Over the years I’ve had the opportunity to build quite a few shed roofs, and no two are ever the same. I’ve done simple gables, slant roofs and a few lean-to’s – and probably a few others I can’t quite recall. And of course, every time I build a new roof, I’m always learning how to build different types of shed rafters.
I figured it was time to put that shed rafter knowledge into an article to share with you. I want to share with you how to easily build rafters for your shed. We’ll take a look at a gable roof, but you’ll be able to apply the rafter method outlined below to most types of shed roof styles.
Below we’ll go through what it takes to construct rafters for a shed, step by step. We’ll also take a look at the materials and tools you’ll need to do the job.
- What is a Rafter?
- Difference Between a Rafter and Truss
- Types of Shed Rafters
- What Size Lumber Should Be Used for Roof Rafters?
- Tools and Materials Needed to Build Shed Rafters
- How To Build Rafters for a Shed
- What Is the Standard Shed Roof Rafter Spacing?
- How to Install Rafters on a Shed
What is a Rafter?
A rafter is the frame of your roof. More specifically, it is a beam that goes from the peak of your roof down to the eve. It rests on top of your wall framing and, when done properly, serves to keep your shed walls in place while supporting a roof.
Difference Between a Rafter and Truss
Rafters typically use larger wood beams and do not have any sort of framework other than the beams themselves. A rafter beam is usually larger than a 2×4 – large homes may have rafters that are 2×12 or more!
A truss, on the other hand, is only made up of 2x4s and is often pre-fabricated in a factory. Trusses use “webs” of 2x4s within the truss structure to support the roof. Trusses are held together with steel gussets and are staples of home construction.
Types of Shed Rafters
Shed rafters come in many different designs, depending on the design of the shed and the shed roof. We’ll take a look at some of the most common shed rafter types and why you might or might not consider them in your next shed project.
A common rafter comprises two beams that extend upwards from the top plate of either side of a shed wall. Each beam is notched at the bottom, called a birdsmouth, so that it rests flat on top of each wall.
At the top, where the rafters meet, they are either angled to meet at a point or attached to a horizontal ridge beam. A ridge beam runs the length of the shed roof, connecting every pair of rafters.
Some shed rafters do not incorporate ridge beams, either due to small size or lack of technical know-how. However, our instructions include making shed rafters with a ridge beam.
When to use common rafters? You can use common rafters on any shed roof, but they make the most sense when constructing a gable roof or lean to-type shed roof where they can sit on or attach to top plates of a wall. Lean-to rafters then connect to a ledger board against a wall of another shed or house.
A hip rafter works in tandem with a common rafter, but when used, it creates a more visually appealing roofline but creates less interior space.
Hip rafters, when used, are beams that sit on two or all four corners of a shed wall and extend upward to meet the ridge beam. They extend diagonally so that one end, or both, of a rectangular shed roof, is slanted perpendicularly to the gable roof in the midsection of the shed.
These rafters require extra measurement to mesh the hip gable to the ridge beam properly. They also make sheathing and adding roofing material a bit more difficult due to the added angles on your roof.
Also known as a “king common”, the king rafter is the center rafter between two hip rafters. It extends from the edge of the ridge beam down to the center of the wall, making it perpendicular to the common rafters. A king rafter has hip rafters jutting from either side of where they meet the ridge beam.
In a traditional hip roof, the king rafter would be the same length as the common rafters you are using. However, since sheds take on all shapes and sizes, you should not take this rule as set in stone.
When to use a king rafter? You’ll use a king rafter anytime you construct a hip-style shed roof.
Hip jack rafters are the shorter rafters that connect to the hip rafters. Since the hips connect diagonally to the ridge board, the rafters close the edges of walls on either side of the hip rafters will be shorter. These are called hip jack rafters.
What Size Lumber Should Be Used for Roof Rafters?
You can’t just use any size of wood you have sitting around for rafters – consult rafter span tables to see what size of wood you can use.
As you can see, the size of wood depends on the span of your shed. Now, your rafter is going to a little longer than half the span of your shed since it is at an angle. The pitch and span of your roof will dictate how long of a rafter you’ll need – use maximum span calculator to help you find your rafter size.
