What you need before you start
A pitched roof sheds water and snow better than a flat one, and it is the most common choice for sheds. Before you cut anything, you need to know three things: the width of your shed, how steep you want the roof (called the pitch or slope), and what materials you are using. The pitch is usually expressed as a ratio — 4:12 means the roof rises 4 inches for every 12 inches it runs horizontally. A 4:12 or 6:12 pitch works well for most sheds and sheds snow without being difficult to build.
You will also need to decide whether to build the roof frame on the ground and lift it onto the shed, or build it in place on top of the walls. Building on the ground is faster and safer if you have help, but requires space to work. Building in place takes longer but uses less space and is easier alone.
Key Takeaways
- A pitched roof needs two sloped sides that meet at a ridge beam running the length of the shed, supported by rafters that rest on the top plates of the walls.
- The pitch (slope) determines the angle of the rafters and affects how much headroom you have inside; 4:12 or 6:12 pitch is standard for sheds.
- Rafters are usually 2×6 or 2×8 lumber spaced 16 or 24 inches apart, with collar ties connecting them to prevent the roof from pushing the walls outward.
- The roof frame is covered with plywood sheathing, then roofing felt, then shingles or metal panels — each layer fastened with nails or screws in a specific pattern.
- Building the frame on the ground and lifting it onto the shed is faster than building in place, but requires at least two people and a safe way to raise it.
Calculating rafter length and angle
The length of each rafter depends on the width of your shed and the pitch you chose. If your shed is 10 feet wide, the rafters run from the top of one wall to the ridge beam in the middle — that is 5 feet horizontally. With a 4:12 pitch, the rafter rises 4 inches for every 12 inches it runs, so it rises 5 × (4/12) = 1.67 feet, or about 20 inches. The actual rafter length is the hypotenuse of that right triangle, which you can find with a calculator or a rafter square.
A rafter square (also called a speed square) is a triangular tool with numbers printed on it that does this math for you. Place it on the rafter board with the 4 mark on the top edge and the 12 mark on the side edge, and draw a line along the hypotenuse — that is your cut angle. The rafter length is printed on the square as well. If you do not have a rafter square, use an online rafter calculator and enter your shed width and pitch; it will give you the length and angle.
Cutting and assembling the rafter pairs
Cut two rafters for each pair — they are mirror images of each other. One rafter has its top end cut at an angle to meet the ridge beam, and its bottom end cut to sit flat on the top plate of the wall. The other rafter is identical but flipped. Lay both rafters on a flat surface and connect them at the top with a piece of plywood or 2×4 lumber nailed across them — this is called a collar tie and it prevents the rafters from spreading apart under the weight of the roof.
Space the collar tie about one-third of the way down from the peak. Use 16d nails (3.5 inches long) or 3-inch screws, at least two per side. Test the angle by setting the pair upright on a level surface — the peak should be directly above the midpoint of the base, and the base should sit flat on both sides.
Building the frame on the ground versus in place
On the ground: Assemble all your rafter pairs on the ground with collar ties in place. Build a temporary base the same width as your shed top plates, and set the rafters on it. Add a ridge beam (usually a 2×8 or 2×10) running the full length of the shed, nailed to the peak of each rafter pair. Once the frame is complete and braced, you lift it as one unit onto the shed walls. This requires at least two people, a way to raise it safely (a crane, a rented lift, or a system of ropes and pulleys), and space to work.
In place: Set the ridge beam on temporary posts at the correct height above the shed walls. Nail one rafter pair at a time to the ridge beam and the top plates, working from one end of the shed to the other. This is slower but does not require lifting equipment or extra help. Brace the ridge beam as you go so it does not sag or shift.
Fastening rafters to the walls and ridge
Each rafter sits on the top plate of the wall and is nailed or bolted to it. Use three 16d nails per rafter, driven through the rafter into the top plate, or use a metal rafter tie and bolts for a stronger connection. The rafter should rest flat on the top plate with no gaps. At the ridge, the two rafters meet at an angle and are nailed to the ridge beam with at least three 16d nails per rafter, driven from the side of the rafter into the beam.
Space the rafter pairs 16 or 24 inches apart along the length of the shed (16 inches apart is stronger but uses more lumber). Once all rafters are fastened, add horizontal bracing between them if the shed is longer than 12 feet — this prevents the roof frame from racking (twisting out of square).
Sheathing, felt, and shingles
Cover the rafter frame with plywood sheathing, usually 1/2-inch or 5/8-inch thick. Lay the sheets perpendicular to the rafters, starting at the bottom edge of the roof. Stagger the seams so they do not line up from row to row. Nail or screw the sheathing every 6 inches along the rafters and every 12 inches in the middle of each sheet. Leave a 1/8-inch gap between sheets to allow for expansion.
Once the sheathing is on, roll out roofing felt (15-pound or 30-pound) over the entire roof, overlapping each row by 2 inches. Nail it down with roofing nails every 12 inches. Then install shingles or metal panels according to the manufacturer's instructions — asphalt shingles are nailed with four nails per shingle, and metal panels are screwed down with rubber-washer screws to prevent leaks.
Flashing and finishing
Install flashing at the edges and peaks to direct water away from the shed. At the ridge, use a ridge cap or ridge flashing that covers the peak and overlaps both sides of the roof. At the eaves (the bottom edges), install drip edge flashing that hangs over the edge and directs water into a gutter or away from the walls. Seal all nail holes and seams with roofing cement or caulk rated for the temperature range in your area.
If your shed has a door or window, install flashing around the opening before you shingle, so water runs over the flashing and down the roof rather than into the opening. Test the roof by running water from a hose along the ridge and watching where it goes — it should flow down both sides and off the eaves without pooling or running back toward the walls.
Frequently Asked Questions
What pitch should I use for a shed roof?
A 4:12 or 6:12 pitch is standard for sheds. A 4:12 pitch is gentler and easier to build, while a 6:12 pitch sheds snow and water faster. Anything steeper than 8:12 is difficult to work on safely and is rarely needed for a shed.
Can I build a pitched roof alone?
Yes, if you build the frame in place on top of the walls. Building the frame on the ground and lifting it requires at least two people and lifting equipment. Building in place is slower but safer and more practical for a single person.
What size lumber do I need for rafters?
For most sheds, 2×6 or 2×8 rafters spaced 16 or 24 inches apart are sufficient. The exact size depends on the span (distance from wall to ridge), the pitch, and the snow load in your area. A local building inspector or lumber supplier can tell you what size is required for your location.
Do I need a ridge beam or can the rafters just meet at a point?
A ridge beam is stronger and easier to build with, especially if you are building in place. Without a ridge beam, the two rafters must be cut and fitted precisely to meet at a point, and the roof is more likely to sag over time. A ridge beam is the standard approach for sheds.
What is the difference between roofing felt and roofing paper?
Roofing felt is made from fiberglass or wood fibers and is more durable than roofing paper. Both serve as a water barrier under shingles, but felt lasts longer and is worth the small extra cost. Use 30-pound felt if you live in a hot climate, as it resists melting better than 15-pound.