The fastest fixes for draughty sash windows are brush pile seals in the sash channels, a compression strip at the meeting rail, and a check of your sash cords for wear. All three are realistic weekend DIY jobs. For the biggest long-term gain in warmth and quiet, secondary glazing is worth the extra cost, though re-bedding rotten timber or replacing failed cords is best left to a tradesperson.
TL;DR:
- Fitting brush pile seals in sash channels and a compression strip at the meeting rail can significantly reduce drafts with minimal DIY effort and cost.
- Sealing the sash channels and meeting rail addresses the largest leak points first, providing quick comfort improvements before considering more extensive repairs or secondary glazing.
- Properly diagnosing leak points with hand tests and incense or candle checks ensures sealing efforts are effective and prevents wasteful fixes.
- Secondary glazing offers substantial thermal and noise benefits but is more expensive; it is best reserved for cases where sealing alone cannot achieve desired comfort.
- Structural issues like timber rot, broken sash cords, or fogged glazing require professional repairs before draught-proofing can be effective.
Table of Contents
- What makes sash windows so draughty in the first place?
- Quick checklist: what to fix first and what it costs
- How do I know if my window is draughty?
- How do I fit brush pile seals on a sliding sash window?
- How do I seal the gap at the meeting rail?
- What other DIY fixes are worth doing while you’re at it?
- Is secondary glazing worth the extra cost?
- When should you call a tradesperson instead of DIYing it?
- Draught-proofing a heritage home without losing its character
- Where to go for more guidance and materials
- Why most sash window advice misses the point
- Sources
- FAQ
What makes sash windows so draughty in the first place?
Sash windows are draughty by design, in a sense. The very gaps that let the upper and lower sashes slide past each other are the same gaps that let cold air through. The most common leak points are the sash channels, meeting rail, and parting bead, because timber sashes need a small margin of clearance to move freely.
Add a century or more of paint build-up, swelling and shrinking timber, and old glazing putty that has dried and cracked, and you get a window with half a dozen separate air paths instead of one obvious problem. That is worth knowing before you reach for a tube of sealant, because plugging the wrong gap can jam the sash without stopping the draught at all.
The main culprits, in rough order of impact, are:
- The meeting rail — where the top and bottom sashes overlap, often the single largest gap.
- The staff bead and parting bead — the timber strips that guide the sash up and down.
- The sash channels — the vertical gap between sash and frame.
- Glazing putty — cracked or missing putty around individual panes.
- The frame-to-wall junction — gaps where the window frame meets the brickwork or render.
Quick checklist: what to fix first and what it costs
Before committing to a full weekend of work, it helps to know which fixes deliver the most comfort for the least effort. Here’s how the main options stack up.
- Brush pile seals in the channels — DIY, 2 to 4 hours per window, low difficulty, materials from roughly $15 to $40 per window. Preserves sliding action and is fully reversible.
- Compression strip at the meeting rail — DIY, 30 to 60 minutes per window, low to moderate difficulty, under $20 in materials. Targets the biggest single gap.
- Sash cord check and replacement — DIY if you’re comfortable removing staff beads, otherwise a trade job; 1 to 2 hours DIY or a short professional visit.
- Re-bedding glazing putty — DIY with patience, half a day per window, moderate skill, under $30 in materials.
- Magnetic secondary glazing kit (renter-friendly) — DIY, 1 to 2 hours per window, low difficulty, from around $60 to $150 per window depending on size.
- Bespoke secondary glazing — professional install, one to several days depending on the job, highest cost but the biggest thermal and noise improvement.
- Full timber restoration with draught-proofing — professional, timeline varies with damage, priced per project rather than per window.
Renters and anyone on a short lease should lean towards brush pile seals, compression strips and magnetic kits. None of them require altering the frame, and all can be removed without a trace when you move out.
How do I know if my window is draughty?
