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Roofing 101: Can You Build a Roof Over Your Existing Roof?

October 14, 2020

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When a homeowner needs a new roof, they often ask, “Can you build a roof over an existing roof?” Adding a new layer of shingles over the existing roof, called reroofing, saves on the cost, hassle, and mess of a tear-off, all of which are good reasons to consider this option, if possible!

home with a needed roof replacement

If your home’s current roof is functional but needs more than a few repairs, you might be able to build a roof over the existing roof layers. You’ll need to note building codes, the condition of existing shingles and decking, and the home’s structural stability before deciding if reroofing is an option for you.

Since not all homes are good candidates for reroofing, it’s helpful for homeowners to note when you can choose reroofing versus a tear-off, and why your home might need an entirely new roof instead. Homeowners might also ask if they can increase the pitch of a roof or change its shape with reroofing or other such simple changes, for better drainage or an improved appearance.

To ensure you’re keeping your home in good repair and always looking its best, consider these simple tips about reroofing versus a new roof installation, and how to attach a new roof to an old roof. You can then discuss all your options with a roofing contractor near you, and make the best decision for your home.

Can You Build a Roof Over an Existing Roof?

A roofing contractor near you is the best source of information when it comes to your roof repair or re-roofing options and needs; however, you might note some details that they typically look for when it comes to your home’s roof and what might affect your choices for new roofing and repairs.

  • First consider local building codes, which typically restrict how many roof layers are allowed on a home; in most cases, you cannot add more than one additional layer over the existing roof. If your home already has a reroofing layer over the original roof, you might need to remove those shingles no matter their condition.
  • Asphalt shingles are very heavy; if your home is older or has structural issues for any reason, adding a new roofing layer over an old might result in damaged joists, wall studs, and foundation concrete. You might also face roof repairs sooner rather than later!
  • In most cases, you can build a roof over an existing roof only if you have asphalt shingles currently. You cannot mix materials, such as putting clay tiles over asphalt, with the exception of installing metal panels over shingles.
  • Asphalt shingles also need a flat and even surface for installation. If current shingles are curled, buckled, or otherwise uneven, they must be removed before new shingles are installed.
  • A roof is created in layers; roof decking goes over the joists and rafters, to create a solid foundation for underlayment and then shingles or tiles. If that decking or underlayment is damaged, it should be removed and replaced, to protect the home from roof leaks and resultant water damage and mold growth.
  • Reroofing will give a home’s roof a slightly raised, three-dimensional appearance. While many homeowners appreciate this added depth, some might not realize that the home’s roof won’t look the same with a new roof layer as it does with just the original roof.

While there might be many reasons you cannot opt for reroofing and need a complete tear-off, note that adding a new roof layer over an old roof means less cost and hassle, as well as less mess and trash. Asphalt shingles are recyclable but this process often creates lots of fumes and emissions, if you can even find a company willing to recycle shingles! Opting for a reroofing where possible means keeping those shingles out of landfills, making it a very eco-friendly choice for homeowners.

roofer standing on the roof replacing over existing

Reroofing Versus a Roof Replacement: Which Is Better?

While re-roofing or adding a new roof to an old roof is an excellent choice in many cases, there are times when this simply will not work for a home, and when a roof replacement is best. Roof decking damage should be addressed before new shingles are added, as one example, to prevent interior water leaks, structural damage, and mold growth.

Aspects of Re-roofing & Roof Replacement to Consider

  1. A homeowner might also consider a few other factors before deciding on reroofing versus a roof replacement. One consideration is if you might sell the home anytime in the near future. If so, you might not want to invest in the cost of a full-scale roof replacement, while reroofing offers a solid roof in good repair, making your home more attractive to potential homebuyers.
  2. A homeowner might also check with a property appraiser and note if reroofing or a new roof will add the most value to the home. In some cases, both choices might add the same value, if any, while a new roof installation might increase your home’s worth enough to make it the right choice for your property.
  3. Someone homeowners on a budget might also spread out roof replacement costs, having a section of their roof repaired every year. If you reroof just one section of the roof, however, this will cause it to become raised over the surrounding sections, for a very uneven and unsightly look. If you must spread out your roof repairs over a few years, invest in a new roof installation rather than reroofing.
  4. One last consideration is if you might opt for something other than asphalt shingles; metal roofs, for example, might last 50 years or more and provide added insulation against outside weather and sound. If your roofer cannot place those new metal panels over asphalt shingles, you’ll then need to opt for a full-scale roof replacement rather than reroofing.

How Long Does Reroofing Last?

Asphalt shingles typically last anywhere from 10 to 30 years, depending on their quality. Metal panels over asphalt might last some 50 years or more.

For the longest roof lifespan, leave this work to a pro! Professional installation helps ensure shingles stay in place even in high winds, increasing their lifespan. A high-quality installation is even more important when reroofing or adding a new roof over an old, to ensure those shingles are attached properly and the roof is in good condition before work begins.

While weather conditions also affect asphalt lifespan, so does the way you maintain your home’s roof over the years. Invest in regular roof washing, to remove damaging storm debris and drying soot, dust, air pollution, and other such residues. An annual inspection also allows you to make repairs as soon as needed, keeping damage to a minimum and ensuring your home’s roof is always in good repair.

roofers toolbelt left on a reroofing project

How Do You Attach a New Roof to an Old Roof?

