Low Slope Roofing: Metal, Shingles

Low Slope Flat Roof & Metal Roof
Low Slope Flat Roof & Metal Roof

General Roofing Systems Canada installed low slope roofing systems throughout Canada. Roof installation; Calgary, Red Deer, Edmonton, Fort McMurray, Lloydminster, Saskatoon, Regina, Medicine Hat, Lethbridge, Canmore, Banff, Cranbrook, Kelowna, Vancouver, Whistler, Winnipeg, Toronto and points between. British Columbia. Alberta. Saskatchewan. Manitoba. Ontario.

When re-roofing low slope roofing systems it is important to be sure you are using the right material for the right roof slope, local building code, and roof material manufacturer specification.

Below we provide a guideline for low slope shingles, roof membranes of flat roofs, and metal roofing.

Low Slope Roofing Shingles

Serious consideration is required when you are considering re-roofing a sloped system that is less than a 4/12 pitch.

For roofing with a 3/12 pitch, regular shingles can usually be installed with a two-ply 15 lb. roofing felt paper as underlay.

The GRS specification for installing roofing shingles is to never use felt paper. Instead, we use Ice & Water protector on eaves, valleys, around chimney flashing, etc. and use synthetic roof underlay such as titanium. In this instance (with a 3/12 roof), I would consider seriously using only an Ice & Water membrane versus the two-ply roofing felt. This is especially important around chimney and skylight flashing, and any roof vents, valleys, and openings.

A roof that has a 2/12 – 3/12 slope is more tentative and the risk increases. Some shingle manufacturers such as IKO with the Cambridge shingle will put a 12-year warranty on low slope roofs. Malarkey shingles will honour a 30-year warranty.Malarkey Roofing

A roof that is 2/12 or less in slope should have a “flat roof” or traditional “low slope membrane” installed. We like to see any roof that is less than a 4/12 slope get a low slope membrane that is fully adhered, mechanically fastened, or ballasted.

Other information (PDF):

Malarkey Shingle Installation Guide – Includes Install Instruction for Low Slope 2/12 – 4/12

IKO Low Slope Shingle Bulletin – Installation of Asphalt Shingles on Low Sloped Roofs

IKO Roofing – Applying Asphalt Shingles on Low Slopes (covers 3 tab shingles, eave protection, etc)

IKO Shingles
IKO Shingles

Low Slope Roof Membranes (Flat Roofing)

Low slope membranes for flat roofing come in a few categories:

  1. Single-ply membranes in the form of EPDM (rubber), TPO (thermal plastic), or PVC (polyvinyl chloride). They are either fully adhered, mechanically fastened, or ballasted.
  2. Two-ply membrane, the primary choice being SBS modified bitumen that can be torched down or cold applied.
  3. Built-up roofing (BUR). Another way of describing multilayer roofing. An examples would be the traditional tar and gravel roofs, or flat-top tar roofs.
  4. New BUR. More recently, modern technologies have advanced the built-up roof so that they utilize environmentally friendly products and modifiers versus the tar or bitumen commonly used in tar roof systems. These newer versions are extremely tough, will outlast almost any other roof (in our opinion), and are VOC-free, making them sustainable offerings to low slope roof assemblies. The GRS liquid rubber built-up flat roof is an example of a modern system with 800% elasticity and environmentally-friendly synthetic fabric between layers, as opposed to employing the use of traditional tar felt paper.
  5. Spray Foam Roofing.
Low Slope Roof
Low Slope Roof

Low Slope Metal Roofing

Low slope metal roofing (steel, cladding, standing seam) has been used primarily in industrial and commercial settings for decades.

With residential roofing, metal is more typically found on steeper residential roofs. We install a lot of metal systems at mountains villages like Squanism, Canmore, Banff, Cranbrook, Fernie, etc. We also do a lot of residential metal roof shingle installations in cities like Vancouver, Edmonton, and Calgary. Residential metal panel and shingle installations are growing in popularity, but the greatest volume of metal work is on industrial facilities by far.

Low Slope Metal Roof
Low Slope Metal Roof

At issue with metal roofing is that no other form of roofing material expands or contracts as much as metal does. The seams between roof panels, the fasteners, roof openings at vents, chimneys, flashings, and skylights are expanding and contracting all the time. Ultimately, metal roofing leaks due to this expansion and contraction.

Also, condensation with metal or steel roof systems can be an extremely frustrating situation. Many roof leaks with homes or businesses are actually not leaky roofs. Instead, it is water coming through the ceiling as a result of condensation.

Dealing with the potential leak or condensation issues with metal roofing in advance of installing a new system is key.

We solve the problem of metal roof leaks with installing a premium roof membrane under the metal roof system, using a premium caulking tape at the seams, and installing hidden fasteners. If you really want to solve the potential of leaks or condensation in advance, torch an SBS modified membrane or spray liquid rubber in advance of putting the metal roof on.

For commercial roofing and industrial roofing that already has a metal roof on that is leaking, typically we will coat the roof with liquid rubber and it will be good for another 10 years or more. Trying to locate metal roof leaks and deal with them in an isolated way is not usually a good investment of time. Click here to visit the roof coating section of our website.

Until next time,

The Team at GRS


General Roofing Systems Canada (GRS)
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