Base structure for modern oriel window / window seat?

[DC1977]

Hi all

Looking into installing one of these on the rear of our house. Got some rotten French doors to remove, and the opening will be partially bricked up. The "oriel window" will extend out by 300mm so needs a base structure to sit on. The window manufacturers have given me a drawing showing a steel frame for it to to sit on, but for a cavity wall (our external wall is solid 9 inch).

So after discussing it with some builders the frame could go through the wall and angle down and be fixed on the inside (make sense??). Ive been told the steel could create a cold spot inside though? Could this frame be made of timber? The width of the opening is 2.4m wide (!) x 1.5 height and 300mm depth.

Any thoughts!? Ive attached the tech drawing, a photo of an example window and our opening where the window would go (on the right of the rear of the house, not the large opening for future set of sliding doors)....



Cheers for your help!

 

[Deleted member 174758]

I have built large oriel windows (two of the biggest were about 2.5 metres high x 3.5 metres across) where we used timber framing to keep the weight down. In that instance (and 2 of the other 3 oriel windows on the same building) we were fixing into SFS (metal wall framing) - and all the walls were very thick. I suppose the weight of the glass, the timber frame and its' cladding, together with the amount of projection from the wall are all factors you'd need to take into consideration. The biggest issue might well be pull out of the lintel and masonry above the window

In the instances I was referring to the structure comprised four 4 x2in softwood ladder frames with 18mm plywood glued and screwed to both sides of the frames and to the front faces. They were insulated and over cladding was in zinc.

If you have any doubts about the wall you could also consider adding a couple of gallows brackets beneath the oriel

 

[DC1977]

Thanks for your reply @JobAndKnock, when you say timber framing do you mean the base that the three panes of glass will fix directly into? These panes then should be able to support the glass roof of the oriel window?

 

[Deleted member 174758]

The structure we used was effectively four ladder frames fixed together ar the corners to form the oriel. The frame outsides were clad with plywood, gaps filled with insulation, then the insides were plyed-out as well. We did strap to the wall above the opening (in fact our strapping went up to the floor joists on the floor above) but didn't have much by way of strapping to the wall below, although ours weren't designed to be window seats as well and the walls were double skin

 

[Tigercubrider]

Does the window seat support need to be in physical (thermal) contact with the support system of the widow? Wouldn't it make sense to support the seat separately from the window?

All I was imagining was a pair? Of angled brackets in the cavity extending into, but not supporting the window. Low enough for some insulation to be added before surfacing with some timber which would act as support for the deck of the seat? If the brackets were inserted into the concrete raft, they could be surrounded by foam in the cavity?

Or if your cavity wall was thick enough, would it be possible to use something like a timber jetty under an indoor lintel that ran along the bottom of the window? Would that lintel transmit the load to the walls?

 

[DC1977]

Hi @Tigercubrider there is not cavity wall its a solid external wall, the drawing is from the installers where they have assumed its a cavity wall. So if the steel frame needs to be fixed on the inside of the external wall, wouldnt the steel create a cold spot?

 

[Tigercubrider]

I honestly don't know.
Is there a "wonder material" made from say, recycled plastic like some substitute decking materials that has a good thermal insulation property?

 

[Deleted member 174758]

In construction there are very rarely any "wonder materials" (although resins and Mitre Mate can come close!). The problems with plastics is that they are aren't very stiff, they flex under load and to get any strength in them they need to be thick.

I'm pretty confident that a torsion box structure made using plywood skins glued and screwed onto a joinery grade timber framework is going to be strong enough to carry both the glass and a couple of people. Have you got any dimensions? Can the load be transferred into the roof or floor above the window?

 

[DC1977]

In construction there are very rarely any "wonder materials" (although resins and Mitre Mate can come close!). The problems with plastics is that they are aren't very stiff, they flex under load and to get any strength in them they need to be thick.

I'm pretty confident that a torsion box structure made using plywood skins glued and screwed onto a joinery grade timber framework is going to be strong enough to carry both the glass and a couple of people. Have you got any dimensions? Can the load be transferred into the roof or floor above the window?

2.2m wide, 1.5m high, oriel window is 300mm depth, window seat within window and back into recess is700mm

Ignore the measurements on the attached photo but this is quite similar to
What we are looking to do

 

[Deleted member 174758]

How thick is your wall?

 

[DC1977]

How thick is your wall?

9 inch, ignore my comment about 700 mm on previous post