How to Lay Out a Lean-To From an Existing Building

Updated April 17, 2017

A lean-to is a good way to add extra space for a minimum cost. The lean-to is built by using the wall of an existing structure for support, so that the builder is just constructing two or three sides to the building. Some are left open in the front and back and just provide a roof covering for the area. Prepare a layout before you construct your own lean-to structure.

Determine the length, width and height of each side of the lean-to. Use a piece of paper and pencil to sketch out your measurements.

Measure the distance of the support beam along the side of the building using the 16-foot steel measuring tape. Use a pencil to make a beginning mark and an ending mark on the existing building to indicate the location of where you want to attach the first support beam.

Decide how much distance you will put between each rafter. Rafters are usually set from 12 inches to 24 inches apart, depending on sturdiness of the construction. If the lean-to you are building will be exposed to heavy snows, a 12-inch to 16-inch rafter spacing is advised.

Use the steel measuring tape to measure the desired width of the lean-to from the beginning mark made on the building and drive a stake in the ground with the hammer where the post will be. Repeat this procedure at the other end of the lean-to and drive a stake using the hammer to indicate the location of the post. If the length of the lean-to is more than 8 feet, decide how far you will put the additional posts. Eight feet between posts is acceptable. For example, a 16-foot-long lean-to would typically have 3 support posts.

Decide how tall the post side of the lean-to will be. This is the height on the post that you will install the second support beam. Once the layout of your lean-to is complete, you are ready to begin construction.


Determine how much slope you will place on the roof, and take into consideration that a wet climate will need more slope than does a dry climate, so the precipitation will move more rapidly off the roof. Pre-made rafter hangers save time in construction and are relatively inexpensive.


Installing rafters with wide distances between them will produce a weaker roof structure.

Things You'll Need

  • Pencil
  • Paper
  • 16-foot steel measuring tape
  • Wooden stakes
  • Hammer
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About the Author

Jeannine Lowe is a business technology teacher at McKenzie High School in Tennessee. She has been writing on business and marketing topics since 2007. Lowe obtained her Master of Science in education through Walden University, specializing in integrating technology into the classroom.