When your shed or other storage building no longer provides enough room, you may want to consider adding a lean-to addition onto it. If the existing shed is structurally sound and has exterior wall which allows for attaching your lean-to, this can be a fairly simple project.
Step 1
Determine you have a genuine need for additional work or storage space. Building a lean-to is a laborious, and somewhat expensive project, and doing so without a clear purpose and need probably is not practical for most people.
Step 2
Consult the local building authorities to code requirements, permitting, and property set backs for storage buildings. Many local government jurisdictional agencies do not regulate small projects like sheds, barns, or other out buildings as long as they are under a minimum square footage area, and there are no plans to install any utilities such as electrical and plumbing in them. Still, regulations vary from one location to another, and approved construction plans and permits may be required for this type of project in your area.
Step 3
Plan your project. This should involve considering how you will attach the lean-to structure, how the roof of the addition will interface with the existing roof, the length and width of the addition, and other characteristics of your lean-to.
Step 4
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.
Step 5
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:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
Step 6
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.
Step 7
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.
Step 8
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.
Step 9
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.
Step 10
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.
Step 11
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.
Step 12
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.
Step 13
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.
Step 14
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.
Step 15
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.
Step 16
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.
Step 17
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.
Step 18
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.
Step 19
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.
Step 20
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.
Step 21
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.
Step 22
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.
Step 23
Fasten your metal roofing with a suitable fastener. Wood screw threaded hex screws with neoprene gaskets are very good for this purpose.
Step 24
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.
Step 25
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.
Step 26
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.
Step 27
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.
Step 28
Clean up the worksite and put the tools away.
