Supporting a large bow window in wall with cathedral ceiling

I'd assume a roof as well....
JC, I don't have a problem with what the contractor has said. I'm quite sure that the requirement is either-or (support from above or below), but if he is offering to add the knee braces as well at your request, then that sounds like the right choice. There is no reason not to assuming that there is enough room for them to be installed effectively.

I agree. Not that's it's any official requirement to have both, but with a unit that large, this is the time to get it right and both would be my preference.

The reason I brought up the roof or collar is that they can't very well hang a bow properly if they are going to install a roof over it. If you tie the cables at an angle to the wall you end up pulling the top of the window inward past the drywall ...unless you screw a board to the top of the window up next to the wall. Even with that it's not a good way to hang a window. And since more than one company were talking about using cables it leads me to believe they are all thinking about installing a 3'-4' tall angled collar. Ugh.

There will be a roof... the contractor didn't say what kind but I would assume a hip roof. The cables do attach to the wall at an angle. Very good point about the cables at an angle and the tendency for them to pull the window inward past the wall. My wall is part of a cathedral ceiling. It is made of 2X4s and there are of course no rafters near the window, just a 2X4 wall... which was one of my main concerns. I thought that the pulling force of the cables might pull on the 2X4 wall and bow it. The greater the angle from horizontal the greater the upward force instead of horizontal force applied to the wall... thus a collar would be great in that regard.

The projection dimensions I received are 15-7/8" inside and 24-5/16 outside. I am not sure where these dimensions are taken from, but those are the numbers he gave me. Do they make sense?

Thanks for the comments.

Changing gears a bit, this window is an Infinity by Marvin, which has the fiberglass outside and inside. I have heard Marvin makes a good window. Has anyone had any problems with these Infinity windows?

I want to thank all of you that have taken your time to discuss my questions. I appreciate it greatly!

Ok lets call it 16" and 24". The way those make the most sense is 16" is the approx projection of the window past the stone and the 24" is the total into out, both of these at the deepest points.
So knee braces and cable still are the best choice.
Cable instructions have angles that have to be observed. a 12/12 or 45% angle on the roof will do this.
If it was me I would remove existing unit, fab and secure knee braces. lift window into the hole setting on top of KB, screw window into RO framing, level sill and check vents for square, insulate, install and load cables, fab and complete roof, finish exterior of window, trim interior,
clean up, demonstrate operation, collect payment, go home.

No lunch break? .... Good explanation, sounds just right.

On the window, if you like fiberglass (Infinity/Integrity), the Marvin products are the best choices available IMO. There are some vinyl products that have substantially better performance, however the main reason that people choose fiberglass is for looks, so I'd assume that is the case here. Either way, it is a very good window and will serve you well.

I agree completely.

I do like the look of fiberglass. However, it is my understanding that the coefficient of thermal expansion for fiberglass is low and is similar to that of glass, which would mean the frame and glass move (expand) together and thus the seals would not fail as often as that of wood, vinyl, wood-vinyl composite, aluminum, etc. I think this is a big advantage.
http://pdf.archiexpo.com/pdf/infinity-w ... 12-_7.html

I am interested to know the vinyl products which have substantially better performance. I may look at those.

I have looked at your web site Home Sealed and noticed you do not offer fiberglass. Is there a reason?

JC, thats a bunch of salesmanship. For one, while fg will in fact not expand/contract as much as vinyl, the difference is negligible as it pertains to windows. Secondly, the glass (ig) is a sealed, separate, unit from the frame, this it will gave no bearing on glass seal failure.
In terms of our offerings, we do actually offer the Marvin Integrity as well as some other products that are not on our site (updates are in the works) .... We do however install more vinyl than anything for the reasons that I mentioned above.

So, I am assuming that the spacer is also fiberglass since that is what really holds the glass unit together and would be responsible for seal failures?
No? ....it's stainless steel? How could that possibly work into that coefficient of thermal expansion the salesman was pulling your leg on?

Pure bunk.

Just like the other guys have said.

If Fiberglass were the end all be all, that is all we would sell and we already do sell a decent bit of fiberglass.

Hmmm, that is a good point. If the expansion/contraction rate of fiberglass and glass are so similar, wouldn't it be a good idea to make that spacer fiberglass? The seals on my current double pain windows failed. Looks ugly with that cloudiness in between the panes.

I'm going to e-mail Marvin/Infinity and ask about their claims.

No, because it's not important that the spacer have similar expansion rates as the extrusions. It's important that it allow for expansion of the glass. That's more a function of design than it is matching materials.

Doesn't make a bit of difference as long as it is accounted for like Eco said.

If it were truly and issue...wouldn't the large curtain walls of glass fail all the time. Aluminum has a high coefficient of expansion so it would be reasonable to expect failure. Couldn't be farther from the truth.