Setting the Posts for your Lean-to Pergola
Dig five holes for the pergola posts that are 14x14 inch squares and 20 inches deep. The holes should be a maximum of eight feet apart.
Pour concrete into the holes four inches deep. Place the pergola posts in the holes and fill with concrete to the surface. Make sure that the posts are level before the concrete sets.
All the concrete to dry (2 to 3 days), then trim the top of the posts to the height you desire for the lean-to pergola.
Cut an L shape out of the top of each post for beam placement. The L should be eight inches deep and two inches in.
Bolt 2x8 foot beams to the posts with 1/2 inch galvanized bolts and washers. Check to make sure the posts and beams are still level.
Building the Frame for your Lean-to Pergola
Attach ledger plates at a level line under the eaves of your house. Use cache screws to attach the ledger plates through the studs or lintels of the house frame. Seal around the screws with silicone sealant.
Prepare the rafters based upon the measurement of the roof sheets. For example, for 96 inch roof sheets, the rafters should be 91.25 inches long. Cut the angle at one end of the pergola rafters for the slant you desire for the roof.
Space rafters 30 inches apart. Attach the angled end of the rafters to the ledgers with joist hangers and the other end of the rafters to the beams with skew nails and angle brackets.
Place four rows of purlins (nogs) along the edges between the rafters. The first row of purlins should be four inches from the top of the rafters, the bottom row four inches from the end of the rafters and the other two rows spaced equally between.
Adhere fascia board to the ends of the pergola rafters and to the sides of the two end rafters. Brace the frame of your lean-to pergola diagonally, from corner to corner, with metal strap braces.
Attaching a Roof to your Lean-to Pergola
Measure and cut PVC / polycarbonate sheet roofing as needed to fit the top of your lean-to pergola frame with garden scissors or a fine tooth saw.
Pre-drill 8 to 10mm holes in the sheet roofing. Be sure that the holes are 2mm larger than the shaft of your screws to account for expansion and contraction from weather. Position the holes in a high portion of the sheet roofing corrugation.
Use hexagonal head screws for the easiest means of attaching the roof to the lean-to pergola frame. Attach the sheet roofing at every fourth corrugation overall, and every second corrugation at the gutters, ridging and overlaps.
Things You Will Need
- Galvanized bolts
- Rafter boards
- Ledger plates
- Cache screws
- Silicone sealant
- Joist hangers
- Skew nails
- Angle brackets
- Fascia board
- Metal strap braces
- Roofing pitch
- PVC / polycarbonate sheet roofing
- Electric drill
- Hexagonal head screws
- If the exterior of your house where you're installing the lean-to pergola is made of concrete, brick or block, use masonry anchors to attach the ledger plates (rather than cache screws).
- The rafters should be at a right angle to your home, squared up and at the desired angle for your roof. The roof has to be at an angle so that water runs away from the home.
- The purlins (nogs) can go on the top of the rafters if there's enough room between the rafters and eaves.
- The recommendation is to use ten degree pitch so that you will avoid additional weatherproofing.
- Use a stick or small piece of wood with a hole in it to guide the drill and keep it steady when pre-drilling holes in the sheet roofing.