How to Install Sash Window Draught Proofing
How to Draught-Proof a Double Hung Sash Window
Draughty sash windows are one of the biggest sources of heat loss in older homes — but you don't need to replace them. Draught-proofing is a genuine DIY job you can finish in an afternoon, and the difference in comfort, noise and energy bills is immediate.
Did you know that in Australian summers, a staggering 87% of the heat entering our homes comes through our windows?
If you have double hung sash windows, chances are they rattle, let in cold air, and make your heating and cooling work twice as hard. The good news is you don't need to replace them. Draught-proofing a sash window properly is a genuine DIY job that can be done in a few hours, and the difference in comfort, noise and energy bills is immediate.
There's a common misconception that old windows are inefficient and should simply be replaced. But many historic sash windows have stood the test of time and can be just as effective as modern alternatives once properly sealed — with proper draught-proofing and care, traditional sash windows can actually outperform modern replacements.
Draught-proofing is one of the most effective and affordable upgrades you can make. Many homeowners spend thousands on double or triple glazing, yet neglect to seal the gaps around their windows — rendering that investment far less effective.
"The best time to draught-proof your sash windows was ten years ago. The second best time is today."
Benefits of draught-proofing your sash windows
The right draught-proofing system for sash windows
The correct approach for a double hung sash window uses replacement timber beading fitted with a brush pile seal — importantly, one with a central plastic fin, not foam tape or stick-on strips, which deteriorate quickly, look unsightly, and simply don't perform. Lock & Latch's draught-proofing system is a series of brush piles that entirely seal the perimeter of the sash window. The process involves taking off the existing stop (staff) and parting beads and replacing them with Draught Seal Stop / Staff and Parting Beads.
Why brush seals instead of foam?
Double hung sash windows slide — they don't compress. Foam and rubber seals are designed for casement windows and doors, where the surface closes against the seal. On a sliding sash, a compression seal wears away every time the window moves. Brush pile bristles flex with the sliding motion instead, creating a lasting draught barrier without wearing down, and adapt better to uneven gaps — making it far more effective for older windows where frames may not be perfectly square.
A proper brush pile beading system seals the entire perimeter of your sash windows — including the top of the top sash, meeting rails, lower rail of the bottom sash, parting bead and staff bead — creating a complete barrier against draughts. It comes pre-assembled with the brush pile seal already fitted, so there's no fiddly separate installation.
Lock & Latch stock a complete range of draught seal beading specifically for Australian double hung sash windows — available in the sizes and profiles needed for most homes.
What you'll need
Materials
Tools
The step-by-step process
Measure up (measure twice, cut once)
Getting your measurements right is the first step to a successful installation. Before removing anything, note the width of your existing stop bead — standard sizes are 22mm x 18mm and 30mm x 18mm.
Stop / staff bead: measure the height of the frame and multiply by 2 (left + right side), then the width and multiply by 2 (top + bottom). Add all four measurements together, and add at least 100mm to each individual length to allow for mitre cuts.
For example, a 900mm wide x 1200mm tall window: height x 2 = 2400mm + 100mm allowance = 2500mm. Width x 2 = 1800mm + 100mm allowance = 1900mm. Total stop bead needed ≈ 4400mm (4.4 metres).
Parting bead: measure vertically from the sill to the head of the frame, multiply by 2 (needed on both sides), and add 100mm per length for cutting allowance. For the same 1200mm tall window: 1200mm x 2 = 2400mm + 200mm allowance ≈ 2600mm (2.6 metres).
Remove the old stop bead
The stop bead (also called staff bead) runs vertically down both sides of the window frame and holds the lower sash in place. Run a knife around the edge of the beading to cut through the paint, then use a flat pry bar or chisel to lever it off the frame.
Once removed, the lower sash can be tilted or lifted out of the frame. Keep the old bead as a reference for sizing your replacement.
Remove the bottom sash
With the stop bead removed, carefully lift the lower sash out of the frame and set it aside. This gives you access to the parting bead channel.
Remove the parting bead
The parting bead sits in a groove in the centre of the frame, separating the upper and lower sashes vertically and at the top (head). Run a knife around as much of the parting bead as possible to loosen the paint, then use a chisel or flat pry bar to lever it out of the groove — all the way around the frame, including the top.
Remove the top sash
With both sashes removed, you now have full access to every part of the window. This is the ideal time to:
- Assess the window for rot and repair using a timber epoxy repair system before proceeding
- Weigh and rebalance your sashes to ensure they're correctly weighted and sliding freely — see our re-balancing guide
- Remove sash weights and re-hang, changing them if required
- Replace pulleys if required
- Scrape back the frames and release any excess paint build-up
Seal the meeting rail
The meeting rail — the horizontal point where the top and bottom sashes meet in the middle — also needs sealing. This product features a self-adhesive PVC carrier with a pre-inserted polypropylene brush pile and twin central fin, which enhances sealing by forming a continuous barrier against air and water infiltration.