If you look at the rafter span chart, you’ll notice that 2x4s can be used for rafters on spans up to 11 ½’. Anything beyond that you are looking at using 2x6s for most sheds.
Tools and Materials Needed to Build Shed Rafters
- Miter Saw
- Circular Saw or jigsaw
- Cordless Drill
- Measuring tape and speed square
- 2x4s – not pressure treated
- 2×6 – long enough to span the entire length of the shed
- ⅝” plywood
- 1 ½” 8d galvanized screws
- 1 5/8” deck screws
- Construction adhesive
- Simpson RR Connectors and hurricane ties
How To Build Rafters for a Shed
Let’s get down to business and build some rafters. Now that you’ve got a decent idea of how big your rafters are going to be, we’ll go through how to build them step by step.
As an example, we’ll use a 10×8 foot shed, with the span being 8 feet. The process will generally be the same for a shed of any moderate size, but be sure to use the rafter sizing calculator above to find the correct rafter length and size for your shed rafter project.
We’ll be using a ridge beam for this project, so each set of rafters will meet a horizontal 2×6 at the apex, which will run the length of the shed and connect to all of the rafters.
Remember that for rafters, you’ll always use a ridge beam one size larger. So in our case, 2×6. If you use 2×6 lumber for rafters, your ridge beam will be 2×8.
Determine the Pitch of the Rafters
First, you’ll want to find the pitch of your rafters, which will help you find the length of your rafters. Use this calculator to find your rafter length.
Many conventional roofing products, such as shingles, mandate a slope no lower than 2:12. More, they usually claim that 4:12 is the lowest you can go without any special underlayment. Our roof we will be constructing will be 4:12.
Calculate the Length of Your Rafters
We’ll be building a 4:12 pitch roof, with an 8’ span with 1’ of overhang. With this set of specs, we are looking at a rafter length of 5’ 3 ½”. This total span is well within the load capacity of 2×4 rafters, but how far apart can we space the rafters?
If you look at our rafter spacing chart, you’ll notice that 2x4s can span an 8’ gap on a 4:12 roof. However, you’ll also notice that that is only for #1 kiln-dried wood, which might not be available to most of us. In fact, #2 grade 2x4s seem to be more common.
Assuming then that we are using #2 grade 2x4s, we’ll have to space our rafters at 16” on center. This gives us plenty of support for our roof without having to worry about snow or other debris caving our shed roof in.
Cut the First Rafter Tail and Ridge Cuts
The handiest tool in your toolbox for this job will be the speed square. You’ll notice that your speed square has regular measurements on one side and degrees on the other. You’ll also see that the end with degrees has a set of numbers, 1 – 24, just above it.
Those single numbers correspond to the roof pitch. So since we are using a roof pitch of 4:12, we’ll use the number 4 in that row to help us make our miter cuts.
To start, I already know that my rafter length is going to be 5’ 3 ½”. I’ll use my speed square to measure my first cut on one end of my 2×4 rafter. I’ll use the corner of the speed square on one edge of the 2×4, where it says “pivot”. I’ll then rotate the square on the pivot until the 4 is lined up with the outside edge of the rafter.
I’ll mark a line along the edge of the speed square. This gives me an exact 4:12 cut. Now, I could do a few calculations and know that 4:12 is roughly 18.5 degrees, but a speed square is so quick that I don’t need to do that.
If you want to use a miter saw, you can simply rotate your miter saw to 18.5 degrees and cut.
When cutting the other end, be sure both cuts are parallel! If the length of the cut is 5’ 3 ½”, then you’ll be measuring only on one side from end to end. Using the miter saw, simply slide the wood through after you make your first cut. This ensures you keep the cuts parallel.
Then use a measuring tape and measure from the furthest, top point of your first cut. Make a mark and use your speed square just as you did the first time.
Cut the Birdsmouth Joint
The birdsmouth joint can be tricky, but if you use your unfinished shed floor as a template, then it’ll go much quicker. Lay a set of rafters down on the floor and align them to where they would sit on the walls (if the walls were already there). You’ll need to lay down a 2×4 on its edge at the apex of the two rafters to act as a ridge board – for spacing.
