The Importance of a Proper Window Installation


The proper installation of a window is equally as important to the total performance of a window as the manufacturing process and materials used.

The quality control measures taken in the manufacturing plant, which ensure a high quality window that meets or exceeds current performance standards, can be voided if any step in the installation process is not performed properly.  Poor installation can not only affect a windows thermal performance, but also its safe and smooth operation.  Aside from seal failures, over 80 % of service problems with windows result from poor installation practices.

At Beingessner Home Exteriors, we pride ourselves on quality window installations using only high quality products for maximum performance.


– Protect the structural integrity of the window in that, the window should not support any other load than its own weight

– Be an airtight seal around the window

– Be a continuous and unbroken thermal insulation between the frame of the window and the wall

– Have some allowance for differential movement between the window and the wall opening

– The installation must serve to maximize the performance of the energy-efficient features of the window


Getting the dimensions right and checking the squareness of the opening are the fundamental first steps of any installation.  These dimensions should then be checked against the dimensions of the window itself.  There should be a gap measuring about 13mm (½”) wide around the perimeter of the window.  This gap will allow for movement between the window and rough opening as well as room to level the window, place proper shims, and properly insulate around the window frame.


Windows must be properly aligned along many different planes when installed into a rough opening.  The window must be square, level and plumb to ensure a uniform finish, prevent water infiltration, and allow proper operation of moving window components and prevent premature failure.

Square: the window must sit freely and squarely in the window opening.  Any pressure at any point on the frame can push the window out of square and compromise the seals, put stress on the glazing to the point of fracture and impede moveable components.

Level: when the window is level along the horizontal axis no water pockets will be created in the frame of operating windows and the visual lines of the window will be in sync with the other lines of the house.  When it is level along the vertical axis, all the seams around the interior perimeter of the frame will be uniform.

Plumb: when the window is plumb, or level from top to bottom, the integrity of the sill slope is maintained so it can shed water as designed.  The weather stripping will also engage properly and the window will operate correctly.


Shims are used to wedge the window into position.  They allow the installer to ensure the window is square, level and plumb as well as providing solid support for the window.

Once the window is secured in place with shims, but before any fasteners are installed, the window should be checked for squareness, plumbness, horizontal and vertical levelness and that all movable parts and locking mechanisms operate properly and freely.

Anodized, or rust protected, screws are the fastener of choice.  Once the window is fastened it should then be checked again to ensure it is square, level and plumb, and that all movable parts and locking mechanisms operate properly and freely.  At this point, the protruding ends of the shims should be cut off and the window insulated.

The gap around the window must be insulated.  It is important to use products that will easily fill the gap without creating any stress on the frame of the window.  When properly applied, low expanding poly-urethane foam is well suited to the job because it will expand to fill all cracks and crevices without applying excessive force on the frame.  After the foam is dry, it can be cut off to be flush with both the interior and exterior wall surfaces.

If fiber insulation is used, it’s important not to pack it too tightly and always use backer rod and caulking to seal the insulated space.

Reconfirm that the window continues to be square, level and plumb, fully operational and not twisted or warped.

After cutting off the shims apply caulking to the ends before installing interior trims.  Weatherproof the exterior accordingly.

There are two types of installations: Complete tear-out and retrofit.  When we come out to your home, we would assess the pros and cons to each type of installation for each specific application.  Generally, complete tear-out installations are best as they allow for the insulation and weather sealing all to be redone, however retrofit installations have their place as well and are better for certain situations.

Source of Information: Sill to Sash

For more information on window installations, please visit Sill to Sash or Window Wise or contact our office at 519-664-2346 or send us an email to

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