A Complete Guide to Flat Roof Repair

In contrast to sloped roofs, a flat roof is almost level. While they are easy to construct, Flat roofs are more difficult to repair because they lack the drainage system found in pitched roofs. When water does not run off the roof properly, it can puddle and eventually lead to leaks.

There are two types of Flat roofs: Low-slope roofs have a pitch less than or equal to 3 in 12 and are nearly level. A pitch below this means that the roof is too flat for ice and water to run off properly, so it is more susceptible to ponding water and leaks. Pitched roofs have a steeper angle and may be anything above 3 in 12. The flatter the roof, the greater chance there is for ponding water, which can cause leaks.

When do you need to repair your flat roof? 

If you notice any of these signs, it’s time for repairs:

Sign # 1. Ponding Water:

When rainwater or melting snow puddles on your roof and doesn’t drain within 48 hours, this is a sign that your roof isn’t draining properly and needs to be fixed.

Sign # 2.Cracks or Splits in the seams or flashings:

These are places where water can enter your roof system and cause leaks. 

Sign # 3. Blisters:

Blisters occur when trapped gases form bubbles under the asphalt surface of your membrane roof system. These blisters can eventually turn into cracks and splits.

Sign # 4. Alligatoring:

Alligatoring occurs when the top surface of built-up roofs becomes cracked and dried out, causing them to resemble an alligator’s skin.

Sign # 5. Growth of moss or algae:

Organic growth on your roof can retain moisture and lead to premature deterioration of your roof system.

How much will it cost to repair my Flat Roof? 

The cost of repairing a flat roof depends on the roof size, type of damage, Pitch (slope), accessibility, and time required for repairs. For example, fixing a small tear will cost less than fixing major structural damage caused by severe weather conditions. The average cost to repair a flat roof is $500-$1,000; however, more extensive damage can cost upwards of $4,000-$8,000 or more. 

How can I prevent needing repairs?

You can do the following to prevent repair needs:

1. Have your Flat Roof Inspected Annually:

An annual inspection by a qualified professional can identify potential issues before they cause costly repairs.            

2. Keep Your Gutters Clean:

Clogged gutters can overflow and cause water damage around eaves, flashings, and penetrations.            

3. Remove Debris from Your Roof:

Things like leaves and branches can hold moisture against your roof system and promote organic growth such as moss and algae.            

4. Fix Cracks & Splits Promptly:

Catch these early on before they have a chance to widen and cause larger problems 


Since Flat roofs don’t have adequate drainage systems like pitched roofs, so they require special maintenance to prevent costly repairs down the line. Be sure to have yours inspected annually by a professional as well as keep an eye out for common issues such as ponding water, cracks or splits into seams/flashings, blisters, alligatoring, and growth of moss or algae between inspections. By doing so you will extend the life of your flat roof!

Contact the best roofing company in Ottawa to learn more.