Maintaining membrane roofs, asbestos materials, and bitumen-impregnated cellulose fibre roofs.
Maintenance of membrane roofs is often crucial to ensuring your home remains weathertight, as this material is often used on balconies or decks.
Sheet membrane roofs
Sheet membrane roofing is often used on low slope roofs and may be subject to foot or vehicle traffic. This makes it prone to surface damage.
Low slope roofs should always have an overflow outlet for each main outlet in case the down pipe gets blocked. Roofs enclosed with parapets should have a minimum of two outlets. Also see balconies and decks.
Ponding water: This happens when the roof has insufficient fall to promote run-off, or drains are blocked or not adequate to cope with water run-off, or not enough outlets. It can also be caused by settling of the substrate.
If the problem is blocked drains, clear the blockages. If necessary, increase the size or number of drainage outlets. Place a piece of plastic or wire netting in the drain entrance to keep out leaves and other debris which might cause blockages.
For major ponding, either lift the existing roof, reform and lay a new membrane or lay a new roof, with a greater fall, over the existing roof. This is a job for the professionals.
Bubbles under the membrane: This can be due to excessive moisture coming from below or poor adhesion to the substrate.
Cut the membrane and allow it to dry out before injecting adhesive underneath and patching. Check with the manufacturer to ensure you use compatible products. Address the cause of any moisture in the roof space.
Membrane splitting: This can be due to movement in the substrate. Repairs depend upon the type of membrane used. Check with the manufacturer. Repair by installing a slip layer between the membrane and the substrate and replacing the membrane.
Damage to the weather skin: This can be due to vehicle or foot traffic, or nails popping. For sheets, patch with matching material. If the area is subject to traffic, check that the surface is suitable for the amount and type of traffic. Consider laying loose paving or duckboards to protect the surface.
Joints lifting: This can be caused by adhesion failure, wear and tear, or water ponding. Follow the manufacturer’s recommendations when carrying out any repairs. See ponding water for solutions to that problem.
Paint-on membrane roofs
Paint-on membranes must be regularly re-coated, generally at 7-10 year intervals. Many site-applied membranes are covered by a manufacturer’s warranty. Approach the applicator for redress under the warranty if the membrane is failing prematurely.
Surface cracking: This happens when there aren’t enough waterproof movement joints, or due to UV breakdown. Waterproof movement joints will need to be installed in the membrane or the roof resurfaced. This is work for the professionals.
Substrate showing through the membrane: This may be due to the membrane not being thick enough. It may also be caused by wear due to foot traffic or sunlight exposure. Recoat or consider resurfacing with a more suitable product for the volume of foot traffic. Resurfacing may require that the old surface is removed.
Consider providing protection over the membrane, for example with paving slabs or boards. If you consider this option, you need to ensure the structure is able to cope with the additional load and the membrane is protected from damage by the surfacing.
Nails popping: Due to the timber shrinking. Replace with stainless steel screws then re-seal the membrane with a new application.
Chalking: Due to UV degradation. Recoat to the manufacturer’s specifications.
Ponding water: Due to blocked or insufficient outlet drains, insufficient fall or differential settling of the substrate. Clear blockages. Increase the size or install additional outlets. For major ponding either lift the existing roof, reform and lay new membrane or lay new roof with greater falls over the existing roof.
Surface damage: Due to foot traffic and weathering. Patch punctured areas with a new coating of the membrane.
Asbestos materials should only be removed or handled by a contractor experienced in this type of work. Look under ‘Asbestos’ in the Yellow Pages.
Some homes built before 1983 may have been built with materials that contain asbestos – for example, profiled asbestos cement sheeting, old shingles and some roof membranes.
Provided the materials containing asbestos are in good condition and have a sound coat of paint, it is not likely to be a health risk. Unpainted asbestos cement roofs should be left alone. Do not attempt to walk on asbestos cement roofs as they become brittle with age.
However, if the asbestos cement is exposed or is being removed, it can be a health hazard. Asbestos dust and fibres can cause diseases such as mesothelioma (a cancer of the chest lining) and asbestosis. These diseases are crippling, very painful and usually fatal. There are no known cures.
The only way to find out for sure if a material contains asbestos is to have it tested in an approved laboratory. If your maintenance involves removing or sanding materials that might contain asbestos, or if you are unsure what the materials are made of contact the health protection officer at your local District Health Board. Do not obtain a sample without consulting them first. Also see Aucland Regional Public Health Service's Environmental health sheets on asbestos.
For weathered asbestos cement roofs or walls, paint degradation, surface damage or cracks in asbestos cement, get specialist advice.
DO NOT TRY TO REPAIR OR REMOVE ASBESTOS CEMENT YOURSELF. LEAVE IT TO THE PROFESSIONALS.
DO NOT WATERBLAST ASBESTOS-BASED MATERIALS.
Bitumen-impregnated cellulose fibre
This is a pre-finished sheet product used in both wall and roof claddings.
Impact damage: Replace damaged sheets. When you’re on the roof, remember to use a plank to walk on.
Erosion of the coating: This is normally due to weathering. Check if the coating is still under warranty. If not, repaint to the manufacturer’s specifications, using a bitumen-compatible water-based paint.
Moss and mould growth: This is caused by moisture buildup. Treat with water-based chemical treatments only. Consult suppliers of roof cleaning materials for suitable products.