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What is a Low-Slope/Flat Roof System?

A roof that is nearly flat or slightly pitched is called a flat roof or low slope roof – No roof should be dead flat because it must have at least a slight slope to drain.

Low-slope & steep-slope terms describe roof slope, the slant of a roof.

  • A low-slope roof is one that has a slope of less than 3-in-12.
  • This means that for every horizontal foot, the roof level goes up less than 3 inches vertically.

A steep-slope roof (typically a shingle roof) depends upon gravity to cause water to flow in one general direction so it can “shed” the water over the breaks & fasteners in the shingles until it flows to the edge.  A low-sloped roof or flat roof can’t depend upon the water to flow in any particular direction so it must form a watertight, monolithic membrane that stays watertight all the way to the drains or edge.

Modern low-slope roof or flat roofs tend to use a continuous membrane covering which can better resist pools of standing water.  These membranes are applied as continuous sheets, bonded together with heat-welding or adhesives.  A more expensive low-slope or flat roof option  include sealed metal roofs using copper or tin. These are soldered interlocking systems of metal panels.

Traditionally, low-slope or flat roofs would use a built-up (“tar and gravel”) roof, but today this traditional type of roofing suffers from performance, cost & environmental concerns requiring better value solutions.

Besides performance in wind, freeze-thaw cycles & UV radiation from the sun, a low-slope/flat roof must also withstand expansion & contraction & remain 100% watertight.  This requires well-engineered attachment, seaming & weathering characteristics to meet these performance demands.

Types of Low Slope/Flat Roof Systems

Built-Up Roof

  • Multiple layers of roofing felt (often called “tar paper”) are mopped in place with hot asphalt or coal-tar pitch (bitumen) to “build up” a strong watertight membrane.
  • Membrane is then surfaced with a coating or gravel imbedded in a pour-coat of more hot bitumen.
  • This type of roof has a long history of performance.
  • This roof system is not known as a flexible membrane, may have some environmental concerns & at times cost-prohibitive due to crude oil prices.

Flat Roof System

 

 

 

 

 

 

 

Modified Bitumen

  • Asphalt is chemically modified to allow flexibility & constructed over a heavy polyester or fiberglass mat for strength.
  • Proven track record of performance
  • Superior waterproofing characteristics
  • Broad range of application methods
  • Wide choice of top-surfacing, including “Cool Roofing” options
  • With insulation, provides an even better-performing building component
  • High tensile-strength
  • Available as part of a fire, wind, and/or hail rated roofing system
  • Competitive life-cycle cost
  • Long-term warranties are available with many MB systems

Flat Roof System

 

 

 

 

 

Flat Roof System

 

 

 

 

 

 

 

 

 

 

Single Ply

  • Entire membrane roofs are manufactured in factory-controlled conditions that can then be installed as a single ply.
  • Thermoplastic membrane roofs are heat welded single-ply membranes.
  • Usually white which makes them very heat-reflective and highly-scored Energy Star products.
  • Roof seams are very durable since they are welded together.
  • These roofs are generally more environmentally friendly in their manufacture, transportation, installation, performance & disposal.
  • Thermoplastics are the fastest growing type of low-sloped roofing.
  • Proven track record of performance
  • Broad range of application methods
  • Available as part of a “Class A” fire-rated roofing system
  • With insulation, provides an even better-performing building component
  • Wide choice of top-coatings, including “Cool Roofing” options
  • Superior waterproofing characteristics
  • High tensile-strength
  • Competitive life-cycle cost

 

 

Flat Roof System

 

 

 

 

 

Flat Roof System

 

 

 

 

 

 

No matter what the problem is with your low-slope roof or flat roof, Best Roofing  will give you good advice on the best solution for your roofing needs.

 

3 Responses

  1. Hey Klowe, On a similar note,, I have a two story building with a flat roof. Our neighbouring building is 9 story high. The tenants of 9 story building has been throwing bricks, and other garbage on my flat roof. In doing so so they have damaged my flat roof, that is now leaking. Smashed skylights, and threw all sort of garbage, even a dead mice. I need to get protected from these low life creatures. What and how I can erect a protecting sloped cover, so that the thrown items slide back to their property. All suggestions, smilar or alternatives will be appreciated. Don't tell me talk to the building management, or call police. All that did no help. Kindest Regards
  2. Thanks for the information! I didn't know that there were so many benefits to using a low slope roof before reading this article. I've always thought that roofs with a higher slope were better because water seems to slide down them easier. It's interesting that they can remain watertight, and resist wind, and UV sun radiation. I suppose another perk to having a low slope roof on your house is that they would be easier to repair since they seem to have less of a safety hazard once on top of the roof.
  3. thanks for that pic with roof layers

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