“ Ceiling joists and rafters shall be nailed to each other in accordance with Table R802.5.1(9), and the rafter shall be nailed to the top wall plate in accordance with Table R602.3(1). rafter tie, Section R802.3.1 of the IRC specifies the following for ceiling joists in a conventional system: To ensure proper performance as a member in tension, i.e. In addition to providing support to any vertical attic ceiling loads, the ceiling joists must also be designed and constructed to withstand the tension along their length, caused by the outward thrust at the exterior walls. 1).įigure 1: Diagram of conventional system with ceiling joists acting as rafter ties.

In this configuration, the ceiling joists also function as rafter ties (Fig. In a “conventionally” framed roof, a roof is constructed with rafters along each slope with ceiling joists along the bottom enclosing an attic space. “ RAFTER TIE – A structural framing member located in the LOWER THIRD of the attic space that ties rafters together to RESIST THRUST from gravity loads on the roof.” Its function and location is summarized in the following definition from Wood Frame Construction Manual (“WFCM”) produced by the American Wood Council (“AWC”): A rafter tie is a horizontal framing member that extends across the roof span to resist the outward thrust at the bottom of the rafters and effectively “tie” the rafters into their proper triangular shape. the triangular shape flattens down and out. When vertically loaded, the ridge tends to deflect downward, and the bottom of the rafters tends to push outward, i.e. The most common type of residential roof is a simple gable or hip configuration, consisting of a peak (ridge) and sloped sides, resembling a triangular shape when viewed from the side. Similar requirements and principles exist across other IRC editions and industry standards as well.

Code references throughout our discussion come from the 2015 edition of the International Residential Code (“IRC”), the most common edition currently adopted across the United States. In Part 2, we will discuss the difference between rafter ties and collar ties (and no – they are not the same thing!). Part 1 on ridge boards and ridge beams can be read here. This three-part series aims to provide an overview of these critical components in an effort of providing an overview of residential roof framing basics, code requirements, and common deficiencies. In our experience performing hundreds of forensic evaluations related to residential roof framing per year, the problems often stem from misunderstanding of the following three critical components of residential roofs: Errors in the design and construction of residential roof framing are common causes of property damage, liability claims and litigation.

Flat roof rafter ties in to another