Retrofit vs. Full-Frame Window Replacement: What Each One Is, What Each One Costs, and the Four Times You Need Full-Frame

The numbers

What a retrofit actually is

The installer takes out the old sashes, the stops and the hardware, and leaves the old frame in the wall. The new window is built to fit inside that frame, so it is an inch or two smaller each way. It gets screwed through its own frame into the old one, foamed at the gap, and the outside joint gets capped with aluminum or caulked. Inside, the old casing usually stays. An hour or so a window, two people, no drywall, no siding touched.

It is a good job when the old frame is sound, square and dry: a 1990s vinyl or a well-kept wood frame in a brick house. It is the wrong job when the old frame is the problem, because you have just sealed the problem in with a new window on top of it.

What a full-frame actually is

Everything out: sashes, frame, interior casing, exterior trim or brickmould. The rough opening gets looked at, which is the point. Rot gets cut out, the sill gets a pan or a sloped sill flashing, the sides get flashing tape lapped like shingles so water that gets behind the siding runs out and not in. The new window is sized to the opening, shimmed plumb and level, screwed through the frame, foamed, and the outside gets new flashing, trim and sealant. Inside, new jamb extensions and casing. Two to three hours an opening, and the wall around it is disturbed, which is why it costs 40% more.

It is the only window installation that lets anyone see the framing. In a house with any history of leaks, that is worth the money on its own.

The four times you need full-frame

1. The old frame is rotten, or you cannot tell. Soft wood at the sill corners, stains on the drywall under the window, a sash that has sagged in a frame that is no longer square. An insert in a rotten frame is a new window with a 5-year life.
2. You are residing or re-bricking. The siding is off, the flashing is exposed, the extra cost is small because half the work is being done anyway. Do it once.
3. The windows are the old aluminum or steel ones. A 1960s aluminum slider has a frame the width of a pencil and no thermal break. There is nothing worth keeping, and an insert inside it would be the size of a mail slot.
4. You want the glass back. Three generations of retrofits on one house can lose 6 in. of width. On a small bedroom window, the fourth retrofit is a porthole.

How to tell which one a quote is for

If the quote does not say, it is a retrofit; nobody leaves full-frame off a quote because it is the one they can charge more for. Ask three questions in writing: Does the existing frame come out? Is the rough opening flashed with tape or a sill pan? Is new interior casing included? Three yeses is full-frame. Three noes is a retrofit. A mix is a company that does not know the difference, which is the answer to a different question.

The quote comparison page puts the retrofit-or-full-frame line at the top of the grid for this reason.

Where homeowners go wrong

1. Comparing a retrofit quote to a full-frame quote. The cheap one is not cheap. It is a different job.
2. Retrofitting over a leak. The stain under the window is the old frame or the flashing. A new insert on top of it changes nothing except that the leak is now warrantied by nobody.
3. Paying full-frame prices for a retrofit. It happens. The three questions above, in writing, stop it.
4. Expecting the installer to fix the wall. Full-frame finds rot; it does not include a carpenter rebuilding a rim joist. Ask for the unit price for framing repair before the first window comes out.

Sources and further reading

• Keeping the Heat In: Natural Resources Canada. The free guide to windows, doors, air sealing and insulation written for Canadian houses.
• Ontario’s Building Code: the official page, with the current regulation. Egress is 9.9.10, glazing and windows 9.6 and 9.7, energy is Supplementary Standard SB-12.