Low Pitch Roof

This post discusses low pitch roof. Roof pitch refers to the vertical rise divided by the horizontal span, or what is commonly known as the slope of the roof.


Usually, the pitch is expressed as a ratio of the number of inches of incline for every 12 inches of span.

In this manner, it is a common occurrence to find the pitch expressed as 3:12, 5:12, and 4:12, amongst other expressions.

Great importance is usually attached to the roof pitch during construction, since it affects various components of, not just the roof, but the entire building. Understanding the low slope roof definition is crucial to a low slope roofing project.

Whether you are looking to put up low slope metal roofing or steep slope asphalt shingles, the pitch will determine several considerations, such as the roofing material used, the proportions of the building to be covered by the roof, the walkability of the roof, and usually, the overall architectural design of the whole structure.

Plenty of low pitch roof options are available. This is why roof pitch determination is preferred at the onset of the construction project, not when it is time to set up the roof.


There are two types of roofing systems – Low slope roofing systems and steep slope roofing systems. Steep slope roofing systems are also known as residential roofing systems, and in their classification, they are roofs with a slope of 21:12 and higher.

This roofing system is residential roofing system, simply because it is usually adopted in constructing the residential units. It is common to find it as the predominant system in most homes, apartment complexes, duplexes etc.

One notable thing about steep slope roofs is they are visually appealing, adding aesthetics to the residential units. For instance, the roof for most residential buildings usually constitute up to 40% in volume of the external visual appearance of the house.

Steep slope roofing is also known to last much longer than low slope roof systems, like low slope metal roofing.

These roofs are efficient, because they redirect water more efficiently, and they have less exposure to the harmful UV rays of the sun, so they can last longer than flat roofs.


So what is a low slope roof? Low slope roofs are also known as commercial roofs. This is because they are the predominant roof type used in commercial buildings, such as industrial parks, shopping malls, office complexes, warehouses etc.

A low slope roof design typically has a pitch of between 2:12 and 4:12.

Just like any other roofing system, low slope roof designs will have several effects on the overall construction of the building, including the interior volume, the style, and design of the house, the drainage system, and the material used for covering.


According to low slope roof definitions, low slope roofing can be classified into five main categories. It is out of these categories that other designs, such as low pitched gable roofs or low slope metal roofs, are derived. They include the following:

  • Built up roof membranes (BUR) – This system is formed by creating a finished membrane of reinforcing fabric and alternating layers of bitumen. When applied directly to insulation or roof decks, they are considered fully adhered with industry standards.
  • Single Ply Membranes low pitch roofs – These comprise thermoplastic membranes and thermoset membranes.
  • Polymer modified bitumen sheet membrane – These systems use multiple layers of reinforced fabrics and are normally installed as 2 ply systems in most applications.
  • Metal panel roof systems for low pitch application – This system uses a structural metal panel for low pitched metal roofs, due to their ability to form a formidable barrier for water. This system can also be used for the steep roofs.
  • Spray polyurethane foam based roof systems – They are also known as SPF roof systems, and they are constructed by spraying and mixing two types of liquids that act like the base of a roof system that has been adhered.


Usually, low slope roof systems, including low pitched roof extensions, have three principal components. The components are as follows:

They have water proofing layers – Most of these roofing systems will have one or more water proofing layers. This is, by far, one of the most important components, since it is crucial in keeping water from entering the roof system, adding to the longevity of the roof.

Surfacing – This offers protection to the reinforcement and the weather proofing of the system. It will ensure the roof is adequately shielded from the harmful rays of the sun and the rain water. Sometimes, the surfacing will provide additional benefits, such as fire resistance, hail resistance, increase the solar reflectivity of the roof, and enhance roof traffic.

Roof reinforcement – Due to the challenges that low pitch roof systems face, low pitch roof design should have necessary reinforcement; hence, this is one of the basic components of this kind of roof. The reinforcement adds strength, makes the roof system more resistant, and increases the dimensional stability of the membranes.

Low Pitch Roof

Since there are different low slope roofing options, it is important to understand that some roof membranes will perform better than others.

This will affect the quality, cost, the installation styles, the design, and other components of the roofing systems.

With the assistance of experienced roofing technicians, the right system should be decided upon, without compromising the aesthetics and the integrity of the structure.


Low slope roofing options have some inherent problems, which will always occur at some point in the roof’s life.

The occurrence of most of these problems can, however, be mitigated during design and installation, but there are no guarantees they will not occur, once the roof system has been in place after several years.

Here are some of the common problems for low slope roofing systems you need to watch out for:

Wind damage

Wind damage is one of the greatest risks that threaten many low pitch roof definitions. Strong winds have the potential of opening the seams and, eventually, causing the roof to blow off.

Sometimes, the force of the wind can be so strong that it will wreck the single ply systems, even if they are perfectly installed. Though the menace of winds can be attributed to installation or maintenance issues, it can also result from using cold adhesives not allowed to cure properly on the roof system, leading to them being compromised.

To curb this issue, the contractor should come up with a specific roofing system that will factor in the wind strength in the region to minimize the damaging effects of wind on the roof.

Water Leaks

Water leak is the least welcome and the most insidious problem in low slope roof designs. Water can have devastating effects, when it gains access to the building via the roof.

It has the potential of damaging the inventory, amongst other contents of the building, leading to massive losses to the business.

Roof leaks can arise when laps are installed against the natural flow of rainwater, adhesion failure, or incorrect flashing done at the seams. The leak problem will increase if there are physical damages on the roof.

Leaks can, however, be detected and corrected through regular roof inspection and maintenance.

Membrane normalization

There are certain types of membranes in low slope roof designs that may be subject to contraction or normalization. This is especially rampant with the single ply systems mechanically attached.

To reduce the risk of normalization after roof installation, building owners must have their roofs inspected regularly and ensure there is no additional tightening or induced loads on the roof sections.

Normalization will first be noticed at the flashings, and if this is ignored, then it could lead to deterioration along the perimeter of the membrane.

Blisters and Ridges

Blisters and ridges are a common tendency in Build Up Roof systems, when installed by inexperienced contractors.

Though small blisters may not need a lot of attention, the appearance of large blisters under the lap areas should never be ignored.

Blisters will occur if the substrate was wet during installation or due to improper torching of the membrane or when cold bitumen was applied to the system.

Blisters will not leak if they don’t break, but the roof should be inspected when the blisters are spotted, and a lasting preventive measure should be taken.

Lack of regular maintenance

Whether it is a steep slope roofing system or a low pitch roof design, like the lowest roof pitch for shingles, absence of regular maintenance might lead to the integrity of the roof being compromised.

Inspection and maintenance are important in detecting problems on the roof systems and coming up with preventive measures before serious damage occurs. A qualified roof inspector should inspect the roof at least two times a year and provide detailed and comprehensive reports on the status of the roof.

In this manner, all the problems will be discovered before they become serious, and this will save you from spending lots of money on maintenance and repairs that could have been prevented.

Founder & Editor

Hi, I’m Jim. I was a roofing constructor for 20 years, before deciding to start myrooff.com and gather the best content about roofing. I love woodworking and construction and it was only natural for me to start this passion project of mine. Thank you for visitng.