![]() Today it would look like this where rafters meet ridge should look much like this, as in no big gaps between the meeting members, No "large" quakes just normal ones, no lahars either for that matter Here's a ridge board, generally a 2x12 or so, although in the old days, 30 years ago and more a 1x was or could be used, here's a ridge board 1圆, 60 year old house, my own, a hip roof 2圆 rafter, some what over spanned in lenght, we'd never be able to build this house this way today, yet it's 60 years old and survived at least 3 earthquakes in this area. Rafters "birds mouthed " over the top of the exposed BEAM, beam solidly supported at both ends so not sagging / wall spreading can take place. Ridge beam, as Mtn.D has shown can be placed below or partly below the rafters , Ī Ridge board is part of a roof system "that one part helps/ augments another" to create a greater stronger "whole" in the system. roof dead load=24 psf, and the live load = 20 psf construction duration.Ridge BEAMS and ridge BOARDS are two different critters.Ī Ridge Beam is a bigger timber, generally solidly supported to bearing (foundation / ground ) at points (either end ). The roof slope was only 3:12, so the thrust was large. the plate assembly is "l"-shaped as you look at it in plan, so the wall corner could take the outward thrust (tension in the wall double top plate). thru-bolts in the hip beams (6 x 10) and lag bolts to the top plate. ![]() We recently did a 16' x 24' accessory building with a ridge beam supported by hip beams restrained by connecting to the top plate of the wall with a welded plate assembly. i think i'll try to talk the architect into using scissor trusses or something to support the ridge beam such as columns or trusses.Ī tension ring or flat ceiling around the perimiter that acts as a tension ring is a good idea but would interfere with the other portions of the home in this caseĪt each of the four corners create two plywood shear walls acting as vertical diaphragms ( total 8 walls, each at least 6 feet long) with tie down anchors at each end to take the horizontal hip thrust as an uplift force to the foundation. ![]() it's done by connecting cables to the tails of the hip rafters which resist the horizontal thrust of the roof. I don't think that works because the ridge beam is supported by the hip beams (not a gable end condition).Īlthough i've never designed one, i've seen a tension ring type of design used. the architect got the open effect he was looking for. i once used 3圆s at 8 ft on center in each direction. See if the architect will accept tension ties at the bottom of the rafters. If you have a beam support, you can likley put in a strap tie at the ridge to hold the opposite pieces together and then only deal with vertical loads at the walls. obviously, the slope on your cathedral ceiling would vary slightly (less steep) from your roof framing rafters but would still provide the architect with the cathedral ceiling look on the inside. The flat area "truss" can be an actual truss designed for this purpose, and hung from the rafters, or it can be some form of plywood structural panel with built-up 2x chords and webs of plywood.Īnother option would be to design a "scissors truss" (inside your building section profile) which would take care of the horizontal trust from the roof loads. This flat area can be utilized as a horizontal truss spanning from wall to wall and taking the horizontal thrust to the sidewalls where it can be properly resisted. If you drop the ceiling slightly, this allows for a small, flat area around the perimeter of the ceiling between the wall and the point where the ceiling begins to slope upward. Should i send this back to the architect? it seems to me this is a unstable design. can the roof sheating act as a diaphram to oppose the trust? if so how can this problem be modeled? What if anything can be used to oppose the thrust forces generated at the outer walls?. the roof is rectangular 48' x 28', roof pitch 6:12, snow load 25 psf. the interior is pure cathederal with no columns supporting the ridge or hips and no collar ties. the roof system consists of a ridge beam and 4 hip beams. ![]() ![]() I am reviewing a set of plans in which a hip roof with a cathederal ceing is specified. ![]()
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