This pitch is determined by the angle cut into both ends of the rafter. As mentioned earlier, these boards dictate the pitch or slope of the roof. In most situations, this is a small board like a 2” x 4”, but some homes will need a rafter built from much larger lumber like a 2” x 12”. Rafters start out as a simple pieces of lumber. Rafters can be made to accommodate roofs with very steep pitches as well as buildings with nearly flat roofs. Rafters are usually made on-site and installed in rows with even spacing. Rafters are perfect for any roof with a pitch including commercial buildings, residential homes, barns, and storage buildings. This provides structural support for the entire roof from the very top (ridge) to the very bottom (fascia).
In a basic four-sided structure, rafters would typically extend from the lowest part of the roof to the highest. In modern construction, trusses often replace the majority of rafters and joists, but both rafters and joists are still commonly used either alone or in conjunction with trusses. The use of rafters and joists usually requires more bearing points for support, which is why most ranch-style homes have a weight-bearing wall near the center of the structure. This is most evident in a ranch-style home, which is why the design became so popular. In older construction, rafters and joists were an integral part of essentially any wooden structure.īefore trusses were commonly used in residential construction, rafters and joists, along with other framing components were standard. In roof framing, joists connect rafters together at ceiling level to prevent them from separating under the weight of the roof. A rafter provides the slope, or pitch of a roof and serves as a connection point for roof decking and shingles. No, but they do work together to provide support for a roof. In a floor, joists provide the horizontal support for the subfloor, floor coverings, and serve as the connection point between a structure’s masonry foundation and the subfloor. As part of a roof, joists provide the horizontal support for ceiling drywall and tie rafters together. Will it fall down without building the exactness (which includes safety factors) that engineers have specified as minimum starting points for modern framing? It didn't before and probably won't now, but the point of this blabber is to give you insight so you can decide what makes you feel comfortable.In cooperation with rafters, joists typically support not only the weight of the structure but also hold the structure together. In Canada YMMV, but that is the gist of figuring it out. AND, because you have a 1x ridge board (not a ridge beam), putting purlins/king posts here and there down from the ridge board to the middle wall doesn't accomplish much, especially if there is no foundation under that middle wall. AND raising those ceiling joists reduces the carrying capacity of the rafters to 0.76x(span), so if your 2圆 rafters were rated to span 11'-9", they are now reduced to 8'-11" in its capacity to carry the roof load. BUT, you raised the ceiling joists 18" of the total 6' distance to the top of ridge from the top plate, so you need to increase the amount of nails to 1.33x(6) = (8) nails. spacing - you would need (6) 16d nails to hold against outward thrust (same on the ceiling joist lap splice). Say you have a 4:12 roof pitch, 30psf snow load, 20ft span with the 16"o.c. I think I see (3) nails on the ceiling joist/rafter connection, that is probably not enough. The distance you raise the ceiling joists affects the ability of the existing rafters to carry your roof load and the strength of connections at both the ceiling joist/rafter and the ceiling joist lap splice (in your case straps). There should be a strap across every ceiling joist tying both sides together. Here is a good explanation of the function of rafter ties vs. Adding joist hangers will help some, but only if you use screws instead of nails to attach them to the wall.Ī more effective solution would be to add metal tension strips across the top and bottom of each ceiling joist pair to "join" each ceiling joist to the opposing ceiling joist. Unfortunately, your ceiling joists have a butt joint, and butt joints are terrible at resisting tension.
they need to have a "lap" joint where the nails are in shear to resist the tension loads. Your rafter ties (or ceiling joists) need to be continuous across the whole house. They serve as tension members to prevent spreading of the outer walls due to snow load. Rafter ties, by definition, need to be located in the lower 1/3 of the rafter. Your ceiling joists need to act as functional "rafter ties" when no structural ridge beam exists, as is the case here. Your roof framing lacks proper rafter ties. Percyj, this framing definitely appears improper to me.
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