Roof space

Types of roof structure

Most types of roof in New Zealand are pitched, although flat roofs are also common.

Pitched roofs form a ridge or apex, and often have an overhang (eaves) that shields the upper part of the external walls from the elements. Wide eaves protect a building from rain, the high summer sun and also from snow melt coming off the roof. Pitched roofs are traditionally based on a triangle for strength, although complex roof designs are now also common. Rafters carry the external roof covering. Low-pitched roofs (less than 10°) are less tolerant of construction flaws. Especially roof slopes around 2° to 5° can have drainage compromised through inaccuracies in construction or settlement.

Common forms of the pitched roof are framed rafters or trussed roofs. Trussed roofs are often prefabricated off-site. Do not remove any section of a trussed roof as it can cause the structure to collapse. It will also invalidate manufacturer’s and builder’s guarantees.

Another common design is the skillion (sometimes called cathedral) roof: Here, the internal ceiling lining is parallel to the roof cladding. Skillion roofs only have small, inaccessible roof spaces. Potential problems are therefore difficult to recognise early.

Moisture and leaks

Moisture problems in the roof space can have two different causes: leaks through the roofing envelope or water condensing on cold parts, especially the underside of the roof cladding. Once a problem has been recognised, it is important to determine the cause.

Signs that your roof space is too damp include:

• moisture on the underside of the roofing underlay
  
• signs of mould growth on the roofing underlay and timber
  
• water pooling on the ceiling lining, sometimes dripping down from light fittings
  
• water stains on the roofing underlay, rafters or ceiling
  
• wet or damp insulation
  
• drooping roof underlay at the eaves.
  

Leaks can generally be identified by signs of moisture that are more localised. For example, if stains or mould are found in close proximity to penetrations in the roof such as chimneys, pipes or roof fixtures a leak is the more likely cause. Also, if the problem is worse after rain, the explanation is more often a simple leak in the roof.

Find and repair any leaks. Replace any water-damaged materials. Patch torn roofing underlay sections. If your blanket insulation may be able to be dried out and put back in. However, if it’s too far gone you may need to replace it. If you have loose fill insulation, small amounts can be dried out but large amounts will need to be replaced.

Condensation moisture issues are generally more wide-spread. This lies in the nature of the problem: the air in the attic is too moist and once the roof deck cools down, this moistures condenses on all the cold surfaces.

The key to reducing condensation is reducing the moisture level in the attic air.

• Warm, moist air tends to move up. Make sure the air in the living quarters downstairs is dry.
• Try to make the ceiling as air-tight as possible. Old-style downlights are often very open and offer an easy pathway for air to move into the attic. If you replace downlights with LED fittings, make sure they don’t have gaps around the body.
• Make sure your kitchen, bathroom or laundry extractor fan doesn’t vent into the roof space. If it does, extend the venting to the exterior of your house. Under the Building Code, newly installed fans must vent to the outside of the house.
• Add passive ventilation elements to the roof space. This enables moist air to be replaced with fresh outside air. Seek professional advice for the installation. In general, two types of vents are needed:
  • intake vents at the eaves to allow fresh air in
  • exhaust vents near or on the ridgeline to allow air out. However, installation of a ridge vents only, without eaves vents, must be avoided.
    
• Drooping roof underlay at the eaves can be particularly common in tiled roofs, where water is blown up under the tile, and indicates moisture is getting in. Use an anti-ponding board to provide support under the roofing underlay to allow water to drain.

Displaced insulation

If insulation isn’t installed properly or has moved since installation, it will be less effective.

If insulation is being disturbed by the wind, find where the wind is entering and seal the gaps, then re-level the insulation. Leave a gap of 25mm between the top of the insulation and the roof underlay.

Borer

Borer loves damp or untreated timber. See our article on borer for more information.

Sagging rafters/ridge beams

This can be caused by poor design, settlement of the foundations, heavy roofs (concrete or clay tiles) or, more unusually, timbers damaged by borer.

You may need to get professional advice about how to support the timbers by adding under-purlins, new members or struts. If your roof is still under warranty, contact the manufacturer before doing any work. You may want to get a professional to inspect the roof before carrying out any work.

Rodents/birds in the roof space

Find out where they are getting in and block the hole with rolled-up wire netting. Lay poison or traps to deal with resident rodents.

Damaged/loose electrical wires

If the wiring has deteriorated, it could be a fire or electrocution risk. Have damaged wiring replaced by an electrician. Ensure wiring is secured and supported.

Money savers

Roof insulation: Up to 40% of the heat in your home can be lost through the ceiling, so make sure the roof space is well insulated. If you only have insulation in one place, make it the roof.

New houses must be insulated, but many older (pre-1970s) houses are not. There are different products available for the roof space. Some you can put in yourself such as blanket, segments or rolls.

Professionally installed options, such as loose-fill insulation are worth considering if cost is a concern; if you have a low-pitched roof that makes it difficult to access the ceiling space; and/or if you don't need to get into your roof space very often. It can also be blown into the inaccessible corners and edges of low-pitched roofs.

Remember to leave a 25mm gap between the insulation and the roof underlay.

This page was put together with the help of BRANZ.