Measure twice, buy once? Now you tell me.

June 20, 2009 7:59 AM

How much vertical clearance is needed to frame a window opening?

I'm pretty sure I did something dumb. I bought an awning window for my bathroom, armed with only a rough estimate of the size of the space. I want the window to go above the tile shower surround, on an exterior wall.

The window is 18 inches high, and the space between the tile and the ceiling is 22 1/2 inches. Is there enough clearance to properly frame out the window? (I've got plenty of horizontal space.)

Possible additional complication? The exterior wall is on the side of the house, which has a Dutch hip roof with a gable on the front.

If I need to buy a new window, what size should I be aiming for? What other information would be helpful to know, for both me and the carpenter (besides "don't be impulsive at Lowe's," which I think I've figured out)?

[If I've messed up and can't use the window here, I'll save it for when we renovate another bathroom, in which we'll be retiling the shower and doing more demo.]

Thanks for the help!

posted by Sweetie Darling to home & garden (7 comments total)

You need a minimum of 1 1/2" top and bottom and side to side for shimming the window into the rough framing.

22" - 1 1/2"= 20 1/2"

The wall will have a dbl top plate which is used in all proper construction. The highest you could go with the window is - 3 1/2" from the ceiling. Not recommending this option as you haven't put some form of a header in place.

20 1/2" - 3"= 17 1/2"

You need to rough in some type of header to accommodate the load bearing of the wall. At the minimum you'd need to turn a 2 x 4 on its side and double it up for adequate framing.

17 1/2"- 3 1/2"= 14"


I would get another window for this situation just because the space you are working in is so tight on the vertical face. The window would need to be no higher than 14" roughly. You don't want the window pushed up to the ceiling height as it leaves that section of the wall structurally unsound. The window isn't designed to bear any load beyond it's own weight.
posted by Gravitus at 8:27 AM on June 20

Depending on the width of the window you may not need to install a header. As long as you don't cut a stud no header is needed. IE: the rough opening is less then 13 or 21" depending. And the bottom horizontal (you only really need a single in this case) 2X4 can be installed behind the tile maximizing the vertical distance. If the stud is placed in the centre of the space you could install two windows to make it look a bit less awkward. Glass block works well in this application as well.

The best way to do this is to frame out the hole and then order the window. That way you can give the window supplier the exact rough opening dimension. Generally speaking the window will be an inch smaller than the rough opening leaving a 1/2" all around for adjustment though I've squeezed things a lot tighter than that.
posted by Mitheral at 8:46 AM on June 20

Header size minimums are specified by your local building department. They might have it on their website, or you may need to give them a phone call. (Any experienced and competent local carpenter will know those minimums, too, at least for standard situations.)

Here is a randomly found page from a US city; for a small window, they would allow a doubled 2x4 header (two 2x4s, with a plywood spacer), which would allow the top of you window to be about 7 inches from the ceiling (3.5" for the double top plate, plus 3.5" for the header -- but your house may have been constructed differently, so take these numbers with a lot of salt).

Rather than buying a window randomly from the big box store, have the estimator from a local glass shop stop by and measure the space, or get a competent contractor who can do both the measuring and installing of the window. So much depends on your house's peculiarities, and your local planning and building regulations, that well-meant internet advice is almost guaranteed to send you in the wrong direction.
posted by Forktine at 9:07 AM on June 20

Most houses would be or should be 16" OC. especially on exterior walls. I imagine that a window less than 13" wide and 14" tall would not be very much of a window at this point. And remember that the window will be visible to others on the exterior of the house.

The problem with squeezing windows, doors, etc.. into improperly sized openings is that there is no room for the movement of the house. Trim pulls apart, windows stop operating, doors stick, sheetrock cracks, etc..

I do agree that he/she should rough out the hole before getting the window if possible but it isn't necessary to do so. I am a firm proponent of doing things the right way versus mickey mousing them for immediate gratification.

Plus this guy/girl is going to need to trim the exterior of the window so that it has a finished look. Imagine a series of 13 x 14 windows below a dutch hip roof, roughly spaced 1 1/2" apart. The trim job on the exterior would look funky as they are not a single unit per the jam a window between the studs advice. That would involve now ripping down trim and hoping that any windows installed were set to the exact same elevation, everything is square in relation to the other windows, etc. They do have single light windows in packs that give you this look, but they are still assembled into 1 unit.

Basically you would have saved time making the opening only to spend 3x's as much time to trim the thing out.

Forktine is on the right path also. Lot more to the whole thing then cutting a hole and jambing a window into it.
posted by Gravitus at 9:17 AM on June 20

Pages 33-36 of this pdf from the Mecklenburg County Residential Technical Answer Center give required header dimensions in common residential applications (assuming that your profile location is where the house is -- if not, your local building office should have a similar publication). It sure looks like you are ok with a doubled 2x4 header, but you would need to confirm that for your situation, and it would depend entirely on the width of the window.

Most building departments put a lot of effort and outreach into helping homeowners stay legal with DIY projects -- there is a lot of good information on the page I linked above and this one, for example.
posted by Forktine at 9:27 AM on June 20

It appears that the limitations of height might not allow you room to put in a regular window, frame and header. As an alternative for light you might consider a row or two of glass blocks. You still need a frame and header but you don't need a sash so it wouldn't look as strange as a very skinny regular window.

For ventilation, you could install a vent fan in the ceiling.
posted by JackFlash at 11:05 AM on June 20

Thanks, all.

The window is for ventilation, not light. We have a vent fan already, but the room gets unbearably hot - especially when using a hair dryer - and I desperately want fresh air. I just went and talked to the very nice man at Lowe's and I can't return the window, but I think I can probably use it in the other bathroom and they won't look too weird from the outside. Worst case, I'll donate it to the Habitat Restore and consider it a lesson learned.

I'm now thinking instead about a slider window, which comes in a 12 inch height, for this project.

I appreciate the help, even though it wasn't the answer I was hoping to hear!
posted by Sweetie Darling at 1:18 PM on June 20