A: Thanks for your inquiry, it is a common question. Although it is usually legal to overlay a second (but not a third) layer of asphalt shingles it's not recommended.

The building code, and most municipalities, will allow you to overlay a second (but not a third) layer of shingles on an existing shingled roof. You will need to check with your building inspections department to be sure.

If you are doing the roofing yourself, you will save the extra labor and the problem of disposal. I know first hand, I put myself through graduate school in Waco, Texas roofing houses and it is hard work - no way around it! However, it is not the recommended procedure for the following reasons:

• If there's any curling of the old shingles, the new shingles will not lay flat.
• Moisture can get trapped under the heavy layers and cause premature rotting of the wood.
• You do add excess weight to the roof framing, which can cause the decking or roof joists to bow and cause a ripple effect in the roof.
• Overlay will not work well at all with dimensional shingles, only three tab.
• If you do overlay, you have to cut off the tab of the first course which will give you a "bump" about 6" up the roof all the way around the roof.
• You must pull off both layers before you roof next time. Many times the cost for a double tear-off is more than doing it two separate times.
• Tear off will give you the opportunity to examine the decking for any rot and make repairs now before it gets worse (and more costly).
• If you do remove the old shingles, you will end up with a nice fresh layer of felt on the roof deck.

To find several reputable roofing contractors to gather estimates and options for installing your new roof, visit Home Advisor to be matched with the ideal service professional in your area!

David Radcliff, Certified Remodeler

-- Tips courtesy of HomeAdvisor.com