Hip roof with cathedral ceiling
Hip roof with cathedral ceiling
(OP)
I am reviewing a set of plans in which a Hip roof with a cathederal ceing is specified. The roof system consists of a ridge beam and 4 Hip beams. The interior is pure cathederal with no columns supporting the ridge or hips and no collar ties. The roof is rectangular 48' x 28', Roof pitch 6:12, Snow load 25 psf.
What if anything can be used to oppose the thrust forces generated at the outer walls?. Can the roof sheating act as a diaphram to oppose the trust? If so how can this problem be modeled?
Should I send this back to the architect? It seems to me this is a unstable design.
Thanks in advance.
What if anything can be used to oppose the thrust forces generated at the outer walls?. Can the roof sheating act as a diaphram to oppose the trust? If so how can this problem be modeled?
Should I send this back to the architect? It seems to me this is a unstable design.
Thanks in advance.






RE: Hip roof with cathedral ceiling
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.
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.
RE: Hip roof with cathedral ceiling
Another 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. 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.
Hopefully it helps
:0)
RareBug
RE: Hip roof with cathedral ceiling
Dik
RE: Hip roof with cathedral ceiling
RE: Hip roof with cathedral ceiling
I don't think that works because the ridge beam is supported by the hip beams (not a gable end condition).
RE: Hip roof with cathedral ceiling
RE: Hip roof with cathedral ceiling
A 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 case
Thanks again.
RE: Hip roof with cathedral ceiling
At 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. Also create a continuous top chord member around the full perimeter of the building using 2 -2x6 at the top of the stud wall. Using 2x6's for the wall should also add stiffness.
RE: Hip roof with cathedral ceiling
The roof slope was only 3:12, so the thrust was large. The roof is concrete tile. Roof dead load=24 psf, and the live load = 20 psf construction duration.