Working out exactly where the cold air is coming in saves you from sealing the wrong spot, which is the single biggest waste of a Saturday afternoon on this job.
- Run the hand test first. On a windy or cold day, run your open palm slowly around the full perimeter of the closed sash, including the meeting rail and both channels. A cold streak against your skin marks the leak.
- Follow up with the candle or incense test. Light a candle or a stick of incense and hold it a few centimetres from the frame edges. A flickering flame or wavering smoke trail points to airflow that your hand might miss on a still day.
- Check the meeting rail specifically. This is where the top and bottom sashes meet, and it’s usually the worst offender. Run both tests here even if the rest of the window feels tight.
- Test the sash operation. Open and close each sash fully. Sticking, grinding, or a sash that won’t stay up on its own often means broken sash cords or swollen timber, not just a sealing problem.
- Inspect the timber for rot. Press a screwdriver gently into the sill and lower rail. If it sinks in easily or the wood feels soft and crumbly, you’re looking at a repair job before any draught-proofing will hold.
- Look at the paint and putty. Flaking paint, cracked glazing putty, or gaps between the putty and the glass are common secondary leak points worth noting for later.
If the sash moves smoothly and the timber is sound, you’re clear to tackle every fix in this guide yourself. If you find rot, broken cords, or a sash that won’t stay open, note it now. You’ll need it dealt with before or alongside any draught-proofing.
How do I fit brush pile seals on a sliding sash window?
Brush pile seals are the standard fix for sash windows because the fine bristles allow the sash to keep sliding while still blocking airflow, unlike foam strips which compress and lose effectiveness once the sash rubs against them repeatedly.
- Measure the sash channels. Measure the depth of the gap between the sash edge and the timber guide (the staff bead and parting bead) on both sides.
- Choose the right pile height. Brush seals come in a range of pile heights, typically 4mm to 10mm. Pick a profile slightly larger than your measured gap so the bristles compress against the sash rather than sitting loose.
- Gather your tools. You’ll need the brush pile strip (self-adhesive or with a fixing flange), a sharp utility knife, a tape measure, and a fine-tooth saw if you’re cutting into a routed channel.
- Remove the sash if needed. For a proper job, lift out the sash by removing the staff bead, giving you clean access to the full channel length.
- Clean the channel. Sand back flaking paint and wipe away dust so the adhesive backing (if fitted) has a clean surface to grip.
- Cut the strip to length. Measure twice and cut once. A strip that’s too long will bunch up and stop the sash closing fully.
- Fit the seal. Press the self-adhesive strip firmly along the channel, or tap a routed flange type into a shallow groove cut with a router or multi-tool.
- Refit the sash and test. Slide the sash up and down several times. It should move smoothly with light resistance from the brush, not a hard drag.
- Repeat on the opposite channel and the second sash.
Pro Tip: Run the candle test again once the brush seals are fitted. If you still feel a draught at the same spot, the gap may be too wide for the pile height you chose. Go up one size rather than doubling up two strips, which can jam the sash.
Once fitted, brush pile seals need little maintenance beyond an occasional vacuum with a narrow nozzle to clear dust that builds up in the bristles over a few years.
How do I seal the gap at the meeting rail?
The meeting rail, where the bottom of the upper sash overlaps the top of the lower sash, tends to leak more than any other single point on the window. It’s also the trickiest to seal well, because the fix has to compress against two moving surfaces without stopping either sash from locking.
- Compression strips are the most common material here. A slim foam or rubber strip with a self-adhesive back, fitted to the underside of the upper sash rail, compresses against the lower sash when the window is closed and latched.
- V-strip (tension seal) is a folded strip of plastic or metal that springs open slightly to fill the gap. It’s more durable than foam but needs more careful fitting to sit flush.
- Combination brush and compression kits, sold as sash window draught excluder kits, cover both the channels and the meeting rail in one purchase.
