Built-up roofs are a very popular choice for commercial buildings due to their low cost and ease of maintenance. They consist of alternating layers of roofing felt and asphalt. The roofing felt helps prevent water from leaking into the building and provides structural support for the roof, and the asphalt binds all of the multiple layers together.

Roofing felt and asphalt are both very inexpensive, which makes built-up roofs one of the most cost-effective types of commercial roofing on the market. Like any roof, however, built-up roofs can fail as they age. When a built-up roof fails, rainwater will slowly work its way through the multiple layers and enter the building below, causing a leak. Replacing your built-up roof as soon as it starts to show signs of failure will prevent large leaks that can cause substantial water damage to the interior of your building. To learn about some signs that your built-up roof may be failing, read on.

Blisters Appearing on the Surface of the Roof

When raised blisters start appearing on the surface of a built-up roof, it's a sign that the top layer is leaking. Asphalt and roofing felt are moisture barriers, so any rainwater that seeps through a crack or hole in the top layer won't evaporate. It will collect underneath the roof and create a blister on the surface.

Since built-up roofs are constructed using multiple layers, it will often prevent water from entering the building interior if only the top layer is leaking. However, the blisters that form due to a leak in the top layer will rapidly damage the roof. The blisters can burst when the asphalt and roofing felt shrink as outside temperatures drop, which will tear a hole in the roof. If you notice blisters appearing on the surface of a built-up roof, its surface leaks need to be patched as soon as possible in order to prevent damage to the layers underneath.

Extensive Alligator Cracking in the Top Layer

The asphalt that binds the multiple layers of roofing felt together will eventually turn brittle due to age and sunlight exposure. Brittle asphalt will crack easily as the roofing layers shift due to thermal expansion and contraction.

When the asphalt in a built-up roof turns brittle, numerous alligator cracks will form in the top layer. If these cracks go deep enough, they can expose the layers underneath and the building below to rainwater. If the asphalt in your built-up roof is cracking apart due to age, you'll most likely need to replace the entire roof — it's at the end of its usable lifespan.

Roofing Felt Coming Apart at the Seams

Thermal expansion and contraction can also pull apart the layers in a built-up roof. It will start coming apart at the seams where the rolls of roofing felt meet, and the surface of the roof will also look uneven.

When the roofing felt starts coming apart, it creates gaps that water can flow through. This can result in rainwater making its way through all of the layers to the building below. In order to prevent your building from leaking, you'll need to tear off the warped built-up roof and replace it.

If you think that your built-up roof may be failing, call a commercial roofing contractor in your area and have your building's roof inspected. You'll need to completely remove and replace a built-up roof that's failing due to age. Thankfully, built-up roofs are inexpensive, and replacing your failing built-up roof will reduce the risk of a roof leak causing severe water damage to the interior of your business.