Flat Roof - Maintenance and Assessment

Maintenance and Assessment

In general, a flat roof lasts longer if it is properly maintained. The life expectancy of a flat roof can be proportional to the maintenance done on it. Some assessors use 10 years as an average life cycle, although this is dependent on the type of flat roof system in place. Some old tar and gravel roofers quietly acknowledge that unless a roof has been neglected for too long and there are many problems in many areas, a BUR (a built up roof of tar, paper and gravel) will last 20 – 30 years. There are BUR systems in place dating to the early 1900s.

Modern cold applied liquid membranes have been durability rated by the British Board of Agreement (BBA) for 30 years. BBA approval is an important benchmark in determining the suitability of a particular fibreglass roofing system. If standard fibreglass polyester resin is used such as the same resin used in boat repairs, then there will be problems with the roof being too inflexible and not able to accommodate expansion and contraction of the building. A fit-for-purpose flexible/elastomeric resin system used as a waterproofing membrane will last for many years with just occasional inspection needed. The fact that such membranes do not require stone chippings to deflect heat means there is no risk of stones blocking drains. Liquid applied membranes are also naturally resistant to moss and lichen.

General flat roof maintenance includes getting rid of ponding water, typically within 48 hours. This is accomplished by adding roof drains or scuppers for a pond at an edge or automatic siphons for ponds in the center of roofs. An automatic siphon can be created with an inverted ring shaped sprinkler, a garden hose, a wet/dry vacuum, a check valve installed in the vacuum, and a digital timer. The timer runs two or three times a day for a minute or two to start water in the hose. The timer then turns off the vacuum, but the weight of water in the hose continues the siphon and soon opens the check valve in the vacuum. The best time to address the issue of ponding water is during the design phase of a new roofing project when sufficient falls can be designed-in to take standing water away. The quicker you get the water off the roof, the less chance there is for a roof leak to occur.

All roofs should be inspected semi-annually and after major storms. During the roof inspection particular attention should be paid to the flashings around all of the roof top penetrations. The sharp bends at such places can open up and need to be sealed with plastic cement, mesh and a small mason's trowel. Additionally, repairs to lap seams in base flashings should be made. 90% of all roof leaks and failure occur at the flashings. Another important maintenance item, often neglected, is to simply keep the roof drains free of debris. A clogged roof drain will cause water to pond, leading to increased "dead load" weight on building that may not be engineered to accommodate that weight. Additionally, ponding water on a roof can freeze. Often, water finds its way into a flashing seam and freezes, weakening the seam.

For bitumen based roof coverings maintenance also includes keeping the tar paper covered with gravel, an older method, currently being replaced with bituminous roofing membranes and the like, which must be 'glued' in place so wind and waves do not move it causing scouring and more bare spots. The glue can be any exterior grade glue like driveway coating.

Maintenance also includes fixing blisters (delaminations) or creases that may not yet be leaking but will leak over time. They may need experienced help as they require scraping away the gravel on a cool morning when the tar is brittle, cutting open, and covering with plastic cement or mastic and mesh. Any moisture trapped in a blister has to be dried before being repaired.

Roof coatings can be used to fix leaks and extend the life of all types of flat roofs by preventing degradation by the sun (ultra-violet radiation). A thickness of 30 dry mils is usually preferred and once it is fully cured, you will have a seamless, watertight membrane.

Infrared thermography is being used to take pictures of roofs at night to find trouble spots. When the roof is cooling, wet spots not visible to the naked eye, continue to emit heat. The infrared cameras read the heat that is trapped in sections of wet insulation.