Roof replacement is expensive and time-consuming, so homeowners try to get around it by installing a second layer of shingles on top of the old one. While installing the second layer is easy and affordable, it comes with its fair share of drawbacks. Here are 8 problems with two layers of shingles as given by roofing companies:
The layers add weight to the roof.
Good quality composite shingles can weigh between 350 and 450 pounds per square, so you can imagine the weight you add to your roof when you add two layers. Most roofs are designed to handle only one layer, so when you add an extra layer, you increase the chances of your roof collapsing.
The second layer doesn’t sit well.
While shingles of the second layer resemble the first ones, they don’t do an excellent job at bridging over gaps, humps, and dips. Experienced roofers have tricks to lay new shingles over the old ones, where they install them at the same step-ups between courses.
Despite this, if the old shingles are curled, cupped, or have other issues, the defects “telegraph” through to the new layer. To prevent this, roofing experts recommend you use dimensional or laminated shingles for re-roofs as they are thicker than standard shingles and often have staggered edge profiles that hide any dips or high spots in the old roofing.
You can’t replace the underlayment.
During roof installation, roofers place building paper between roof sheathing and shingles to prevent water from getting under shingles. If the roof is too old, chances are the underlayment is also old and deteriorated, so it won’t protect your roof deck from water.
In snowy climates, roofers install an ice and water shield along the eave to protect against ice dams. If re-roofing, you don’t have this option, which puts your roof at the risk of developing ice dams and other issues.
A double layer is unattractive.
Roof shingles are designed to lie on a flat and even surface, which gives the roof a sleek, beautiful look. When you install two layers, you give your home a bulky, lumpy look that is extremely off-putting.
If placing the new shingles on old, curled shingles, the new shingles don’t lie flat on the roof, which affects the appearance of the roof.
The second layer hides roof problems.
Most roof problems can be fixed when identified early. Catching the issues is easy when you have a single layer of shingles but an entire ball game when you have several layers. The extra layer means you hide the problems deep inside so you can’t find them when inspecting the roof.
What is the consequence of this? You don’t identify or fix the problem early enough, so it gets worse with time to the extent the entire roof comes down.
You have a problem with selling your house.
If looking to sell your house, later on, you have a problem doing it as the home inspection professionals give a negative report every time they inspect your house. When potential buyers see the house has a double roof, they avoid it. This means the house stays in the market for too long. In some cases, you are forced to sell it at a loss.
It’s expensive to remove the double roof.
If you have a major roof problem such as a leak that causes the deck and other parts to rot, you have to remove both layers to diagnose the problem and fix it.
Since you have two roofs, you pay the contractors a premium price as they do double work.
The roof has a short lifespan.
The second layer of shingles traps heat, which can lead to the decomposition of the roof layers. Due to the decomposition, you have to replace the roof earlier than expected. According to roof repair companies Greenwich CT, adding an extra layer of roof reduces the lifespan of the roof by up to 40%.
As mentioned above, adding another layer puts a lot of weight strain on the roof, and the extra weight stresses and damages the original roof and home structure. The extra weight also puts the roofing system at the risk of sagging between rafters, which can trap moisture leading to serious damage.