Easy Rafters from Attention to Detail

Previous Next

Bay Roof

A bay roof is a three sided roof framed against a vertical wall of a building, usually covering a projection from the building such as a bay window or nook. A projection with four or more angled faces is a bow and cannot be calculated with Easy Rafters.

Framing a bay roof can be very frustrating, often times even an experienced roof framer will resort to "trial and error" cutting and fitting of the pieces required for a bay roof. Sure signs of this are fascia boards that aren't level or taper from one end to the other, soffits that vary in width, or unequal slopes for the three sides of the roof. Easy Rafters greatly simplifies this task by calculating the rafters needed to frame a bay roof with equal slopes for all sides, level fascias, and consistent soffits.

Once all the bay dimensions have been entered, the preview window will display a plan and elevation view of the bay roof that reflect the actual bay dimensions. Note that the front elevation is a view of the finished roof with overhangs and fascia boards while the top view does not include overhangs.

The bay roof drawing pages display dimensioned side views of the bay common, bay hip, bay ledger, and bay center ledger rafters. Bay hip and ledger drawings also include schematic top views to illustrate the location of the measuring lines and the types of bevel cuts required.


The Parts of a Bay Roof

Bay Common Rafter
The bay common rafters extend perpendicular from the outer wall plate to the bay center ledger.

Bay Hip Rafter
The bay hip rafters extend at an angle from the intersections of the outer and side walls to the points where the side ledgers and center ledger meet. They have a single bevel cut at the peak where they meet the ledger rafters and double bevel cuts at the tail for the fascia. A left and a right hip rafter with opposite top bevel cuts is required.

Bay Ledger Rafter
The bay ledger rafters extend from the side wall plates where they meet the house wall, to the ends of the center ledger. They have a square cut at the top where they meet the center ledger and a single bevel cut at the tail end. A left and a right ledger rafter with opposite bottom bevel cuts is required.

Bay Center Ledger
The bay center ledger is the horizontal piece that fills the gap between the side ledger rafters. The length of the center ledger will vary according to the dimensions of the bay. It is possible to design a bay where no center ledger is required because the side ledger rafters meet in the center to form a peak.

Jack Rafters
A bay roof has two different types of jack rafters, hip jacks that frame against the hip rafter and ledger jacks that frame against the side ledger rafters. The tails of both jacks are identical to the common rafter tails, but the top cut of a hip jack requires a bevel equal to one half of the bay angle while the top cut of a ledger jack requires a bevel equal to the complement of the bay angle (90 degrees minus the bay angle). The common differences for both types of jack rafter are listed in the bay hip and bay ledger printouts. The number of each type required will depend on the size of the bay and the spacing of the rafters.