Reroofing is a job best left to a qualified roofing contractor near you. Being on a roof or ladder is dangerous enough in any circumstance, but even more so when you’re using a nail gun, pry bar, and other such tools. If you are considering DIY roof repairs, however, note how to attach or layer on a new roof over an old roof.

  • Start by removing the ridge caps. This allows you to reach all areas needing new shingles. Use a small pry bar to pull up those caps.
  • Next, remove any obstructions such as vents and pipe flashings. Don’t worry if you damage shingles while you do this, as repairing them is your next step!
  • Repair damaged shingles; if a shingle is torn, glue the pieces to the area under them. If a shingle is missing a section, cut a new patch and nail or glue that in place. Ensure you have a flat, level surface for attaching new shingles.
  • Sweep the roof before you do anything else! Ensure you remove dirt, dust, nails, glue residues, and other debris that might get in the way of those new shingles.
  • Install flashing around vent openings, valleys, and other such areas.
  • Install a starter strip; this should butt up against the second row of shingles along the roof eave or gutters. The starter strip ensures an even installation and helps direct water off the roof.
  • Start installing shingles. The thicker the shingle, the more they’ll hide imperfections and provide better insulation for your home’s interior.
  • As you work, butt succeeding rows of shingles against the bottoms of existing shingles and drive nails above the tab slots.
  •  To reapply the vent, use roofing cement to keep it in place and provide a waterproof seal.
  • When you meet walls such as along a chimney stack, use step flashing. This will provide a seal between shingles and that wall and allow water to run off the roof. Once finished, install a new ridge cap.

Once you’ve finished reroofing, rake the roof again. This will ensure you collect any loose nails and connectors and that the roof is clean and free of debris.

changing the shape of a roof

Can I Change the Shape of My Roof?

While adding a new roofing layer over the existing roof might raise it a slight bit, the only way to change the shape of a roof is by replacing its interior and exterior structural materials. This includes the rafters and joists that create roof shape.

Changing out the walls, ridges, and rafters can change the roof shape and entire appearance of your home but this job is typically expensive and involved, and requires a permit. However, a more sloped or pitched roof can encourage added water runoff, protecting those roofing layers, and potentially increase your home’s value. Talk to a real estate agent or appraiser if you’re thinking of changing the roof shape to enhance property values.

What Are the Different Types of Roofs?

If you are looking to change the shape of your home’s roof, you might familiarize yourself with their various shapes and types. You can then discuss your options with a home renovation contractor or roofer near you as needed.

  • Gable Roof: The term “gable” refers to a standard triangle roof. A gable roof is very common as it’s easy to build and allows for lots of water runoff.
  • Hip Roof: A hip roof is similar to a gable but has four sides rather than two. Hip roofs offer added stability in high winds, making them a popular choice in the tropics or the Midwest where hurricanes are all too common.
  • Dormer Roof: A dormer roof includes a window and roof over it jutting out from the surface of the home’s roof. A dormer is an excellent choice for adding space in the room directly under the home’s roof, whether that’s an attic or bedroom.
  • M-Shaped Roof: An M-shaped roof includes two gable roofs side by side. M-shaped roofs are often used for duplexes where each owner is responsible for his or her side of the roof, or for adding style and visual interest to a home.
  • Gambrel Roof: A gambrel roof is often used on barns; these roofs have sections added in something of a slope. Gambrel roofs are very stylish and also offer more headroom in an attic or upper story.
  • Shed Roof: A shed roof is like one side of a gable roof, although not typically as steep. Shed roofs are often used for sunrooms and other outside additions; a gable roof might be too difficult to construct while the slope of a shed roof allows for water runoff.

roof replacement

If you’re not sure about the right roof style for your home or addition, tell your contractor what you want to accomplish with the roof; are you just looking to add a bit more visual interest to your home’s exterior? A gambrel or M-shaped roof might do the trick. Do you need more space and light in an upper room or attic? Add dormers or a gambrel roof. If you’re tired of fixing water and storm damage, it might be time for a hip roof on your home.

How Do You Attach a Roof Rafter to a House Roof?

For added protection against the elements and a bit of shade over your home’s patio, consider adding some roof rafters extending from the house roof. First, calculate the sightline clearance height and then determine the beam size you’ll want to use. Choose your roof pitch and style; a shed roof, mentioned above, is probably the easiest to construct and offers lots of shade and water runoff protection.

Stain the wood pieces before installation, to protect them from outdoor elements and ensure an even covering. Fasten the post bases to the ground with what are called lag bolts; make sure they sit plumb and level. Cut the rafters so they sit flush on those post bases and cut an angle along the top of the post base to accommodate; ensure you install those beams on the posts and not to their sides, as bolts aren’t strong enough to support the weight of those rafters.

Cut the outer rafters so they sit flush on top of the house roof and attach them to the posts. Once all the rafters are in place, install horizontal planks to form the patio roof. If you’ll be adding shingles rather than opting for a pergola look, attach plywood decking over the rafters and then roof felt. You can then install roofing shingles.

A Word From Our Roofers

This information is proudly presented to you by United Better Homes. If you’re still wondering, “Can you build a roof over an existing roof,” or know that your home is ready for roof repairs or full-scale roof installation, call the pros at United Better Homes today. We stand behind all our roof repairs and installation work with an industry-leading warranty and use only the highest-quality, name brand materials built to last! For all your re-roofing and installation needs, rely on the name you can trust, United Better Homes. Contact us today for roofing services in Rhode Island & Massachusetts!


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