How to Add a Lean To Onto a Shed

| December 22, 2010 | Comments (0)

How to Add a Lean To Onto a Shed

  • Choose the materials you will use. Lumber is a fairly strong and inexpensive material for framing, and tin is a suitable roofing and siding material. Other options include shingle roofing, rolled roofing, metal studs for framing, and cementious board or composite sidings, may be more suitable for your project and location. In reference to the addition in the photos accompanying this article, wood and tin were selected for the primary building materials. Some metal framing was used simply because it was available as surplus, and was suitable the project.
    1. Poles for supporting the eave framing. 4X4 pressure treated southern yellow pine will support a lightweight roof framed with 2X4 boards, spanning less than 15 feet or so. For a longer, heavier roof span, 6X6 timbers or even steel columns may be more suitable.
    2. Rafters for framing the actual supporting structure of the roof will need to be strong enough to support the weight of the lathing, decking, and the workmen who will walk on the roof while installing it. A somewhat typical span of less than 10 feet may be framed with southern yellow pine if the rafters are free of large or loose knots and are otherwise structurally sound. Lodgepole pine, spruce, and other softer pine species may not be used for roof framing members because of the lesser strength and knottier nature of these lumbers. For roof spans 10 feet or greater, 2X6 nominal framing or larger, should be used.
    3. Rafter nailers spanning between the posts on the eave side of your lean-to must be strong enough to support the load of multiple rafters, so a minimum size of 2X6 nominal southern yellow pine is recommended.
    4. Nailers attached directly to the wall of the building onto which the lean-to is being added can be the same size lumber as the rafters themselves, provided the nailer is attached securely to the wall of your building, and code required anchors (such as hurricane anchors, according to the Southern Building Code) are used.
    5. Lathing strips, or the framing members that lay across the rafters that the metal roofing is attached to should be sound southern yellow pine or a similar lumber. 1X4 lathing lumber is sufficient to support a normal load on spans where the rafters are located at 24 inch center spacing or less, but 2X4 lumber is easier to fasten to (it bounces less when nails are driven into it), and may not be significantly more expensive than the 1X4s.
    6. Fasteners. Nails should be large enough to penetrate the attached member and the supporting member deeply enough to secure the two pieces. Screws may be used to attach dissimilar materials, such as metal framing, roofing, or siding to wood framing, or even for joining two separate wood members.
    • Figure the amount of each material you will need, price them, and purchase them. If you draw a small floor plan, your local lumber yard or home improvement store may be able to help with doing a take off of the materials you will need. Here are some basic items a lean-to addition for a tin shed would use:
    • The area after clearing, with the outboard posts installed. Lay out the area within the footprint of your addition. Remove any debris or vegetation that will be a problem during construction or future use, and grade the soil to a suitable elevation. If you are going to leave an earth floor in the addition, compacting the soil probably will not be necessary.
    • The deeper you dig your support posts in, the stronger they will be. Dig your post holes for the supporting posts. Measure the distance out from the wall you will fasten the lean-to to, then align the post with the location the starting corner will be made. For an addition that will span the full length of the structure you are adding to, you can simply pull a string line across the end of your building, or even eyeball a starting point for your post.
    • These posts are set directly into the soil, but concrete would anchor them more securely. Set the opposite end post, then pull a line between the two ends to align the intermediate posts. You can use a measurement between the building an each individual post, and between posts to set the intermediate posts, but using a string line will make the task easier.
    • This string is set level, so intermediate posts can be aligned, and the height of the notches can be marked. Use a line level or builder’s level to mark a bench elevation (a reference grade) on each post, then determine the bearing height of the rafters. You can again mark the end posts, and use either a plain line or a chalk line to mark the intermediates.
    • The support post is notched for the 2X6 to rest on. Notch the top of your posts so the rafter nailer, or rafter supporting joist will rest on the notch. If you choose to, you may simply nail directly into the side of the post, but doing so places all the weight on your fasteners, so you must nail or screw the nailer very solidly if you do.
    • Set the nailer on the notches. If the nailer is not long enough to span the total length of your shed, make sure any joints set on a post to insure there is no loss of bearing potential for the nailer. Nail the nailer into place, making sure the spacing between your posts remains correct.
    • Plumbing up and packing one of the corner posts. Plumb the outboard wall and backfill the posts to hold them in place. For areas where high winds or severe storms are likely, backfilling the posts with prepackaged concrete mix.
    • Here, we reuse metal studs for purlins to fasten the siding to. They help hold the exterior wall in line while rafters are installed.  Attach any purlins you plan to use, if you are siding, or building a solid wall, on the outboard side of your lean-to. Remember to nail everything solidly as you install it, so you will not overlook a critical connection before moving to the subsequent step in the project.
