When we talk about a metal roof for your shed, we can go with a standing seam metal roof, the same type of metal roof you would have put on your home, or corrugated metal sheets.
The standing seam roof takes a little skill and some time to install, but since we’re talking about a shed rather than a home, it’s not the daunting task you might think. It just takes a little know-how and care, and your roof will probably last longer than you will stay in your home.
Caution. Be sure to wear rubber-soled shoes for this job. Besides being less likely to slip, rubber soles are less likely to damage the roofing when you walk over it. You may want to purchase a safety rope and anchor system for safety, especially if your shed is large. They can be purchased at most home improvement stores.
Permits. Be sure to check with your local building code enforcement agency as to what you plan to do. They may require an underlayment whatever type of roofing you use and may have other restrictions, such as using a drip edge. You may also need a building permit. Come prepared with a drawing containing measurement so that you can show just what you plan to do.
Step by step metal roof installation – Standing seam roofing
Old roofing. If you’re replacing your shed roofing, you’ll need to remove all your old roofing, depending on the type. This is especially true for the common standing seam roofing. Make sure also that no old nails are sticking up.
While some metal roofing can be installed over asphalt shingles, standing seam roofing can actually be damaged by installing it over shingles. The gravel on the shingles will rub against the steel underside during expansion and contraction caused by temperature changes. This will rub off the protective coating, allowing rust to form where you can’t see it. The additional weight will put unnecessary strain on your rafters.
Measure. This is one of the most important parts of step by step metal roof installation. Measure your roof exactly so you know what to order. Add two inches to each panel to allow for the drip edge. For insurance, it’s a good idea to order an extra panel in case one gets damaged during installation. Many panels come in 16-inch widths but be sure to check on this from your supplier before you order.
Tools. You’ll need a claw hammer for pulling out nails, a utility knife, a marker or carpenter’s pencil, sheet metal snips, a rubber mallet, and a tape measure. A tool belt will come in handy. A vital tool is a sheet metal hand seamer/folder. Look into 1-1/2 inch plastic cap nails for the underlayment. You’ll need flathead screws for metal roofing. Leather gloves are recommended for handling metal roofing.
Underlayment. Some sources advise against using felt or tar paper, instead opting for a breathable synthetic underlayment. Asking the roofing manufacturer about this is a good idea. Start installing it at the bottom so you can overlap the rest of the rows. For a lower slope roof, the underlayment should be overlapped by a foot. On steep slopes, this can be reduced to six inches.
Make sure to run it right up against anything sticking up above the roof, such as a vent or attic fan, running it up the sides a few inches if possible. The flashing can then be attached over it. 1-1/2 inch plastic cap nails are great for installing the underlayment. They are rust-proof and won’t damage the material and are usually available at any home improvement store.
Instructions. The step by step metal roof installation guide below contains general steps to follow when installing standing seam roofing. Each manufacturer of standing seam roofing may have a special method or two that is preferred when installing their product.
Ask whether instructions will come with your order. If not, ask for them. Go over them before starting your project and you’ll less likely to come to a spot where you’re a bit confused as to what to do next or a detail or connection that doesn’t look familiar.
Drip Edge. The drip edge is installed after you’re finished with the underlayment. You can use either screws or nails about 8-12 inches apart in a staggered pattern on center. Overlap the sections by at least two inches, opening up the overlapping section so it fits in with the last.
Your drip edge can also be used on the gable edges or you can order a separate gable trim. Ask your supplier for recommendations if you’re not sure what size to order. The gable trim can be installed either before or after your metal panels, or you may not even need it.
Installing the panels. You’ll need to bend the bottom of each panel about 7/8-inch to create a hook-lock for the next panel. Hook the first panel into the drip edge, installing one screw near the top to hold it in place. The clips should be on center spaced about 10-12 inches apart. Install screws into the outside holes in the clips.
With the next panel, hook it into the drip edge, then insert the tip of the single snap lock into the double snap lock and slide it up. Use the rubber mallet to snap the seams. You can use your hands for this, but you’ll turn to the mallet after you do this for two or three panels. Repeat this with all the other panels.
Ridge caps. You’ll use Z-bars, also called Z trim or Z flashing, for the ridge cap installation. Cut the bar a little less than the width of one panel. Use some type of peel and stick foam tape or caulking underneath the Z-bar. Attach it with three screws, then caulk the side gaps to keep water out.
Start your ridge caps by forming the end caps. This is where your metal snips come in handy. Take a section of the ridge cap, cut a two-inch line down the middle bend on one end, cut two inches off the lock, then bend down the flaps you just created. Hook it into the Z-bar.
