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BigJimmy 01-01-2008 06:50 PM

RO size vs. window unit size, new construction
In the spring, I'm going to be replacing all of the built in windows in my front living room with new construction units. I have chosen windows that are taller than the existing and as such I will need to increase the height of the RO's after I remove the existing units. My basic question is this: When a RO is framed, does it need to be larger than the window (or door) that will be installed in it? Are RO's typically somewhat larger than the window/door to account for bad lumber (i.e. twisted, warped, etc) or inaccuracies in the framing itself? If done carefully, is there any reason that a RO couldn't be framed to exactly fit the window or door to be installed therein?

In my instance, I have been told by several people to frame the head 1/2"-3/4" taller than the windows to account for any sag in the header which seems reasonable. But, I was simply curious if there was any reason that a RO needed to be larger in width at least than the unit to be installed in it?


ericwar 01-01-2008 08:05 PM

RO Vs window size
Jimmy, The advice given to you about the head height is correct, You do want to allow for header sag. In regards to your question about the width of the rough opening. You should try to allow at least 1/2" gap on each side of the window. Not all rough openings are plumb especially in an old house. You will appreciate the extra room when trying to install them. Also more importantly you need to allow for proper insulation. When a window is to tight it wont operate correctly. The unit needs to be installed square. Even with door instalation you need to allow that gap on the sides for future adjustment if the house settles.

troubleseeker 01-01-2008 09:58 PM

Unless we have actual access to the windows to verify the stated rough openings, we always frame them an inch wider and taller than speced. It is a lot easier to install a piece of 1/2" plywood filler on each side than to start cutting studs out. Manufacturing specs often change long before the tables for rough openings in the literature catch up. On a presently working job, we had to close in two rough opening for triple casement units by three inches when they arrived on site. The framers had the dimensions exactly as called for in the manufacturer's chart. Lucky we needed smaller.

BigJimmy 01-02-2008 07:34 AM

Thanks guys. In my case, my existing RO's will need some work since I'm raising the head. Also, the existing arrangement is a panel of 5 single pane, single hung windows whereas the new layout will be 3 casements (each topped with a non-operable transom) distributed across the existing RO width. I will do as you recommend though.

I have another issue with the lack of any existing headers in these window openings (house is balloon-framed, est. 1911). Whoever built this thing originally used only a pair of 2x4's spiked together and laying on their side for the headers (if you can even call it that). In an 8 ft. wide opening, there is no intermediate support between any of the existing windows either. Certainly doesn't seem code-legal by today's standards. I will follow up in a separate post with pictures so that you can appreciate the craziness!


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