Should You Remove the Old Roof?

If it has been decided that it is time to replace an existing roof, one of the most important issues you must address is whether or not to remove the existing roof. When you install a new roof over an existing one you can certainly save money because you do not have to pay to remove the old roof. In fact, the cost to remove it can be substantial. Owners are justifiably eager to save the money if they can.

It’s All About Moisture
Generally, the reason you replace a roof is because it has been leaking (which may seem obvious, but it isn’t always the reason). When a roof leaks, not all the water that actually goes through the top surface of the roof comes out on the inside of the building. Some gets trapped within the roof assembly. The amount that is trapped can vary. We have seen entire roof areas full of water and no water leaking inside a building at all and we have seen roofs leak and leak and leak without leaving a trace of water behind in the roof or insulation. Assuming there is trapped water, is it a problem? It can be and it often is.

If water gets trapped in the roof’s insulation layer, there are several problems that can occur. First, the insulation will normally lose insulating properties and you will certainly waste energy. Secondly, the insulation will tend to hold the water against the roof deck and, if it is metal, can cause it to rust. If unchecked the deck can rust away under a roof and create an unsafe condition and/or cause a new roof to fail prematurely. Also, trapped water can migrate from the original roof up into the new roof system, damaging it from below.

Finally, even if the deck does not rust, fasteners that hold either the insulation or roof in place are also susceptible to rusting because many of the insulation products used in roofs release mild acids when they get wet. If the fasteners rust off and become loose, they can puncture a roof from the bottom side or make it more susceptible to wind damage which is not good. Florida Building Code requires us to remove existing wet material, but it is imperative that you make a determination about the presence and extent of trapped moisture because it can have a huge impact on the installed cost of a new roof. If you have a failure on a warrantied roof and the manufacturer determines that the roof failed because the original roof was wet, your warranty will likely not be worth the paper it’s written on.

Core sampling the existing roof can often help identify wet areas, but it is not always a sufficiently accurate method for determining moisture content either. Often Thermal Infrared scanning is done and this can be a highly accurate method if the existing conditions allow for our thermal cameras. At RAMCON, we do both for you at our expense!

Other Factors
You may also decide to remove the existing roof because of structural concerns about adding additional weight or because the existing roof does not provide a suitable substrate for the new type of roof you have selected.

If the building has been previously reroofed, which is common on older buildings, often there are already two roofs in place. If this is the case, Florida Building Code requires that you remove the systems down to the deck. Plus, if two roofs are already in place all of the issues previously mentioned concerning weight, energy efficiency, and trapped moisture apply double.