Flat roof and detailing around sliding doors

[Porthole]

Hello

I've just been given detailing from our architect of the flat roof extension structure (first draft before structural elements) and I had some questions. If anyone can help then we'd be very grateful. It's not a great image but hopefully you can get the gist of what is there. I've had to query a few things recently with the architect so thought it would be helpful to get some views from others for peace of mind. The structural input is not there yet, just the architectural details.

 

Guttering - is a gutter at the end of the extension above the sliding doors a good idea? Just wondered if maybe a better structure might be if the rainwater ran to the sides rather than to the front of the extension? Although I guess this would result in 2 down pipes for the surface water and maybe 2 soak aways?

 

Does the detailing around the steel beam at the end of the extension look sensible? Would sliding doors just be screwed into the steel beam?

 

Membrane for flat roof - GRP has been specified- does anyone know if this is a good option? I know there are various different types e.g. EDPM? Any one better than the other?

 

The build up of the warm deck roof appears to be:

- Membrane

- OSB (18mm)

- insulation (210mm)

- vapour membrane

- ply (22 mm)

- joist

- plasterboard and skim (12.5mm plus skim)

Do these elements sound sensible? We were trying to keep the roof thickness quite small to be within permitted development but seems to be quite thick.

 

Any advice much appreciated, as always.

 

 

 

 

 

 

[Porthole]

Sorry ignore the images above - for some reason I couldn't delete - this image is much clearer. Thanks

 

 

[PeterW]

How wide is the opening ..?? That steel is taking all the roof load and the parapet wall so may need to be a fair size. 

[Porthole]

The opening is 7.5m. Steel still being specified but I think 203 or 250.

[PeterW]

19 minutes ago, Porthole said:

The opening is 7.5m. Steel still being specified but I think 203 or 250.

Joists running onto it..??! For that opening with the joists onto it, you’re easily going to need 305 or larger to keep the self deflection below something that won’t cause problems for the doors below.