What is a Built-Up Roof?

A built-up roof, or BUR, is a roofing system for flat or low-pitched roofs. BURs combine several layers of material built on top of each other.

These roofs have been around for over 100 years, although the material contractors use today differs from what you’d see a century ago. And since you can’t use traditional asphalt shingles on flat roofs, BURs are among the top roofing choices.

Built-Up Roof

Here’s what you should know if you’re considering a built-up roof for your project.

What is Built-Up Roofing Made Of?

Built-Up Roofing Made OfView in gallery

At a basic level, built-up roofs have at least three materials: ply sheets, layers of bitumen or asphalt, and a surfacing material like stone or gravel. 

A modern BUR’s base is thick roof insulation with a cover board. On top of the board are alternating layers of bitumen and ply sheets, such as roof felt. The bitumen can be “cold,” which means an adhesive application, or “hot” applied with a torch. The top layer is a surface material such as small stones or gravel. 

Some BURs, especially in commercial spaces, have a UV layer under the aggregate for heat resistance.

Are Built-Up Roofs Good?

Built-up roofs are one of the top choices for flat and low-sloped buildings. The insulation sheets increase a home or building’s energy efficiency, while the aggregate at the top of the roof is fire resistant. 

The alternating layers provide a tight seal that protects against water leaks. 

How Long Do Built-Up Roofs Last?

The average built-up roof will last from 15-30 years, but if well maintained and in an area with a mild climate, it can last for up to 40 years. 

Factors that decrease the time a BUR will last include cold and snowy climates, air conditioning units that sit on top of the roof, and pooling water. To maintain a BUR roof and increase longevity, ensure proper drainage and deal with pooling water as quickly as possible.

You should inspect a BUR at least twice yearly to look for cracks, pooling, blistering, split joints, and other signs of damage.

What are the Pros and Cons of BUR Roofs?

If you’re considering a built-up roof for your project, here’s a look at the pros and cons.

Pros:

  • Multiple layers offer superior protection – The multiple layers on a built-up roofing system protect a building from water leaks.
  • Energy efficiency – Modern built-up roofs contain a thick layer of roof insulation at the base, boosting the energy efficiency of the building.
  • Fire resistant – BUR roofs are fire resistant thanks to the aggregate used.
  • Long-lasting – A BUR roof is the longest-lasting flat roof material with a lifespan of 15-30 years.

Cons:

  • Toxic fumes during installation – A BUR roof installed with a “hot” method can release toxic fumes during installation.
  • Cracks – If you live in an area with cold winters, you’ll be more susceptible to your roof cracking. The most common cause of cracks is water freezing and thawing on the roof.

How Much Do BUR Roofs Cost?

BUR roofs cost an average of $3.50 to $7 per square foot installed. While the roofing material is inexpensive, the labor cost drives the price up. The actual cost will depend on the materials, the slope of your roof, and your location.

BUR vs. Modified Bitumen Roof: Which is Better?

Modified Bitumen is asphalt combined with additives such as rubber or plastic and reinforced with fiberglass. It comes in rolls; you can apply it to a roof with heat, adhesive, or self-adhesive membranes. Modified bitumen is flexible and waterproof, making it ideal for flat and low-sloped roofs.

Like BUR, modified bitumen can also be applied in a multi-layer fashion or in two layers. Modified Bitumen is easier to DIY, while BUR requires professional installation.

Built-up roofing systems tend to last longer than modified bitumen. But, both materials are durable and efficient for flat and low-sloped roofs. If you’re not sure which is better for your structure, consult with an experienced contractor.

Frequently Asked Questions (FAQ)FAQ

Is a built-up roof the same as a tar and gravel roof?

Most people use the terms built-up roof and tar and gravel roof interchangeably. Tar used to be the main component in built-up roofs, but roofers no longer use it. Instead of tar, built-up roofs contain bitumen or asphalt.

What do blisters or bubbles on a built-up roof indicate?

If you see blisters or bubbles on your built-up roof, there’s air or moisture trapped in the roofing system. Consult a roofing contractor for repair.

Can you use a built-up roof on a house?

A built-up roofing system is an excellent choice if your house has a flat or low-sloped roof. You can’t use regular shingles on flat roofs because they cannot shed water.

Final Thoughts

Built-up roofs contain several layers of roofing material, starting with a thick sheet of insulation at the base. These roofs alternate between ply felt and bitumen or asphalt, topped with an aggregate. These materials protect flat and low-sloped roofing systems from leaks and increase energy efficiency.

BURs are one of the top choices in durability and longevity if you have a flat roof. One of the next best options is a modified bitumen roof which provides similar benefits.