Not every wet ceiling is a leak. In a lot of Wellington homes the water comes from inside the house. Warm, moist air from showers, cooking, drying washing and breathing rises into the roof space, meets the cold underside of the roofing on a clear night and condenses. It then drips onto insulation and ceilings, stains timber and feeds mould. Plenty of people pay to chase a leak that is not there.
We assess roof spaces for condensation and damp and install ventilation that suits the roof: vented ridges, eave and soffit vents, ventilated battens and roof vents. If the cause turns out to be a real leak, we say so and point you to the right repair. Ventilation is also worth planning into any re-roofing project, when it is easiest and cheapest to add.
Pricing: every roof gets a free on-site measure and an itemised written quote, with a fixed price agreed before any work starts.
Signs your roof space needs ventilation
Condensation problems are usually worst on cold, clear winter mornings and above bathrooms and kitchens. Watch for:
- Droplets or rust spots on the underside of steel roofing or around nail points
- Damp, flattened or stained ceiling insulation with no obvious leak above it
- Black mould on rafters, sarking or the back of ceiling linings
- A musty smell in the roof space or upstairs rooms
- Stains that appear on still, cold mornings but not during heavy rain
- A roof space that never seems to dry out between winter fronts
Why condensation forms under a roof
BRANZ explains that in a typical pitched roof the space between the roofing and the ceiling insulation is effectively outside the insulated part of the house, so it cools to near outdoor temperature at night. Steel roofing also loses heat to a clear sky, so its underside can drop below the dew point of the air in the roof space. BRANZ research on underlays found that condensation on metal roofs tends to run to the low points of the profile and passes into the underlay where the two touch, which is one reason underlay condition matters.
The more moisture that reaches the roof space from the house, the worse it gets. Unsealed downlights, ceiling hatches, fans venting into the roof and gaps around pipes all let damp air through. Ventilation removes moisture that gets in, but cutting what goes up matters just as much. For rental homes, the Healthy Homes ventilation standard already requires extractor fans in kitchens and bathrooms that vent to the outside.
How It Works
Wellington conditions that make it worse
Winter is the wettest season across the region, according to NIWA, and much of the region gets 1,000 to 1,200 mm of rain a year, with more in the Hutt Valley and Wainuiomata. Homes on shaded, south-facing hill sections in suburbs like Karori and Khandallah, or down in the valleys can go weeks in winter without much sun on the roof, so the roof space stays cool and damp. We see condensation most often in skillion and cathedral-ceiling extensions, in older steel roofs with no underlay, and where insulation has been pushed hard against the roofing.
Wind matters too. Many Wellington sites sit in High, Very High or Extra High NZS 3604 wind zones, and some need specific design. Any vent that forms part of the roof has to suit that wind zone and be flashed so it does not become the next leak. If you are unsure whether you have a leak or condensation, a roof inspection will tell you which.
Ventilation options we install
The right option depends on the roof shape, pitch and cladding. Gable, hip and skillion roofs move air differently, so we look at where air can come in low and leave high, and how the existing roofing and underlay will be affected.
- Vented ridge or hip systems that let warm, moist air out at the highest point
- Eave and soffit vents that let drier outside air in low down
- Ventilated battens under steel roofing, usually fitted during a re-roof
- Roof-mounted passive vents where ridge venting is not practical
- Bathroom and kitchen fans ducted outside rather than into the roof space
Building Code and product approvals
Building Code clause E3 Internal Moisture covers condensation and mould inside buildings. Earlier wording in its Acceptable Solution was widely read as discouraging ventilation of insulated roof spaces, and the NZ Metal Roofing Manufacturers association reports that clause has since been removed. BRANZ modelling found ventilation helps remove excess moisture from roof spaces, while noting many New Zealand roofs perform well without it.
Ventilation products should be suitable for the site's wind zone. One BRANZ Appraisal for roof ventilation battens and vents, for example, covers profiled metal roofs in wind zones up to Extra High and leaves detailing to the designer. We use appraised or manufacturer-specified products and follow their details. Adding vents to an existing roof is usually minor work, but we confirm the consent position with you before starting.
What affects the cost
A few vents on an easy roof is a modest job, while a skillion roof with no cavity may need the roofing lifted to add ventilated battens. Your quote reflects roof type and access, the number and type of vents, whether roofing or underlay needs lifting or replacing, fan ducting, and repair of any damaged insulation or ceilings. If damp has already marked the ceilings, our roof repairs team can fix any related damage. Added during a re-roof, ventilation usually costs little extra because the roof is already open.
Why Choose Cheeky's Roofers for Roof Ventilation
Leak or condensation, diagnosed
We find where the water is coming from before recommending anything, so you do not pay to fix the wrong problem.
Whole-path thinking
We look at how moist air gets into the roof space as well as how it gets out.
Detailed for your wind zone
Vents are chosen and flashed to suit Wellington wind, so they do not become a new leak.
Built into re-roofs
When we re-roof, ventilation is part of the design rather than an afterthought.
Roof Ventilation FAQs
How do I know if it is condensation or a leak?
Condensation is usually worst on cold, clear mornings and shows as droplets across the underside of the roofing. Leaks follow rain and show in particular spots. An inspection confirms which.
Does a steel roof cause condensation?
Steel cools fast at night, so its underside can reach the dew point of damp roof space air. Good underlay, ventilation and less moisture from the house all help.
Will roof vents let rain in during a Wellington southerly?
Not when the right product for your wind zone is installed and flashed correctly. Poorly detailed vents can leak, which is why installation matters.
Should my bathroom fan vent into the roof space?
No. Fans should be ducted outside, otherwise they just move moisture from the bathroom into the roof.
Do I need more insulation instead?
Insulation and ventilation do different jobs. Insulation jammed against the roofing can make condensation worse, so we look at both together.
Can you add ventilation without re-roofing?
Often, using eave, soffit or roof vents. Ventilated battens usually need the roofing lifted, so they are best added during a re-roof.
Roof Ventilation Across Wellington
We cover every region: Central Wellington, the Eastern and Southern Suburbs, the Western and Northern Suburbs, the Hutt Valley, Porirua, the Kāpiti Coast.
Related Roofing Services
Roof Ventilation Guides
See the roof replacement cost guide or every service we offer.
Sources and further reading
- BRANZ: Cold roofs? Warm roofs?
- Build 120: Roofing underlay and moisture (BRANZ research)
- BRANZ Appraisal 979: roof ventilation products
- NZ Metal Roofing Manufacturers: roof space ventilation and E3/AS1
- Tenancy Services: Healthy homes ventilation standard
- NIWA: The Climate and Weather of Wellington
- Level (BRANZ): Wind zones