Essential Parts of a Flat Roofing System

Flat Roofing Toronto

Every roof is constructed for the purpose of keeping out the rain, cold or heat. This requires a watertight roofing system and insulation to match. However, it seems very often that watertight roofing system are rarely the case. Flat roof leaks and moisture problems result from compromised roofing systems and can cause ongoing problems and headaches if not dealt with in a timely manner. The following is a list of essential elements that all flat roofing systems possess, essential areas that require extra attention to detail when performing a flat roof inspection, repair, or replacement.


Flashing DetailsFlashing defects are one of the leading causes of flat roof failure. Flashing is the material surrounding ventilation, pipes, and rooftop protrusions. It is also used as a transitional material, which means that it connects flat roofing membranes to components of the structure that are not considered part of the roof (i.e., parapet walls and chimneys).

Flashing defects usually present itself in the forms of cracks, broken seams and membrane separation. The most common areas that tend to spring leaks are around flashing areas of skylights, vent pipes, door sills, chimneys, railing posts, and sidings.


Ponding Water on Flat RoofThe most important quality of any flat roofing system is its ability to shed water. If water can not drain off a flat roof in a reasonable time, then the chances of ponding water increase which lend to the deterioration of a flat roofing system as a whole. Ponding water promotes the corrosion of metal components, such as fasteners and flashing, which will ultimately lead to leaks if the situation is not fixed.

When water is standing on a flat roof the following is possible:

  • Water leaking through a very small crack or seam
  • Deterioration and loss of bonding properties in tar, roofing cement and caulking products
  • Standing water will freeze over winter and cause problems such as trapped moisture
  • Debris will accumulate and cause moss and other plants to grow

Membrane Seam SeparationSeam breaks, holes and separations are a major concern when it comes to flat roofing. Whenever membranes are overlapped, their seams must be properly sealed to maximize waterproofing properties. The number of seams in your flat roofing system will depend on the area of the flat roof itself. Larger flat roofs require multiple sheets and many lengths of seams. The hot and cold temperature extremes experienced in Canada cause thermal shock (expansion and contraction) of the flat roofing membranes. This causes stretching, sagging or even separation at the seams, along the edges and around stacks, pipes and HVAC units.

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