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The right seal profile, matched to your window
Window weatherstripping is the compressible seal between an opening sash and its frame, and replacing it is often the cheapest way to stop a draft. GTS Windows & Doors has been replacing worn seals on casement, awning, slider and hung windows across Kitchener-Waterloo since 1986. We work for homeowners, landlords, property managers and builders throughout Waterloo Region, Guelph and Wellington County.
The catch is that weatherstripping only works when the new seal is the right profile. Window makers use dozens of different bulbs, fins, piles and kerf sizes, and a generic foam strip from the hardware store rarely seals properly or survives more than a season or two of opening and closing. Matching the original profile, or the closest modern equivalent, is where most of our effort goes, because a seal that is a few millimetres off either leaves a gap or stops the sash from closing.
This page covers the seals on the moving parts of the window. The fixed sealant joint between the frame and the wall is a separate job, handled by our window caulking and sealing service, and both sit within our full window repair offering. Our crews are licensed, insured and WSIB covered, and every job starts with a written quote.
A simple test: close the window on a strip of paper and pull it out. If it slides out with no resistance at several points around the sash, the seal is not making contact there.
Before blaming the seal, check that the lock pulls the sash fully closed. A lock that no longer engages produces the same symptoms, and that fix is covered on our window lock and latch repair page.
Seal type follows how the sash moves. Windows that press shut need a compression seal, and windows that slide need a seal that can be brushed past thousands of times.
Casement and awning windows close by pressing the sash against the frame, so they use compression seals: hollow bulbs of EPDM, TPE or silicone, or foam-filled seals such as Schlegel's Q-Lon. Most casements have two lines of seal, one on the sash and one on the frame, and both need checking.
A bulb that has taken a permanent set stays flat and stops sealing even though it still looks intact.
Sliders and hung windows move along their seals, so they use pile weatherstrip, a dense brush of fibres on a backing strip. Better versions have a thin plastic fin running through the pile, which blocks air far better than pile alone.
Pile is sized by backing width and pile height, and a strip even slightly too short leaves a gap the full length of the sash.
Most modern windows hold their seals in a kerf, a narrow slot in the sash or frame, with a barbed flange that presses in. Kerf-mounted seals stay put through years of use and can be replaced cleanly.
Adhesive-backed strips are a fallback where no kerf exists, and they tend to peel in cold weather, so we use them only where the window leaves no alternative.
We start by identifying the window: the maker's label or glass marking where one exists, the frame material and the window type. Then we pull a short sample of the old seal, measure the kerf width, flange, bulb or pile height, and match it against profile catalogues from seal makers such as Schlegel and Ultrafab.
Where the original profile is discontinued, we find the closest one that fills the same gap without making the sash hard to close. Too large a bulb can stop a casement from locking and too tall a pile can make a slider stiff, so we test fit one window before doing the whole house.
Windows we commonly reseal:
Slider seals are often replaced along with worn rollers and latches, which our sliding window repair service covers in the same visit. Hung windows get their pile replaced with the sashes tilted in or removed, so the seal runs continuously along each side.
If you are not sure whether your windows are casement, awning, hung or slider, our window styles guide shows the differences. Knowing the style tells us which seal family to bring.
We check how each sash closes, confirm the lock pulls it tight and cut a short sample of the old seal for matching.
Old seals are pulled from the kerf, and any leftover adhesive, paint or debris is cleaned out so the new flange seats fully.
New seal is cut slightly long and pressed in so the corners meet tightly without stretching, which would open gaps in cold weather.
We close and lock every sash, run the paper test around the edge and adjust hinges or keepers where the new seal changes the fit.
Both fix drafts and leaks, but at different places. The quickest way to tell is to find exactly where the air or water is coming in.
| Where the problem is | Likely cause | The fix |
|---|---|---|
| Between the moving sash and the frame | Worn, flattened or missing seal | New weatherstripping |
| At the sash edge, only on windy days | Seal gap or a lock not pulling tight | New seals, lock adjustment |
| Around the interior trim | Failed perimeter air seal | Interior sealing |
| Water stains below the window | Failed exterior sealant joint | Exterior caulking |
| Water pooling in the sill track | Blocked weep holes | Clear the drainage, not the seals |
On a windy day, hold a lit incense stick close to each joint of a closed window and watch the smoke. If it moves at the sash edge, the weatherstripping is the problem; if it moves at the trim, the perimeter seal is.
Many windows have both issues at once. We check the seals and the perimeter on the same visit and quote them separately, so you only pay for what is actually failing.
These are typical 2026 ranges for Waterloo Region, including seals and labour. Custom-sourced or discontinued profiles and second-storey access raise the price, while doing every window in one visit lowers the cost per window.
Our installations carry a 20-year parts and labour warranty, and your quote spells out the coverage on replacement seals.
| Job | Typical price (2026) | What moves the price |
|---|---|---|
| Casement or awning, both seal lines | $120 to $250 per window | Profile availability, sash size |
| Slider or hung window pile and fin | $100 to $220 per window | Number of sashes, sash removal |
| Original wood sash, retrofit seals | $150 to $350 per sash | Routing new kerfs, sash condition |
| Whole house, 10 to 20 windows | $1,200 to $3,500 | Mix of window types, access |
Quality compression seals on casements often last 15 to 20 years, while pile on sliders and hung windows usually wears faster, often within 10 years on windows used daily. Sun exposure, harsh cleaners and paint on the seal all shorten its life. Seals on south and west windows tend to go first.
If the draft is at the edge of the moving sash, yes, in most cases. It will not fix air leaking around the trim, cold radiating from single glass, or a sash that no longer closes square. If a window has several of these problems at once, our guide on when to replace windows can help you weigh the options.
Yes. Original wood sashes can take modern seals, often by routing a small kerf into the sash or stop so a durable kerf-mounted seal replaces tacked-on strips. Any rot is repaired first, as described on our wood window frame repair page.
Late summer and early fall, before the heating season, when seals are warm and flexible and you get the benefit all winter. Replacement can be done in winter too, with windows open only briefly on cold days. Booking early in the fall avoids the pre-winter rush.
Send us a photo of the window and a close-up of the old seal, and tell us roughly how many windows are drafty. We will match the profile and quote the replacement in writing.
Call or text226-806-0597