How to Build an A-Frame

Whether you’re looking to build a rustic retreat or the off-grid home you’ve long dreamed about, the A-frame cabin offers a simple, incredibly sturdy and comparatively low-cost option.

| November 25, 2011

The following is an excerpt from Cabins & Cottages (Fox Chapel Publishing, 2011). Ready to make the leap from sheds and chicken coops to larger-scale DIY projects? Or just looking to expand your repertoire of carpentry skills? Meet Cabins & Cottages, your comprehensive resource for building simple, affordable, permanent living spaces. From the woodworking and crafting pros at Fox Chapel Publishing, Cabins & Cottages leaves no know-how stone unturned, and it details how to design and build your structures to withstand some of the worst Mother Nature can dish out (heavy snow, flooding, high winds), making the book a worthy companion for any builder. This excerpt is from Chapter 3, “Four Simple Structures.” 

One of the sturdiest of all structures is the A-frame, whose skeleton consists simply of a row of triangles. The bases of the triangles are the joists that support the floor, and the sides are the rafters that hold the combined walls and roof. The simplicity of construction and comparatively low cost make it a popular choice for vacation cabins or an off-grid home. Any style of foundation can serve as its base.

Planning Your A-Frame

The most common shape is equilateral — joists and rafters are equal in length and set at angles of 60 degrees to each other. You can use different angles to modify the shape, however (see “Common Floor-to-Rafter Angles,” below). An A-frame can be built to almost any size simply by varying the number of triangles and their dimensions, but a cabin with a sleeping loft must have rafters at least 20 feet long to allow adequate headroom on both floors. For a small structure like the one described here, three people can lift the assembled triangles into place without the assistance of special equipment. A structure with rafters greater than 24 feet may prove too unwieldy for a crew of amateurs. Frame doors and windows in the end walls. For a large A-frame, plan a lot of windows to keep the interior from being too dark.

A-Frame Tools

  • Screwdriver
  • Circular saw
  • C-clamps
  • Electric drill
  • Hammer
  • Carpenter’s level
  • Carpenter’s square
  • Plumb bob
  • Wrench
  • Saber saw

A-Frame Materials

  • 1-by-2s, 2-by-4s
  • 2-by-6s, 2-by-8s
  • Pressure-treated 2-by-6s, 2-by-10s, 4-by-4s
  • Exterior-grade plywood (3/4-inch)
  • Wood glue
  • Common nails (2-inch, 2 1/2-inch, 3 1/2-inch)
  • Galvanized common nails (2 1/2-inch, 3-inch, 3 1/2-inch)
  • Ring-shank nails (2 1/2-inch)
  • Wood screws (1 3/4-inch No. 8)
  • Roofing materials
  • Carriage bolts (5/8-inch-by-6-inch; 1/2-inch-by-4-inch, 6-inch)
  • Lag screws (1/2-inch-by-4-inch)
  • Multipurpose and framing anchors and nails
  • Wooden ladder
  • Concrete mix

Anatomy of an A-Frame

This 20-foot-per-side equilateral A-frame rests on tripled 2-by-10 pressure-treated beams supported by masonry block piers. The triangles, spaced 24 inches apart, are formed of 2-by-8 rafters joined at the apexes with plywood gussets and sandwiched at the bottom by pairs of pressure-treated 2-by-6 joists. (A cabin larger than this structure would require correspondingly larger framing lumber.) At the end walls and under the sleeping loft, horizontal 2-by-6 collar beams are fastened between the rafters. The rafters of the end walls are doubled to provide a flush nailing surface for the exterior sheathing. The sleeping loft, reached by a ladder, is framed by a railing secured to posts and rafters. Knee walls along the sides of the cabin provide concealed storage areas. The deck rests on 2-by-6 joists set 16 inches apart. Posts for the railing are secured to the deck joists. The stairs are set on concrete footings and are attached to the deck with metal framing anchors. All exposed wood is pressure-treated lumber. An asphalt-shingle roof is shown.

Common Floor-to-Rafter Angles

(Rafter length, joist length, rafter/joist angle, rafter/rafter angle)

16 feet, 12 feet, 68 degrees, 22 degrees
16 feet, 14 feet, 64.1 degrees, 26 degrees
16 feet, 16 feet, 60 degrees, 30 degrees
20 feet, 12 feet, 72.5 degrees, 17.5 degrees
20 feet, 14 feet, 69.5 degrees, 20.5 degrees
20 feet, 16 feet, 66.4 degrees, 23.6 degrees
20 feet, 20 feet, 60 degrees, 30 degrees

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