Can You Install New Shingles on Top of Old Shingles?

new shingles, old shinglesWhen it’s time for a roof replacement, some homeowners may request installing the new shingles on top of the existing ones. Is this a feasible option, or does it just create additional problems down the road? Here’s the truth about installing new shingles on top of old shingles.

Why Homeowners Request Installing Shingles on Top of Shingles

The answer is simple: it’s cheaper. By not having to tear off the existing roofing, homeowners save an average of $1,000 on labor costs. This is off the total installation project and pertains towards the average-size residential roof.

Now, let’s examine why the initial savings from not removing the existing shingles might be counterproductive in the long-run.

Too Much Weight

Homes have a roof weight limit. The typical shingle weighs about four pounds per square foot. By leaving the existing shingles in place, you double the weight, potentially exceeding the limit. Multiple roof layers cause a risk of sagging, especially between the trusses and rafters.

Can’t Evaluate the Underlayment

The underlayment is the area between the shingles and sheathing that protects the home from water intrusion. If you leave the old shingles in place, the contractor has no way of examining or replacing the underlayment. Even a second layer of new shingles will not prevent a roof leak if the underlayment is compromised.

Shorter Lifespan

Heat can become trapped between the two layers of shingles. This can cause the shingles to prematurely deteriorate. Also, existing mold and algae in the old shingles can spread from the additional heat and moisture. You are also unable to remove them since they are concealed under the new shingles.

We Seldom Install New Shingles Over Old Shingles

Urbizo Bros Roofing handles residential and commercial roofs for Mukilteo properties. See our gallery to view our work. We hardly ever recommend placing new shingles on top of old shingles; it’s not worth the possible implications.

Residential Shingle Installation

Quality roof replacement & repair in Edmonds, Seattle, Lynnwood, Mill Creek, Mercer Island, Mukilteo & South Everett