Metal roof

Dear Donnie
We need a new roof on our existing home and we are looking to possibly install one of the new colored metal roofs ourselves. Our house is about 50 years old with a low sloping roof with a covered back porch and a chimney in the center of the roof. How well do the new metal roofs last and can we install it over the old roof without removing the shingles first?
Bill and Laura
Dear Bill and Laura
 Yes, you can install a long lasting metal roof over existing shingles as long as there is only one layer of shingles on the home and the substrate and existing shingles are level. It is not advisable to install the metal over two existing layers of shingles. You will need to put a layer of 30# roofing felt down over the shingles before installing the new metal roof. If the roof is uneven and solid you can add wood strips on top of the roof on 16” centers to attach the metal to.
 Metal roofs have been around for a long time and are becoming more widely used again on residential homes. Metal roofs have always been common on barns, commercial buildings and storage type buildings with great results and they come in several types and styles which include steel, tin, copper and aluminum.
The more common styles are;
  • Standing seam; this is where the metal is joined with a seam that is standing straight up with a water tight overlap which requires special tools and is usually installed by professional roofers.
  • 5-vee pattern; which is typically what is installed on barn roofs.
  • Pre-formed crimped style; which is the most common today are produced by taking large flat rolls of colored metal stock and shaping it within a large machine with a set pattern of rollers that allows the metal to be a specific color, shape and length. The ability to create exact lengths in a variety of colors makes a dramatic looking roof. When these type roof systems are installed they are very dramatic looking because of the straight lines and no visible overlap seams.
 If you feel comfortable and are planning to install your metal roof, here are a few basic installation procedures. I am going to discuss the crimped style of metal, but the basics are the same for most metal roofs with the exception of a standing seam roof. You will need to get accurate measurements of your roof surface and take the measurements to one of the local manufacturing companies. They will figure the amount of metal you need and manufacture it to fit your roof with a minimum amount of fabricating on the job site. Getting accurate measurements is important to allow for overhang and the type of ridge cap you want to install. You will need to measure and allow for valleys, dormers and chimneys on your roof when you are ordering materials. Be sure to get the proper fastening screws and any foam rubber closure strips and talk with the manufacturer to see if they require the use of butyl tape with their products.
 First you will need to install roofing felt over the entire roof. Install wood strips if you are going to use them, and make sure everything is straight and as square as possible. You will need to install drip edge along the bottom edge of the roof. Depending on the brand of roofing and the look you want to achieve you may need to install the rake edging before the roof panels are installed, this is the edge that runs up the gable end of the roof. All valleys will need a “W” shaped flashing installed and nailed about every 10” along the edges. Flashing will need to be installed for dormers, chimneys or any intersection you need to keep water out.
 When you are ready to start installing the roof panels make sure to start straight and keep the edges straight. Keep everything as square and symmetrical as possible which includes running the screws in a straight line. You can achieve this buy drilling pilot holes in the roof material several sheets at a time in the correct pattern to align with the woods strips or start the metal sheets and stretch a chalk line and use self tapping screws as you walk the roof installing them straight as you go. There is an age old argument whether to place the screws on the flat surface or the raised ridges on the roof, I have installed them both ways with good results but keep one thing in mind; follow the manufacturers instruction especially if there is any warranty involved.  
 When working on the roof try not to scratch the colored surfaces or walk on the roof with any grit that can scratch the surface to avoid future rust or failure of the painted coating. When you install the panels you will have to cut the valleys by hand, you can pre-measure closely and install them straight as you go or cut the panels close leaving out some of the screws and come back and mark with a chalk line and hand cut them with shears.
 When working with any overlaps such as valleys, ridge cap or at the drip edge you will want to install rubber or foam closure strips that match the shape of the metal to keep water from penetrating during blowing rain or heavy melting snow. There are also special rubber boots made for the plumbing vents that are easily installed.
 The last installation is the ridge cap which will either need closures to prevent leaking, or install a mesh designed to allow air flow creating a ridge vent.
 Following these basic steps will get you a good solid long lasting roof. Never compromise your safety; on a big job like this never overestimate your ability to perform the work at hand. Working with heavy metal in high places without using caution can result in serious injury. Never hesitate to call a professional roofer if needed.
 This article is written by Donnie Bentley a Home Inspector in Lenoir City TN working in the greater Knoxville TN area. Donnie has written many articles published in the Knoxville News Sentinel new paper on Sunday. Donnie is a TN State licensed Home Inspector, ASHI and NACHI certified. He is a NAARP Certified Radon Mitigation system installer and is a TN Licensed pest control operator.

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