The corners are held together by the sheathing and top plates. The ordinary rafters' tails are the thing to be concerned about. You can create a square hip roof without using ceiling joists. But it's easier if you do because then you don't have to worry about locating joists that will be hidden under the shingles.
Ceiling joists are important for support. They prevent objects above from falling onto the roofers working on your house. Also, they provide a place to mount lights or other accessories. If you want to use wooden beams instead, they only have to be strong enough for the weight expected on them. The size of the beams doesn't matter as long as they're wide enough to span the distance between their attachment points.
Ceiling joists aren't necessary for flat roofs. But they do help stabilize such roofs and give them some extra strength.
Here are some things to consider before you build a house with a hip roof: Will you be living in it? If not, why not? Does its shape work with your design philosophy? Are there features you want but cannot afford? These are all questions you should ask yourself before starting construction.
If you decide to go with a hip roof, there are two types you can choose from: sloped and peaked.
By employing the wall plates as tension members and the roof deck for stability, a hipped roof may be constructed without rafter ties or internal columns. The wall plates provide all of the support needed for the roof structure. They are attached to the walls at floor levels and extend upwardly into the center ridge of the roof where they connect with other wall plates or coverings if desired.
The roof panels used on a hipped roof should be selected based on size and design. Larger panels can be used in high wind areas such as Hawaii while smaller panels are preferred in less severe conditions. Wall plates also determine the height of the roof since they must be installed to the same level as the walls they connect to. If the walls are six feet high then the roof plates should be placed six feet off the ground.
Hip roofs are commonly used on barns because they are efficient at using materials while still providing adequate stability. They are also easy to repair or replace when necessary.
As with any type of roof, care must be taken not to install too many loads across one panel. This could cause it to fail prematurely.
Roof ties are important components of a tied-house construction and should be included in any plan to ensure that the structure is stable.
A rafter is one of a sequence of sloping structural parts, such as wooden beams, that reach from the ridge or hip to the wall plate, downslope perimeter, or eave and are meant to support the roof shingles, roof deck, and the loads they support. A "couple" is a pair of rafters. A "stringer" is a long beam running parallel to the roofline; it may be made of wood or steel. The word "rafter" comes from the French for 'dry stick'.
The three main types of rafters are: flat, half-round, and full-round.
Flat rafters are very common and easy to build. You can cut them out of a single piece of lumber with a flat-bottom miter saw or by using a compass to mark out several straight cuts across each board. Flat rafters lie flat against the roof surface without protruding beyond it, so they don't need to cover any edge length. If you do want the rafters to extend past the walls of your house, you can cut them into two pieces with a flat bottom and glue them together. Half-round rafters have a curved bottom similar to the curve of a half-ball ball field. They sit at a slight angle against the roof surface and usually project just enough beyond it to allow for the placement of sheathing or other exterior building materials. Full-round rafters are exactly what they sound like - round.
If your roof is drooping, it may be stabilized or jacked up to its former position. The ceiling joists are designed to support the walls against the weight of the roof pressing outward. If this load is not removed, the wall will collapse in on itself.
The best way to address sagging roofs is with a stabilization/jacking system. These systems use steel cables attached to special hooks mounted on the building's structure. The other end of the cable is then pulled up through the roof, lifting it back into place and preventing further damage from occurring.
Roof jacks operate on much the same principle as their hydraulic counterparts do but instead of using water to generate pressure, they use air. Air jacks consist of an air compressor connected to a valve system that can control the amount of air released by the jack in order to lift different weights. Roof jacks are available for homes built before 1978 when most roofs were constructed with asphalt shingles which are easy to cut with a knife blade. Asphalt shingle roof jacks are usually only used when repairing small areas of the roof because they are difficult to drive over long distances.
Metal roofing is becoming more common these days because it is so durable and affordable. Metal roofing comes in several types including standing-seam metal, rolled metal, and panelized metal.
There are two popular methods for building a house's roof: premanufactured trusses or rafters and ceiling joists, sometimes known as "stick framing." In both cases, the roof is supported by beams that are perpendicular to the wall surfaces. The type of support used for these beams is called a "structure" if it is manufactured and shipped in one piece before being assembled at the job site or a "truss" if it is built up section by section at the job site.
The premanufactured truss method uses steel or aluminum connectors that are attached between the top of the beam and the bottom of the next lower beam. These connections can be seen in photographs of traditional barns that have been rebuilt after destruction caused by fire or wind. The premanufactured truss has several advantages over stick framing. It is usually easier to install since there are no nails or screws to drive into the wood beams. Also, the truss design allows for the use of thinner timbers which reduces the weight of the roof while still providing adequate support.
Ceiling joists are only used for simple shed-type roofs. They are thin boards that are spaced evenly across the roof and supported on the walls below. Ceiling joists do not need to be straight nor do they need to be perfectly square.
On all sides, a hip roof slopes inward. It is more hurricane resistant than a gable roof because it lacks a triangular gable end wall, which frequently falls under the strain of heavy winds. Hip roofs are also self-bracing. The suggested bracing for gable ends is shown below, which makes them a little more sturdy. A well-designed hip roof should have no need for additional support.
Gable roofs slope outward from the center of the house to the edge. They are easy to build and relatively inexpensive, but they get most of their strength from the sharp angle of the roofline at the peak. This strong vertical corner is what allows a gable roof to hold up so much weight. As you can see in the photo below, large holes must be drilled into the roofing material at the apex of each panel to allow water to escape.
Because of this weak spot, gable roofs are usually only able to withstand about half the wind load as a hip roof. However, if you want to be completely safe, you could reinforce a gable roof with polycarbonate or other lightweight material.
The strongest type of roof is one that combines the ease of construction of a gable roof with the sturdiness of a hip roof. These "triple-teaked" roofs are very common in Canada and the United States. They are generally made out of steel or aluminum and can weigh as much as 200 pounds per square foot.