Types, Advantages, and Applications of Built-Up Roofs

Pros and Cons of Built-Up Roofing

Built-up roofing
••• Photo J Rodriguez

Built-up roofing is the most popular material used on low-slope roofs. It's composed of several layers of bitumen surfaces and is finished up with an aggregate layer or coating. 

Built-up roofing is nothing new. The concept been around for over 100 years, although it's certainly evolved during that time. The most recent built-up products incorporate a rigid insulation layer. The fabrics or layers used on built-up roofing are called ply sheets. These sheets are commonly reinforced with fiberglass mats or organic mats depending on their application. Ply sheets are commonly produced in a standard width of about 36 inches.

How Does Built-Up Roofing Compare to Other Roof Types? 

Built-up roofing is not a style of roofing, such as a bonnet or gable roof, but rather it's a type of roofing. It refers to the components of roofing material used. Depending on the climate and the exact materials, built-up roofing has an average life expectancy of 15 to 30 years. It tends to fare better in warmer climates. 

Contrast this with a slate roof, which can hold up for 100 years or more, or an asphalt roll roof which might functionally last for only 10 years or so. Standing seam metal roofs last somewhat longer than built-up roofing, sometimes as long as 50 years, whereas wood shingle roofs, wood shake shingle roofing, and composite shingle roofs all fall a bit more in line with built-up roofing with regard to longevity,  

Types of Built-Up Roofing

Built-up roofs include smooth asphalt built-up, either hot or cold, and ballasted asphalt built-up. All types are generally comprised of three parts: bitumen material, ply sheets, and one or more surfacing materials. The type of surface coating used can be instrumental in cost and durability.

The bitumen material commonly used in built-up roofing systems is either asphalt, coal tar, or cold-applied adhesive. The surfacing and materials are varied and depend entirely on your project and your budget. Ballasted asphalt is being used more regularly these days because it can provide an excellent finish surface and its material is a better fire retardant agent.

Cold built-up roofing is also available. This can be sprayed or applied with a squeegee. It doesn't require hot asphalt for application, and it doesn’t give off toxic fumes when it's applied. It's often preferred for environmentally sensitive projects for this reason. Cold built-up isn't dependent on weather and it has a better performance when compared to hot built-up roofing.

Other Pros and Cons of Built-Up Roofing

Built-up roofs tend to provide excellent waterproofing and ultra-violet protection. They're low- maintenance and this means low life cost maintenance. They last longer and stand up better to weather inclemency.

But the process has some drawbacks as well. Installation is slower and with the exception of cold built-up, there can be hazard fumes and vapors involved when it's being installed. Overall, installation costs are higher and some types of this roofing can be susceptible to wind and water damage.

Built-up roofs can become damaged as time goes by, and proper maintenance should be given to restore these areas.

How to Repair Open Joints 

Add some cement under the open seam and make sure to hold it down so it can adhere to the substrate. If this doesn't work, try cutting a large piece of felt and place it over the open joint. Secure it with nails and put some cement on the nails. Spread some gravel over the cement and let it dry.

How to Repair Small Blisters 

Small blisters can be easily repaired using a knife to cut the blister. Allow the spot to dry as much as possible first. If the top layers are damp, keep cutting down until you've reached a dry layer. Remove the felts and install new felt over the area. Apply the asphalt and cover it with chippings. You can use liquid-applied coatings on top of the repaired area if chippings aren't available.

How to Repair Undulations 

Repair built-up roofing undulations by simply adding layers on top of the area to level it. Make sure the substrate is in good condition before proceeding.

How to Repair Cracks 

Cracks on the asphalt surface should be an easy fix. Start by cleaning the area of any gravel and debris. Apply a coat of asphalt cement over the area and install some roofing felt. Make sure there's at least 4 inches of overlap to guarantee that you're covering the area. Repeat this process again and apply a final coat of asphalt cement. Apply gravel on top of the cement.