Original roofs may need maintenance or replacement.
Check the condition of the roofing.
Especially check the condition of the laps of corrugated roofs and the joints in pan roofing.
If it is in good, well maintained condition it will not need to be replaced. Careful surface preparation, the application of rust treatment and a good quality paint system can prolong the life of a metal roof. However, for metal roofs, particularly those in coastal locations, the original 1970s roof cladding may be nearing the end of its serviceable life.
Replacement roofing options include pre-painted or unpainted longrun zinc/aluminium alloy coated steel, profiled aluminium roofing, or a pressed metal tile. Manufacturers may recommend a higher performance metal roofing product in coastal situations. If roofing is to be replaced, the roofing underlay (unless in as-new condition) should also be replaced.
The early pressed metal tiled roofs tended to lose stone chips over time (Figure 1). If this has occurred but the roof is otherwise still in good condition, the roof can be resurfaced with stone chips or paint. This should be carried out by a professional. Some pressed metal tiles deform easily and can be damaged when, for example, television dishes are installed on the roof. Repair or replacement may be required.
Concrete roof tiles are durable and will last for a long time, but they should be inspected regularly and may require occasional maintenance. Tiles are relatively brittle and care is needed to ensure that access onto the roof does not cause more problems.
Tile maintenance primarily involves routine visual checking from the roof edge for:
- loose, damaged or broken tiles - replace broken tiles. New concrete tiles are available, but if a tile with the same degree of weathering as the remainder of the roof is required, try building demolition yards.
- debris accumulation on the roof - remove debris such as leaves and branches as they can block gutters, valley gutters and downpipes
- loss of pointing from ridge or hip tiles - re-point as required
- corroded metal - replace metal valley gutters and flashings as required.
An asbestos-cement roof can typically last about 50 - 60 years, so the roof cladding on houses built in the 1970s may not require replacement yet.
Asbestos materials become health hazards when asbestos fibres are released and can be breathed in. The asbestos fibres in asbestos-cement roofing are not readily released unless the material is disturbed through damage or weathering, or through actions such as cutting, waterblasting or aggressive cleaning - so avoid these activities.
A roof that is sound is best left as is, but will need to be properly and regularly maintained. However, any asbestos-cement roofing that shows evidence of damage such as broken roofing or noticeable surface weathering may need to be replaced.
Where an uncoated surface looks 'fluffy', have an asbestos specialist assess the roof. As asbestos-cement products age they absorb more moisture, which may accelerate deterioration and result in increasing moss and lichen growth.
Note: Corrugated asbestos-cement roofing is likely to be brittle and must not be walked on. If you must access the roof, planks or a roof ladder should be used to avoid standing directly on the asbestos sheets. Alternatively, consult with a professional person experienced in dealing with asbestos removal. Any removal or recoating of an asbestos-cement roof should be carried out by a specialist contractor.
Removal and replacement
If the asbestos-cement is extremely weathered and can be crushed by hand, it must be removed professionally. Work with asbestos (including removal work) is covered by the Health and Safety at Work (Asbestos) Regulations 2016. A licensing scheme applies to asbestos removal. You must notify WorkSafe New Zealand of licensed asbestos removal work at least 5 days before work commences. You can find more details here.
Even when the material is still intact, precautions must be taken and the asbestos-cement must be disposed of appropriately. Precautions required when removing these products include:
- extract the fixings rather than trying to prise up brittle sheets which may break
- keep the asbestos-cement wet during removal
- lower the pieces of asbestos-cement to the ground instead of tossing them down.
See Asbestos for information on handling and removing asbestos safely.
The replacement option for corrugated asbestos-cement roofing is usually long run profiled metal laid over new roof underlay which can usually be laid over the existing purlins.
Maintenance, if required, primarily includes the removal of lichen and mosses but could include painting if the roofing is still sound, although BRANZ recommends that this only be done by a specialist contractor.
Prepare the roof for painting by removing dirt and contaminants, but under no circumstances use a waterblaster as this can blast asbestos fibres free of the roofing. Collect dirt and contaminants and dispose of correctly (see Asbestos).
Lichen and mosses should be removed by treating with a proprietary moss and mould treatment product.
Existing asbestos reinforced bitumen-impregnated roofing may not require replacing (note that removal must be done by a suitably registered contractor because of the presence of the asbestos). Typical problems include:
- hardening and cracking allowing moisture to penetrate the membrane
- differential movement between the roofing material and the substrate
- insufficient elasticity in the roofing resulting in stress cracking
- loss of any protective coating to the membrane
- moisture deterioration of the substrate
- insufficient slope to drain water effectively.
Butyl roofing may still be sound (the original roofing membrane may have had a 20 year warranty) but could be showing deterioration:
- at the glued lapped joints
- along the lines of the joints in the substrate below where the membrane will be stressed
- at abrupt changes in direction where the membrane may have been stretched and/or has pulled away from the substrate
- in the substrate where there has been high moisture levels within the roof space.
As membrane roofs were generally laid to low pitches that were slow to drain, they are more likely to have suffered water penetration through imperfections that may have developed in the roofing membrane. Over time this may result in failure of the roofing and of the roof structure.
If the roofing membrane requires replacement, the substrate has sufficient slope and is in good condition and is of the required thickness and durability (17.5 mm for plywood and CCA treated), a new membrane roofing system may be applied.
If the substrate is in poor condition, it and any water damaged framing should also be replaced. It may be worthwhile considering increasing the roof fall, and increasing insulation, before re-roofing. Check internal gutters for depth, width and fall against current building requirements.
Options for new membrane roofing systems include:
- single-ply, roll-out materials with lapped side joints such as butyl rubber, EPDM or PVC
- two-layer torch-on modified bitumen
- water-based liquid-applied membranes such as an acrylic emulsion.
Original profiled polycarbonate or fibreglass roofing is likely to have lost its translucency (become opaque), become brittle and will likely need replacement. Options for replacement include new:
- polycarbonate sheet
- glass-reinforced plastic (GRP)
Note: Do not walk on new or old sheets. They will not support a person's weight, and material becomes brittle with age. Treat as for asbestos-cement roofing by installing planks or a roof ladder.