The national average materials cost to install a shingle roof is $4.01 per square foot, with a range between $3.31 to $4.72. The total price for labor and materials per square foot is $7.42, coming in between $6.37 to $8.47. A typical 2000 square foot project costs $14,832.67, with a range of $12,733.50 to $16,931.84.

Roof Shingles Cost per Square

On average, it costs from $1.20-$4 per square foot to tear off and replace a roof with asphalt shingles. For a 1,700-2,100 square foot ranch-style property, that costs about $1,700-$8,400. However, roof replacement costs increase when you use higher-end roofing materials.

The answer is yes, you can lay new roof shingles over old ones. You can’t do it with wood or slate, for example, and you should never mix materials, such as laying asphalt shingles over cedar shakes. Also, the old roofing has to be in pretty good condition.

If any areas of the roof have become severely damaged, it’s usually better to remove the old shingles and start from scratch. If you’re going to add a roof on top of an old one, it’s a good idea to remove any loose shingles and apply a new layer of 30-pound roofing felt before laying the new shingles.

In most cases, more than two layers of roofing shingles does require a tear-off. Laying new shingles over old shingles is easily prone to leaks and reduces the life of the new shingles. This alone ought to be reason enough to do a tear-off; it’s just a bad value not to.

While a repair job can often be more convenient and somewhat more cost-efficient, placing new shingles over old ones is never a good idea. Whether repairing one section of roof, or a replacing a whole one, it’s always best to pull up the old shingles before putting down the new ones.

Black and dark-colored roofs. In general, dark-colored roofing materials will absorb the heat and cause your attic and/or the top of your house to be warmer than a lighter colored material.

In almost every case, the answer is yes, you can lay down a new metal roof over an existing shingle roof. This is one of the many reasons metal roofs keep growing in popularity – their installation doesn’t require completely tearing off the existing roof, which is a time-consuming and expensive job.

As long as the new plywood itself can span the distance and carry the roof, wind, seismic and snow loads for your region, adding new ply over old is just fine. The new plywood thickness should be at least equal to the exusting plywood thickness.

If you want new asphalt shingles installed then solid sheathing must be applied first. This can be exterior grade plywood or oriented strand board (OSB). Be sure that the roofer uses rated sheathing; most is rated by the APA – The Engineered Wood Association base right here in the Puget Sound Region.

You can generally install a metal roof on top of shingles as long as there are fewer than four layers of shingles on the roof, but the exact standards vary by area.

OSB takes longer than plywood to get saturated, but also takes much longer to dry out. When used as roof sheathing, this tendency to hold moisture means it will degrade faster than plywood when exposed to chronic leaks.

…or a non-laminated panel, such as this OSB. Either one is acceptable. The typical thickness of roof sheathing is about 7/16-inch, which is just under 1/2-inch. If you find 3/8-inch plywood installed as roof sheathing, it’s a good idea to make your client aware of its presence.

Osb is stronger than plywood in shear. Shear values, through its thickness, are about 2 times greater than plywood. This is one of the reasons osb is used for webs of wooden I-joists.

CDX is the grade of plywood most commonly used for roofing (CDX plywood means it is Construction Grade for exterior purposes). The wood is graded on each side from A to D, depending on the level of imperfections, (A being free of all imperfections and knots and D being un-sanded and considerably defected).

Contractors generally recommend treated plywood rather than regular plywood for roof decking because condensation can build up on the sheathing and cause rot. Roofers understand that when it comes to the roof deck, the amount of water that gets on the wood is a concern.

Your price could vary depending on how much the roofing company charges for labor, but generally, you can expect to spend between $70 to $100 for each sheet of plywood. A 4 x 8 sheet of plywood covers about 32 square feet of roof area—and the average roof measures about 3,000 square feet.