To fit a compression strip, close and latch the window first, then mark the exact contact line where the two sashes meet. Clean both surfaces, cut the strip to the width of the sash, and press it into place along the marked line on the upper sash’s lower edge. Close the window again and check the latch still pulls the sashes fully together. If it doesn’t, you’ve used a strip that’s too thick for the gap.
Foam compression strips typically last two to four years before they compress permanently and lose their seal. V-strip in metal or durable plastic can last considerably longer, often a decade or more, which makes it worth the slightly higher cost if you’re not planning to redo the job every couple of winters.
What other DIY fixes are worth doing while you’re at it?
A few smaller jobs round out a proper draught-proofing effort, and some of them cost next to nothing.
- Refresh external caulk around the frame where it meets the brick or render, using a paintable, flexible exterior caulk rather than a rigid filler that will crack with seasonal movement.
- Re-bed cracked or missing glazing putty by removing the old, brittle material with a putty knife, priming the bare timber, and pressing in fresh linseed oil putty before it’s painted over.
- Check and replace worn sash cords if the window won’t stay open on its own or feels heavier than it should. This is a DIY job if you’re comfortable removing the staff bead, but a fair few homeowners hand this one to a tradesperson.
- Fit a magnetic secondary glazing panel as a renter-friendly, fully removable option that adds an extra layer of still air against the glass.
- Hang heavier curtains or fit a draught snake along the sill for a genuinely temporary, zero-tool measure that helps through a cold snap.
Pro Tip: Never pack expanding foam into a sash channel or around a meeting rail. It hardens permanently and can jam the sash solid, turning a cheap draught fix into an expensive timber repair.
One more habit worth breaking: painting straight over an existing brush or compression seal. It looks tidy for a season, but the paint stiffens the bristles or foam and the seal stops moving with the sash.
Is secondary glazing worth the extra cost?
Secondary glazing is a second, independent window fitted inside the existing sash frame, and it’s the single biggest upgrade available short of full sash replacement. It works by trapping a layer of still air between the original glass and the new pane, which cuts heat loss and, usefully, reduces external noise more than most other fixes.
- DIY magnetic kits use a thin magnetic strip around a perspex or acrylic panel that clips onto a metal frame fixed to the window reveal. These are the cheapest entry point and fully removable, which suits renters and heritage overlays that restrict permanent alterations.
- Bespoke professional installs use toughened glass in a slim aluminium or timber frame, custom-measured for each window. These cost considerably more than a DIY kit but sit almost invisibly against the original sash and last for decades.
- Reversibility matters for period homes. Because secondary glazing doesn’t touch the original sash or frame, it’s typically the preferred option where heritage overlays or personal preference rule out replacing the existing windows.
Full replacement or a structural restoration becomes the right call when the timber itself has failed. If you’re seeing widespread rot, sashes that won’t sit square in the frame, or glazing that has fogged between panes, no amount of sealing will fix the underlying problem.
When should you call a tradesperson instead of DIYing it?
Some problems on a sash window aren’t sealing problems at all, and pushing ahead with brush pile or compression strips over the top of them wastes money and delays the real fix.
- Rotten or soft timber in the sill, meeting rail, or lower sash rail needs proper timber repair or splicing before any seal will hold.
- Failed or snapped sash cords that leave the window unable to stay open on its own are a straightforward trade job, and a cheap one compared with most restoration work.
- Fogged or delaminated double glazing (in later sash windows fitted with insulated glass units) means the seal between the panes has failed. That’s a glazing replacement, not a draught-proofing task.
- Persistent draughts after a full DIY effort usually mean a gap you haven’t found yet, often at the frame-to-wall junction or behind old architrave, which is easier to diagnose with experience.
A professional service typically starts with an inspection to separate sealing work from structural repair, then quotes separately for each. For a single window with brush pile and meeting rail seals, expect a same-day or half-day job. Full sash restoration, including cord replacement, timber splicing, and re-glazing, usually runs to several days per window depending on the extent of decay.
