Draughts coming through gaps in your ceiling insulation are one of the most common reasons NZ homes feel cold and expensive to heat. The good news is that many of these gaps can be found and fixed with basic DIY skills — but you do need to work safely and know your limits.
Why Ceiling Draught Gaps Are Such a Problem
Heat rises, so your ceiling is where the most heat escapes in winter. Even small gaps between batts, around light fittings, or where pipes and cables penetrate the ceiling can allow significant air infiltration — cold outside air sneaking in and warm inside air leaking out. This is sometimes called the stack effect. According to BRANZ, uncontrolled air leakage can account for a large portion of a home's heat loss, making draught-sealing one of the most cost-effective improvements you can make.
For rental properties, landlords should also be aware that Tenancy Services Healthy Homes Standards require ceiling insulation to meet minimum R-value requirements, and gaps undermine compliance.
Step 1 — Find the Gaps
Before you can fix anything, you need to locate where air is getting through. Common culprits include:
- Gaps between insulation batts — batts that have shifted, shrunk, or were never butted tightly together
- Around ceiling penetrations — downlights, exhaust fans, plumbing pipes, electrical cables, and ceiling roses
- At the ceiling perimeter — where the ceiling meets the top plate of exterior walls
- Around manhole (access hatch) frames
- At internal wall top plates — walls that don't reach the roof framing leave open cavities
On a cold, still day, hold your hand near suspected areas to feel for air movement. A lit incense stick (used carefully) can also reveal draughts by the way the smoke moves.
Step 2 — Gather Your Materials
For most draught-sealing jobs in the ceiling space you'll need:
- Polyurethane expanding foam (low-expansion type for smaller gaps)
- Acoustic or fire-rated sealant (for gaps near penetrations — check the product is appropriate for the location)
- Insulation offcuts or new batts to fill voids
- Draught-sealing tape for manhole hatches
- A torch, dust mask (P2 rated), safety glasses, and knee pads
You can find suitable products at Bunnings or Mitre 10. Always read the product data sheet before use.
Step 3 — Seal Gaps Safely
General gaps between batts
Push batts firmly together so there are no visible gaps. If batts are too short or damaged, replace them with new material of the same or higher R-value. Make sure batts sit flat and fill the full depth of the joist cavity without being compressed — compression reduces their effectiveness.
Around pipes and cables
Use low-expansion foam or an appropriate sealant to seal around plumbing pipes and electrical cables where they pass through the ceiling. Keep foam away from electrical wiring unless the product is specifically rated for that use.
At the ceiling perimeter
This area is often overlooked. Use insulation offcuts or foam to block the gap where the ceiling meets the exterior wall top plate. This is one of the biggest sources of draught in older NZ homes.
Manhole hatches
Fit self-adhesive draught-sealing foam tape around the hatch frame, and consider adding a layer of insulation to the top of the hatch board itself.
Downlights — A Special Case
Recessed downlights are a major source of both draughts and heat loss and must be handled carefully. Standard insulation batts cannot be placed directly over most downlights due to fire risk — the heat build-up can cause a fire. You have two main options:
- Install an IC-rated (Insulation Contact) downlight cover/hood — a sealed, fire-rated box that sits over the fitting and allows insulation to be placed on top. These are available at electrical suppliers.
- Replace the downlights with IC-rated LED fittings — this is restricted electrical work and must be carried out by a registered electrician (see EWRB).
Never cover a standard downlight with insulation without an approved cover — this is a serious fire hazard.
Safety First in the Ceiling Space
Working in a ceiling space carries real risks:
- Only step on ceiling joists, never on the plasterboard between them — it will not support your weight
- Wear a P2 dust mask — old insulation, dust, and fibres can harm your lungs
- Watch for electrical wiring — never cut, move, or disturb cables
- In older homes (pre-1980s), be aware of the potential for asbestos in some ceiling materials. If you're unsure, contact a licensed asbestos assessor before disturbing anything. WorkSafe NZ has guidance on identifying and managing asbestos safely
- Ensure the ceiling space is well ventilated and that someone knows you're up there
When to Call a Professional
Call a qualified insulation installer (find one on tradedirectory.co.nz) if:
- The ceiling space is too confined or unsafe to access
- You suspect asbestos-containing materials
- The existing insulation is severely degraded and needs full replacement
- You need downlights replaced or new electrical penetrations sealed — this is restricted electrical work requiring a registered electrician
- Your home has complex roof geometry making DIY access difficult
For new insulation installations, check with your local council whether a building consent is required. Many insulation top-ups fall under Schedule 1 exemptions, but it's always worth confirming — see MBIE Building Performance for guidance.
