Is a flat roof really flat?

From the Series: "Home Construction & Maintenance in Mexico"

By J. Brad Grieve, P.Eng. MBA Copyright© 2006
His Web Site

It is there above us, protecting us from the sun, the wind and the rain, however generally we are not worried about our roofs until we see water leaking through them.Typically, roofs here at Lake Chapala, where I live, are constructed using the bóveda construction technique where red bricks are arched between steel beams and the top or exterior is capped with a mixture of mortar and concrete. The basic roof structure is then typically covered with a flat tile and sometimes, if the roof is inclined, overlaid with a traditional rounded red tiles that overlap each other to cover the roof surface. The rounded tiles are generally decorative since the porous tiles alone will allow water to filter through. They do help the roof pitch the rainwater away from the roof surface below and, of course, provide solar protection to this waterproofed roof surface.

The key element of waterproofing a roof surface is the final layer at the top of the roof structure. Typically, this surface is painted with an impermeable paint or roof coating to prevent water from entering the roof structure. These paints are typically elastic and resistant to the small movements of the roof structure and will fill in any cracks in the roof surface.Some roof sealing products work with a fibrous cloth, which acts as a reinforcing medium for the sealant to help the roof sealant to resist the future formation of small cracks on the roof surface. Other roof sealant products have different recipes of ingredients, which will help the roof sealant resist deterioration caused by the ultraviolet and infrared rays of the sun. Also the various sealants will have different guarantees as to the durability of the product, claiming it will last anywhere from one to five years.

Some homes have flat roofs, which is a euphemism since they are typically not perfectly flat. If they were, the rainwater would not easily flow off the roof. Typically the roof surface is pitched towards a central roof drain or a drain along the edge of the roof. These types of roofs will also have a parapet of varying height around their perimeter. Usually, an interior corner filler where the interior of the parapet and roof meet, is installed to help water pitch from the parapet towards the centre of the roof rather than allowing it to settle into this same corner. A primary concern on these flat roofs is to prevent any “puddling” of water on the roof, which would allow the water to have time to find a small crack and enter the roof structure. Care is taken during construction to assure that roofs pitch towards any given drain on the roof. The quality of these details will determine the long-term ability of the roof to shed rainwater quickly and avoid roof leaks.

The best prevention of leaks. . .

Subscribe and read all the complete articles . . .

Author's Mexconnect Page:



Series Index

	Published monthly. ISSN #1028-9089 For MexConnect.Com LLC & Conexión México S.A. de C.V. © Mexico Connect 1996-2008