When it comes time to replace the roof on your commercial building, you will usually have two options: you can either have the old materials removed and then have the roofing installed or just leave the old roof in place and install the new materials over it. The latter is a layering process that most commercial roofing experts agree can provide certain advantages. Take a look at some of the pros and cons of layering old and new commercial roofing materials. 

Pro: The roof will be even better insulated with multiple layers. 

Heat and cold transfer through the roof is a big issue in large commercial buildings, especially those that don't really allow much in the way of ceiling insulation. If you do decide to leave the old roofing materials in place and have the new materials installed over them, you will have an added layer of insulating protection on the rooftop. 

Con: Leaving the old materials in place can make the roof a little less even. 

Depending on the type of underlying materials you have in place, layering new and old roofing materials can mean the surface becomes a little less even. This is especially true if the old roofing materials are not in good condition. For example, if you have old shingles on the roof that are broken and deteriorating and have a TPU or rubber roof installed over the old material, the end result can be a little bumpy. 

Pro: Layering the roofing materials will mean the project is less costly and won't take as long. 

Part of the reason for getting a new roof installed on a commercial building takes so long is the fact that removing old materials takes a while to do. Not to mention, the time it takes to remove the old materials is something that will be included in the bill. Therefore, if you opt for layering when you can, you are likely to see the project cost less and take less time to complete. 

Con: Layering materials can mean more heft for the rooftop. 

Most roofs are capable of supporting a substantial amount of weight, so layering the roofing materials really won't matter. However, if you have an older building that has a bit of structural weakness overhead, layering does add more heft to the rooftop, and it can cause some concern. Before recommending layering old and new materials, the roofing contractor will thoroughly examine the roof to make sure it is not going to generate problems.