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What are the layers of a built-up roof?

Aug 25

BUR (built-up roofing) is the most popular type of roofing material for low-slope roofs. It comprises layers of bitumen (asphalt) with reinforcing fabric.  

The top layer is usually of stone or gravel. BUR is best for flat roofs, which have a low slope. It creates a continuous seal. On the other hand, roof shingles are not sealed and must have a steep roof slope to shed water efficiently.

Types of built-up roofing

Built-up roofing has been around for a while. Although the concept has been around for over 100 years, its design and installation have changed significantly. Modern products include a rigid insulation layer to improve energy efficiency.


Most built-up roofing comprises three components: bitumen material and ply sheets. Bitumen can either be heated to melt during installation or "cold," which acts more like an adhesive. You can spray or apply cold-built-up roofing with a squeegee. It doesn't emit toxic fumes and is not affected by the weather. It is also more durable than hot-built-up roofing.


Unique fabrics are used to reinforce the ply sheets in built-up roofing. Each layer is placed over hot or cold bitumen to bond the ply sheets to the roof. Most ply sheets come in a standard width of around 36 inches.


Depending on the application, the top layer comprises either small stones or finer aggregates. This top layer gives the roof a finished appearance and protects it from sun damage and falling debris. The roof is also safer to walk on. Ballasted roofing is a type of built-up roofing that uses large stones (1 1/2 to 2 1/2 inches) as the top layer. 


Ballasted roofing does not attach the lower layers to the roof structure. Instead, the heavy surface layer holds the roofing in place.

Built-Up Roofing Lasts a Lifetime

Built-up roofing can last between 15 and 30 years, depending on its materials and climate. However, some constructions can last as long as 40 years. Built-up roofing is more resilient in warm climates than in colder regions. 


Built-up roofing is comparable to composition (asphalt shingles), lasting between 15-30 years depending on the quality.


Some roofing materials last longer. Standing seam metal roofing, for example, has a lifespan of approximately 50 years. Slate roofing, however, can last up to 100 years.

The pros and cons of built-up roofing

Built-up roofs provide exceptional protection from the sun and water. They are fire-resistant, thanks to their aggregate top layer. Built-up roofing requires little maintenance and is therefore very affordable over its lifetime.


Built-up roofing is slow to install and can emit hazardous fumes except for cold bitumen. Installation costs can be pretty high, and certain types of roofing may be vulnerable to wind and water damage.

Basic Repairs to Built-Up Roofing

As with all roofing types, damaged roofing should be fixed as soon as possible to avoid further damage to the roofing and the materials beneath it. Many common problems can be fixed with simple repairs.

  • Repair joints and seams that are separated: Add cement to the joint. Make sure you hold it down to ensure it sticks to the substrate. You can also cut a large piece from the felt and place it on the joint. Then secure it with nails and then cover it with roofing cement. Spread some gravel on top of the cement, and let it dry.


  • Blisters You can quickly repair small blisters by using a knife. Let the area dry completely. Keep removing damp layers. Continue to reduce until the surface is dry. Take off the felts (plies) and place new felt on the area. Cover the asphalt with chippings. If chippings are unavailable, liquid-applied coatings can be applied to the area.


  • Repair built-up roofing undulations with layers. Before you do any repairs, ensure the substrate is in good shape.


  • Cracks Cracks should be easy to fix. Clean the area thoroughly of all debris and gravel. Install roofing felt and apply asphalt cement to the area. Have at least 4 inches of overlap to ensure the area is covered. Continue this process and add a final coat with asphalt cement. Add gravel to the cement.


If you are searching for a professional built-up roofing company in Toronto, then just go for Woodbridge Roofing Company as they have professional, experienced, and well-trained roofers.