How to Extend a Roof Shed

Use a sheet of graph paper and pen to create an accurate drawing of the preexisting shed, transcribing the center-to-center spaces between the studs -- the upright “ribs” that support the walls and roof -- and the dimensions of the studs. Draw in the ridge beam. Also note down the sizes of the sheets used to make the walls, the roof and the floor. If the shed is supported off the roof it stands on, make a note of what it stands on and the dimensions of that material.

Make a detailed plan of the extended project on a second sheet of graph paper, transferring the same materials to the extension as are used in the preexisting shed. For instance, if the studs are spaced 18 inches apart and you want to extend the shed 3 feet, this will require two extra studs per side, plus the extra studs for the roof and the floor supports (if any). Apply this logic to the panels that comprise the floor, walls and shed roof also; this will give you your shopping list.

Don’t forget fasteners such as nails and/or screws, and the hardware for making corners, attaching the walls to the floor and attaching the roof to the walls. Duplicating the original structure in terms of the hardware used, the intervals between fasteners and the size of the fasteners will result in a strong extension.

Remove the appropriate end or side of the shed from the original structure, so that the open face points in the direction you will extend the building. Because most sheds are assembled from premade panels that include doors and windows as fixtures, this process should be relatively easy. Study the way the shed was assembled, then reverse the process. Retract the fasteners holding corner brackets in place, and any that pass through the roof and floor panels into the walls; this should allow you to lift the panel away.

Assemble the studwork that will form the “skeleton” of the extension exactly according to your second plan, so that it matches the preexisting template. Once the studwork that will support the floor, the walls and the roof is all in place, install the panels. Work from the bottom up.

Reinstall the end or side panel you removed, attaching it to the extension in exactly the same way it was originally fixed to the preexisting shed. Reuse the old brackets and ties if they show no signs of warping or weakness, but use new fasteners.

Continue the original shed’s roof onto the extension if the original has an exterior coating such as aluminum paint, or a layer of waterproofing material such as shingles or rubber-roll roofing. Only climb onto the roof when all the other construction work is entirely finished.