Window Retrofit

Apart from improving the quality of living for the inhabitants, high-performance windows can conserve energy as well. Still, if retrofitting is not done correctly, or the wrong window is installed, energy savings, along with the comfort can go down the drain. Not to mention the safety issues caused by inexpert installation. Retrofitting to save energy requires knowledge that goes beyond understanding U-factors and solar heat gain.

Standard vs. safety glass

A common mistake in retrofitting is using standard glass. Also, if something used to be considered a standard, it doesn’t mean that it should be considered the same today. The building safety codes are being upgraded regularly, and now, safety glass should be installed in all the rooms where windows might be subjected to human impact. This includes entrance doors, windows adjacent to a door and windows larger than 9 ft2 when the bottom is less than 18 inches from the floor.

Emergency exits

If retrofit windows are installed in the existing window frames, the clear opening can be significantly reduced. As a result, emergency exits may be obstructed. It means that in case of fire, occupants may not be able to go out and rescuers may not be able to go in. Building codes propose exit requirements for sleeping rooms located on the first three floors. At least one window or door needs to be installed by safety standards, with minimum width of 20 inches and height of 24 inches. In some jurisdictions, retrofit windows have specific egress requirements.

Retrofit window too large

There must be adequate space between a retrofit frame and the rough opening. If the space is too tight, seasonal expansion and contraction can distort the window frame and damage the weather seal, which in return leads to water leakage into the window cavities. As a result, the insulating properties are reduced, and in some cases even the glass can break.

Window not aligned

Unless the window is level or squared, not even the best double-glazed windows will do their job properly. You will not be able to close the sash properly and achieve the weather seal. If the sill jamb is not level, squaring the whole frame will be impossible. When you center the window in the opening and secure the bottom, open the sash just above the edge of the frame to see if the gap is equal along the whole edge. If not, adjust the jambs and secure them at the top, once the alignment is even. Repeat the same for vertical alignment.

Flawed frame support

If the retrofit frame is not supported properly, especially at the bottom, the frame may contort and allow the sill to loosen over time. It may lead to rough sash operation, incomplete closure, leakage of air and water, and it can cause damage to the perimeter caulk. The frame support is especially critical at the sill jamb, as it holds the entire window level.

Inadequate insulation

Improperly insulated cavities around the retrofit window can increase the pressure on the window frame, distorting it and obstructing smooth operation of the sash. Expanding foam is definitely not recommended here. You need to be careful even if you use non-expanding foam like one-part polyurethane, and make sure you remove excess foam if you see any distortion.

Inadequate flashing

Flashing is a thin continuous piece of material that is installed around windows to create a seal, which prevents water from leaking around. The most commonly used materials are 30-lb felt, bituminous impregnated kraft paper, or standard sheet-metal flashing, made of either galvanized steel or aluminum. Flashing width should be no less than nine inches. Regardless of the window style and type of opening, the procedure is always the same. First, install the sill flashing and extend it on both sides beyond the edges, by a distance over the strip width. Repeat the same for the vertical jambs and finally for the top jamb.

Sliced moisture barrier

Often times, installers need to cut out a strip of exterior siding to reveal the nailing fin so they can remove the existing window. In this process, they usually slice through the moisture barrier. As a result water can penetrate the envelope and cause structural damage. Every time the existing barrier is damaged in this way, you need to reseal once the window is refitted. Overlap the damaged spots with additional material and sealant. If the cut is longer than 1 inch, you may want to reinstall flashing and seal around the outer perimeter. If the cut is less than 1 inch, you can spread a continuous layer of sealant over the exposed wall surface instead.


A window grade is the structural capability of the window, or the capacity to resist wind loads and seal against water penetration, which is particularly important in certain climates. For instance, when installing double glazed windows in Perth, which receives high seasonal rainfall and powerful cold fronts with winds  up to 100 km/h,  if the retrofits of an insufficient grade are used, the combination of wind pressure and driving rain may force water through the seals.

Choice of caulk

Even the best-quality window can be compromised if the external seal is defective. Caulk needs to be flexible, especially at the top of the retrofit, where it prevents frame damage when the header flexes. Polysulfides, polyurethane and silicone adhere well to most surfaces and remain flexible over time. Bear in mind that certain caulks, like silicone cannot be painted, so you may want to paint and dry the surfaces before applying the caulk, or you can use color caulk.

Proper caulk application

Another common mistake is applying the quality product in a wrong way. Manufacturers always give instructions on surface preparation, application temperature and joint type and size. If the surface contains loose or cracked caulk, dirt, debris, oily residue or moisture, caulk will not adhere, and the seal will not be weatherproof. The same way, you should apply caulk only when the outside temperature is within the range defined by the manufacturer.

Caulking in the right spots

The seal will not be watertight if the caulk is not applied in all the right places. For finned windows, caulk should be applied in such a way that some of it squeezes around the entire fin perimeter. Once the window is secured in place, the squeezed-out caulk needs to be tooled to seal the fin edge. If caulk didn’t squeeze out along the entire fin, you need to apply more and spread until you create a continuous seal. Other places that need caulking are the corners of mechanically joined frames, gaps between the edge of the siding and gap opening, and any wood strips installed to fill the gap when siding is removed.

Different material in contact

If dissimilar metals are placed in direct contact with each other, it can result in accelerated corrosion and premature damage of the weather seal. This process is called galvanic corrosion and occurs if the two metals have different conductivity. It can be prevented by inserting a sheet of nonabsorbent plastic or elastomeric tape between dissimilar metals.

Before the windows even arrive at the site, check your local building code. Research what type of window fits your needs. Finally, study the local building requirements on safety glass, emergency egress and grade before looking for the most reputable supplier.

By Editor

HIHC has great articles & tips to help with Inexpensive Home Improvement,Home decor. Home Remodelling Estimates and products to get a good Home Renovation completed.

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