Metal roofing has taken over in my neighborhood. It seems like everyone is replacing their shingle roof with metal, and no wonder – it looks really good. However, when I heard how much it cost a friend of mine, I realized it might be out of my price range. But then I immediately thought of my shed. Which got me thinking about how you would install metal roofing on a shed.
Installing a metal roof on a shed requires a solid deck beneath or battens, but only if the interior will not be heated. Install the fascia and leave edging pieces. If using roof underlayment, it will go over the top edges of the edging. Install metal roof according to manufacturer instructions. Use flashing to cover raised intersections, such as on a gable roof.
Metal roof installations can vary widely due to the wide variety of manufacturers making metal roofing panels. While most home reno big box stores may only sell one or two brands, each will have its unique way to install. They will also have proprietary edging and flashing pieces, too.
In this article, we’ll go over how to install a standard corrugated metal roof on a shed, from the materials you’ll need to a finished roof.
- Metal Roof on a Shed: Pros and Cons of Metal Roofing
- Is Underlayment Necessary for a Metal Roof?
- Where Do You Screw Metal Roofing?
- How To Install Metal Roofing On A Shed
- Step by Step Metal Roof Installation
- How Much Should a Metal Roof Overhang?
- Can You Install Metal Roof Over Shingles?
- How Much Does a Metal Roof Cost?
Metal Roof on a Shed: Pros and Cons of Metal Roofing
A tin roof has a much higher return on investment than an asphalt shingle roof for a variety of reasons. Let’s take a look at some of the advantages of having a metal roof.
- Corrugated roofing lasts longer, plain and simple. The average lifespan is 50 years. Asphalt shingles have an average lifespan of 15 to 25 years – and it is usually less than that.
- While subjective, the look of metal roofing is extremely attractive as it comes in a wider variety of styles and colors than asphalt shingles.
- At the end of the life of your metal roof, you can recycle it. It is more eco-friendly than asphalt shingles.
- Tin roofing is lightweight, making installation easy and lessening the load on your roof.
- Resale value on your home is higher with a metal roof due to durability. On average, homeowners are getting around a 70% return on their metal roof when selling their home.
- Metal roofs are nearly maintenance-free
- Some tin roofing systems feature hidden fasteners, for a cleaner look and improved durability.
- You can install a metal roof over your existing shingle roof.
- Metal roofs are more expensive than asphalt shingle roofs. If you opt for a metal roof that is higher-end, expect to pay double the cost of asphalt or more.
- Installing metal roofing is more complex than asphalt shingles. You’ll need special tools to cut the metal and bend the flashing.
- Corrugated roofing can get dented by hail. Repairs require you to replace an entire panel.
- Colored metal roofing will fade in direct sun over time. If you have to replace a panel, the color will no longer match.
- Metal roofing requires special screws, not nails, which cost more than roofing nails.
- The ridge vents on a metal roof are more conspicuous.
Is Underlayment Necessary for a Metal Roof?
No, underlayment for a metal roof on a shed is not necessary. A properly installed metal roof does not need a second waterproof layer on a shed. If you intend to heat your shed, however, then you will need underlayment to protect against condensation damage.
Neglecting to use underlayment isn’t a bad choice for shed owners unless you don’t install your metal roof properly. In that case, your roof sheathing will rot, decay, and eventually have structural failure if you don’t rectify the problem in a timely manner.
Tar paper or Tyvek wrap can be used, too. Tar paper is weather resistant, absorbs moisture and will let it evaporate over time. The drawback to tar paper is that if you have a constant leak, it will become too saturated and destroy the wood beneath it.
Housewrap, such as Tyvek, is a more durable alternative to tar paper but more expensive. It is waterproof but not a vapor barrier, so you’ll still get condensation on the underside of your metal roof. However, the wrap will still largely keep the water from getting onto your roof sheathing.
The best underlayment for a shed metal roof is waterproof self-adhering membrane. Once you apply it, you can rest easy. This membrane is like having two roofs on top of each other – it is durable, waterproof, serves as an air barrier and holds up well in extremely hot and cold climates.
Where Do You Screw Metal Roofing?
Depending on the manufacturer you can either screw in the “high” point of a corrugated metal roof – the raised rib – or the “low point” where the panel is flush with the surface of the roof sheathing.
Both methods of fastening are fine as long as you follow the directions outlined by the manufacturer of the panel. In both instances, when screwing into the panel, you want the rubber washer to sit snug on the screw hole, but not be too compressed. If you screw to the extent in which the metal gets indented, then you’ve sunk the screw too far.
Screwing in the low, non-raised part of a tin roof results in a more secure connection. Most of the screw is sunk into the roof sheathing, making it more likely to survive extreme winds. The downside is that moisture such as rain or melting snow will pass right over the screw. If it comes loose or isn’t installed properly, moisture will find its way into that screw hole.
