Advantages of Flat and low-slope roofing
- Thermal advantages – They can help keep the interior warmer by absorbing sunlight at a higher rate than slated roofs.
- Accessibility – They are also more accessible, allowing for easier inspection processes.
- Economical – Flat roofing, for smaller areas, is generally considered to be a more affordable option at the point of construction and involves considerably less materials and labor than a pitched roof, and requires less support from the foundation walls.
- Easy replacement – Full replacement of the roof, when the time comes, can usually be completed in a single day.
- Wind resistance – The flat and symmetric surface of the flat roof offers less resistance to the wind as compared to the angled roofing systems. Wind resistance matters in the case of storms that have the potential to replace the shingles and tiles that are placed on the angled roof structure.
- Ideal HVAC location – Flat roofs help accommodate equipment like AC vents and exhausts, the flat roofs are best. The plain surface offers the symmetry to stabilize heavy equipment even when they are working. And A/C systems are always more efficient when the cold air enters from above.
- Energy Conservation – A flat roof system is ideal for placing solar panels for energy conservation.
Disadvantages of Flat and low-slope roofing
- Standing Water – This is one of the primary causes of flat roof leakages. Water will start to damage your roof material if it does not drain or evaporate within 72 hours. That means regular inspection is particularly important during winter and spring months. This problem is usually caused when there is insufficient drainage or the roof itself is just too flat. Despite the name, there should always be a small amount of slope for effective drainage. Snow build-up can also be problematic as snow and ice can block drains and gutters.
- Blistering – Even small amounts of trapped moisture can result in your flat roof membrane detaching from the layer below and cause roof ‘blisters’. This is the most common roofing problem and it tends to get worse during the day when the heat of the sun causes the trapped moisture to expand. When blistering occurs it is vital to identify the source of the moisture.
- Thermal movement – Repeated cycles of heating and cooling cause flat roof materials to expand and contract. Materials must be equipped to deal with these movements without cracking under the pressure to avoid water penetration.
- Exposed layers – Taking all a Canadian year, weather wise, has to throw at you isn’t easy. Throw continual roof traffic (accessibility has its downsides) into the mix and it’s only natural that, over time, your roofs protective layers will suffer a bit of wear and tear.
- Flashing defects – Given the importance of drainage on a flat roof, it’s vital to regularly inspect the condition of the flashing. This is used to prevent water from penetrating a junction and problems can occur when it has been poorly installed or damaged and bent over time. Flashing damage can also be caused by fungus growth from moisture build in problem areas pushing away flashing.
There should be no such thing as a “Flat Roof”
It’s crucial to get a slope of at least a quarter-inch per foot in a flat roof, although many roofers past and present have thought otherwise. Slope-free roofs pond and become breeding grounds for mosquitoes, mold and other less-than-desirable substances.
But ponding water isn’t only a problem for what it attracts. At 5.5 pounds per square foot per inch, water is heavy. Water ponding across a 400-square-foot roof, one inch deep, means there is, literally, a ton of weight on top of your building.
Most manufacturers require that, for the warranty on their products to be valid, the water be drained or surfaces pitched so the roofs don’t pond the water.
What if you already have a problem?
If you have a flat roof with no slope, and ponding or leaking developing, it may be required to tear everything back down to the deck, and put the roof on the way it should have been.
Completely replacing such a roof can require contractors to remove the old roof system down to the structural deck, then replace bad decking and install wood blocking at the perimeter.
The wood blocking should be equal to the thickness of insulation on three sides, and a little less at the drip edge to allow for better drainage.
Next comes thermal insulation, a cover board, foam and roof board – followed by roof deck screws and plates. Finally, a fully adhered, liquid rubber membrane provides a crucial layer of protection without seams or overlap.