How to build a carport


basic carportBuild a carport. This single carport is free standing, I.e., it is not attached to any other structure. It is 6000mm (20ft) long by 3000mm (10ft) wide. It is the most basic of carports.
Because each site is different, and individual preferences vary, we have given options for post installation and options for bracing.

The frame is made of wood. The roof has a minimal fall. The roof cover can be plastic PVC, tin or other metal. Choice of roof cover could well be decided by the type of conditions that the carport is likely to confront.

These plans make no allowances for extreme conditions.
Is your area subject to frosts? Find out the depth of the frost line and if applicable check to see if the footings require any special consideration. Usually the bottom of the footings should be below the frost line to prevent movement.

Check with your Local Authority to see what plans, permits, consents etc may be required to erect such a structure.

Wood sizes and measurements

The measurements throughout this project are given in both Metric (mm) and Standard/Imperial inches.
The metric measurements (mm) are given first followed by the imperial measurements (inch) in brackets (). For example 150mm x 50mm (2″ x 6″).
In the above example 150mm x 50mm means wood that is 150 millimeters wide by 50 millimeters thick.
And the equivalent in standard…
2″ x 6″ means wood that is 2 inches thick by 6 inches wide.

The wood used for this project can be either sawn (rough sawn) or dressed (gauged, surfaced, smooth finish). The measurements given throughout this project are for sawn wood.
If dressed wood is preferred, make allowances for the difference in wood thickness and width.

Use a wood suitable for in-ground applications for the posts and use a wood suitable for exterior applications for the rest of the carport structure. Any lumber merchant or supplier will be able to advise on the types of wood most suitable.

Identifying the members

carport part identification

(a) Posts 100mm x 100mm (4″ x 4″)
(b) Beams 200mm x 50mm (2″ x 8″)
(c) End rafters 200mm x 50mm (2″ x 8″)
(d) Rafters 150mm x 50mm (2″ x 6″)
(e) Blocking 150mm x 50mm (2″ x 6″)
(f) Galvanized bolts
(g) Joist Hangers
(h) Galvanized Angle Bracket

The height

The height of a carport is in most cases, common sense. A tall person should be able to walk comfortably under the lowest end of the carport. 2100mm (7ft) from the finished ground to the underside of the lowest end rafter, is a good height.

The slope

The roof slope (fall) should be at least 100mm (4″).
If using a clear PVC roof, then a steeper slope is advisable, as a steeper fall means faster water run-off, and therefore a cleaner roof.

The plans

The plans show a flat plan “bird’s-eye view” and an elevation (side) plan giving all dimensions. Refer to these plans for any required measurements throughout the project.

carport plans

Setting out

The carport is a 6000 mm x 3000mm (20ft x 10ft) rectangle.
Mark out the four corners, and erect wood profile boards (batter boards) out from each corner and also out from the middle to take in the two center posts. Set the profile boards (batter boards) back at least 600mm (2ft) from the building line (carport perimeter) to allow room for hole digging etc.
For instructions on setting the profiles go to

The building line (in this case) is the perimeter of the carport (the very outside edge). It is a 6000 mm x 3000mm (20ft x 10ft) rectangle.
The posts however, will need to be off-set in from the building line, 50mm (2″) in from the sides and 300mm (12″) back from each end (front and back).
Use string lines (attached to the batter boards) to make a rectangle that will determine the post positions.
As mentioned, the posts will be off-set 50mm (2″) in from the sides of the building line, and 300mm (12″) back from the ends (front and back) of the building line,
thus, the stringline should form a rectangle 5400mm x 2900mm (18ft x 9ft-8in).

carport setting-out detail

Installing the posts

carport post installation

Method 1. Post set in concrete

Dig post holes 300mm (12″) square by 600mm (24″)deep. Place 100mm (4″) of concrete into the bottom of every hole.
Commence putting the posts in the holes against (but not touching) the string line.
Using a spirit-level on both a front and side face, check that each post is plumb (vertical) and almost, but not quite, touching the string line.

Fill the hole with concrete to within 50mm (2″) of the finished ground level.
Check again that the post is plumb and not quite touching the string line.
Because of the depth of the hole, the concrete will support the post without the need for bracing, providing of course that the concrete mix isn’t too runny and there isn’t a gale blowing.
Continue until all posts are concreted in.

Method 2. Galvanized post brackets set in concrete

Dig post holes 300mm (12″) square by 600mm (24″) deep. Fill the holes with concrete and set the brackets in position while the concrete is still soft. Ensure the brackets are at the right height, taking the finished slab (carport floor) into consideration. Some temporary packing, props or bracing may be needed to support the brackets until the concrete stiffens up. Wait until the concrete has cured (usually at least four days) and then install the posts plumb (vertical) in the brackets and hold in place with temporary bracing.

Method 3. Galvanized post brackets bolted to existing concrete slab

Fix the brackets to the slab, in position with masonry bolts or anchors. Install the posts plumb (vertical) in the brackets and hold in place with temporary bracing.

Trimming the posts

Mark the rear posts a minimum of 2300mm (7′ 8″) above the slab, or finished ground level. Ensure the height marks on both rear posts are level. Use a spirit-level on a straight edge to achieve this or a water level. For instructions on how to make and use a water level go to .

Mark the front two posts 100mm (4″) higher than the rear posts. Fix a string line between the front and back posts to mark the height of the middle posts. Cut the tops of the posts off at these marks.

The beams and rafters

carport beams and rafter detail

Cut the two beams 6000mm (20ft) long with 45° miters each end and then clamp them in place to the posts so that the tops of the beams are flush with the tops of the posts and protrude past both the front and rear posts by 300mm (12″).

Drill and bolt the beams to the posts with 12mm (1/2′) Galvanized bolts, (two at each meeting).

Cut the two end rafters 3000mm long with 45° miters each end and fix them in place to the beams with 75mm (3″) Galvanized nails and then with Galvanized angle brackets, each bracket fixed with four 12mm (1/2″) Galvanized bolts, two through the beam and two through the rafter. (See diagram).

Cut the six intermediate rafters 2900mm (9′ 8″) long and fix them in place to the beams with Galvanized metal joist hangers. Space the rafters at 900mm (3ft) centres (crs, o.c.). Refer to the plan.

Finish off with a longitudinal row of blocking down the middle in between the rafters.

carport rafter plan

The bracing

carport bracing detail

If the posts are concreted into the ground, and the posts are bolted to the beams with two bolts at each meeting, then no further bracing should be required. If, however, the posts are not in-ground, but supported by Galvanized post brackets, then additional bracing is required. One such scenario is to fix upper post diagonal bracing (see diagram), two to each post, each about 900mm (3ft) long (more or less), and fixed to the post with nail plates and fixed to the beam/rafter with bolts.

Another scenario is to fix full 100mm x 100mm (4″ x 4″) diagonal braces running from the bottoms of the middle posts to the tops of the end posts and secure with bolts, nail plates or Galvanized brackets at each end. A similar diagonal brace is also required between the two rear (end) posts. With this latter scenario, the diagonal braces could be replaced with diagonal trellis (lattice) between the two end posts and the end post and middle post each side (three panels in all).
Both bracing methods mentioned in this scenario also require roof plane bracing to ensure the front of the carport is rigid. This can be 25 mm (1″) wide flat Galvanized metal strapping stretched from corner to corner and fixed with Galvanized nails to the tops of each rafter.

The roof

You can now apply your chosen roof.
Different types of roof will have different fixing instructions from the manufactu

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