A Design & Materials Guide for Residential Flat Roofing Systems

TABLE OF CONTENTS:

1. Flat Roofs Are Everywhere–But What About Homes?
2. Why Are Flat Roofs Less Common For Houses?
3. Flat Roof Drain Types
4. It Looks Good
5. Flat Roof Space Is Usable Space
6. It Performs and Protects Well
7. Examining Flat Roof Myths–What Are The Drawbacks?
8. Parts Of A Flat Roof
9. Other Flat Roof Components
10. Warm vs. Cold Roofs
11. Flat Roof Designs For Houses
12. Built Up Roofing (BUR)
13. Single Ply Membranes
14. Thermoset (Synthetic Rubber)
15. Thermoplastic
16. Modified Bitumen (or Polymer Modified Bituminous Materials)
17. Liquid Applied Roofing
18. Spray On Roofing
19. Metal Roofing
20. Can you have a flat roof with shingles?
21. How to Make a Flat Roof Last
22. A crowning feature

Flat Roofs Are Everywhere – But What About Homes?

Flat roofs are a familiar sight throughout North America. Any typical mall, warehouse, apartment building or school usually features a flat roof. This roof type is easier to install over large surfaces and is the most common choice for commercial, industrial and institutional buildings.

From the start, you’ll likely have questions, including: is a flat roof the right choice for a home? Is it more expensive that a steeper pitched alternative? Is it harder to install? What about ongoing maintenance?

Whether choosing a roof design for a new home, or replacing/repairing a current flat roof, IKO Industries offers much of the information needed to make informed decisions for a lasting, sturdy cover for your investment. Explore the following guide to answer many of your flat roof-related questions:

Why Are Flat Roofs Less Common For Houses?

Also known as low slope roofs, flat roofs are less common in North American residential construction because the low slope of a flat roof has an increased tendency to collect water rather than shed, like its more steeply pitched alternative. This may make it less ideal for rainy or snowy climates.

Keep in mind, all flat roofs have a slope of between five and 15 degrees to allow water to flow into drain systems (such as eaves, drainage holes or outlets).

So, even though flat roofs are ideal for drier landscapes, in climates with heavy precipitation, a properly installed flat roof can be a fine choice for a homeowner – especially thanks to ever-improving waterproof materials and installation techniques.

It looks good

Flat roofs are an attractive aesthetic choice that give homes a unique form. If you love the landscape or cityscape around your home, a flat roof can help complement that without obscuring the view.

Unlike a steeply pitched roof, most of the square footage of a flat roof is available for use. This offers the option to add a unique application such as a rooftop patio, garden or green roof. Solar panels also are popular among homeowners and are much easier to install – and hide from view – on a flat roof.

Any of these applications will require certain design considerations (such as adding guardrails and other safety protections and/or using more heavy duty materials to handle roof traffic and weight). Special permits may be required from the local building authority, but these efforts may result in an entirely new feature to enjoy on your home.

It Performs And Protects Well

Flat roofs are a cost-effective option for homes – thanks to generations of use in commercial flat roof construction, modern materials and application techniques – as viable, protective and long-lasting alternatives to pitched roof counterparts.

By choosing the proper materials, hiring an experienced professional to build and install the flat roof, and committing to regular inspection and maintenance, homeowners may count on many years of reliable performance when selecting a flat roof solution.

Flat roofs are hard to replace

Some observers suggest it’s harder to replace a flat roof than a traditional pitched shingle roof because of the labor required to remove its layers (especially on older flat roofs). But now, flat roofs often are constructed with fewer layers because of improved waterproofing technology. This could mean flat roofs may not raise the same red flags they used to among prospective homeowners who may want to replace or remodel the roof once they move in.

Prone to water damage or leakage

Many of the potential problems a flat roof may attract – such as water pooling, leakage and resulting rot or damage – are due to poor installation or poor maintenance. Pay careful attention to the roof at the construction phase and throughout its lifecycle to help prevent these problems in the first place.

Parts Of A Flat Roof

To an untrained eye, one flat roof looks very much like another (especially from the ground level!) but, in fact, there are several different flat roof systems to choose from.

At the most basic level, a flat roof consists of three basic components:

• Weatherproofing
• Reinforcement
• Surfacing

Depending on the materials selected, these might be combined into a single product, but all these functions should still be there.

Other Flat Roof Components

Underneath the basics, flat roofs are usually constructed with a ceiling, nailed to joists which support a deck (usually wood in residential construction), a vapor barrier, insulation and a roof board. From there, the flat roof system you choose will determine the materials you apply.

Consider geography, budget and use for the roof to determine the best option.
 

Warm vs. Cold Roofs

A note to consider before construction: if insulation is installed below the flat roof deck this is called a “cold” roof. Generally, roofers discourage this method for cold climates because it can promote condensation and requires ventilating the roof, which may be difficult to do in small or tight spaces. On the other hand, a “warm” (or hot) roof is one where the insulation is installed above the deck. This situation is suited for cold weather climates. (See more details here).

Here is a diagram of a typical warm roof:

Roofing experts discourage the use of shingles on a flat roof. As few points of sealing as possible will reduce potential for leakage. This is why most flat roofs use large squares or single sheets of materials. In some cases, a homeowner may choose an option such as a Self-Adhering Membrane Residential Roof System, which offers the multi-layer protection of a membrane roof, with the traditional granule look of a shingled or built-up roof. These offer lasting protection against snow, ice and elements – and hold up well to foot traffic on low-slope roofs. They’re peel-and-stick cold application, and availability in single, double or triple layer reinforcement make them a popular choice for roofs with at least 1:12 slope.

How to Make a Flat Roof Last

It is incumbent upon the owner of a flat roof to regularly inspect and maintain the roof. This will make a significant difference in maintaining its integrity and longevity.

A basic inspection is suggested twice a year and after any major rain storms. We recommend consulting a roofing professional who is fully versed in rooftop safety techniques and precautions.

Flat Roof inspection checklist:

• In normal circumstances, wait until 48 hours after a rainfall to clean and inspect the roof. Any water should have evaporated by this time. If it hasn’t, that’s a sign of a problem with roof drain parts or the drainage system.
• To help see where any water might be collecting, clean any debris from the flat roof surface, including sweeping or gathering fallen leaves or branches and clearing any loose debris or gravel that may block drainage holes.

• Inspect flashings around the chimney and skylights. If the flashing material is cracked or rusty, you will want to have it repaired as soon as possible.
• Inspect the integrity of the top layer of protection (often a gravel or chipped mineral mixture) to ensure it hasn’t dispersed and left a bald patch. This is key to protecting the membrane underneath while also providing sun and fire protection. On a built-up roof, when gravel becomes sparse, the asphalt layer underneath can dry and crack under the sun. This could lead to “alligatoring,” which may eventually cause the layer to leak and fail.
• Check for any damage, puncturing, rips or wrinkling of the membranes. This might be difficult to see if a layer of chipped material or gravel is on top. Regardless of your flat roof design, take time to thoroughly check the surface for flaws.
• Any damage should be repaired immediately to return watertight protection to the roof and prevent further deterioration.
• If the top layer of gravel needs to be replaced or replenished, consult a roofing professional for proper application over the surface of the roofing material.

(Source: CAA Quebec.)

Education is the key to choosing a flat roof that fits your budget, style and geography.

Regardless of the type of roof selected, with an experienced contractor and a solid understanding of materials and maintenance, you’ll be well on your way to constructing a protective, lasting feature for your home.

Transitioning from a flat roof to a shingle roof requires special attention. Read more in our article on how to join a flat roof to a shingle roof.