The initial step in roof framing is to plan and cut a rafter pattern. How this roof rafter rises and runs will define the height of your ridge board, the length of any valley rafters and other elements of a conventional framed roof.
Roof framing falls technically under expertise of framing carpentry. It is a skill that’s hard to acquire and needs long experience. Not every carpenter has been adequately exposed to this dying art. Trussed roof systems are now popular, and has overshadowed conventional roof framing which has been around for centuries before. But while trussed roofing can fit almost every need, there are still rare occasions where only roof framing will do.
Conventional roof framing is adequate for adding a garage, shed or similar structure to an existing building. They lower delivery costs, can work with space constraints and are lighter than a truss roofing. Here is how you can calculate rafter lengths for roof framing.
Roof Framing Rafters – How To Design Them
As used in roof framing, a common rafter has several components including the tail cut, birdsmouth cut, plumb cut, ceiling joist, wall stud, ridge board and more. Calculating roof framing rafters needs to begin with estimating the pitch, rafter length, lumber size and spacing for rafters.
The span of your roof framing rafter is the measure of overall width of your building, at the point where your rafters will sit. The run is one half of your span and is obtained by dividing the earlier measurement by two. This is the horizontal distance your rafter will run to meet the one from the opposite side.
Selecting Lumber for Roof Rafters
You will have to select lumber length for roof framing based on the horizontal run of the rafter, and not the length or span. Determine rafter length using a roofing calculator. There are many online roofing calculators available to help you do this. In roof framing, remember to always use the next larger size of lumber than rafters for the ridge board. And when ordering lumber, don’t forget to factor in the length of the eave.
Choose a piece of lumber from the pile that is straight, light and long enough. You will be creating a pattern for your roof framing when completed. Depending upon how many rafters you will require eventually, the lighter rafters will be a welcome decision.
When you’ve chosen your lumber, place it on the saw horse after marking out the length carefully and cut at the proper angle. Then make a mark on the rafter indicating the outside edge of your building. With a framing square on the rafter, mark using a plumb line a measure that indicates the outside edge of the building.
Cutting the Birdsmouth
Roof framing involves cutting out the birdsmouth from rafters. This is where the rafter will rest upon the outside wall of the building. Unless it is at least 4 inches, this will not achieve full bearing. You can achieve the desired cut by sliding the framing square along the rafter until you have reached the mark you made on it.
Types of Roof Rafters
Roof framing with rafters involves knowledge about the 7 different kinds of rafters that can be used to construct even the most complex roofs. Three different rafters are used more often than others in roof framing. These are the common, hip and hip jack rafters.
Roof framing is a forgotten art that is on the cusp of another surge of interest. Learning about roof framing and knowing when a frame roof is better than a prefab truss is important. Roof framing can be very helpful in maintaining the structural integrity and aesthetics of your building for a long time to come. Roof framing appears complicated, though it is primarily an acquired skill. Simple roofs are easy to construct if you understand the basics and a bit of geometry.