Have a Flat Roof? You Could Benefit from a Tapered Roofing System

Having a flat roof can bring with it many challenges, including the challenge of creating an effective drainage system. Positive drainage is an absolute must for preventing ponded water and ensuring the longevity of your commercial roof. If you're considering a roof replacement or having a roof designed as part of new construction, you should consider a tapered roofing system and how it could benefit your commercial building.

A Tapered Roof Can Help With Drainage Issues

Snow melt, rainfall or equipment runoff that accumulates on a level roof deck (also known as "ponded water") can pose many issues for your existing commercial roofing system:

  • The inevitable water seepage can infiltrate the roof membrane, exposing the underlying insulation to water damage and loss of thermal efficiency. Water seepage can also severely compromise wooden roof structures.
  • The sheer weight of the ponded water can also cause deformation of the deck structure, compromising its structural integrity.
  • The freeze and thaw cycles brought on by below-freezing temperatures can allow ponded water to erode the roof membrane over time.
  • Standing water can also spur the growth of algae and other potentially harmful vegetation and provide mosquitos with a convenient place to breed and thrive, or clog drainage inlets to create additional ponding.

A tapered roofing system helps alleviate these issues by varying the height of the roof deck at various points. This creates several slopes which are used to channel rainwater towards drainage points along the roof structure.

The most common way these slopes are achieved is by using expanded polystyrene (EPS) insulation underneath the roof membrane. This material is commonly chosen for use on tapered roofing systems due to its cost-effectiveness and effective resistance against moisture. Other materials, including perlite and polyisocyanurate, can also be used as insulation paneling for tapered roofs.

Multiple Layout Design Options Can Provide Customization

Tapered roofs can be created using one of four common layout designs, each with their own unique advantages:

  • One-way slope—Considered the most basic layout design for a tapered roofing system, this layout features a single high point that slopes towards a gutter or building edge.
  • Two-way slope—Unlike a shed roof, a two-way slope features two separate slopes that point inward towards centrally-located drains or outwards towards a building edge or drain.
  • Three-way slope—Commonly used on smaller structures attached to larger buildings, this layout channels water to a small drainage area located to one side of the smaller structure.
  • Four-way slope—This layout uses four slopes to channel water towards the center of the structure or, when inverted, towards the outer edges of the building.

A Tapered Roof Can Provide Additional Advantages

In addition to effective rainwater, snowmelt and runoff drainage, tapered roofing systems also have other benefits for commercial building owners:

  • Tapered roofing systems can help commercial building owners ensure compliance with their local building codes as well as International Building Code requirements regarding positive drainage and roof slopes.
  • EPS panels for tapered roofing systems not only provide the slopes needed for a tapered roofing system to work effectively, but it also provides effective long-term thermal performance.
  • The overall performance of a tapered roofing system can help extend the longevity of your existing roof while lowering maintenance costs.
  • In addition to eliminating the overwhelming stress placed by ponding water, tapered roofing systems can also eliminate most concerns about ponding water and its effect on roofing system warranties; most warranties become void if ponding water is present for more than 48 hours.

Potential Drawbacks

There are a few downsides to consider when it comes to tapered roofing systems. For starters, installing such a system could prove expensive, leading many building owners to cut corners when it comes to engineering their roof systems. This can create design and installation compromises that could have several devastating long-term impacts, from reductions in overall drainage and insulation efficiency to code violations due to improper materials or installation techniques.

It's also important to choose a tapered roof layout that's appropriate for your roof's overall design and drainage needs. Otherwise, you could be faced with roof drains that are constantly overloaded. Slope steepness can also have a significant impact on drainage effectiveness. For example, an unnecessarily steep slope can also cause overloading.

To learn more about your options, contact a commercial roofing contractor. 


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