When you decide to replace your asphalt shingle roof, you have the option of either removing your roof and replacing it or overlaying your existing roof with a new layer of shingles. When you overlay your roof, you won't have to pay the labor costs associated with removing your current roof — this can save you a significant amount of money on roof replacement. However, overlaid roofs can experience a number of problems that typically make a complete roof removal and replacement a better decision. Below are the four biggest reasons why it's better to remove your roof and install a new one instead of overlaying it with new shingles.
1. A Roofing Overlay Doesn't Allow You to Inspect the Decking
When you remove your roof, the roofing company will have a chance to assess the condition of your decking. This is the most important reason to remove your roof instead of simply overlaying it with another layer of shingles — if your roof sheath is rotting, you'll want to know about it so that you can replace it immediately. Overlaying your existing roof with new shingles doesn't give the roofers a chance to inspect your decking, so you may end up installing your second roof over rotted decking. If the decking is in very poor condition, your roof may partially collapse.
2. Two Layers of Shingles Add Extra Weight to Your Roof
It's best to consult with a structural engineer before overlaying your roof with another layer of shingles — after all, you're doubling the weight of your roof. The engineer needs to ensure that the structure of your home can support the increased weight and the overlaid roof won't sag or collapse. Tearing down and removing a roof when you replace it doesn't require this extra step, since the weight of the old roof and the new roof will be the same.
3. Water Traveling Between the Dual Shingle Layers Makes Finding Leaks More Difficult
When you have one layer of shingles and notice water damage on the ceiling of your home, there's a good chance that the leak is right above where the water damage occurred. However, having two layers of shingles on your roof makes it much more difficult to find leaks. Water can enter in through a hole in the topmost shingle layer and travel along the roof before it finds a hole in the bottom layer to leak through. When the water travels along your roof, the location of the hole in the topmost shingle layer and the location of the water damage on your ceiling may not be anywhere near each other. Because of this, hunting down leaks will require a thorough examination of the entire roof.
4. Overlays Increase the Risk of Water Damage From Ice Dams
Overlaying your roof with another layer of shingles also makes it more likely that you'll suffer water damage from ice dams. Snow and freezing weather can cause ice dams to form on your roof — a solid block of ice forms on the edge of your roof, trapping the water from melting snow above it and preventing it from draining off of your roof. While all roofs can suffer water damage from ice dams, an overlay is particularly vulnerable. The water trapped by the ice dam can be wicked up into the small space between the two shingle layers and become trapped there, rapidly causing water damage to both layers.
Even though overlaying your existing roof with new shingles is cheaper than removing your old one, it carries a number of problems. Worse, you can only put a maximum of two layers of shingles on your roof — next time you replace it, you'll pay approximately double in labor costs in order to remove both layers. If you're considering overlaying your roof because you can't afford the labor cost of a complete roof removal, you should instead contact several residential roof installation companies to see if one will remove and replace your roof at a price that fits in your budget.