About lumber sizes.
The lumber sizes referred to in this project are the nominal sizes.
The nominal size of a piece of lumber is the size of the lumber before it is surfaced/dressed or seasoned and is the size generally referred to when purchasing from the lumber yard.
The actual size, or dressed size of the lumber will be less than the nominal size so please make necessary allowances.
For example, a piece of 100x50 (2x4) lumber when dressed may be 90x45 (1 1/2"x 3 1/2") actual size.
STEP 1: The footings and posts.
Dig five footing holes 350x350 (14"x14") and 500 (20") deep. Refer to
for hole positions. Max span between any two posts must be no more than 2400mm (8ft)
Place at least 100mm (4") thick pad of concrete at the bottom of the footing holes, place the posts in position and fill the footing holes up with
Check the posts for plumb (vertical), brace if necessary and leave till concrete sets.
STEP 2: Trim the posts
Trim the top of the 5 posts at the desired height. Refer to the
Work out the height of the top of the posts in relation to the required rafter fall.
The fall should be at least 10 degrees (1 in 5.7) if possible.
In this example, trim the top of the posts off 316mm (12 1/2") below the highest point of the underside of the rafter. (see drawing).
STEP 3: The beam
Check out the top of each post for the beam
marking a horizontal line 200mm (8") down from the top outside edge of each post.
Cut along the pencil mark with a power saw to a depth of 50mm (2") (the thickness of the beam) Do this to all posts.
Scribe a line 50mm (2") in from the outside edge of each post from the top, down 200mm (8"). Cut down that line using a sharp handsaw.
Bolt the 200x50 (2x8) beam to the posts using m12 (1/2") galvanized bolts and washers. (see diagram).
Ensure all posts are plumb (vertical) and parallel
STEP 4: The ledger plate
In this example the ledger plate is bolted to the fascia board just below the spouting.
Sometimes this is not possible due to lack of free fascia board or fixing area below the spouting in which case the ledger plate will have to be fixed to the house wall beneath the eaves.
SCENARIO (1) FIXING TO THE FASCIA BOARD
Mark a level line just below the spouting. Use a spirit level or a water level .
Fix the ledger plate to the level line on the fascia board using coach screw at least every 1200mm (48") apart, penetrating through the fascia board and into solid timber,
usually the end of a roof rafter or eaves sprocket.
SCENARIO (2) FIXING TO THE HOUSE WALL.
Mark a level line just below the eaves. Use a spirit level or a water level .
Fix the ledger plate to the level line with coach screws penetrating through the cladding and into the studs (house frame uprights) or lintels (beams above windows and doors).
Seal around coach screws with weatherproof silicone sealant.
If the wall is masonry (concrete, brick, block) fix the ledger plate to the wall using masonry anchors every 1200mm.
Before fixing, place DPC (Damp Proof Course) between the ledger plate and the wall.
STEP 5: Rafters, purlins, fascia and brace
Cut the rafters to length and angle cut each end to suit. Work out the rafter length to suit the roof sheets if possible (so as the roof sheets wont need cutting). In this
example cut the rafters 2280mm (91 1/4") long for 2400 (96") roof sheets. Thus ledger 50mm (2") + rafter 2280mm (91 1/4")
+ fascia 20mm (3/4") + roof overhang 50mm (2") = 2400mm (96")
for reference if necessary.
Fix the rafters @ 750crs (30" O.C.) that is, spaced every 750mm (30") apart, to the ledger with joist hangers and to the beam with skew nails (nails angled in, toe nailed) and angle clips or Z nails.
Ensure the rafters are square, at right angles to the building.
Fix four rows of 100x50 (2x4) nogs on edge in-between the rafters as in
the flat plan
These are the nogs (purlins) that the roofing is fixed to.
Fix the top row of nogs (purlins) 100mm (4") down from the top of the rafters and fix the bottom row of nogs (purlins) 100mm (4") up from the end of the rafters.
Fix the other two rows of nogs (purlins) equal distance apart.
Alternatively the purlins can be fixed on top of the rafters if there is enough room
between the top of the rafters and the eaves.
Fix fascia board along the end of the rafters and also up the sides of the two end rafters (barge board).
Brace on top of the frame diagonally from corner to corner with metal strap brace. see
Continue - The Roof
How to build a Lean-to Pergola back to start