The braces (struts or kickers) should be within every 4' and should not be at a greater than a 45 degree angle towards the roof slope (lower side). The purlins are supported by vertical or slightly angled bracing. Purlins are placed under rafters in a perpendicular position on edge (not flat).

Purlins on a roof frame serve the purpose of preventing rafters from being over spanned and sagging. Seperate rafter ties need to be run at the roof frame / rafter level area shown.Ībove- The photos show local framing inspections where the ceiling joists are run prependicular with the rafters, so the joists can't serve as rafter ties. Proper attchments / fastening needed from both sides of joists and rafters and down into top placte of wall, securing all components adequately together.Ībove- The 2 photos show a scenerio where the joists are run parellel with the rafters but can't serve as rafter ties due to the rafters and joists being at different levels. Rafter ties (not serving as ceiling joists) that are running above and perpendicular with the joists can sit on the joists and also be fastened to them thus also serving as strong backs to help prevent ceiling joists from twisting and sagging.īelow- The 2 photos show Joists run parellel with the Rafters but are not secured up against them to properly serve as Rafter Ties.Ībove 2 photos show Joists up against Rafters but not properly secured to them to serve as the required Rafter Ties. spacing or every three rafters on a 16' on center spacing. These rafter ties running perpendicular above the joists need to be a maximum of 48' on center apart, which would be every other rafter on a 24' o.c. Rafter ties when not also serving as ceiling joists are required to be at least a 2x4 material and should be on edge. When the ceiling joists are running perpendicular with the rafters then rafter ties are run above the joists in the direction of the rafters and are fastened to them. Ceiling joists can serve as Rafter ties when they are running the same direction as the rafters and are properly tied tied together with them at the exterior wall. Spreading walls will create a sagging roof. Rafter Ties- Rafter ties are required to be installed in the lower third of the roof frame area to help prevent exterior wall cans from spreading. Photos below show properly installed collar ties at 2 other framing / predrywall inspections. Photos above show missing (required) collar ties at the construction of 2 different roof frames at JWK Inspections Framing / Pre Drywall inspections in the San Antonio area.

Also, an engineered truss roof frame does not ordinarilly have a ridge. This is on a conventional stick frame (non-truss) structure, as engineered roof trusses do not require collar ties from a framing material as they are tied together with metal plates / gussets. Collar ties as per current IRC code are required to be at least 1x4(nominal) material but are most commonly 2x4's. Metal Brackets or Straps can be an acceptable alternative in lieu of the more common use of the wood framed collar ties. Collar ties prevent rafter separation and uplift. Collar Ties are connections between opposing rafters at the upper one third of the roof frame area just below the ridge and they are required at a 48' (4') maximum spacing which is every other rafter of a 24' on center spacing and every third rafter with 16' on center spacing.

Roof rafter tie location on rafters