Then go on over the whole ridge, hooking them into the Z-bars as you go, using the second end cap you modified at the other end. You can bend the Z-bars as needed to make them fit the ridge cap sections. Close the open lock or lip on one side of the cap. The hand seamer then is used to crimp both sides.
Step by step metal roof installation – Corrugated metal sheets
Measure. Panels may come in different widths and lengths. Check with your supplier to see what’s available to figure out your order. Remember that larger panels may seem to make the job go more quickly, but they are harder to handle, especially when a breeze blows up. Since corrugated metal roofing can come in different colors, try to stick to lighter colors to reflect the sun’s rays.
Tools. Use an angle grinder or circular saw with a blade for metal. The angle grinder may be quicker. For the circular saw, plan to go through more than one blade. Nibblers or tin snips are fine but take time. Nibblers do come in power models to speed up the job. Any slivers left after cutting should be removed, especially if your panels are painted.
A drill with a 3/16-inch bit will allow you to pre-drill screw holes. Use #10 2-inch screws with polycarbonate washers to attach the metal panels. Wear leather gloves to prevent cuts.
Underlayment. Underlayment goes on top of the rafters and below the furring strips. While it’s possible to install corrugated metal sheets without an underlayment, the underlayment provides extra protection against moisture a does quite a bit to lessen noise. It’s also good insulation on hot days.
Furring strips. These strips should be installed after your underlayment. They are usually 2×2-inch strips. Besides providing a good base for installing your metal sheets, the airspace they make forms additional insulating and noise reduction. These strips are installed horizontally on your roof from the top down, starting two feet from the ridge and two feet apart with 16d common nails.
Installing the panels. It helps to pre-drill your screw holes, or you can use sharp-pointed screws. Using a power screwdriver will help speed things up. Start at the top on the side farthest from the prevailing wind, with the outside edge hanging over about two inches. Starting from the side against the wind will mean that the top edge of the overlap is less likely to get caught by the wind.
Overlap the panels on the long sides at least 2-1/2 inches. They should overlap top and bottom by 6 inches. Insert the screws into the valleys, or low parts of the roofing. Using caulk on the overlapping parts will help keep out water and will strengthen the joint. Fasten them firmly but not too firmly, so as not to dent the panel.
Ridge caps. These are specially formed for the job. You can cut the ends down the middle and fold the ends under to go over the ends.
Is Underlayment Necessary for a Metal Roof?
Underlayment is an important part of step by step metal roof installation. It provides extra insulation, helping to keep your shed cooler in the summer. Temperature fluctuations will be lessened with the changes. It also acts as a noise barrier. Finally, it provides a smooth, even surface for your roofing.
Does Metal Roof Need Drip Edge?
Having a drip edge is best to ensure that rainwater runs off the roof. It’s usually used with standing seam roofing. It also keeps water from seeping under the underlayment. It should be installed before the metal panels. However, some people just make sure that corrugated metal roofing overhangs the roof edges by an inch or two. Be sure to check with your local building codes, as they may have something to say about it.
Do You Need Furring Strips for Metal Roof?
For a standing seam metal roof, you’ll be installing underlayment over sheathing, so you won’t need furring strips. If you are just installing corrugated metal sheets over your rafters, you’ll need furring strips. This will give you the option of nailing down your sheets between the rafters so that they are less likely to lift up with the wind. It will also take care of the problem of the spacing between your rafters not lining up quite right with the width of your metal sheets.
Can You Put Metal Roofing Directly on Rafters?
If you’re using just plain corrugated metal sheets, you can install them directly over the rafters, although you may want to install furring strips or purlins to aid in the installation of the metal sheets. Standing seam roofing panels may or may not line up with your rafter spacing, or the overlap required with corrugated metal panels. In any case, you need a good base for your underlayment.
How Much Should a Metal Roof Overlap?
Corrugated metal sheets should overlap at least 2-1/2 inches. The corrugations should aid you in this. For top and bottom, the overlap increases to 6 inches.
Can You Install Roofing Over Shingles?
Metal roofing shingles or corrugated metal sheets can be installed over asphalt shingles, but not standing seam metal roofing. This is one reason that metal roofing has gained in popularity. The only caveat is that there should be no doubt as to the condition of the roof sheathing underneath.
If there’s any sign of leakage or any place that shows signs of moisture seeping in, the roof sheathing should be checked there and replaced if necessary. If your asphalt shingle roof is old and shows signs of several cracked or missing shingles, it might be better to go ahead and remove the old shingles to make sure the sheathing is in good shape.
Installing a metal roof, whatever the type, is not a huge project for a shed. Be sure to ask if the manufacturer provides a step by step metal roof installation for their particular product, especially if using standing seam roofing, as they may have a special instruction or two. This way you won’t have a problem with an unfamiliar part or two. Once you get started, you’ll get into it and be done before you know it.