No More Gutters
After forty years working in the building industry, I should not be surprised by the ineptitude or lack of thought given to roofing. I get to examine many buildings because of their failure to keep out the rain. This has led me to harbour a fairly prejudicial attitude towards sealants (their abuse) and also led me to consider roofing from a performance perspective.
Many factors contribute to water penetration into buildings during inclement weather. In these notes I only consider the roof design, materials used and the methods of collection and discharge of stormwater.
The traditional cottage roof is designed to shed stormwater to its perimeter, collecting in valley and eaves gutters which generally run around the entire building discharging via downpipes to water tanks or a subsoil drainage system. Eaves gutters are a fragile building element requiring ongoing maintenance. As evident from the photograph above, valley gutters and eaves gutters do not work well with each other in areas where there are trees as the eaves gutters tend to promote the accumulation of leaf matter at the bottom end of the valley gutter even when leaf guards are installed.
Despite the familiar form of the hip and ridge pitched roof, it is not designed with the best performance requirements of our local (Australian) environment. Rainwater is a commodity that can be stored and used for a building's grey-water services. We do not have to contend with snow so why shed stormwater to the roofs perimeter. This is only creating a need to install a complex guttering systems.
In environments with extreme temperature variation, roof materials need to be selected that can withstand such change and accommodate expansion/contraction. In areas with lots of trees, designers need to consider how debris might accumulate on the roof and how this will effect the drainage system. There are a multitude of additional factors to consider. The effect of high winds, insulation, maintenance access, roof mounted equipment, the labour and cost burden of ongoing maintenance are but a few.
Larger buildings of four stories or more generally have one of three types of roofs:
- Tile roof.
- Concrete and applied membrane.
- Metal roof ( zincalume, copper etc.)
Tile roofs are usually sarked as heat insulation and to stop water penetration into the roof space periods of high winds. Because of the height of multi-storey buildings, tile roofs are difficult to maintain. Perimeter gutters are also an ongoing maintenance issue.
Concrete roofs with applied membranes on the other hand are not effected by high winds however they also have ongoing maintenance issues usually due to the ease of access which is unique to most flat concrete roofs, Membranes are often damaged by workmen servicing roof mounted equipment . They also offer no insulation against heat if they are not covered with insulating material.
The main disadvantages with torch-on membranes or-any sheet membrane for that matter-is the difficulty when they are used over very large areas of concrete. Once water gets under the membrane it can travel for a considerable distance making finding the damage or fault difficult to identify and rectify when they occur and when it is found and fixed there is no guarantee that there isn't additional damage or failures.
The advantage of membrane roofing is they can be used to solve difficult roof detailing.
Metal roofs are often the preferred roof for cost reasons. They can be more susceptible to wind damage than other types of roofs. Metal roofs can also have the most ineffective or inappropriate detailing. Metal roofs have a high degree of expansion and contraction.
The roof can be a number of smaller sections divided by box gutters. I have discovered that these gutters often rust out or suffer expansion and contraction damage or clog up with debris. Inevitably they fail in some way and flood the ceiling space.
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