Get some scrap 2×4 pieces. Cut four of them into lengths of a couple of feet or so. Screw each piece so that there is one above and below each rafter. Do it carefully so that rafters are not out of place. You can now remove your rafters and insert another pair – you’ve created a jig to cut your birdsmouth joints.
With rafters in your jig, use a pencil to outline the cut in either rafter. Since both rafters are hanging off the edges of your shed, you’ll just outline the corners of the shed onto the 2x4s. You’ll be outlining underneath each rafter, but you’ll use the edge of the shed floor as a guide, so you don’t have to see what you are doing because the edges of the floor are your guide.
Once you’ve outlined either rafter, flip them over. You’ll have a triangle. This isn’t the exact cut you need to make, however. You still need to take a speed square and extend the vertical line you drew to the bottom of the underside of the rafter.
Now – one last measurement. Remember that your rafters sit on the top plate of your shed walls. But the vertical cut on your birdsmouth will not be snug with the top plate. Why? Your shed walls still need sheathing, and that will fit up and under your birdsmouth cuts, so you need to extend the horizontal cut hanging over your shed walls by at least ½” or ⅝” to account for your wall sheathing.
Draw another vertical line ½” or ⅝” away from your initial vertical on your rafter – it should be closer to the outside of your rafter. Then extend the horizontal line from your initial cut to meet this new line.
That new vertical and the horizontal line you drew extending toward the inside of your shed are the cuts you’ll make – a triangle.
I use a jigsaw to make this cut, although a handsaw or circular saw works, too. If using a circular saw, you can make your cuts, flip the wood over, cut out from the other side, then use a finishing handsaw to remove the rest. Or you can just use a handsaw and cut slowly.
See a close-up view of the birdsmouth cut, below:
Mark and Cut the Other Rafters
Use the initial rafters on top of new ones as a guide for birdsmouth cuts.
After you’ve cut all the rafters, line them up side by side to check for accuracy. You might think that since you used the original pair as a template that there wouldn’t be any discrepancy, but you’d be surprised at how much variation can occur!
Additional Steps for Roofs without a Ridge Beam
If you aren’t using a ridge beam, then you’ll want to use plywood gussets to reinforce the connection at the apex of each set of rafters. For an 8×10 shed, one sheet of ⅝” plywood should be fine.
You are going to cut out triangles that will cover the apex of each set of rafters. The rule of thumb is that the gusset should be twice the width of the wood you use for your rafters. So roughly 7 – 8” long for a 2×4.
Each side of the gusset will be 8” long, but only 8” tall. Layout your sheet of plywood on sawhorses. Facing the long side of your material, measure down from the top edge 8”. Then draw a line across the width of the plywood from that mark. Use a circular saw or jigsaw to make the cut.
Now you have a piece of 8” x 48” plywood. Use this piece to mark out the rest of the plywood. Now you need to cut your smaller piece into three triangles. Starting at one long edge, mark off points every 8”. Now do the same on the other long side. Connect the dots so you have three triangles, each 8” high and 16” long.
Use a circular saw to cut them out. Use the finished gussets as templates to mark out the rest of your wood, and cut accordingly.
Attaching the gussets requires 1 ⅝” wood screws and construction adhesive – I use Gorilla Heavy Duty Construction Adhesive and it works great. Make sure you use gloves when handling. Remember that your sets of rafters on either end will only have a gusset facing the inside of the shed. All interior rafters will have gussets on both sides.
What Is the Standard Shed Roof Rafter Spacing?
For standard shed roof rafter spacing, see rafter span chart.
There is no standard spacing – it depends on what size of rafters you want to use, and the span of your shed. For instance, #2 grade 2x4s at 16” on center will span just over 9’. If you get premium, kiln-dried lumber, then you could span 10.5’ with the same size of lumber and rafter spacing.
When it comes time to install your rafters, consider rafter size, cost, and especially safety. Be sure your lumber and rafter spacing adheres to the load chart.
