Are you worried that your flat roof might start leaking or need frequent repairs sooner than you’d like? Are you concerned that weather conditions, like constant rain and pooling water, could wear down your flat roof faster than you expect?
When you’ve spent so much money on your roof already, the last thing you want is to be hit with unexpected repair costs. That’s why it’s important to be aware of what can go wrong with your flat roof (especially if you have concerns already) and how long it should last.
We at RoofSmart educate hundreds of customers every year on why their roofs didn’t last as long as they should have. In addition, we help them compare the lifespans of different roofs so that this time around they can find the one that works best for them using our SmartMatch Needs Analysis.
By the end of this article, you will know which factors impact the life of different flat roof materials and the signs indicating that your roof needs to be replaced. This will help you determine how much longer your roof should last or if it’s time to call someone out to check on your roof.
What are the average lifespans of different flat roof types?
| What is it made of? | Average lifespan | |
|---|---|---|
| Torch Down | This is made of bitumen, which is a mixture of asphalt and rubber. Some versions are smooth on the top and some versions have a granule layer instead. Applied with a blowtorch. | 12 years |
| PVC | This stands for polyvinyl chloride. It is a plastic material that has a lot of plasticizers in it, making it pliable and flexible. There is a layer of fiberglass mesh in the middle. Hot air gun melts it into place. | 30 to 40 years |
| TPO | This stands for thermoplastic polyolefin. It is a rubber-based product with multiple layers. A hot air gun (at lower temp than PVC) melts it into place. | 15 to 20 years |
| EPDM | Ethylene propylene diene terpolymer is another rubber-based product made of ethylene and propylene. Chemically bonded seams. | 20 to 30 years |
What are the factors that can impact the lifespan of a flat roof?
Reflections from Low E windows
Reflections from Low E windows magnify and amplify solar radiation. So if you have this type of window and the sun hits it, the Low E reflects the UV ray, and all that solar radiant energy gets bounced back onto the roof. All of the roof types are sensitive to damage from extra UV rays, but TPO is the most susceptible to it.
UV rays are damaging to most roof types (beyond just flat roofs), so any extra concentration of these rays will increase wear and tear and lead to a shorter lifespan for the roof.
Lack of cut-edge sealant
If your roofing contractor doesn’t use sealant on the cut edges of your flat roof, then this can lead to premature damage to the roof.
The need for sealant does depend on whether your roof has a wicking or non-wicking scrim (see “How Much Does A TPO Roof Cost?”). A wicking scrim will absorb water, so it needs a sealant to protect it.
Duro-Last® PVCs don’t need cut-edge sealant because they have a non-wicking scrim, so you don’t have to seal it. But other brands of PVC and all TPO have a wicking scrim. They absolutely do need sealant.
If that water gets into the roof material through the exposed cut edge, it will either freeze or get really hot (depending on the temperature outside). This will cause expansion (either steam expansion or ice expansion). Once this happens, the roof is damaged and needs to be repaired in the affected area. Or, if the damage is extensive enough, it might need to be replaced.
Broken welds
Another issue is the welds meant to adhere the roof material to the roof deck can break. If your roofing contractor doesn’t get the technique or temperature exactly right when welding, they can create a cold weld. This means that the roof material didn’t attach properly and it is separating from the roof, which causes leaks.
It’s a helpful analogy to think of it as a rooftop swimming pool. Basically, with flat roofing, you have to be perfect.
Extra movement in the deck
Let’s say for example that you have a chimney through your roof. A chimney has a different foundation than the rest of the roof and moves independently of the house. If there was an event like an earthquake or windstorm, this could cause tearing in the material around the base of the chimney.
This is an issue because an unreinforced (no fiberglass mesh) membrane has to be used in place of some of the typical roof types around things like chimneys because the regular flat roof material is not flexible enough. This is very common with TPO because it is more stiff.
Unreinforced membranes can be torn easily, which will lead to leaks in the roof.
Mechanical damage
This could be a tree branch, or it could be somebody going up on the roof to do work. For example, they might be working on HVAC or cleaning gutters.
These roofing materials are very delicate (like a swimming pool liner) and can easily be punctured if proper precautions aren’t taken. Anyone who goes up on the roof should be aware of what shoes they’re wearing.
To avoid this issue, it is helpful to use a hard backing on your roof deck like plywood or Densdeck gypsum roof backer board. It’s an added expense, but it can provide more peace of mind and help mitigate this issue.
Condensation issues
If condensation builds up under the roofing material, it can cause the roof deck to rot completely. Condensation can happen when there is a tear in the roof or a section isn’t properly sealed, so that condensation has room to build up underneath it.
Here is an example of the impact that condensation can have on your roof deck:
Improper installation of flashing
With a rooftop deck on a flat roof, it is important to properly apply flashing at the door because otherwise the door will leak underneath the membrane. It’s very likely that the whole thing will be rotten by the time anyone discovers this issue.
Here is an example:
Pine needle and leaves
This one is particular to torch down roofs. The other types of flat roofs aren’t affected by this. Just like with asphalt shingles, torch down roofs will degrade much more quickly when pine needles or leaves are left on them. This builds up moisture and ensures that any covered spots stay wet for extended periods of time.
Scuppers
A scupper is a hole in the roof used as a drain. This is common practice for flat roofs.
Torch down always leaks the scuppers, because all you can do is glue it. This is not as strong of a seal as torching provides. All roofs are more vulnerable where holes are drilled, but torch down is particularly susceptible to leaks around scuppers.
As an example of the damage a leaking scupper can cause and what it should look like, here are some before, during, and after pictures of a flat roof repair job we did:
Leaking scupper that also did not drain properly.
Rotting wood from excessive leaking underneath that scupper.
The new roof with properly sealed scuppers on all four corners.
What can you do to avoid issues and expand the life of your roof?
Aside from regular maintenance (cleaning of pine needles and leaves), there is not much that can be done. These roofs are designed to withstand water, but you should do your best to ensure that water does not stay pooled on your torch down roof for long periods of time.
Really, the best thing that you can do is find a roofer who is an expert at installing the type of flat roof that you want and hire them. Installing flat roofs properly requires skill, patience, and expertise.
How do I know when my flat roof needs to be replaced?
If you notice any of the following issues, then your flat roof needs to be replaced:
- Cracking
- Crazing (this is a network of small, thin cracks caused by the loss of plasticizers)
(Various stages of crazing from Lexis Coatings)
- Delamination
These issues will lead to leaks, failed seams, and the loss of flexibility. When these roof types are aging properly, you can weld a new patch onto them. But, if it doesn’t melt anymore then you know the roof is beyond repair and must be replaced.
How to Know When It’s Time to Replace Your Flat Roof
Understanding the expected lifespan of your flat roof and the factors that can shorten it is crucial for avoiding unexpected repairs and replacements. Many issues can impact how long your flat roof lasts, such as UV damage, improper installation, or mechanical wear.
If you notice signs of wear such as cracking, delamination, or failed seams, it may be time to consider replacing your roof.
After reading this article, you know how to identify these signs and to carefully assess the situation. You are now able to determine with confidence if your roof is still good to go for a while, or if it has faced some of these issues and it needs to be replaced (or at the very least, looked at by a roofing professional).
After reading this article, you may be wondering how to determine if your roof should be repaired or replaced. Check out our article “Roof Repair vs. Roof Replacement: Which Is Right For Me?” to help guide you through this decision.
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