How to build a hip roof without rafter or collar ties
MarcUlan
| Posted in Construction Techniques on
Hi,
I am building a 10×20′ 2×4 framed pool house with a 6/12 hip roof. I’d like to keep the ceiling underneath completely open, without rafters or collar ties. I understand that it is possible to do this, but I cannot find a description of how to do it. My understanding is that the common rafters will want to push the pool house walls out, and that there needs to be some accommodation to support that load.
Does anyone know how I can accomplish this?
Thanks,
Marc
Replies
Engineered LVL ridge beam probably 4x14 but maybe 4x16. Talk to a structural engineer for size and how roof load will be supported. If you're in earthquake country it may not be possible.
If the open space requirement is a visual thing, steel cables or rods instead of rafters have a much lower visual impact at modest cost.
If the space must be physically clear: ( from conventional to unusual)
-Scissor trusses or beams instead of rafters.
-Structural assembly of ridge and hip beams to transfer all loads to corners of building. Steel or LVL with steel fittings.
-Ridge beam extended through hip to vertical support at end walls.
-Buttress the wall to react horizontal load
-Horizonal beams at top of wall to form a ring. LVL, truss or steel. Can be built into soffits.
-Cable suspended roof
Lots of ways. All are engineered solutions.
10' wide structure is fairly small for a hip roof. Why not a gable or shed roof?
Thank you for the replies. I like the look of the hip roof, and the requirement to have the ceiling open is really just for looks also. I've thought about using steel rods, and I think that can have a nice clean look. I am building a 6' loft on one side of the pool house, and the loft joists will tie the two 20' walls together, for 6' at least. I know that this is an engineering question, but could that be enough to offset the horizontal load from the roof?
Joists for 6 ft at one end will not support a 20 ft wall.
As the building is only 10 ft wide, scissor trusses may be the easiest solution if you really want an open space. Could be as simple as 2x6 or 2x8 lumber with properly sized connector plates at the apex.
A beam 5' in from each end could easily support a king post, which in turn would support a 10' ridge beam and the hip beams. No other structure would be necessary. The loads would be minimal so engineering would be easy. By my calculations the point load in the center of the beam would be 1126#. This would require a 4 x 10 df beam. A 4x 8 ridge would do. If it were me, assuming no insulation, I'd frame the whole thing in 4x lumber and use 2x t&g for sheating leaving the whole underside exposed.
If the open space requirement is a visual thing, steel cables or rods instead of rafters have a much lower visual impact at modest cost.
If the space must be physically clear: ( from conventional to unusual)
-Scissor trusses or beams instead of rafters.
-Structural assembly of ridge and hip beams to transfer all loads to corners of building. Steel or LVL with steel fittings.
-Ridge beam extended through hip to vertical support at end walls.
-Buttress the wall to react horizontal load
-Horizonal beams at top of wall to form a ring. LVL, truss or steel. Can be built into soffits.
-Cable suspended roof
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