Porch Roof Rafter Spacing

The same concept holds true for roof trusses.

Porch roof rafter spacing.

An essential part of planning a patio roof or gazebo project is determining the number size and spacing of rafters beams and posts according to the loads they will carry. This table agrees that 10 12ft is the max span for typical grade lumber at typical spacings for a 5psf dead load. Keep in mind that these figures depend on the size and spacing of joists and the overall structural loads. A 4 by 10 can usually span up to 12 feet between posts.

The minimum pitch for a roof is 1 4 12 which translates to 1 4 inch rise to 12 inches of run. Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run. If you move up to 4 by 8 you re usually allowed to span up to 10 feet between posts. However you can only use this pitch with built up roofing or specialized synthetic roofing.

Once the beams are in place mark the spacing for the trusses normally 16 inches apart. If your project had a rafter length of 8 or less a safe and strong method is to use 2x8 framed 16 on center. For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are spaced 24 apart can have a maximum span of 10 feet 3 inches 10 3 if designing for a live load of 40 lbs ft 2. Squaring the beams and bracing them to ensure the maintain square is essential to the roof building process.

If your local building authority has a rafter spacing code you may not space rafters wider than required by code. So the space between rafters can be greater without reducing the maximum span. Both 16 inches and 24 inches are common measurements for rafter spacing. Rafters must be strong enough to hold the roof sheathing and the shingles.

Typical rafter spacing codes will specify a minimum spacing of 16 inches 19 2 inches or 24 inches. In general the maximum span for a 4 by 6 beam is 6 feet between 4 by 4 posts. Maximum rafter spans for a patio roof in areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot. Common spacing for trusses on this type of building is often between 2 and 4 feet but trusses built with advanced designs may allow spacing as great as 8 or 12 feet.

If this calculator from the american wood council is to be believed and if my assumptions about your materials and load are correct the max span is about 10ft for a pine 2x6.