Wooden roof for back porch over PVC windows/door

[supaev]

We are renovating our house bit by bit. Our present back porch is only 4 feet by 4 feet (External) with rotten wooden window frames, single brick built on top of a concrete path with no foundations as far as we know. I have battened the internal walls covered with aquapanel and tlled. This has been satisfactory.
The roof is plywood and felted. It mainly houses the tumble dryer (not much room for anything else!) which is vented to outside. What I propose is something similar but 8 foot X 4 foot external dimensions; still single brick dwarf walls as double would take up too much space; 2 feet of concrete foundations. concrete floor. the 8 ft X 4 ft is just under the 3 sq meters for exemption from planning.
Battened and aquapanel and tilled dwarf walls as now . Plastic windows and door on one 8 foot side. Plastic window frames and plastic panels on other long wall. End wall to be one or two plastic windows. If the double glazers fit corner posts at each corner I would like to know if just the double glazed and door sections would support a wooden roof frame made out of 4" x 2" with such timber forming a wall plate all round and spars at 16" centres. Flat roof to be a sheet of 8 ftx 4 ft ply ( say 1 inch thickness) with wooden facia on three sides and tarred felt roof. This would give us access to the bathroom window above. I know I will have to ask my PVC installer but apart from them and the felter I will be doing the rest myself so I would just like to know whether this is feasible.
If the PVC double glazing is not designed to carry much load then an alternative method would be to put 50mm x 50mm galvanised steel square tube fabricated with plates at top and bottom at each corner tight up to the brickwork,to take the weight of the roof taking into account snow loading. These could be erected with the roof frame on top ready for the PVC to measure up before manufacture.
Thanks
Paul

 

[Gazman16]

The corner posts have an aluminum section inside and are strong enough to hold a few tons of glass roof for conservatory's using an aluminum wall plate.

I'm not a structural engineer but I would say it would be fine, You could always over engineer it a bit with heavy duty aluminum couplers between any window frame joins and possibly in the corners where it meets the wall as well.

For example have the front 8ft section made of 2 PVC frames with a coupler between them to prevent any sagging in your wall plate and spread the load a bit more evenly.

As I say thats probably over engineering it a bit but I expect a 4x2 would probably sag a bit more than an aluminum wall plate.

They say PVC isn't load bearing but its fine for things like this

 

[supaev]

Thanks very much for your reply. On reflection the roof timbers would be better at 6" x 2 " as the window cleaner will have to stand on the porch roof to clean the bathroom window particularly as there is a soil pipe right next to the porch. I know this will damage the felt over time but I understand it needs replacing every 10 years anyway, so I can live with this.

I am interested in the aluminium couplers and the aluminium wall plates. Presumably these would be put in by the double glazing installers. What is a typical section of the wall plate? In the set up I have thought up these would presumably replace the timber wall plates.
Having said that I really wanted timber wall plates and spars so I could run the electric cables through these and possibly fit an aquapanel ceiling as plasterboard would get damp with no heating.

Just sticking with wood at the moment I don't think 6"x 2" would flex over 8 foot.
On the presumption that the PVC would support a 6" x 2" roof framework. which would have to be confirmed with the double glazing firm before an order was made how could this fixed to the plastic below?
The wooden fascia might not overlap the PVC if the "wallplate" was 6" x 2" on end. I would fit plastic fascia but I don't think these would get on with
the roofers hot torch.
Thank you
Paul

 

[Gazman16]

The Ali wall plates and ring beams are part of glass and polycarbonate roofs so you will just need to stick with wood.
You can just screw up through the frames into the wood before putting the glass in.