Often the success or failure of window installation begins with the proper measurements and opening status information – or lack of it. Most installers or measurers are trained and record accurately the width and height of the opening. These measurements should be done with regard to the type of window and construction of the wall. Whatever method is used and/or described, it should be consistent between installers or measurers and openings and wall construction. In this way, the specified window is consistent and regardless of who measures and specifies, any installer working for the company will have the proper window and expectations at the job site. No surprises. In addition to the width and height, there are 6 other states or conditions of the opening that need to be measured, observed, and recorded so that the natural (or otherwise) idiosyncrasies of the opening are non ahead of time and can be accommodated in the specification of the needed window or door, and so that the proper materials and tools for correction will be known and provided at the job. Square Because some openings have become out-of-square over the years, it is important that the “squareness” of the opening be accurately measured. Measure the diagonals (upper left to lower right, and upper right to lower left) as accurately as possible from a point inside the stool to a point against the inside stop at the header. Record the two dimensions. If they are roughly equal, the opening can be assumed to be square. If they are not, then it is possible that the opening is out-of-square enough to cause the new window to be forced into an out-of-square condition during installation. If the new window is forced out-of-square, the inter- lock, sill and header seals can leak air and possibly water. Also the cam locks will not operate correctly and the window will wear out prematurely. Determine Square by measuring the corner diagonals (upper left to lower right, and lower left to upper right). Record both dimensions. The difference between them is the square condition. If the diagonals are not equal use the following simple equation. If the difference between your measured diagonals is greater than the allowable value, it may be appropriate to order a window 1/8” to 1/4” smaller than indicated by your measured width. This will allow the new window to be installed square in the opening. Then adequate sealing of the perimeter of the new window will complete the air-tight installation. Formula: DL2 - DS2 = W DL = Longer Diagonal DS = Shorter Diagonal W = Width of Opening The difference between the sum of the squares of the measured diagonals cannot be greater than the opening width. Example 1: Opening 36" wide by 48" high. The Long Diagonal is 60-3/8" and the Short Diagonal is 60- 1/8". Squaring the Long Diagonal (60.375 x 60.375) equals 3,645.14". Squaring the Short Diagonal (60.125 x 60.125) equals 3,615.02". Subtracting them finds a difference of 30.12". The difference is less than the width of 36" so the opening is square enough to accept a window designed to fit a 36" x 48" opening. Example 2: Opening 28" x 60". The Long Diagonal is 66-3/8" and the Short Diagonal is 66-1/8". Squaring the Long Diagonal equals 4,405.64". Squaring the Short Diagonal equals 4,372.50". Subtracting equals 33.14" which is greater than the opening width of 28". The opening is out-of-square enough to warrant consideration of a window 1/8" to 1/4" narrower than a window designed to fit an opening 28" x 60". Level When installing a vinyl window, it is important that the sill on which the window is resting be level. Out of level sills can cause havoc in the operation of large windows, casement windows, awning windows, slid- ers, and even double and single hung windows. The main reason for this problem is that out of level sills will distort the frame to an out-of-square situation. Imagine a sill that slopes and the sides of the window are made plumb. By definition, the window frame will become a parallelogram where the header and the sill will be parallel, and the sides will be parallel, but the sides will not be at right angles (90°) to the sill or header. This will make it nearly impossible for the sash, which will be square at the corners, to nest properly, lock properly, and seal out wind and moisture properly. As the sash is “forced” into the out of square frame, undue pressure will be placed on the corners, the hardware, and even the glass and its seal. DL W DS Window Fitters Guide to Window Installation 23 ©2022 AWDI, LLC Do not reproduce without permission 32” Sills can be 1/8” out of level & still meet code. Some sills are even worse. SAMPLE MANUAL
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