18×20 A-Frame Cabin Plans with Loft

About This Design

Sixteen feet is where a classic A-frame becomes possible; eighteen is where it becomes comfortable. The two extra feet of span buy about a foot of floor either side at standing height, and they buy it without touching the entry: the door sits on the centreline under the peak on every classic here, so width goes to the room, not to clearing a post.

Eighteen feet is also the ceiling. Past it the floor and loft joists outrun a 2×12 at sixteen-inch centres, and the building needs an interior beam that would spoil the one thing an A-frame is for — an uninterrupted room under an uninterrupted roof.

So this is the shorter of the two plans at the catalog's best width: three hundred and sixty square feet on the main level, an eight-foot loft under the ridge, and roof planes running clean to the deck on both sides.

Key Features

• True roof-to-deck A-frame — no knee walls, no side walls
• 360 sq ft on the main level plus an eight-foot loft
• Full-height 36×80 entry centred under the peak
• About 10½ ft of floor at full standing headroom
• Ridge beam, entry header and posts sized PRELIMINARY against the site loads
• Full rafter, ridge, post and loft framing in the drawings

Build Notes

Read the load path before you cut anything, because it is not the one most A-frame articles describe. A bolted heel joint cannot make its required end distance in a tie this shallow, so these plans do NOT rely on the floor frame acting as a rafter tie. The rafters land on a structural ridge beam, and that beam delivers its load through a built-up post at each gable end to bearing below.

The entry sits on the centreline, under the peak, so the front post lands on an engineered LVL header over the door and a jack pack each side carries it down. Once a jurisdiction is set, the engine sizes that whole chain — beam, header, jambs, post, and the transfer beam or slab pad under it — against the pinned site loads and prints each member with its utilisation ratio. Every one of those sizes is PRELIMINARY: a registered design professional confirms them, and the set says so on every sheet until one does.

Build the deck dead square first: the rafters reference off it directly and there is no top plate to correct an error with. Set the beam and its posts, then bring the rafter pairs up from both gable ends toward the middle.

Best For

The A-frame to build when you want one room that works rather than one room that photographs. Three hundred and sixty square feet at eighteen feet wide takes a kitchen along one side, a stove and seating at the open end, and a bathroom under the loft without any of it fighting the slope. The loft sleeps two or three. Shorter than the 18×24 and correspondingly cheaper, on the same frame and the same details.