Box Bay window

Joined
2 May 2007
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Location
Sussex
Country
United Kingdom
Hi,

I’d like to replace this window:

FD78B454-8BD3-482E-ABD8-5D709B427A90.jpeg



With this:

EF72CBB3-A4B2-442B-9777-F536EE0643EA.png



Inside it would look something like this:

3C046562-73CA-48ED-AA2B-77CC8522AC2B.jpeg





I was wondering what the best way of framing it was.
I was thinking 6 x2 verticals bolted (wall anchors) against the wall either side, 4x2 horizontals something like this:

CBFFB34D-EC2D-4EBE-B35F-907CAA6A81DE.jpeg


The existing bay has four supports from the rafters above which I could use. I could add two steel angle brackets below to add to the three wooden ones.

Rockwool or celotex in the gaps, OSB or plywood shell, plywood cill, wrapped in tyvek membrane.

Then to finish ... not sure yet! Aquapanel and rendered or aluminium pressings?


That’s what I was thinking anyway. Any chance any experts can tell me how to do it properly?



Thanks!

ps. The window and frame weighs 142kg!
 
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It's a form of bay window called an oriel window. I've done some larger ones on commercial buildings where we framed-out with 4 x 2 or 6 x 2 treated CLS screwed together and onto steel brackets at the top and bottom (these ended-up inside the cladding when the job was finished). The whole shooting match was then overclad with WBP plywood. The last ones I did were surfaced with zinc sheet over membrane, although I've also done them where they were lead-covered afterwards
 
Thanks for the info!

Am I on the right track then?

For steel brackets I just found these:

7ED53E94-6D24-42FF-8BEC-1F54C05C7087.jpeg


and

D70D5265-6AEF-4723-A4D7-0CF5E7CEAC0C.jpeg
 
The steel brackets we used were welded-up by a steel fabricator - the ones you link to are lightweight shelving brackets and simply won't carry the weight. You need something which will transfer the load into the brick wall both at top and bottom.
 
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Projecting square bays are often built with cantilever joists that run across the cavity wall and have steel straps on the internal skin. Its all hidden under the plaster.

Externally the joists run forward and stop under the window frame
 
Make sure it is very strong, as you can bet one day a couple of people will be sat on it chatting and not want to crash to the floor!
 
thumbnail.jpg

Wood canterleaver noting that loading on outerwall (at lower edge of window hole) and innerwall (at upper edge of window hole) needs to be strong enough to take the rotational (and leveraged) load. This load is dependent on how far out you want the window to be.
 
Thanks.

The structure will only project 400mm from the wall, but the window is 143kg so with the structure call it 170kg. I suppose two people could sit on it (plus the dog) so lets say an additional 200kg. With a 1.5 safety factor that would be around 550kg. With a span of about 3.4m, would 4 brackets each with a rating of 140kg each do it?
 

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