supporting a bay window

[RustyShackleford]

As part of a renovation, I'm installing a "bow" window, which is kind of like a bay window except it's five panels in a smooth arc (see attachment). These are installed in a rectangular rough opening like any window; however, the outward bulging load cannot be cantilevered, instead needing add'l support. There are two methods: angle or 45-degree braces underneath, or a "cable system". No one seems to know much about the latter, including local dealers, so I'm not sure exactly how it works - sounds like it suspends the load from the overhanging rafter tails (I'm getting the "17-5W" width, which projects 10", and my roof overhang is 2ft). My question: can anyone tell me about this cable system, and which method do you recommend ? I'd prefer the cable - not liking the way the bracing underneath might look - if only I understood it.

 

[Dobish]

i have used the cable system. you can attach at a couple of different points, but you will generally go back at an angle (assuming there is a separate roof line above the window)

You would tie into either the rafters, or the wall studs/and or the header. You then adjust them with the tension screws, and cover it up. you obviously need to support it when you are putting it in, but after that, you don't have any braces underneath and you are good to go. If you are really worried about it, you can also put a metal rod/lag bolt through underneath the bottom of the window and the insulation, and that would give a little bit of added strength as well, but probably not necessary.

 

[RustyShackleford]

Ok, thanks. Was yours a Marvin window ?

Marvin's inscrutable installation instructions (see attach) don't seem to address how the cable would be attached to the house. I'm starting to think that the cable is just to attach the headboard to the seatboard more securely, in which case it seems like it ought to be part of the window (and not an add-on).

 

[Dobish]

not a marvin, those cables look like they are designed to hold the seats in place, not necessarily for attaching the window to the frame?
http://hqbacklinks.com/windows/wp-content/uploads/2011/04/Hanging-Support-Roof.png
http://hqbacklinks.com/windows/wp-content/uploads/2011/04/Hanging-Support-Roof.png

this is more what I was talking about.

 

[RustyShackleford]

not a marvin, those cables look like they are designed to hold the seats in place, not necessarily for attaching the window to the frame?

Yeah, that's what Marvin's instructions seem to be saying. Talked to a local dealer who said maybe it's something inspectors want to see ?

http://hqbacklinks.com/windows/wp-content/uploads/2011/04/Hanging-Support-Roof.png
this is more what I was talking about.

That looks righteous. I'm not gonna be buildling any kind of roof over mine - projection of window is 10" and roof overhang is 24" (plus a gutter) - but OTOH that would be kinda hidden by said rafter tails, and certainly look better that some kind of brackets or braces under the seatboard.

 

[Dobish]

If you are going right up to the rafters, you will have it hidden. You will want to finish off the top of the window frame, it you will get critters and bees. A 45° is optimal, but you could go as little as 15° I would think. It looks like the ones supplied might be able to go through, then all the way up and support from the bottom of the seat through to the rafters

 

[RustyShackleford]

Yeah, I probably want the cables, no matter what. Even if the main support to the rafters is something like you linked, I'll still want to reinforce the seat to headboard connection, at least if I want to avoid any bracing underneath the seatboard.

 

[peakbagger]

Whatever you do, spend some time doing it right. I have seen several angle bays and bay windows that have sagged over the years making the windows inoperable. The structure looks rigid when installed but over time gravity will sag the front edge of the bay down. The cable approach can work but they do need to be tied in securely to the framing, Unfortunately the cable usually ends up tying to the "cripple" studs above the header in the wall. These are not very structural as they are usually toe nailed in after the fact. Ideally the cables need to get tied into something like the top plate which is going to have far less potential to get yanked sideways by the weight of the bay. Ideally you want to bolt through the framing member with a counter sunk nut and washer versus screwing into the wall. If you have to tie into the cripple studs, I would suggest gluing and screwing the exterior sheathing to the cripples and headers in the area above the window so that the cripples are tied firmly into the structure. Someone who understands the physics who is doing it themselves can do a good job, but a contractor in a rush is going to skip details as it could take years before the sag shows up.

 

[RustyShackleford]

Thanks, @peakbagger. Yeah, echo'ing my thoughts pretty closely. There are no cripples above the header, as it is right below the top plate. Definitely going to glue plywood sheathing, and use two king studs and two jacks at each end, to make the wall stiff.

However ... I think we are ditching the bow window; I just realized the lights (the actual glass pieces) are only 11" wide, with 6" or mulling in between - not too psyched about that. So probably going to frame out a rectangular bulge, with some sort of "normal" window in it, and then either tall skinny fixed glass on the sides, or maybe corner windows on the sides.

I talked about this in:

https://www.hearth.com/talk/threads/shallow-rectangular-bay-window.154969/

... but no response. But now I've got a couple of smart guys tuned in ...

 

[RustyShackleford]

So I got a bay window - a big central fixed glass with operable casement flankers on each side - and installed it.

Also got the cable kit, and the instructions are a bit more forthcoming, with clamps for attaching the ends to the header above the window. The two cables thread down through the millwork where the windows join, and you're meant to drill holes there and secure the threaded-stud cable ends with fender washer and nut. The bottom of the window is nothing but a single piece of 3/4" plywood, so we added a piece to the bottom of the rough opening. Still, just two fender washers seems minimal, so I bought a piece of angle-iron to go between the two threaded cable ends.

So now if I can just secure the top ends of the cables to the header adequately, the bottom of the window will be supported very well indeed, so I hope to be able to avoid any support underneath the window at all (helped by the fact that the "projection" is only 8-1/2" or so). The clamps to secure the cables look pretty heads-up, about 1x3", with two pieces the cables runs in between, and 4 screws to clamp it down good. Two of those screws are long wood screws meant to screw into the header, so hopefully the withdrawal rating of those screws is sufficient (I reckon the window weight about 300lb, and of course some of the weight of the window is on the bottom of the RO itself, so 150lb should be sufficient, though because of the way the cable will be "levering" against the two screws holding the clamp, each screw should be able to handle the 150lb). Also the cables will be running at roughly a 45-degree angle, from headboard of window to header, but the cables run thru t-nuts in the headboard, so this ought to hold. It just means the cables will need tension multiplied by sqrt(2) to exert a given supporting pressure on the bottom of the window.

 

[Dobish]

did you put any insulation in the bottom of the window?

 

[RustyShackleford]

did you put any insulation in the bottom of the window?

Will put an inch or so of rigid foamboard - below the two layers of 3/4" plywood (one part of the window, one I added to the RO). Edges will be captured by brickmold.