Email Us


Sign up for our Newsletter


Determining Window Dimensions

First, check the dimensions of the rough opening made for the window:

Take measurements both horizontally and vertically at three different points in the gap, and then extrapolate the minimum value from the three distances, for each direction. Check the aperture for squareness by measuring along the diagonals; these two lengths should not differ by more than 1/8" of an inch [3mm]. Next, check the dimensions of the supplied window, using the same methods as before. There should be a short distance of approximately 3/4" - 3/8" of an inch [9.5 - 19mm] between the opening and the outer edge of the windowframe. Generally, a 1/2 inch [12.7mm] gap around the entire frame is considered suitable.

Most product manufacturers will stress the importance of the "square, plumb, and level" installation technique in order to ensure correct operation of the window or door. This requires using shims around the sash to level the unit. The recommended spacing will allow proper placement of shims to level the frame [if needed], and to maneuver the window into the opening. The extra room also accommodates the insulation and closed cell backer rod for perimeter sealing.

Square: A right-angle [90 degrees]; when all four corners of a frame are square, the joints will not separate from each other and all components will operate smoothly. Plumb: An exactly vertical line; when the window is installed plumb, the designed sill slope is maintained, allowing rainwater to run off rather than build up.
Level: A precise horizontal measure; when applied to a window's frame, it prevents water pockets from pooling and infiltrating the building's interior seal.

Tip - Before installing the window, it is advisable to pre-drill the screw holes to save time and prevent mistakes.

Use the manufacturer-recommended size of wood screws for the job; they make it easier to perform future adjustments to the window as the building settles.


Shims are used to block, or secure, a window around the sill and jamb so that the unit sits square before the final steps of installation. The proper placement of shims at key points around a windowframe establishes the basis for smooth and correct function of any moving parts.

The shims are specifically responsible for creating a level aperture for the frame to sit in, so that the frame does not bend or warp from undue pressure. Squaring the opening that surrounds a windowframe keeps the joints from separating and lets water shed from the sill, instead of pooling and eventually infiltrating at the window's edge. Shims should only be inserted where they will not compress the frame, and in most cases, never at the top of the sill.

Please note - windows that have not been made plumb during installation may begin to leak or develop operational issues.


The addition of insulation and a vapor barrier are essential to eliminate rotting and mold growth around window frames. When combined with proper installation, the efficient thermal performance of a window increases occupant comfort and reduces energy waste.

Any large gaps need to be stopped up using wool fibreglass insulation before the trim and siding is applied. This type of insulation should never be compressed - the air molecules present in the wool fibres are necessary for the filling to function properly. The insulating products should sufficiently fill the empty areas without placing undue stress on the windowframe. For the smaller gaps around the sash, use foam insulation [always in moderation], while ensuring that the window is not slanted or leaning.

At this point, the vapour barrier is attached, covering the interior joint between the building wall and the frame. To completely prevent water penetration, it is important to extend the barrier right to the frame and seal it around the windows' outer edge using a staple gun. The next step is to seal the window at the junctures of the frame and the building wall.


Sealing a wood unit will greatly extend the life of the product and requires only a caulking gun and the appropriate type and quantity of caulk.

The interior sealant fills in the smaller holes between the rough opening and the frame that are often difficult to find by looking; a thin, even bead placed at the juncture of window sash and wall opening will obstruct and prevent air leaks before they develop.

Exterior sealants form the primary weather seal along the outside break in the wall, creating an impermeable closure that should stop all water penetration, if applied correctly. The type of caulking that you may choose will depend on the frame material used and the level of exposure that the window recieves. In order to ensure absolute two-sided adhesion of the sealant [inside and out], a backer rod may be needed to fill the trenched area between the frame and the building.


As soon as the installation is completed, it is advisable to clean any moving parts to free them from debris.

If needed, paint or varnish the frames as soon as possible to prevent warping, and be sure to follow all of the hardware manufacturer's instructions regarding the appropriate care and lubrication of their product.

This document is a brief summary of the recommended methods of window installation. CWDMA recommends that all window installations follow the guidelines set out in CSAA440.4-98 "Window and Door Installation".

Canadian Logo

Canadian Window and Door Manufacturers Association 21 Goulburn Avenue, Ottawa, Ontario K1N 8Cl 613-233-9804 Fax: 613-233-1929

KW Doors & Windows

KW Doors & Windows fully customizes doors and windows to fit your needs.  We focus on amazing our customers.


View our References, Click Here

Contact Info
Contact Us Via Email  1-800-477-1577
Contact Us Via Email  Email Us

646 Meredith Rd, Mill Bay, BC V0R 2P3


Useful Links - Would You Like Your Logo Placed Here? - Contact Us



Courtenay Glass

Central Glass


Copyright ©2016 KW Doors and Windows - All rights reserved. | Marketing by MAC5

Proudly manufacturing Custom Wood Windows and Doors since 1976. Serving Vancouver Island including Victoria, Nanaimo, Mill Bay, Cobble Hill, Duncan, Cowichan, Lake Cowichan, Ladysmith, Cedar, Courtenay, Sooke, Gulf Islands, Saltspring Island, Saanich, Sidney, Gabriola Island, Campbell River & more.