A Comparison of Two Roofing Systems

Now that we’ve defined the two types of roofing systems – low-slope and steep-slope – let’s review the advantages and disadvantages of each.

What are the major differences between a low-slope roof and a steep-slope roof?

A low-slope roof is one whose slope is less than 3:12 or 25% while a steep-slope roof is a roof with a pitch of 25% or greater.

What are the advantages of a steep-slope roof?

  • It drains itself quickly of water, giving wind and gravity little opportunity to push or pull water through the roofing material.
  • Steep-slope roofs can be covered with roofing materials that can be fabricated and applied in small, overlapping units.
  • 50 percent longer lifespan than other roofing installation methods.
  • Lower chance of debris buildup, mold and mildew proliferation.

 What are the advantages of a low-slope roof?

  • A low-slope roof can cover a building of any horizontal dimension, whereas a steep roof becomes uneconomically tall when used on a very broad building.
  • A building with a low-slope roof has a much simpler geometry that is often much less expensive to construct.
  • Low-slope roofs, when appropriately detailed, can serve as balconies, decks, patios, and even landscaped parks.
  • Requires less material to build.
  • Less time to roll out and seal than installing individual shingles.
  • Allows for easy maintenance since it’s a flat surface.
  • Limits extra air and makes structure easier to keep comfortable.

What are the disadvantages of a steep-slope roof?

Cannot cover a building of any horizontal dimension because it becomes too tall on a broad building.

What are the disadvantages of a low-slope roof?

  • Water drains relatively slowly from the surfaces.
  • Small errors in design or construction can cause them to trap puddles of standing water.
  • Slight structural movements can tear the membrane that keeps the water out of the building.
  •  Water vapor pressure from within the building can blister and rupture the membrane.

Whether you’re in need of roofing repair, service, maintenance or installation, Jottan has been doing it right for over 35 years. Visit us at jottan.com or call 800-364-4234.


Roofing Systems Defined – Part 2

Part 2 of Roofing Systems Defined will focus on the six classifications of steep-slope roofing. (Source: National Roofing Contractors Association). Steep-slope roofing includes watershedding types of roof coverings installed on slopes exceeding 3:12 (14 degrees).

Asphalt shingles are composed of a base material that provides support for the weather-resistant components and gives a shingle its strength; asphalt and fillers; and surfacing material that provides protection from impact and UV degradation and improves fire resistance.

The most common form of asphalt shingles are strip shingles also known as 3-tab strip shingles so called because they frequently have three tabs that are exposed along the length of the shingle for visual effect.

Laminated strip shingles, or architectural shingles, are produced in two or more layers providing a three dimensional appearance.

Both types of asphalt shingles contain a strip of factory applied adhesive that is activated by the sun’s heat after installation and seals each shingle to the next course. The seal strip also provides much of a shingle’s resistance to wind uplift.

Clay tiles are produced by baking molded clay into tile. Tiles may be glazed and also may have surface texture treatments applied. Installation methods depend on the nature of the tile being installed, that is, whether it is two pieces, one piece, interlocking or flat.

Concrete tiles are made of portland cement, sand and water in varying proportions. They generally have lugs on their undersides for anchoring to batten strips. There are additional waterlocks or interlocking ribs on the longitudinal edges that impede movement and prevent water infiltration.

Metal roof systems consist of three general categories used for steep-slope roofing applications: architectural metal panel, structural metal panel and metal shingle/shingle panels.

Generally, architectural metal panel roof systems are water shedding and are designed to be used on steep slopes that will shed water rapidly over the metal panel’s surface. The seams typically are not watertight. Solid roof sheathing, or decking, is required for architectural metal panel roof systems, and underlayment is recommended.

Most structural metal panel roof systems are designed to resist the passage of water at laps and other joints, as sealant or anti-capillary designs can be used in the seams. Structural metal panel roof systems possess strength characteristics that allow them to span supporting members.

Metal shingles and metal shingle panels should be installed over continuous or closely spaced wood decking, furring strips, or metal or wood purlins using a batten or counter-batten system. These roof coverings typically are considered to be watershedding roof systems, so the roof slope should be 3:12 (14 degrees) or greater.

Roofing slate is a dense, durable, naturally occurring material that is essentially nonabsorbent. Roofing slate commonly is split so the length of the slate runs in the direction of the grain. Some slate splits to a smooth, practically even surface, while others yield a surface that is rough and uneven. 

Wood shakes and wood shingles are manufactured from western red cedar, cypress, pine and redwood trees. Shakes are split from logs and reshaped by manufacturers for commercial use. Cedar shakes and cedar shingles are available pressure treated with fire retardants and chemical preservatives for increased fire resistance and to prevent premature rot and decay in some climates.

Pine shakes are made from southern yellow pine and are taper sawn. They also are available pressure treated with preservatives to protect against decay and insects. Interlayment felts are required for pine shakes.

“Synthetic” as it pertains to steep-slope roofing materials refers to manufactured products that replicate asphalt shingles, concrete tile, clay tile, metal panels, slate, wood shakes and wood shingles. Synthetic roof coverings contain recycled plastic and/or rubber as a key ingredient.

There are both benefits and drawbacks to synthetic roof coverings. For example, while the reduction in weight of synthetic slate allows it to be installed over conventional roof decks not enough is known about how synthetic roof coverings weather or if they becomes brittle over time. Caution also needs to be taken when considering synthetic roof coverings to ensure that they are recognized within building codes.

The above is provided as a brief synopsis of the six classifications of steep-slope roofing. For more detailed information or to discuss which roofing system best fits your needs, contact Jottan at 800-364-4234.