Single Car Detached Garage | 12 X 20 Design

Learn how to build your own stand alone garage with these easy to follow DIY instructions. These free plans include instructions and post lay out diagram.

Instructions for Post and Beam Garage

Use batter boards for an accurate post layout. The two post for the door need exactly eight feet of clearance between them. There is no need for trimmers this way. Dig or drill the holes ten inches in diameter and twenty four inches deep. Stand the twelve feet four by four’s in the holes. They need a two by four brace on each axis (two braces). Use a sturdy wooden stake to nail the braces to. Plumb all of the posts. Pour concrete around the posts. Make sure not use dry concrete straight out of the bag. Let the concrete dry overnight.

Establish a level mark on each post. Use an optical level if possible. From this mark determine the top of the concrete slab. The slab needs to slope at least three inches towards the door. Nail on a treated two by four on the outside of the posts at the top of the slab. Add three stakes for each form board so it will not bow under the force of the concrete. If there will be a concrete ramp, then form for it now. Use fiber reinforced concrete at least four inches thick. Let the concrete stand at least one day.

Lay out the posts for the wall girts on two feet center and make the two by ten roof beams at least eight feet above the tallest part of the slab. Build the roof beams with a vertical two by ten topped with a horizontal two by four flush with the outside. Use an “X” brace on the side of each post. Make them at least three feet long.

Lay out the roof beams two feet center. Nail the two by ten ceiling joists and two by six rafters. Use a twenty two feet two by eight ridge if possible. If this is just tool large of a board to handle, then cut it in half in the center of a rafter lay out. Nail on the one by four roof battens with a two feet center layout. Nail on the two by four wall girts.

Lay the metal roofing. Use metal roofing for the walls. Use corners where the roof metal meets the wall metal. Set the door. Be sure to follow the instructions.

These instructions are for post and beam construction techniques. This single car garage lay out will also work for any other type of construction style. We prefer to publish the instructions for “pole barn” style of framing because it is simple, low cost, and super strong.

12 X 20 Single Car Garage Post Lay Out


Post lay out for 12 x 20 garage.

This simple detached garage will also work great for a work shop or storage building.