Hip Roofs — Utilihab Wiki

Hip Roofs - Utilihab Wiki

Hip roofs are a variation of the basic gabled roof which encloses the ends of the roof in sloped cover that join along a diagonal split of the roof ridge that slopes to the end corners. Though a bit more complex that the more common abled roof, this form provides additional protection against rain in all directions and is especially well suited to the use of very wide roof overhangs. With the Utilihab platform, it combines well with the Utilihab Pavilion framing system in larger span low height structures when used with a relatively low slope roof design.

The same basic roof framing schemes are used for both gabled and hip roofs but the hip roof adds additional structural elements to carry to the roof ridge to corners at the lower end corners of the roof line along two diagonal ridge beams. For the basic ridged roof frame system, this is performed by using specially formed gusset plates that link the three ridge beams at the roof peak and then to the corners of the main structural framing. Short rafters are then installed along the face of the now three roof slopes and the corner roof ridge beams, again using side-mounted gusset plates along the ridge beams. These gusset plates have a shape specific to the particular slope of the hip roof and in the Utilihab system only a handful of standard hip roof ‘kits’ for several standard room spans will be supported in the standard component set. This arrangement allows for the use of vaulted interior ceilings as with its gabled roof counterpart but the ceiling panels and their associated components along the merging end ridges must be matched to the specific roof form.

For the truss based roof system, hip roofs are based on a combination of hip truss modules and descending half-truss modules that integrate through a transitional girder truss module. The girder truss uses a queens post arrangement to form a rectangular center rather than a triangular peak. The hip trusses link at the points of the queens posts and run diagonally to the corners of the roof line. They have an extension of their upper chord which runs over the girder truss to connect as a rafter to the end of the main roof ridge using special side gusset plates. The half trusses forming now three end slope faces attach either to the girder truss or the hip trusses, their high ends meeting are a right angle along the hip truss. One or more of these along the girder truss may include an upper rafter extension along their top chord as with the hip trusses to link to the end of the ridge beam or along that extension chord of the hip trusses.

In some roof designs the use of a transitional girder truss can be replaced by the use of a retrofit king post at the center of the end truss to which the hip trusses and a central perpendicular half-truss can attach directly without upper extension chords using side-mounted gusset plates. This transitional king post may also be based on a special T-slot profile of octagonal (or partial octagon) shape, which would simplify the end cut and joints for the hip truss modules. This is particularly useful where scissor or fan trusses with a sloped bottom chord are used to accommodate a vaulted ceiling.

Note that for small single-bay cottages and structures, hip roofs may be composed of hip rafter or hip trusses alone with some additional transitional rafters or half-truss modules. The main rafters or trusses thus meet at a point, linked by side-mounted gusset plates, an octagonal key-block, or an octagonal profile king post. For small structures these may need only some additional flush profile purlins to support paneling. Otherwise, shorter transitional rafter or half-trusses are attached along the main diagonal rafters or trusses. This approach would also be used for some specialty structure kits supporting hexagonal or octagonal shaped buildings with a non-standard framing system using hexagonal or octagonal Primary post profiles.

Hip roofs will usually employ a ridge vent system based on the choice of roofing materials used. However, they can support the addition of small ‘Dutch gables’ at the ends of the main roof ridge which can accommodate vents and fans. This is a common feature in Asian and Polynesian architecture employing hip roofs. The Dutch gable is a kind of dormer which is formed by extending the roof ridge a small degree over the slope of the roof end. For the rafter based framing system, this is accommodated simply by a longer ridge beam which then has light Secondary framing placed between ridge beam end and the upper portions of the hip rafters to frame a the dormer-like overhang. Special enclosure panels, windows, or vent covers/screens are then used in this triangular opening and for large fans some additional framing may be suspended from the underside of the ridge beam and hip rafters to create a platform. For structures with vaulted ceilings, this can be an ideal location for certain air conditioning systems.

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