Leaking Flat Roofs
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Old flat roofs
Flat roofs are renowned for their problems. On older roofs this tends to be due to deterioration of the actual roofing felt. This can be caused by age, or sometimes the window cleaner as they walk on it to clean the adjacent windows, or repairs, or poor flashing detail.
Poor flashing on flat roof
Poorly detailed flashing
Just a bit more about flashings. Traditionally, they were carried out in lead and we believe lead is the only material that they can be carried out successfully with for the long term, as the characteristics of lead are so good, allowing both thermal expansion and contraction. If, for example, a felt is used instead it becomes brittle and will crack or blister over the years, or simply come away. Having said that, the lead flashing should be put in place well. We see many newer properties with lead flashings that are literally coming away. This is because they were fitted as opposed to having a tradesperson skilfully install them.
Flat roofs being flat
There is also the age old problem of the flat roof being flat, rather than having a fall on it of approximately 12 to 15 degrees to discharge the water off the roof, and instead the roof is more like an outdoor swimming pool!
Modern flat roofs
Technology has changed and improved flat roofs beyond all recognition. Modern high performance roofing materials tend to last for decades. There are traditional roofs, with elastomeric high performance felt finish or a mineral felt finish. Generally good roofing wouldn't have anything but lead flashings and both falls and insulation, as well as ventilation, have been added to the modern roof.
The inverted roof
Also, inverted, or upside down flat roof, has perfected. This is a roof where is the insulation is above the roof membrane and is normally protected by pebbles or pavers, which are like paving slabs but thinner and a bit lighter.
Single membrane flat roof
This is a plastic or rubber lining; we are not sure of the exact technical term. It is very like a swimming pool or fish pond lining, although we are sure manufacturers would argue that it is technically very different, but this is what it looks like to the lay person. It is very common on fast food outlets as a flat roof material. It has massive benefits in that it is very flexible and that it is glued together in one layer. However, it can be punctured, our experience was where the air conditioning maintenance people strayed from the walkways that we had put on the roof and punctured it, for want of a term.
All flat roofs can leak
In our experience over many years, we have found that flat roofs leak, whether it is down to bad workmanship from the tradesperson, or poor detailing from the architect, or lack of maintenance. The big problem is finding where they leak. For many years it has been a best guess, sometimes it is very obvious as to where the leaks are and other times it's not. For example, the leak could actually be getting in via the parapet wall, rather than the roof itself.
Parapet Walls Defined
These walls are usually above the roof line and often sit on the boundary of the property. Due to their position they are relatively exposed and suffer from deterioration due to the elements.
It is a mystery where the roof leak is coming from
It is very common for the roof leak to be coming in on one area, but actually be coming visible in a different area, often tracking along electric cables or similar points until it is finally out in the open, so to speak.
Infra-red thermal cameras allow the experienced building surveyor to establish exactly where there are leaks, looking at the different thermal conductivity patterns. However, an infra-red camera isn't a magic instrument, as without being able to interpret the readings lots of wrong assumptions can be made.
A flat, flat roof
A flat roof leak
Checking a roof leak with a traditional
Protometer, the red in there
is our hand
Independent building surveyors
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Independent commercial property advice
If you have a commercial property, be it leasehold or freehold, then you may wish to look at our Dilapidations Website at www.DilapsHelp.com and for Disputes go to our Disputes Help site www.DisputesHelp.com .
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If you would like further advice on roofs, roof problems, roof repairs, roof materials , commercial surveys, building surveys, structural reports, engineers reports, specific defects report, structural surveys, home buyers reports or any other property matters then please phone 0800 298 5424 for a friendly chat.