Fastening your roofing screws through the raised rib of a metal roof reduces your chance of leaking significantly. Moisture will never flow or pool on top of a rib, thus the chance water finds its way into a loose screw hole on a raised rib is minimal. On the other hand, your screw will not be sunk as far into the roof sheathing which means the panels are not as secured to the roof.
Screwing through the raised ribs is more difficult because you run the risk of putting dents into the highs if you sink your screw too far. If you still want to screw through the raised ribs but are concerned about the stability of the panel, then you may be able to buy longer roofing screws – at a cost.
Screws should be spaced 24” on center. Many raised rib panels will have their ribs spaced accordingly so that you can adhere to that spacing. Never opt for spacing further than that – if anything, space them closer together. 18” is also commonly found on metal roofing, but you need more screws.
The general rule of thumb is that you need 80 screws per square of metal roofing. Remember that a square of roofing is a 10×10 section of roof – or 100 square feet. If you know the total square footage of your roof, then multiply that number by .80 and you’ll get the total number of screws you need for the project.
The best type of metal screw for roofing will be the ones stated by the manufacturer of your panel. When you purchase your panels, you’ll also buy the screws that go with it. The screws should be stainless steel with a neoprene washer. Screws with domed metal washers covering the neoprene washers are ideal to ensure the longevity of the washer.
Self tapping screws are great when screwing into the ribs of roofing, but not into the “lows” of metal roofing. Since self-tapping screws have a small drill “bit” at the end, they need some space behind the initial surface for the threads to catch.
If there isn’t any space, such as behind the low of a metal panel, you will have a hard time screwing. Use non-self tapping roofing screws and pre-drill.
Also, when it comes to roofing screws, a higher thread count is not always a good thing. Screws with lots of threads are more prone to pulling out – definitely not what you want for a roofing screw. An aggressive, coarse threaded screw is ideal for metal roofing applications on a shed.
How To Install Metal Roofing On A Shed
Installing a metal roof depends on what type of tin roof panel you’ve bought – there are tons of variations. With that being said, the first consideration when installing a metal roof on your shed is if you have gutters. If you do, then you’ll want to make sure the eave overhang is no more than 1.5” so that water gets directed into the gutter and not beyond.
If you don’t have gutters, a metal roof panel can extend up to 3” beyond the edge of the roof without risking panel failure or damage. The rake ends of your roof will not have any overhang, and should get covered by edging provided by the manufacturer of your metal roofing panels.
Remember that metal roofing often does not have a separate drip edge because metal roofing panels will come with edging pieces that install either over or under the rake edges, and under the eave edges. These act as drip edges but are for use specifically with the brand of your roofing panel.
Step by Step Metal Roof Installation
To explain how to install a metal roof, we’ll use a 10×10 shed with a simple gable roof running down the center of the structure, with a 4:12 slope. We’ll also be using a standard raised rib metal panel that uses exposed fasteners to attach the panel to the roof sheathing.
Keep in mind that you can use either OSB roof sheathing or plywood for a roof deck beneath your metal roof panels. You can install a metal roof directly on top of either. The key is making sure they are at least ½” thick, at a minimum.
You can use furring strips instead of a solid roof deck such as OSB or plywood. If you are not heating your shed, then furring strips are totally acceptable. If you do heat your shed, furring strips greatly increase the amount of condensation you’ll have on the underside of your metal roof, so they should be avoided in that instance in favor of a solid roof substrate.
Step 1: Prepare the Roof Surface
You can use metal roofing over old shingles. If you opt to do this, you’ll benefit from using furring strips and a waterproof barrier first. If you think that is overkill and you’ll have an unheated shed, then you can screw directly through the shingles.
Again, if you opt for battens, then you are reducing the weight of your structure and increasing the likelihood of condensation beneath your roof surface. Battens, however, are cheaper than solid decking and totally adequate for a simple, unheated shed.
Underlayment is not necessary, as mentioned above, for an unheated shed. You can screw your metal panels directly to the surface of your sheathing.
Finally, as you prep the roof surface for underlayment and/or your metal roof panels, plan out any roof venting that you intend to install. Mark it out but do not cut a hole yet. You will make your cut after the roof is installed to ensure the sheathing and metal roof panel cut align perfectly.
Step 2: Install Edging and Underlayment
Install the underlayment as per the instructions by the manufacturer. If you are installing edging, which is essentially flashing that works with your metal roof panels, then you should first install the eave edging.
When installing your eave edging, you’ll fit it to the underside of your eave and onto the face – it should cover the entire face of your eave. Screw the eave edging to the underside of the eave, through the lip of the flashing. Then nail the faces with stainless steel finishing nails of the same color as your flashing.
Then install your underlayment so that it covers the eave edging edge. Install the rake edging over the underlayment. It attaches in the same way as your eave edging, except that you use roofing screws to face screw the rake flashing. Ensure the eave end of the rake edging goes over the eave edging.