    • Using a battery operated drill to drive screws into the rafter nailer. Fasten the nailer on the side of your existing building where you will attach the upper end of your rafters. For attaching a wooden nailer to a metal-sided building, use a self-drilling screw with sufficient threads to hold the nailer tightly. If possible, nail through the siding into the building’s framing members. Regardless of what method you choose to attach this member, make sure it is fastened securely, since it will be supporting both the weight of the roofing and framing, and the person who is installing it.
    • Marking the rafter spacing on the lower nailer. Lay out the rafter spacing on the upper and lower nailers. Starting at one end, measure the span you have determined to use while planning the building, and mark each space. Marking the edge of the rafter, rather than its center will make seeing the mark when you position the rafter easier.
    • Using a rafter square to determine the roof slope for the angle cut on the rafters. Determine the roof pitch (if you did not do so during the planning process), by stringing a line from the top rafter attaching point to the bottom one. Hold a speed square(also known as a rafter square) plumb against the top nailer where your string is fastened, and read the angle on the square’s angle scale.
    • Cut one end of your rafters at the angle you read on the speed square. Test the cut by holding the rafter in position, and if the cut does not fit tightly, adjust it. Having a good fit will increase the hold of your nails when you attach the rafters. When you have established the best angle for the top cut of your rafters, cut each one using that angle. Unless you are certain both nailers are exactly parallel, do not cut the lower end of the rafter. This can be done after the rafters are installed, if cutting them is necessary.
    • Toenailing the rafters at the top nailer. Nail the rafters at the top nailers, using a toenail nailing method. Avoid starting the nails too close to the end of the board, as this may split it, and make a strong connection impossible.
    • Toenailing the bottom end of the rafters to their support beam, here, a 2X6 southern yellow pine board. Space the lower end of your rafters on the layout marks discussed previously, and toe nail them in place. Again, use as many nails as possible without splitting the rafter, especially if you are not planning to use a structural anchor like a hurricane clip to supplement the nail’s holding ability.
    • Nailing the lathing to the rafters. 16 gauge metal studs were used in this project because they were free, lumber members work just as well, and don’t require predrilling to nail. Lay out the spacing of your lathing, or the strips that span perpendicular to the rafters for your tin to fasten to. For 29 gauge metal roofing, spacing can be up to 30 inches between centers. Nail the lathing securely, with a minimum of two nails at each rafter, being careful to keep them aligned.
    • Trimming the existing roof after the lathing is installed so the fit between roofs is as tight as possible. Cut back the roofing on the existing building if you need to so the new roof can fit beneath it correctly. Typically, a lean-to roof will lay at a different pitch, or slope than your existing roof, and the lean-to’s roofing will need to fit fairly snugly underneath the existing roof to prevent rain from blowing into your addition.
    • The metal roofing being installed, starting on one end. Note the lean-to roof slides underneath the roof of the existing building. Lay your metal on the lathing, beginning at one end. Be aware that some roof metal profiles have a direction of run, so that the laps fit correctly. This will insure a good, weathertight roof system.
    • Using the battery drill to install neoprene washered decking screws in the metal roofing. Fasten your metal roofing with a suitable fastener. Wood screw threaded hex screws with neoprene gaskets are very good for this purpose.
    • Here, corner trim metal and roof edge metal meet and are fastened. This is more of a flashing metal than an aesthetic trim, but serves both purposes.  Install any trim you choose to finish off your lean-to’s roof. Metal angle will close any gaps between the lathing strips and the roofing so that water will not blow in through them. With a piece of break metal configured in the right dimensions, this will provide a decent finished appearance to these areas, serving two useful purposes in one step.
    • Install any partitions you will use to divide the lean-to’s floorspace into different usable areas. The shed in the photos is ten feet wide and twenty-one feet long, so a partition was installed to create a seven foot by ten foot space on one side, and a fourteen foot by ten foot space on the other. This partition was created by installing steel stud purlins between one of the outboard support posts and a nailer fastened vertically to the existing shed wall.
    • Build doors if they are required. Framing these is a separate process not covered in the scope of the project used to illustrate this article, and is not included at this time.
    • Finishing the roof, making sure all the required screws are installed. Check all fasteners to make sure none were missed during construction. Pay close attention to the screws/nails that attach the roofing components, to the siding, if used, and to trim installed on corners or edges. Make sure any metal corners (if you side the lean-to with tin) are rolled or formed in such a way that no sharp edges are exposed, creating a hazard. Clean up the worksite and put the tools away.

Category: How to Add a Lean To Onto a Shed

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