Draughts through timber floorboards are one of the most common complaints in older New Zealand homes, particularly those built before the 1970s with suspended timber floors over a subfloor cavity. The good news is that most draught-proofing work is straightforward DIY, and tackling it properly can make a noticeable difference to your comfort and heating bills.
Why Timber Floors Let in Draughts
Suspended timber floors sit above a subfloor cavity — the space between the ground and the underside of your floor. In older homes, this cavity is often open to outside air through foundation vents. As the timber dries and ages, gaps open up between floorboards, and cold air is drawn up through them, especially on windy days. Gaps around skirting boards, pipe penetrations, and floor vents are also common culprits.
Step 1 — Find Where the Draughts Are Coming From
Before you start sealing, identify the sources:
- On a cold, windy day, run your hand slowly across the floor to feel for cold air movement.
- Use a stick of incense — the smoke will drift toward draught sources.
- Check gaps between boards, along skirting boards, around pipes and cables that penetrate the floor, and at floor vents (if fitted).
- If you have subfloor access, inspect from underneath with a torch to see daylight or feel airflow.
Step 2 — Fill Gaps Between Floorboards
For narrow gaps (under about 3 mm), a flexible acrylic gap filler or paintable sealant works well. Apply it with a caulking gun, smooth it off with a damp finger, and paint over once cured. Look for products suited to timber movement — rigid fillers can crack as the wood expands and contracts seasonally.
For wider gaps, consider:
- Flexible timber filler or wood putty — good for cosmetic repairs but may crack over time in wide gaps.
- Rope caulk — a soft, flexible rope-style filler pressed into gaps; removable if needed.
- Timber slivers or strips — thin strips of matching timber glued and tapped into wider gaps, then sanded flush. This is the most durable solution for large gaps but takes more skill.
Avoid rigid fillers like standard plaster or cement-based products — they will crack as the timber moves.
Step 3 — Seal Skirting Boards and Penetrations
The junction between the skirting board and the floor is a major draught pathway. Run a bead of flexible acrylic sealant along the bottom of the skirting board where it meets the floor. Similarly, seal around any pipes, cables, or conduits that pass through the floor using an appropriate flexible sealant — Sika makes a range of flexible sealants suitable for this purpose.
Step 4 — Address Floor Vents
Some older homes have floor vents or registers that were originally designed for underfloor heating or ventilation. If these are no longer needed, they can be blocked with a fitted cover plate. If they serve a ventilation purpose, consider fitting a draught-excluding vent cover that allows airflow but reduces cold air entry.
Step 5 — Insulate the Underfloor Space
Sealing gaps is only part of the solution. Underfloor insulation is the most effective long-term fix for a cold, draughty suspended timber floor. Insulation batts (typically polyester or glasswool) are fitted between the floor joists from underneath, held in place with wire, netting, or purpose-made clips.
Under the Healthy Homes Standards, rental properties must have underfloor insulation where it is reasonably practicable to install it — so if you're a landlord, this may be a legal requirement. Even for owner-occupiers, underfloor insulation is one of the best investments you can make for warmth and energy efficiency. Energywise has good guidance on insulation options and potential subsidies.
Minimum R-values for underfloor insulation under the NZ Building Code vary by climate zone — check with your local council or a qualified installer for the correct specification for your region.
Step 6 — Improve Subfloor Ventilation (Without Creating Draughts)
This might seem counterintuitive, but a damp subfloor causes timber to swell, warp, and rot — which worsens gaps over time. Make sure your subfloor has adequate cross-ventilation through foundation vents, and consider a ground vapour barrier (polythene sheet) laid over the soil to reduce moisture rising into the cavity. BRANZ has detailed guidance on subfloor moisture management.
Products and Where to Find Them
| Product | Use | Where to Buy |
|---|---|---|
| Flexible acrylic sealant | Narrow gaps, skirting boards | Bunnings, Mitre 10 |
| Rope caulk | Wider board gaps | Hardware stores |
| Polyester underfloor batts | Underfloor insulation | PlaceMakers, insulation suppliers |
| Polythene vapour barrier | Ground moisture control | Bunnings, Mitre 10 |
When to Call a Professional
Most gap-filling and draught-proofing is straightforward DIY. However, call a qualified builder or carpenter if:
- Boards are badly warped, cupped, or rotted and need replacing.
- You suspect structural issues with the floor joists or bearers.
- You want underfloor insulation installed professionally (especially in tight or difficult subfloor spaces).
- There are plumbing or electrical penetrations that need sealing — any work on plumbing is restricted work under the Plumbers, Gasfitters and Drainlayers Board and must be carried out by a licensed tradesperson. Similarly, electrical work is restricted under the Electrical Workers Registration Board.
A qualified local builder can assess your floor properly and recommend the best approach. You can find experienced tradespeople in your area on tradedirectory.co.nz.