Building a shed roof is an achievable DIY project when approached in the right sequence with the correct materials. The two most common shed roof types are the pent roof, a single slope, and the apex roof, a symmetric two-slope ridged structure. Both share the same basic elements: a structural frame of rafters, a deck of boards or sheet material, and a weatherproof covering.

Pent Roof Construction

A pent roof slopes in one direction from a higher wall plate at the back to a lower fascia board at the front. To build one, fix a wall plate to the rear top of the shed walls, ensuring it is level and at the correct height to achieve the desired slope angle. The front of the shed wall must be lower than the back by the amount needed for the required pitch. Rafters are then cut to length with a plumb cut at the top and a tail at the bottom, spanning from the wall plate to the front fascia. Space rafters at 400mm to 600mm centres depending on the sheet material being used for the deck. Fix the rafters and then nail or screw OSB or tongue-and-groove boarding across them as the deck.

Apex Roof Construction

An apex roof has two equal slopes meeting at a central ridge. A ridge board runs along the top centre of the shed, supported by gable end posts or a temporary prop during construction. Rafters are cut in pairs, each with a plumb cut at the top to butt against the ridge board, a bird's mouth notch to sit on the wall plate at the eaves, and a tail of the required overhang length. The pitch angle determines the rafter length and the height of the ridge above the wall plates. After framing, the deck is laid across the rafters on both slopes.

Roof Decking

The most common decking materials for shed roofs are 18mm OSB or plywood sheets and tongue-and-groove feather edge boarding. OSB and plywood sheets are faster to lay and provide a smooth base for roofing felt or other waterproof membranes. Boards are more traditional and visually appropriate for garden sheds with an exposed underside interior. Fix the decking with ring-shank nails or screws at each rafter and at sheet edges.

Waterproofing

The most common waterproofing for shed roofs is mineral-surfaced roofing felt laid in horizontal strips from the eaves upward, each strip overlapping the one below by at least 75mm. Fix with galvanised clout nails at close centres and along both edges of each strip. At the ridge, the felt from each slope should overlap and be folded over the ridge board and fixed down on the opposite slope. EPDM rubber roofing is a more durable alternative that provides a single-piece membrane without laps and can last 25 years or more. GRP fibreglass is another long-lasting option.

Fascia, Barge Boards, and Guttering

Finish the eaves with a fascia board nailed to the rafter tails to provide a neat edge and a fixing point for guttering. Barge boards at the gable ends finish the verge neatly and prevent water tracking under the felt edge. A gutter and downpipe divert water away from the shed walls and foundations, significantly extending the life of the structure.

Summary

A shed roof is built by framing rafters on wall plates, decking the frame with OSB or boarding, and waterproofing with felt, EPDM, or GRP. A minimum pitch of 10 degrees ensures reliable drainage. Fascia boards, barge boards, and guttering complete the weatherproofing. Both pent and apex roof designs follow the same basic construction sequence with different framing details.