Ensure all surfaces are clean, dry and free from debris before application. Use an 8.0mm straight router bit to create a 3.5mm deep groove for a flush fit, then install the pile and brush carrier into the meeting rail on the bottom sash — these come in 1-metre lengths, generally enough for most windows.
Re-install the cords with correct weights
Re-hang your sash cords and weights before continuing — see our step-by-step re-balancing guide for the full process, including how to correctly weigh and hang the top and bottom sash weights.
Install the new parting bead
Draught seal parting bead from Lock & Latch comes pre-fitted with a brush pile seal on one side. Start with the top parting bead at the head — measure horizontally between the frame and add a few mm so the bead runs all the way across. Pre-drill your holes before nailing, then fix the parting bead in position and nail it in (40mm nails recommended). Re-install the top sash.
Next, measure up for the side parting beads from the sill to the parting bead you just installed. Cut your pieces for the left and right side, then cut each piece in half at the meeting rail — mark the halfway point in pencil first.
On the bottom half of the window, install the parting bead so the pile faces inwards. On the top half, switch the bead over so the pile faces outwards — this cushions the sashes and eliminates gaps. The brush pile seal always faces the sashes, not the frame.
Reinstall the bottom sash
With the new parting bead in place, re-install the bottom sash. It should slide smoothly — the brush pile seal creates gentle resistance but shouldn't bind.
Install the new stop bead
The stop bead runs vertically down both sides of the frame, holding the lower sash in place while sealing the gap between the sash and the frame. Cut the draught seal stop bead to length and position it so the brush pile seal makes contact with the face of the lower sash, then pin it in place with a nail gun or hammer and panel pins.
The sash should still slide freely — if it's too tight, move the bead back slightly.
Test and adjust
Open and close both sashes to check they slide smoothly. There should be gentle resistance from the brush pile seals, but no binding or sticking — if a sash is too tight, loosen the stop bead slightly and reposition.
Run your hand around the edges of the closed window on a cold day. Your draught-proofed sash window is complete once you feel no air movement at all.
Paint and finish
The draught seal timber beading comes pre-undercoated but will need finishing coats to match your windows. Lightly sand and fill any nail holes first, and take care not to get paint on the brush pile seals.
A note on lead safety: older sash windows may have been painted with lead-based paint. Always take appropriate precautions when scraping, sanding, or disturbing painted timber on older windows — see SafeWork NSW's guidelines on lead work before you begin.
Common questions
How long will this take?
Allow around 3–4 hours per window for your first attempt. Once you've done one, subsequent windows go much faster.
Do I need a tradesperson?
No — this can be a DIY job with basic tools. We provide phone support from qualified carpenters to assist you through the process. That said, if your frames are damaged or you have a large number of windows, a professional installer can handle repairs and installation at the same time.
When should you not draught-proof?
If your windows are in very poor condition — rotting timber, broken cords or severely damaged frames — repair these issues first. Trying to draught-proof a window in bad structural shape won't give good results and could make future repairs harder. Need to repair rotten timber first? See our guide to epoxy timber repair.
Will draught-proofing make my sash windows hard to open?
No — actually the opposite. When installed correctly, brush pile seals create gentle resistance but the sashes still slide freely, with a brush instead of wood against wood enabling smoother operation. The seal compresses slightly as the sash moves past it.
Will I be able to see the beading once installed?
No. When the window is closed it's completely invisible. When open, only neat draught seals protrude slightly — a clean, integrated finish with no unsightly strips.
Can I draught-proof my sash windows without removing them?
Not properly. To do the job correctly you need to remove the stop bead and sashes to access the parting bead channel. Stick-on solutions that don't require removal won't seal the window properly and won't last.
Can this beading be used on casement windows or doors?
No — this system is designed specifically for double hung sash windows. For doors and casement windows, see our weatherseal range.
How much does it cost?
Materials for one double hung window typically cost between $115 and $180 depending on size. Compare that to replacement windows and the ongoing energy savings — it's exceptional value.
How long does it last?
Our draught seal beading uses FSC-certified timber and high-quality brush pile seals. When properly installed and the timber is maintained, it will last for many years.
Can I see the product before purchasing?
Yes — you can order samples or visit our warehouse in Warriewood, NSW 2102. Contact us to arrange a visit.
Ready to draught-proof your sash windows?
We supply everything you need to draught-proof your double hung sash windows, plus expert advice by phone or email.
Not sure what you need? Call us on 02 7228 0625 or email sales@lockandlatch.com and we'll help you work it out.
