Flat Roof Eaves Construction Details

Trusses streamline construction but it s important when using them to make sure the resulting eave works with the design of your building.

Flat roof eaves construction details.

The design of your eave is dictated by the construction of your roof. Joists are placed on edge spaced at 400 600mm centres supported by external and internal load bearing walls. Trada and approved document part a give guidance on sizes of joists for flat roofs relating to spans and loading. On larger roofs it s probably cheaper to use tapered foam insulation on top of the roof sheathing.

The main component of any eaves detail is the rafter tail the part of the rafter that extends beyond the exterior wall. With flat clay roofing tiles the first course may be raised with a special starter tile as shown at left in figure 2 27 or by a metal eaves closure raised fascia or wood cant strip. Underneath the basics flat roofs are usually constructed with a ceiling nailed to joists which support a deck usually wood in residential construction a vapor barrier insulation and a roof board. If a sprocketted or bell cast detail is used then eaves courses should beno lower than the minimum recommended roof pitch.

The construction of the flat roof is similar to that of the timber upper floor. The eaves detail shows where the roof members and coverings meet the wall of the dwelling. Fix a rafter spacer tray to provide a clear air path between underlay and insulation. This modest slope can be achieved in a number of ways.

The wallplate is secured to the internal wall separated by dpc. As well as the small selection of roof detail drawings shown here many of the building notes have a related construction detail drawing with specific dimensions eg rafter sizes spans insulations types for purchase with the building specifications. Additional construction details drawings. To determine exactly what the rafter tail will look like i always make a full size drawing on a scrap of plywood of all the eaves elements including framing and finish materials see illustration above.

The wallplate is then used to secure the rafter to. The cavity is closed with a proprietary cavity closer. With a cant strip or raised fascia a beveled wood or foam antiponding strip is required to prevent ponding of water along the eaves figure 2 29 below. Before manufactured trusses the simplest roof construction involved extending exposed rafter tails beyond the walls of the house.