If your roof has been giving you issues, or if you’re just trying to be proactive and get your roof done before it becomes a problem – you may be tempted to do an overlay rather than to remove the old roof. While this can save some cost in the short term, there are pros and cons to electing to overlay your roof rather than remove the old one first.
Let’s dissect what a roof overlay means. A roof overlay is when composition shingles (or possibly metal) is installed directly over the old material. This can seem like an enticing option because it can reduce the price of the installation.
There are advantages to removing the old roof, however. When you remove the old roofing material, you take advantage of the fact that everything will be exposed. Rotting or deteriorated roof decking will be brought to light and repaired. Installing a roof over the existing will simply hide these issues. Roof leaks will be exposed and repaired, which will protect your home from mold and mildew damage. A roof that consists of all new materials will inevitably last longer than one that is installed on top of an already deteriorating roof system.
Aesthetically speaking, there are risks associated with installing a roof over the existing material. The finished product can come out wavy or uneven. Adding extra weight to the roof can also cause settling and cracking through the home and there is possibility of structural damage, especially on older roofs.
The advantages of an overlay are the lower cost because there’s less labor involved. The roof removal process is laborious and messy, so you’re eliminating that part of the roof process. In doing so, you can also have a shorter work timeframe for the construction project. The roof removal process is also where the risk of damage mostly occurs, because the roof removal process involves throwing literally hundreds of pounds of material from the roof into a dumpster or tarp below. This process is inherently imperfect, so if damage is going to occur to shrubs, plants, trees, decks, siding etc. this is where it will most likely occur.
An overlay can only be done in certain situations and over roofs that are in relatively decent condition. It is not recommended to install a roof over highly dimensional existing composition shingles, and you can never install more than two layers on a roof.
When deciding on whether to overlay you roof or start new with a tear off, its important to call an experienced roofer.