondly isn't even the same width as it goes along. The current roof has been made to fit whats there and has obviously been done by a craftsman. Our first problem is that the pitch is approx 17 degrees, the second is of increased load.
Solution one would be to fit an entirely new roof with a steeper pitch but I'm not convinced it would fit as the building butts up to another.

Solution two is our preferred and involves trying to re-use the roof we have. Currently the cement boards are laying on a layer of 3/4 inch tongued and grooved boards these are supported by 50 x 150 purlins at 1.5m spacings then are supported by a number of trusses at a max of @3m I gather if we went for a Redland Cambrian slate then the pitch would be ok but what would be the best way of making sure the roof can hold the extra weight? could we simply double up the purlins? or would we need more trusses to support them. To give you an idea if this comes out its a pic of what we have at the moment!

 

[denso13]

Have a look at http://www.decra.co.uk/

They do a lightweight range of tiles which may suit you better.

Redland Cambrian are made from recycled slate and as a result are relatively heavy, 2-3 times more than Decra, and expensive.

 

[al4x]

sadly its listed so we're pretty limited, cambrians we may get away with but not much else other than real slate

 

[denso13]

Ah ok.

If it's listed I take it you will need planning permission?
And possibly a building warrant if the roof covering is heavier and the structure needs strengthened.

If that is the case then you will probably need a structural engineer to look over it and advise on what is required.

It shouldn't add too much to the cost of the project and would be well worthwhile.

Check with your local planning and building department and they will be able to advise.

 

[al4x]

that is mostly in hand, we will have permission to raise it slightly so that remains an option, at this point I can add a pretty useless architect drew up the plans and I'm not convinced we can raise the roof very simply due to the ancient subsidence you can see on the old building on the left. I'm just trying to weigh up whats possible so I've got an idea before going to building control,