How to Stop a Draughty Aluminium Window from Letting Cold Air In

Draughty aluminium windows are one of the most common complaints from NZ homeowners, especially in older homes built before modern energy efficiency standards. The good news is that many draught problems can be fixed with basic DIY skills and affordable materials — no building consent required for simple sealing work. Here's how to diagnose the problem and fix it properly.

Why Aluminium Windows Draught

Aluminium is a great conductor of heat and cold, which means the frames themselves can feel icy in winter. But the draught you feel is usually coming from gaps in the weatherstripping, worn or missing pile seals, or a sash that no longer sits squarely in its frame. Over time, the rubber or brush seals around sliding and casement windows compress, crack, or fall out entirely, leaving gaps that let cold air whistle through.

Common causes include:

• Worn or missing pile (brush) seals on sliding windows
• Cracked or hardened rubber gaskets around fixed panes
• A misaligned sash that no longer closes flush
• Gaps between the frame and the surrounding wall (perimeter gaps)
• Damaged or missing foam tape on casement window stops

Step 1 — Find the Draught Source

Before buying anything, locate exactly where the cold air is entering. On a windy day, slowly run your hand around the window edges. Alternatively, hold a lit incense stick near the frame — if the smoke wavers, you've found your gap. Check:

• Along the top, bottom, and sides of the sash
• Where the two sashes meet on a sliding window (the meeting rail)
• Around the perimeter where the frame meets the wall or reveal
• The weep holes at the bottom of the frame (these should be open but not oversized)

Step 2 — Replace Pile (Brush) Seals on Sliding Windows

Pile seals are the fuzzy brush strips that run in channels along the edges of sliding sashes. They're the most common wear item on NZ aluminium joinery. Replacement pile is sold by the metre at Mitre 10 and Bunnings — take a short piece of your old seal with you to match the width and pile height.

How to replace pile seals:

1. Lift or tilt the sash out of the frame (most NZ sliding windows lift up and swing inward).
2. Pull the old pile strip out of its channel — it usually clips or slides out.
3. Cut the new pile to length and press or slide it firmly into the channel.
4. Refit the sash and test for smooth operation and reduced draught.

This is a straightforward DIY job that takes under an hour per window.

Step 3 — Replace Rubber Gaskets and Foam Tape

Casement and awning windows use rubber gaskets (also called glazing seals or weather seals) that compress against the frame when the window closes. If these are cracked or flattened, replace them with matching EPDM rubber seal from a hardware store or joinery supplier. Self-adhesive foam draught-seal tape is a quick fix for casement window stops, though it will need replacing every few years.

For fixed panes, check the glazing bead — the rubber strip holding the glass in the frame. If it has shrunk or cracked, a glazier can replace it quickly and affordably.

Step 4 — Seal Perimeter Gaps

If cold air is coming in around the outside of the frame where it meets the wall, this is a perimeter sealing issue. Use a paintable polyurethane or silicone sealant (check it's suitable for aluminium and the adjacent surface). Sika and other brands offer suitable products at hardware stores. Apply neatly with a caulking gun, smooth with a wet finger, and allow to cure fully before painting if needed.

Note: If the gap is large or there are signs of water damage or rot in the surrounding framing, get a professional assessment before sealing — trapping moisture can cause bigger problems.

Step 5 — Consider Secondary Glazing or Window Film

If the window is still cold after sealing, the aluminium frame itself may be conducting cold into the room. Secondary glazing — a second pane fitted inside the existing window — is a cost-effective upgrade that significantly reduces both draughts and heat loss. This is especially relevant under the Healthy Homes Standards for rental properties, which require adequate insulation and draught stopping.

Window insulation film (applied to the glass surface) can also reduce heat loss, though it won't fix frame-edge draughts.

Adjusting a Misaligned Sash

If the sash visibly sits crooked or doesn't close flush, the rollers or guides may be worn or the frame may have shifted. Many sliding window rollers are adjustable with a screwdriver — look for adjustment screws at the bottom corners of the sash. If the frame itself has racked or the building has settled, this may need a glazier or builder to assess.

When to Call a Professional

Call a qualified glazier if:

• The glass itself is cracked, broken, or the double-glazing unit has fogged (failed seal)
• The frame is visibly bent, corroded, or the sash won't close properly after adjustment
• You need to replace the entire window unit
• There are signs of water ingress or damage to surrounding framing

Replacing a window unit may require a building consent depending on the scope of work — always check with your local council first. The MBIE Building Performance website has guidance on what work is exempt under Schedule 1.

You can find qualified local glaziers on tradedirectory.co.nz.

Sources & Further Reading

• MBIE Building Performance — Building Consent information
• Tenancy Services — Healthy Homes Standards
• Energywise — Insulation and draught stopping
• BRANZ — Window and glazing guidance
• Bunnings — Draught sealing products
• Mitre 10 — Weatherstrip and sealing products