Old Roof Sdupport System Inspect Purlin

Purlins are not required or needed unless rafters are overspanned and then the purlins serve as support to prevent roof sag deflection due to the overspanned and or undersized rafters.

Old roof sdupport system inspect purlin.

Conventional roof framing and roof trusses. Roof huggers in place on an old roof. Snap a chalk line horizontally across the roof two feet down from the top. It s hard to fathom that the roof framing would have passed original inspection with this support system or lack therof.

We won t go into attic inspection too deeply since this series of articles from mastering roof inspections is primarily about roofing defect recognition but you should have an understanding of the two main basic roof structure systems. I m not sure if it was original construction or not 1978 duplex though it looked like it. The roof support system is a ridgepole and either rafters which run perpendicular from the top of the walls to the ridge or purlins which run parallel to the ridge. Ply roof systems are also lightweight and utilized for retrofits over existing metal roofs figure 2.

Purlins support the loads from the roof deck or sheathing and are supported by the principal rafters and or the building walls steel beams etc. The use of purlins as opposed to closely spaced rafters is common in pre engineered metal building systems and both the ancient post and beam and newer pole building timber frame construction. Collar ties rafter ties tension beams structural ridge beams. Photo above is from a jwk inspections framing pre drwall inspection in the san antonio south teaxas area showing the actual roof framing componenents.

New panels being installed over roof huggers on an old roof above. With rafters it runs in perpendicular from the walls to the ridge while with purlins it runs to the ridge in parallel. Lay the first purlin at the ridge of the roof down to the chalk line beginning at either corner. Some of these can support the roof and prevent ridge sagging and wall spreading.

The support system for the roof is comprised of ridgepole and rafters or purlins. Many single ply membrane roofs rely on the existing metal roof to function as a structural deck for support and attachment of the roof system including board insulation as well as for support of live snow and wind. Fasten the purlin with 16d common nails into each vertical rafter. Use purlins to create a supporting framework and to transfer the loads imposed by the sheeting onto the primary building structure.

The lack of which imo allowed the purlin to twist away from the rafter. This article describes and illustrates the different types of support that prevents roof sagging and wall bulging at buildings including definitions of collar ties rafter ties and structural ridge beams.