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Revised January 12, 2014

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Types of Roofing

 

Types of Roofing is not to be confused with types of roofing materials.  Types of Roofing defines what types of roofing materials can be used and where.  There are basically two main types of roofing defined by the pitch or slope of the roof:  Steep-Sloped Roofing and Low Sloped or Flat Roofing.  Roofing materials are designed for one or the other.

Flat Roofing is also referred to as Low-Sloped Roofing by many in the roofing industry.  This can be confusing because the term Low-Sloped Roofing can mean additional installation procedures and materials are needed when installing Steep-Sloped Roofing materials on roofs with lower pitches. 

Sometimes Steep-Sloped and Flat roofing materials are expressed as Residential and Commercial roofing materials.  But Steep-Sloped as well as Flat Roofing materials are installed on both residential and commercial roofs. 

Residential actually describes types of structures such as single family homes, townhomes, duplexes, etc. as constructed using the International Residential Code (IRC).  Commercial describes types of structures such as apartment buildings, condos, office buildings, warehouses, shopping malls, etc. as constructed using the International Building Code (IBC). 

Many in the roofing industry use the term Residential Roofing Products to describe Steep-Sloped Roofing Materials.  The term generally means roofing materials that are designed to shed water rapidly with no standing water and are individually fastened to a Steep-Sloped Roof with fasteners.  A Roofing Contractor who describes himself as a Residential Roofing Company means he installs roofs mainly on residential structures and specializes in the installation of roofing materials designed for Steep-Sloped Roofing.

Commercial Roofing Products are also used by many to describe Flat Roofing Materials. The term generally means roofing materials that are designed to withstand the slow drainage of water without developing leaks.  Commercial roofing products are generally rolled roofing membranes or sheets that are adhered to a roof by means of tar, asphalt, glue, heat welded, etc. and have seams that are also completely sealed together.  A Roofing Contractor who describes himself as a Commercial Roofing Company means he installs roofs mainly on commercial structures and specializes in the installation of roofing materials designed for Flat Roofing.

As you can see, this all can be confusing to both consumers and roofers alike.  Below we try to clarify and define some roofing terms used when trying to describe types of roofing and/or roofing materials. 

Again, types of Roofing is not to be confused with types of roofing materials.  Types of Roofing defines what types of roofing materials can be used and where.  There are basically two main types of roofing defined by the pitch or slope of the roof:  Steep-Sloped Roofing and Flat Roofing.  Roofing materials are designed for one or the other.

There are three different types of roofing within Steep-Sloped Roofing: Low-Sloped Roofing, High-Sloped Roofing and Mansard Roofing that are also defined by the pitch or slope of the roof.  

The Type of Roofing is defined by the pitch of the roof and the type of materials that are commonly used for that pitch range.  The slope or pitch of a roof is defined as the ratio of the rise to the run of the rafters.  For an example a 4" rise in a 12" run is expressed as 4:12.

Roofing Pitch Guide

 

(1) Flat Roofing generally refers to roofs with slopes less than 1:12.  However many, including myself, consider anything under a 2:12 pitch as Flat Roofing since only rolled or sheet roofing products and some Standing Seam Metal Roofing Materials are permitted on this low of a pitched roof.

(2) Steep-Sloped Roofing generally refers to roofs having slopes of 1:12 and over.  There are three sub categories of Steep-Sloped Roofing:

Do not work on roofs without the proper rubber soled shoes and safety harness.  Do not even think about working on slopes with more than a 5:12 pitch unless you have experience and feel comfortable walking where your footing is less than sure.  At 5:12 and more, sliding or slipping on a roof becomes imminent and the danger of falling greatly increases.  It is better to leave the installation of roofing to the professional roofers who have the experience and the equipment to walk around on steeper sloped roofs.

The steeper the roof is the more time it takes to install roofing materials.  Installing roofing materials on even a 7:12 or 8:12 roof is far slower than on a 4:12 or 5:12 pitched roof.  The steeper a roof is, the slower the installation is, and can even come to a crawl on very steep roofs.

Common roofing materials used for Flat Roofing and for Steep-Sloped Roofing and the minimum pitch or slope generally required for proper installation are:

Flat Roofing Materials Minimum Pitch
Tar and Gravel 1/4:12
Single Ply Modified Bitumen 1/4:12
EPDM 1/4:12
PVC 1/4:12
TPO 1/4:12

 

Steep-Sloped Roofing Materials Minimum Pitch
Asphalt Shingles standard underlayment 4:12
Asphalt Shingles 2 Plies underlayment lapped 19" 2:12
Wood Shakes & Shingles 4:12
Clay Tile 3:12 & some 5:12
Concrete Tile 3:12
Metal Roofing Shingles 3:12
Metal Panels:
Lapped without lap sealant
Lapped with lap sealant
Standing Seam

3:12
1/2:12
1/4:12
Alternative Roofing Products 4:12 for most

We will be focusing on Steep-Sloped Roofing throughout this website.  Information, articles, and discussions about Flat Roofing and their materials, membranes, products, and installations will be included but limited.