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DyerWolf 10-02-2009 08:54 AM

Replacement vinyl Windows (Measurement / ordering question)
I'm thinking about replacing 5 windows in my home with vinyl replacement windows. I've seen a lot of info on how to measure, so I know my windows sizes.

If I've got a window opening that measures 30 x 48, do I order a replacement window exactly at that size, or do I subtract an eighth or a quarter of an inch from vertical / horizontal measurements to give me enough space to fit the window in?


Scuba_Dave 10-02-2009 09:16 AM

Every window I have seen lists a RO - rough opening size
The RO is the size of your opening
The window is made to fit into that opening & allows for a little room on each side
If an older house verify that the openings are square...or the RO will be smaller for a new square window

fenestrationman 10-02-2009 09:23 AM

I have always used a quarter of an inch deduction on both width and height. You may also want to check the opening for square. Take diagonal measurements of the opening. If they are not the same, you may want to cut the window back a little more. This is just so you don't force a new window into an out of square opening.
Good luck.

DyerWolf 10-02-2009 10:28 AM

They're square (luckily). If I knew the windows would come with shims I might knock off a quarter - but if ScubaDave is right, then I'd be ordering the windows too small.

Decisions, Decisions...

Scuba_Dave 10-02-2009 10:32 AM

Talk to who you will be ordering the windows from
Explain your measurements & concerns to them

paul100 10-02-2009 07:54 PM

If these are replcement windows (no flange) then what we would do is take your exact opening measurements and subtract 3/8" to 1/2". This is called make size. Our window supplier will take either size and give you the proper size window.

The reason for subtracting 1/2" is that once the window is centered that only leaves 1/4" on each side, this allows room to insulate. With the height all replacement windows come with a loose head piece. That fits on top of the window and can be moved up to compensate for your framework being out of level.

I hope this helps

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