Lastly, if you live in a place with heavy, wet and regular snow, then consider your load. Consult the heavy load table, which has different values for lumber sizes, spans, and rafter spacing.
How to Install Rafters on a Shed
Installing rafters with a ridge beam can be tricky, especially if you are doing it alone. Take a look below to see how you can do it all on your own, without breaking your back!
Measure Rafter Placement
Mark out where you are going to place your rafters. If you are doing 16” OC, then start ¾” in from the front edge of your top plate, where your first rafter is going to sit. From there, measure 16” down the top plate. Make another mark. Go until you get to the end.
Your last rafter won’t be exactly 16” away, so your last two will likely be closer than the others, which is fine. After you’ve marked where each rafter will go, it is time to install the top plate to rafter hurricane tie connectors. Be sure to place them so that the notch opening is flush with the top plate of the walls. They are installed so that they will be nailed to the interior sides of the top plates.
You’ll install them so that the mark you made on the top plates is in the center of the notched opening of the connector. These connectors require 10 SDS structural screws. You can’t use any old wood screws with these connectors.
For the rafters on either end, use something like angle connector. Be sure to install these brackets 1 ½” away from the outside edges of the wall on the top plates. Make sure they are near to the side edge of the top plates so that they meet up exactly with the birdsmouth cut. This will give the connector a full face of wood on the rafter to nail into.
Lastly, you’ll want to mark out the ridge beam in the same spots you’ve marked your top plate. I take the ridge beam and lay it on the top plate of one side of the wall, then mark the edge of the ridge beam just where I’ve marked the top plate. Make sure the top plate and ridge beam are aligned exactly.
I then bring the ridge beam to the other wall to check alignment – if the marks don’t line up, then I know I need to re-check my measurement. Once I know the measurements are correct, I use these ridge rafter connectors to connect rafters to the ridge board for all rafters except the pairs on either end.
Install these connectors where you’ve made your marks – this will save you tons of hassle later when you’ve got the whole assembly up.
Do not install the ridge board to rafter connectors on the ends of the ridge beam yet – you will do this at the end.
Make a Ridge Beam Brace
Before I install the first rafters and ridge beam, I need braces for my ridge beam on top of either end of my shed walls. I’ll start by finding the center of my span on both the front and back walls and make a mark.
Use this calculator to determine the length from your ridge beam to the top plate of one wall. Cut one 2×4 to exactly this length, then cut two more about four inches longer than the first.
Sandwich the short 2×4 between the longer ones. Screw them together. The short piece will sit in the exact center of one wall, right on top of the top plate. You can affix it with a couple of wood screws – it isn’t permanent, so it just needs to be able to hold the ridge board.
Do the same thing to the opposite wall. When done, take your ridge board put it up and through the braces. It should fit perfectly without any overhang. If not, then re-check your measurements.
Attach Middle Rafters
Attaching the rest of the rafters requires you to merely line up your rafters in the connectors you’ve already installed. If you measured correctly, this is the easy part. I would suggest you install the rafters in pairs. If you do just one side, all the way down, then the ridge board can come loose or be distorted from all the hammering in the same direction.
Attach End Rafters
Remove the braces you made for the ridge board. Once out of the way, you can go ahead and install connectors on the ridge board. You’ll use the same type of connectors you used on the other rafters, except that you’ll cut one wing off – the one on the exterior shed side.
Install the connector using No.9 1-1/2-inch Simpson structural-connector screws. Now you can install your rafters into the connectors. It should be flush with the outside edge of your top plate.
Repeat on the opposite side. Done!
I hope you were able to get some good information from this article in terms of how to build rafters for a shed and how to install them. Remember, there are many different ways to do these projects, and I’ve attempted to give you a way to do it cheaply, yet safely, while staying within budget.
As always, if you have any questions or suggestions, please drop me a line or leave feedback below. I wish you luck in your next shed rafter building project!
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1 thought on “How to Build Rafters for a Shed: Last Guide You’ll Ever Need”
Thank you. Your instructions are clear and easy to understand. I also like that you included calculators and speed square use. I appreciate the time and effort you put into this so that us tyros have somewhere to go for good, useful information.