Though dependent on some specialized components, arch or barrel roofs are one of the simpler alternatives to the gabled roof and integrate well with the standard Utilihab post-and-beam structural system. There are two basic forms of arch roof systems; supported and self-supporting. The supported arch roof employs curved rafters or trusses reinforced by perpendicular braces or purlins depending on the roof cladding used. It’s most commonly used with roofing materials of limited integral rigidity. The self-supporting form employes a corrugated alloy panel system with very high integral rigidity. This usually employs a single ‘shell’ where shaped rigid panels have corrugations parallel to the arc of the roof shape -as in the case of the classic quonset hut- or an integrally insulated double shell where a semi-rigid inner plank layer that is corrugated to be rigid perpendicular to the arc of the roof is mechanically attached to a semi-rigid outer plank layer that is more rigid in parallel to the arc of the roof -as in the case of more modern commercial arch roof system as the Epic brand systems.

Utilihab employs special curved profiles for the supported arch roof approach. These are either single piece units or butt-joined segments derived from 50mm series profiles in 1x1 1x2, or 2x2 sizes. These are used to make arch rafters or trusses, in combination with conventional profiles, completely spanning a structure. They can be used in the same manner as a gabled roof or, in the form of a partial arch, in the manner of a shed roof -a style often used in eco-architecture and which exploits the riser section to host clerestory windows. They can also be used in the manner of compound shed roofing with arches of two differer heights and, in a clear span compound arch, employ a mid-arch riser reinforced by straight cross beams at the ridge allowing, again, for the installation of vents and clerestory windows. Flexible or semi-rigid roof paneling attaches to these arch rafters or trusses in the same manner as other surface mounting roofing. However, this is often used to support transparent or translucent panels and a glazing profile system may be added to the arch rafters or trusses for this purpose. In some cases, commercial glazing profiles designed specifically for arch skylights and canopies can be used directly with the basic Utilihab framing without additional support structure.

Self-supporting arch roof systems will, depending on type, attach to the outside facing slots of upper frame members using through-bolts or a combination of top and outer facing slot attachment. Single shell systems with forming a half or quarter circle that approaches the vertical at its base will usually attach to the outside facing slots along the upper frame. Shallow arches will more commonly bolt to the top of the frame or a side-mounted angle strip and employ some overhang. In some cases, these can feature wide overhanging eaves. The double-shells systems will usually employ a mount along the top profile slot for the inner shell and a side attachment for the outer shell. These systems often used a grilled or perforated inner shell planking that vents through bottom edge and ridge vents in the outer shell. The inner planking also often features special quick-locks that fit concealed in their corrugations which can support lighting and other fixtures while the deep corrugation channels conceal wiring.

As we can see, this is generally as simple a form of roofing as flat roof systems and well suited to the Utilihab DIY ideal.

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