Before booking anyone, ask what they’ll do to preserve the original timber and profile, whether they use rebated (hidden) brush seals rather than surface-mounted ones, and what warranty applies to both materials and labour.
Draught-proofing a heritage home without losing its character
Professional draught-proofing of Victorian and Edwardian homes commonly follows the principle: fix the timber before sealing it, and choose reversible methods over permanent ones wherever the original fabric can be saved.
Hidden, rebated brush seals sit inside a routed channel rather than stuck to the surface, keeping the original sash profile visible rather than adding a visible strip along the edge. That single choice is often the difference between a window that still looks Victorian and one that looks retrofitted.
Draught-proofing pairs naturally with a broader restoration. If your sashes need re-glazing, re-cording, or timber repair, it makes sense to handle the seals in the same visit rather than reopening the window twice. A guide to protecting period windows without losing their character covers this in more depth, and a Deepdene project shows how timber restoration and weatherproofing can come together on a single heritage home.
— Jarrad
Where to go for more guidance and materials
The Victorian Government’s draught-proofing guidance is a solid starting point for understanding why sealing gaps ranks among the cheapest ways to cut heat loss in an older home. For hands-on product advice from people who’ve done the job themselves, the Bunnings Workshop community thread on sealing sash windows is worth a read before your next hardware run.
Brush pile seals, compression strips, and full sash draught excluder kits for double-hung windows are available from specialist window seal suppliers and most major hardware chains. The same sealing logic applies to doors, and One Day Doors & Closets’ guide to winterising doors is a useful cross-reference if draughts are coming from more than just your windows.
If your sashes need timber repair before draught-proofing will hold, our heritage window repair guide for Melbourne Victorian homes walks through what that work typically involves.
Why most sash window advice misses the point
Most guides treat draughty sash windows as a sealing problem, full stop. That’s backwards.
I’d also push back on the instinct to jump straight to secondary glazing because it promises the biggest number on paper. For a lot of period homes, a well-fitted brush pile seal and a proper meeting rail strip close most of the comfort gap for a fraction of the cost, and they don’t touch the original sash. Secondary glazing earns its price tag when noise reduction matters as much as heat loss, or when the existing timber is genuinely too far gone to seal well on its own.
If you take one thing from this guide, test before you seal. A cold room isn’t always a draughty window. Sometimes it’s a rotten sill wearing a very convincing disguise.
— Jarrad
Sources
- How to draught-proof a double-hung sash window (lockandlatch)
- How to seal and draft-proof a sash window? (Bunnings Workshop)
FAQ
How do I stop draughts coming through sash windows?
Fit brush pile seals in the sash channels and a compression strip at the meeting rail. These two fixes address the two largest leak points on most sash windows and typically take a weekend to complete on a full set of windows.
What’s the best draught excluder for sash windows?
Brush pile seals are generally the best choice because they allow the sash to keep sliding while blocking airflow, unlike foam strips that compress and lose effectiveness over time. Combination kits that add a compression strip at the meeting rail cover the two biggest gaps at once.
How do I fix a draughty window without replacing it?
Diagnose the exact leak points with a hand test and a candle or incense test, then seal the channels with brush pile, the meeting rail with a compression strip, and any cracked glazing putty with fresh putty. Full replacement is rarely necessary unless the timber has rotted.
How do I stop cold air coming through an old window?
Check for gaps at the sash channels, meeting rail, and frame-to-wall junction, then seal each with the appropriate material, brush pile for the sliding channels, compression strip for the meeting rail, and caulk for the frame edges. For the biggest overall improvement, add secondary glazing.
Is my window actually draughty, or is it just cold?
Run your hand around the closed sash on a windy day, or hold a lit candle near the frame edges and watch for a flickering flame. If you feel airflow or see the flame move, you have a genuine draught rather than just cold glass radiating heat loss into the room.
