A “roof over,” technically called an overlay, is a process of installing a new roof system over an existing system. This option can potentially lower the cost of your project or avoid intensive structural modifications.
However, a roof over may not be the best choice in all situations. You must evaluate your options carefully before deciding whether a roof over would be right for your building or project.
Deciding on a Roof Over
Determining whether to choose a re-roof or tear-off is not that easy. One must be careful in choosing which of these jobs would better suit their needs.
When re-roofing, the first place to look is your local building codes to determine how many roofing layers are allowed on your home. This number will vary based on the type of roof deck presently covering it.
The SBCCI (Southern Building Codes Congress International) Uniform Building Codes prohibits re-roofing where any of the following conditions occur:
- Where existing roof or roof covering is water-soaked to the point that an existing roof is not an adequate base for additional roofing.
- Where existing roof covering is wood shake, tile or slate.
- Where existing roof has two or more applications of any type of roofing.
- When building is located in an area subject to severe hail damage.
- Where the roof structure is not strong enough to support the load.
NOTE: Antebellum Roofworks Co Inc will not install another roof over existing roof where 3/8″ plywood decking is present.
Advantages of a Roof Over
Some advantages of re-roofing are that the existing layer will act as a secondary backup and you will save the cost and inconvenience of removing and disposing of the old shingles. Although there is a lack of available documented research, most roofing professionals do agree that re-roofing shortens the lifespan of shingles by 10-20%.
Special Considerations for Overlays (Roof Overs)
Upon arrival of your roof over project, our crews will make sure to do the following:
- Check manufacturer’s specifications and local building codes.
- Check with your local building department prior to overlaying the existing roof.
- Inspect the bundles for moisture upon delivery. If the bundles are wet, we have them returned and exchanged for new ones. If shingles are installed wet, then problems will occur later on such as blistering, mold, mildew, etc., all of which hasten roof deterioration.
- Remove any curled shingle tabs. You want the substrate of the new roof to be flat.
- Make sure the existing roof is dry before we shingle it. Trapped moisture such as dew will shorten the lifespan of your shingles.
- Clean any algae problems before overlaying.
- Cut the existing shingles back approximately ½” to 1″ from the edge of the roof all the way around.
- Before installing a new drip edge, we make sure that it covers the old drip edge material or else it will look ugly.
- Avoid common mistakes, like installing a layer of felt between the systems.
- Tear off the hip and ridge cap before overlaying to prevent large humps forming in the roof along the hips and ridges.
- Use nails that should be long enough to penetrate the deck a minimum of ¾”. 1 ¼” to 1 ½” nails are generally used in overlay applications.
- Install all-new flashings. Remove the old flashings and fill in the void that it causes with shingle material.
- Use four nails per shingle minimum, six nails per shingle in high wind areas.
Nashville Roof Over and Overlay Experts
If you think your roof would qualify for a roof over, we would love to help you come to a conclusion. In the right circumstances, a roof over can save the home or building owner both time and money.
Feel free to consult us to help decide whether or not a roof over would be suitable for your roofing project. Contact us at (615) 794-9111 today or fill out our form with any details or questions you might have, and we will respond as soon as we can.