I have been in the roofing industry since 1978, and I know a great deal about roofing and flat roof. I have roofed over 5 million dollars in both hot tar as well as TPO installations over the years. In addition, I have studied under some of the major roofing material manufacturers in the country, and I am well versed in all aspects of flat roofing.
Should I Tear Off My Current Roof?
One of the most common questions I hear from customers when they are ready for a new commercial roof is whether they should tear off or replace the existing flat roof. Many times, customers will come to me with answers to this question before talking to me. Their opinions may be based on their own research or advice they’ve received from family members and friends (usually not professional roofers or in the roofing industry).
I’ve heard clients say, “I want everything off! I want to start fresh! Replace all the plywood because I can’t sleep at night knowing there might be rotted wood on my flat roof!”
“Hold on,” I say to them. “Let’s take a step back and talk about the benefits of keeping your existing roof.”
When your existing flat roof has only one layer and no unsafe deck issues, it is better to install a lightweight single ply roof system over the existing roof rather than tear off the old one.
Why? There are five good reasons for building over your existing roof:
- The warranty is the same as with a tear-off.
- It costs less to not tear off the existing roof.
- You will be saving the landfills – and our planet – from unnecessary trash.
- The insulation value of the current system will be maintained.
- If your existing roof is gravel and you clear it off, you will reduce the weight by about 200 pounds per 100 square feet. After new insulation is installed, the “R” value is increased, and the weight is reduced.
Why You Should Tear Off Your Existing Roof
The main reason for tearing off an existing roof is because of weight. The roof is too heavy and can cause structural damage. If there is no weight issue, you can and should apply a new roof over the existing one. Keep in mind that hot tar systems create heavy roofs. In fact, the roof weight usually becomes excessive after two layers, although I’ve seen seven hot tar roof layers on a building that was still standing.
The weight of a single ply roofing system is one tenth of a hot tar system and does not create a weight issue. Think about a single ply system as a simple roof coating. Because there is not an excessive load with the single ply roof, tearing off an existing roof is seldom necessary when installing single ply.
What About the Deck?
Now, about the roof deck and damaged wood concerns. When people hear “damaged wood” they liken it to a type of “cancer” that spreads. In most cases, there is no need for concern. Roof decks are usually constructed of plywood and not exposed to the elements. They can last a long time. I have torn off roofs from buildings that are 80 or more years old, and the wood decks have been in good condition because they are encapsulated, meaning they are not exposed to the weather.
Of course, the deck must be safe to walk on. If it is, there are no issues. However, if the deck has weak areas (this is rare), simply replace the damaged sheets of plywood and move on. You don’t have to remove the entire roof to see that the plywood is undamaged. If you can walk on the roof and the plywood underneath is solid, then it’s okay.
So, relax! Take it from a roofing expert with more than 30 years’ experience. Based on the facts and benefits outlined here, it is best to install a single ply roof system, the best flat roof system available today, over existing flat roofs.