We in the Maritimes live in a pretty wet place. For that reason, it’s vital to properly seal wall openings properly during construction. Improper window installation is the leading cause of Atlantic Home Warranty claims!Steps to proper window installation
1) trim the housewrap
Most installers will cut an “x” in the window opening, then pull the material into the home, staple to stud frame, and trim.
2) install or create a flashing pan
If, by chance, there is any water intrusion, it will most usually collect at the bottom of the window. For this reason, the installer must seal this off with a flashing pan (required by Code). This can be a purpose-built section of rigid plastic, a metal pan constructed on site, or, more often than not a flashing tape product. The pan will seal the bottom of the sill, as well as the sides to about at least two inches by Code, but ideally more. It's also important to note the requirement that this flashing pan slope outwards by at least 6 per cent [126.96.36.199(4), and installation standard CSA A440.4]. The idea is that any water collecting in the bottom of the window cannot penetrate the sill. What’s flashing tape? There are several brands of flashing tape on the market, but in general they are strips of semi-flexible synthetic material, six to eight inches in width that can be creating a flexible, entirely waterproof seal.)
Pro tip: The required slope can be obtained by placing flashing tape over a slender piece of wood ripped from dimensional lumber – about 1/8” - to create a slope. Even better: install a section of clapboard (which has a built-in sloping profile) or rip a diagonal section of a 2x4 to create an angled piece of wood over which to lay the flashing tape.
3) Install the window.
Most windows these days have nailing flanges, making installation quite easy. When installing the window, apply a bead of purpose-built sealant to the top and sides that will remain somewhat flexible yet watertight. This sealant is required by Code. (See below.) It is also vital to note that standard hardening silicone is not an approved product in this situation. Further, the bottom should NOT be sealed - the intent is that any water (condensation/penetration) that collects under the window can drain out over the housewrap, down the wall, and out of harm's way.
4) Seal the flanges to the housewrap.
This is done by using flashing tape, again, first on the sides, and then over the top, so the top layer overlaps both sides. This seals the window flange, and ensures that any water has no point of entry. This not required by code, but is best practice.
5) Lap the housewrap
The last step is to fold the upper layer of housewrap down over top of the flashed window. If any moisture gathers above the window, it will flow down the housewrap, around the window, and continue down the second plane of protection to the ground below.
188.8.131.52 (3): Windows, doors and skylights shall be sealed to air barriers and vapour barriers.
184.108.40.206 says flashing is required at:
1) b) every horizontal offset in the cladding, and
1) (c) every horizontal line where the cladding substrates change ...
220.127.116.11(3) Flashing shall be installed over exterior wall openings where the vertical
distance from the bottom of the eave to the top of the trim is more than one-quarter of the horizontal overhang of the eave. [Flashing required over top of window]
18.104.22.168(5) Where the sills of windows and doors installed in exterior walls are not
self-flashing, flashing shall be installed between the underside of the window or door and the wall construction below. [Flashing pan required.]. Also CSA 440.4, Clause 10.2.2.1, 10.2.1.3.
22.214.171.124. Required Sealants
1) Sealant shall be provided where required to prevent the entry of water into the structure.
2) Sealant shall be provided between masonry, siding or stucco and the adjacent door and window frames or trim, including sills, unless such locations are completely protected from the entry of rain.
1) Sealants shall be (a) a non-hardening type suitable for exterior use...