Old Roof Sdupport System Inspect Purlin

Use purlins to create a supporting framework and to transfer the loads imposed by the sheeting onto the primary building structure.

Old roof sdupport system inspect purlin.

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. Roof huggers in place on an old roof. Snap a chalk line horizontally across the roof two feet down from the top. Dale nelson president of roof hugger left with red mcconnohie the product s inventor.

Using a combination of rafters and purlins is common. Ply roof systems are also lightweight and utilized for retrofits over existing metal roofs figure 2. 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. It s hard to fathom that the roof framing would have passed original inspection with this support system or lack therof.

Conventional roof framing and roof trusses. New panels being installed over roof huggers on an old roof above. 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. The support system for the roof is comprised of ridgepole and rafters or purlins.

Lay the first purlin at the ridge of the roof down to the chalk line beginning at either corner. The lack of which imo allowed the purlin to twist away from the rafter. Photo above is from a jwk inspections framing pre drwall inspection in the san antonio south teaxas area showing the actual roof framing componenents. Some of these can support the roof and prevent ridge sagging and wall spreading.

With rafters it runs in perpendicular from the walls to the ridge while with purlins it runs to the ridge in parallel. Collar ties rafter ties tension beams structural ridge beams. 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. Insert two equally spaced nails into the rafter.

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. Fasten the purlin with 16d common nails into each vertical rafter.