Draught-sealing old timber windows is one of the most cost-effective home improvements you can make in New Zealand's often chilly climate. With a few simple products from your local hardware store and a free afternoon, you can noticeably reduce cold draughts, lower your heating bills, and improve your home's comfort — no specialist skills required.
Why Draught-Sealing Matters
Old timber windows — especially single-glazed sash and casement styles common in New Zealand homes — tend to develop gaps as the timber shrinks, swells, and ages over time. These gaps let cold air in and warm air out, making your heating work harder. According to Energywise, draughts can account for a significant portion of heat loss in older homes. Sealing them is one of the cheapest first steps before considering bigger upgrades like double glazing.
If your home is a rental, note that landlords have obligations under the Tenancy Services Healthy Homes standards around draught stopping — so tenants should check what their landlord is required to provide.
Identifying Where the Draughts Are Coming From
Before you reach for the tape, find the gaps. On a windy day, hold a lit incense stick or a damp hand near the window edges, sash meeting rails, and the junction between the frame and the wall. You're looking for:
- Gaps between the sash and the frame (the most common culprit)
- Gaps where the frame meets the surrounding wall or architrave
- Broken or missing putty around the glass pane
- Gaps at the sill
The Easiest Draught-Sealing Methods
1. Self-Adhesive Foam Tape
Best for: Casement windows, hinged windows, and anywhere you need a quick, low-cost fix.
Foam tape (also called weatherstrip tape) is the simplest option. It compresses when the window closes, forming a seal. You simply clean the surface, peel the backing, and press it into place along the rebate (the step in the frame where the sash sits).
- Choose closed-cell foam rather than open-cell — it lasts longer and resists moisture better.
- Available in various thicknesses; measure your gap first so the tape compresses properly without preventing the window from closing.
- Lifespan is typically 2–5 years before it needs replacing.
You'll find a good range at Bunnings or Mitre 10.
2. V-Strip (Tension Seal) Weatherstripping
Best for: Double-hung sash windows and sliding windows.
V-strip (sometimes called tension seal or pile weatherstrip) is a folded strip of plastic or metal that springs open to fill a gap. It's more durable than foam tape and works well in channels where the sash slides up and down.
- Cut to length with scissors or tin snips.
- Slide or tack it into the channel alongside the sash.
- It's nearly invisible once installed and can last many years.
3. Brush Seals (Pile Weatherstrip)
Best for: Sash windows, especially at the meeting rail where the two sashes overlap.
Brush seals use a strip of fine fibres to block draughts while still allowing the window to slide smoothly. They're a popular choice for traditional NZ villas and bungalows with double-hung sash windows. Some come with a self-adhesive backing; others are tacked or stapled into a groove.
4. Silicone or Acrylic Sealant
Best for: Fixed gaps between the window frame and the surrounding wall or architrave — places that don't need to open.
Use a paintable acrylic sealant (not silicone if you plan to paint over it) to fill static gaps around the outside of the frame. Apply with a caulking gun, smooth with a wet finger, and paint once cured. Sika and other brands offer suitable products at hardware stores.
Do not use sealant on moving parts — it will crack and prevent the window from opening.
5. Draught Snakes and Secondary Glazing Film
For a very quick, non-permanent fix at the sill, a draught snake (a fabric tube filled with sand or similar) can block cold air under a window. Secondary glazing film — a thin plastic film applied with double-sided tape and shrunk with a hairdryer — can also reduce draughts and heat loss noticeably, though it's a temporary measure.
Step-by-Step: Applying Foam Tape
| Step | What to do |
|---|---|
| 1 | Clean the rebate with a damp cloth and allow to dry fully |
| 2 | Measure the length of each side to be sealed |
| 3 | Cut tape to length |
| 4 | Peel backing and press firmly into the rebate |
| 5 | Close the window to check it seals and still latches properly |
| 6 | Trim any excess with a sharp knife |
Tips for a Long-Lasting Result
- Clean surfaces thoroughly — adhesive won't stick to dusty or painted surfaces that are flaking.
- Prime bare timber before applying adhesive-backed products if the wood is very porous.
- Check the window still opens and closes easily after sealing — you don't want to accidentally seal it shut.
- Replace any broken sash cords before sealing, as you'll need access to the box frame.
- Consider touching up the putty and paint on the exterior at the same time to prevent moisture getting in and causing rot — a key issue in NZ's wet regions.
When to Call a Professional
Draught-sealing is generally DIY-friendly and does not require a building consent for straightforward weatherstripping. However, call a qualified joiner or carpenter if:
- The timber frame or sill is rotted or structurally damaged — this needs proper repair before sealing.
- The window no longer sits square in its frame, causing large or uneven gaps.
- You're considering replacing windows entirely — this may require a building consent depending on the scope of work; always check with your local council. The MBIE Building Performance website has guidance on what work requires consent.
- You want a professional-grade draught-seal and overhaul of heritage sash windows.
A skilled joiner can also advise on whether your windows are worth retaining or whether upgrading to double glazing makes more sense for your situation. You can find qualified local joiners and carpenters on tradedirectory.co.nz.
Safety note: When working on upper-storey windows, always use a stable ladder and have someone spot you. Never lean out of a window to work on the exterior — work from outside using a proper scaffold or ladder.
