Blog > Roof Replacement

Re-roofing over existing roof

Just the other day I was sitting in a parking lot waiting for someone, when I seen a truck pass by in Melbourne, FL advertising - "Have a new metal roof installed over your existing roof starting at $1.00 per square foot." To most people they might think this was great deal. But is it? About the only advantage I see is a new roof at very low cost and to many people price is everything. Sure everyone wants a bargain but a bargain is not a bargain unless it has value.

Here are some things to consider when it is time to re-roof:

  1. First, most people who are about to re-roof do so because they have a leaky roof or see signs the roof is starting to leak. That said why would one want to re-roof over a roof that has reach its life expectancy. When shingles start to leak they now longer shed water as they were designed to do. As the shingles continue to deteriorate it will have an effect on the attachment (loosen up over time) of the metal roofing material installed over the shingles.
  2. Under the shingles there is an underlayment (usually 30# felt paper) put down prior to the shingles being installed. If the roof was already leaking the underlayment is probably in need of replacement as well. Without taking the roof off entirely the underlayment can't bereplaced.
  3. Regardless of what type of roof is installed the roof deck itself must be in good shape, securely attached to the roof trusses and not damaged such as bowed or holes in it. Again, if the roof and underlayment were not removed there is no way to check the condition of the roof deck for any damage. I can assure you if your roof shingles are in need of replacement you will and I repeat you will have damaged roof decking. By the time homeowners notice the roof is leaking the roof has probably been leaking for six months or longer and sometimes years before a leak is discovered. When the roof start to leak they tend to rot the wood trusses and wood decking well before the leak migrates to the interior of the house. This another reason why the old roof should be removed so the roof deck can be inspected and repaired before a new roof is installed. If you happen to have an roof overhang on your house you may have a roof leak(s) for many years and not even realized because it only leaks when it rains and let's face it who goes out in the middle of a storm to check and see their overhang is leaking. Most roofs when replaced have 100 - 200 square feet of roof decking replaced in addition to any rotted 2 x 4's before the new roof is put down. That may seem a lot but that is only equivalent to 3 to 6 sheets of plywood or OSB board
  4. Another consideration of installing roof over the existing roof is the amount of additional weight being added to the roof structure. Grant you, a metal roof doesn't weight much but if you are installed a new shingled roof over an existing one the weight is now double, which adds additional weight to the roof structure, which includes the roofdecking and trusses, which was never designed to have this much weight to begin with. Typically the spacing between the trusses are 24" on center and the roof decking itself is only 7/16" thick or if you're lucky you may have 1/2" plywood. In reality to see a roof deck any thicker than 1/2" is rare unless the house was built over 50 years ago.
  5. Last of all metal roofs can last up to 50 years if installed correctly and properly maintain of the years to come. However, being installed over an existing roof is like playing Russian Roulette not know if there is any damage to the roof deck or trusses and the life expectancy will be considerable less.
  6. Now the good news! If you remove the old roof and underlayment replacing any damaged wood, by code the roofer is required to re-nail the roof decking with longer nails (8d 2 1/2" long) on 6" centers and install a SWR (secondary water resistant) with is actually self adhering membrane, which acts as a secondary water barrier This way if a shingle or two is lost during a tropical storm or hurricane the membrane would keep the roof from leaking until a new shingle can be installed. Newer houses today are be build with these features already in place, so if you are in need of a new roof you more than likely do not have this extra protection. The best part is it will lower your insurance rates by as much as $500.00 to $1000.00, which can vary greatly from one insurance company to another. All the homeowner has to do is have a wind mitigation inspection completed by HousePRO Inspection Services and submit it to your insurance company. By the way be sure your roofer takes plenty of pictures particular a picture of the SWR installed prior to the installation of the shingles. Your home inspector will need it as proof it was installed.

So if you're thinking re-roofing over an existing roof is going to save you money your wrong. Dead wrong. In the long run you will probably end up spending a lot more in repairs and maintenance not to mention the short life span of a roof that can last 50 years when installed properly. It's been stated before and I'll state it again "You get what you pay for" and it is not any different with a home inspector. If a home inspector offers to inspect your home or any size home for $150.00 and it will take 1 1/2 hours show him to the door. Even the smallest of homes I would expect to be on site for at less 2 hours. The average cost for home inspection today ranges between $300-$400 but you also need to take in consideration what part of the county you live in. InNew York City the average cost may be $500- $600 and in Alabama or Mississippi it may be $250 - $350. Most home inspectors base the cost of the home inspection on the overall square footage of the house. The purpose of a home is not to see how fast it be completed but to spend as much time as needed so that all discrepancies can be identified. Keep in my a home inspection is a non-invasion inspection and not technically exhausting.

For more information on the services HousePRO Inspection Services offer go to our website at and click on the "Services" button and remember "Before You Invest, Let Us Inspect". Housepro Inspection Services provide services throughout Brevard and Indian River Counties and has over 35 years in the construction industry.