Rough opening question

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Old 11-09-17, 05:05 PM
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Rough opening question

From what I understand, the rough opening for a door or window is 1/2" larger than the door/window thereby providing 1/4" spacing all around. However, don't doors typically rest directly on the floor? If so, this results in 1/4" on the sides, 0 on the bottom, and 1/2" on the top. Is this correct? Why have 1/2" on top? And for window installation, do you shim the bottom to raise it up a quarter inch, then nail it in place? Talking about new construction with nailing flanges.
 
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Old 11-09-17, 05:27 PM
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Typically 3/8 to 1/2" on each side. Doors sit on the finished floor or are shimmed off the subfloor as needed. Exterior doors sit on the subfloor or if the finished floor will be extra thick, the rough opening is adjusted upward according to the need.
 
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Old 11-09-17, 05:35 PM
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1/2" on each side? Everyting I've seen says 1/4" each side. IOW, make the rough opening 1/2" larger. So for doors, shimming depends on the anticipated finished floor height, and for Windows you shim upwards to cnter the window within the rough opening?
 
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Old 11-09-17, 05:37 PM
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3/8 to 1/2 per side. Is there an echo in here?
 
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Old 11-09-17, 05:41 PM
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Sorry. Didn't mean to post the same thing twice. 1/2" seems like an awful lot. The instructions that came with my slider say 1/2" total. I'm really just wondering if doors and/or windows should be shimmed upward to center them in the rough opening.
 
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Old 11-09-17, 05:53 PM
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Yes. That's what 3/8 to 1/2 per side means. The bottom is one of 4 sides. It's pretty hard to adequately insulate a 1/4" gap, and shims are usually 3/8" thick.
 
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Old 11-10-17, 02:30 AM
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Okay. I think I'll go with 3/8". Framer is going to kill me. Having a nailing flange helps with the insulation aspect of it does it not? I'd obviously be using spray foam. And when shimming the bottom of the windows to center them vertically, do I remove the shims after nailing the window in place (using the fin) or is it okay to leave the shims in place? Two of the windows will be in the garage, which is unconditioned, so my concern is the drastic temperature and humidity swings (zone 4). In other words, it seems like it would be better for nothing to be in contact with the window casing other than the spray foam.
 
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Old 11-10-17, 06:12 AM
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You shim the bottom, left and right sides of a window, but not the top. You leave all the shims in place and foam around them. The shim should not be pushed all the way out to the fin... it should be left about 1/2" away. After the interior window jambs have been installed, it's good to foam them in too before the casing goes on.

Why would the framer want to kill you? Because you micromanage everything? If the openings are already framed for 1/4" per side, then this is a moot point, that will work too.
 
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Old 11-10-17, 07:48 PM
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Because I told him to make all the window rough openings 1/2" larger than the windows and he already changed them once (because he left no clearance at all.

Trust me, if I didn't micro manage this project like I have been, then they would be redoing countless tbings. I swear I caught at least 20 things. Most I caught early so it wasn't a big deal, but if I had left it up to them I would have been extremely unhappy. Not entirely their fault--they are working from old plans.

I understand why shims are needed on the bottom in order to center the window vertically, but why would I need shims on the sides? The nailing flange holds the frame in place left/right does it not? I always thought shims were used only for replacement windows where you need prevent the frame from flexing when screwing it to the stud.
 
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Old 11-10-17, 07:55 PM
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Look up your window installation instructions if you don't believe me.
 
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Old 11-11-17, 03:24 AM
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Not saying I don't believe you, I just would like an explanation as to why. These windows have a screw with a large flat head centered vertically in the frame. Looks like these alleviate the need for shimming the sides?
 
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Old 11-11-17, 04:32 AM
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I don't know why you would not look up and follow your specific window instructions. Not following them voids your warranty. Here is a sample. https://www.google.com/url?sa=t&sour...oT1vPzat8wxpld

The nailing fin alone does not keep the inside half of a window frame stable. That's what the shims are for. The wide jack screw head is like a shim, yes, but it is to adjust the sides so they are parallel. Mfg's usually require shims every 16" or so in addition to the jack screw. They also often call for shims and installation screws to be paired up so that the screws do not bow the frame as they are tightened.
 

Last edited by XSleeper; 11-11-17 at 04:56 AM.
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Old 11-13-17, 07:18 AM
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Two of the windows are being re-used, so I had to remove them. When I removed them, I noticed there were no shims used at all. So apparently they are not needed with this window. The clearance was 1/4" all around. The company I bought the windows from were the ones that did the install (last year). Windows are Okna 500.
 
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Old 11-13-17, 11:03 AM
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I noticed there were no shims used at all. So apparently they are not needed with this window
Please post his response when you run that idea past your framer.
 
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Old 11-13-17, 03:22 PM
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I'm closing this thread. Windows require shims. The fact the existing window had none is meaningless. Follow the manufacturer's installation instructions. Period. End of story.
 
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