Roof Without Rafter Ties

The prescriptive provisions of the building code require rafter ties on each rafter pair and collar ties every 4.

Roof without rafter ties. Also see our blog post what causes a sagging roof ridge line. The failure of rafter ties in this building combined with snow loading in amenia new york pushed the ridge down and the walls outwards as the building slowly settles down to the earth. The ties usually rest on the joists. C so you can easily cover the underside of the roof with drywall and its outside with plywood.

You can possibly remove them altogether of you include posts in the gable walls to support a structural ridge. Where rafters are oriented perpendicular to the ceiling joists rafter ties should be installed just above the ceiling joists. They have triangulation built into them so any additional structural members to resist the lateral loads are not necessary. You still have rafters 16 in.

From a practical perspective it s difficult to use high rafter ties on a low pitched roof because the force in each tie increases with the inverse of the pitch. The most common reason for installing collar ties is to prevent rafters from spreading apart under load. C and the flat ceiling is eliminated. But the spacing of the ties is reduced to 48 in.

In most homes the ceiling joists also serve as the rafter ties. A lack of rafter ties is a serious structural issue in a conventionally framed roof. If your garage is 24 feet wide and has a 4 12 roof the new rafter ties can be placed no more than 16 inches up from the plate without additional engineering. Rafter ties or ceiling joists acting as rafter ties are required by code unless the house is designed so that the walls or a structural ridge beam carries the full load of the roof.

Without the proper support of rafter ties or a structural ridge a typical gable or sloped roof will sag downwards while pushing the building walls outwards towards a catastrophe such as that shown in our page top photo of a barn in amenia ny. Manufactured roof trusses do not need a ridge rafter or ridge beam. An engineer can design a roof with rafter ties on wider spacings look at the ridge and or wall plate as a beam if doing that. However in a conventionally framed peaked roof like the kind you describe collar ties would probably serve little or no function since the attic floor joists serve as ties to prevent the rafters from spreading.

Typically this is done by leaving every third collar tie and removing the two in between as shown in the drawing. If you are framing a cathedral ceiling there are a couple ways to deal with the need for rafter ties.