How to Attach a Roof to a Cob Cottage

Set anchor bolts into the top face of the cob wall as you are applying the cob. Cob is applied in wet, sticky handfuls and hardens as it dries. The anchor bolts must be set as the cob is applied, with the cob packed tightly around them, and 2 1/2 inches of the bolt protruding vertically above the top of the wall. Set the anchor bolts every 24 inches along the top of the wall, centered between the inside and outside faces.

Drill 7/16-diameter holes into 2-by-4s, spaced 24 inches apart so they correspond to the anchor bolts. Set the 2-by-4s on top of the walls. Place washers and nuts onto the anchor bolts to secure the 2-by-4s. Don't tighten the nuts until the cob wall has had at least a week to cure. If you try to tighten them when the cob still is wet you will dislodge the anchor bolts. Check that the 2-by-4s are level with a 4-foot level.

Place the bird's mouths of the rafters on the 2-by-4 lumber, which is used as the top sill. The bird's mouth is the angular cut at the bottom of a rafter that rests on the top plate of a wall. Secure the rafters to the top plate by screwing or nailing two nails or screws from each side of the rafter down through the rafter and into the top plate.