Note that some rake edging may go over the installed metal panels, not under. In that case, install the metal panels first and the rake edging afterwards. It depends entirely on the manufacturer of your metal roofing panel.
Step 3: Install the Metal Roof Panels
Installing the metal roof panel depends on the type of metal roof product you have, but start at the edge and make sure your first panel overlaps the existing edging by an inch, if applicable. Otherwise run your first panel flush with the rake edge of your roof and 1” over the eave if you have gutters – 3” if you don’t have gutters.
The top of the metal panel should be flush or no more than an inch below the peak of the gable roof. Screw in your panels according to manufacturer directions. See above for rules about how many screws to use – our rule was 80 per square of roofing.
If screwing into the rib of the metal panel, be careful to not screw too far and dent the rib and overly compress the neoprene washer. If you have metal panels overlap at a rib you can also use metal lap screws, which connect the panels but do not go into the sheathing. These are also used for roof edging that go over metal roof rake ends.
If your metal roof product says you need mastic tape and sealant to put beneath the panel seams, then go ahead and apply. Do it slowly as the tape can be difficult to work with.
Chances are your final piece of roof will need a lengthwise cut to fit the width of your shed roof. If so, a circular saw with a metal cutting blade works really well. You can also use tin snips but cutting long pieces with snips is awkward and arduous.
Step 4: Position and Fix Venting
Once your metal panels are in place it’s time to cut any holes for your roofing venting, chimney or other outlets. Use a jigsaw with a metal cutting blade – they have lots of small teeth. You can also use power shears or tin snips, but you’ll need to then use a different saw to cut through the roof sheathing.
When you install your vents or chimney be sure to use lots of silicone above and below the opening.
Step 5: Install Ridge Cap
Your final installation is a ridge cap over the gable of your metal roof. Each manufacturer will have their own specific ridge cap to use with their corrugated panels, so you’ll follow the directions outlined by the product.
If you don’t have directions, then you’ll first need to know that the cap overlaps each side of the gable by 6” and each end by 1”.
On either end of the cap, make two opposing angled cuts of an inch in the center of the cap. You’ll have a triangle cut out. Use a speed square to find the proper angle for the pitch of your roof. Bend the each side of the cutout with a sheet metal bending pliers. You’ll have two flaps of an inch that will fit over the top of the rakes on either side of the gable.
Use butyl tape, foam, and sealant as specified by the manufacturer. If using all three, first apply the tape the length of either side of the gable just above the edge of where the ridge cap will be, then install the foam on the tape, and finally put silicone sealant on the foam.
Metal lap screws will connect through the foam and ridge cap into the ribs of the metal roof panel beneath
How Much Should a Metal Roof Overhang?
A metal roof should overhang the eave end of a roof 1” to 1.5” if you have gutters. If your roof does not have gutters, your roof can overhang up to 3”. A minimum overhang of 1” is always recommended to prevent rain and other moisture from blowing up under the metal roof edge.
You should not overlap the rake ends of your roof with your metal panels. While some overhang is acceptable on the eaves, you should never overlap rake edges as too much surface area of the panel would be exposed to wind and you would risk the panel failing in extreme weather.
Can You Install Metal Roof Over Shingles?
Yes, you can install a metal roof over shingles. The shingles will act as underlayment for your metal roof and provide a solid foundation provided they are not completely disintegrating.
Some will opt to place battens and underlayment over existing roof shingles. The reason for this is to ensure proper connection of the roofing panels to the roof. Old asphalt shingles may not provide enough holding strength for part of a roof screw, so screwing battens to roof rafters or trusses on top of shingles ensures the integrity of the metal roof.
How Much Does a Metal Roof Cost?
To the surprise of many, some metal roofs do not cost much more than an asphalt roof. The difference often lies in the installation costs. Simply put, more roofing companies do asphalt shingles. The more competition, the lower the price.
If you are using a commonly found brand and style of metal roofing, then expecting to pay around ⅓ more than you would for asphalt shingles. Of course, that price can balloon if you want a different color, style, or brand of tin roof.
For instance, one square of asphalt roofing will cost around $100. Metal panels are commonly found in 10’, 12’, and 16’ lengths. A panel that is 10’ long and 36” wide would require 3.5 panels to make a square. If one panel is $30, then you are looking at about $115. Of course, that is for the cheapest type of metal roofing.
When installing a metal roof, it is absolutely critical to heed all warnings and recommendations from the manufacturer of the panels you buy. Make sure to also purchase the corresponding edging pieces, ridge cap (if applicable), and screws to go along with your chosen product.
Also remember to consider the function of your shed. If you plan on throwing a stove in it a few years down the road, then you’ll have to consider underlayment and potentially a different type of roof deck beneath your metal panels.
Regardless of the type of metal roof you get, you are improving the value of your structure and more than likely the aesthetic, too. Do your research to find the right metal panel for your shed, and enjoy it for decades afterwards.