Under Purlin Straps

Under Purlin Straps are used to stop timber roof purlins from deflecting. They are usually a 50×6 flatbar strap with a bolt through the timber at each end and a long tensioning bolt in the centre which is wound against the underside of the purlin to create pressure and upward lift to compensate for any sag caused by the weight of the roof tiles. Sometimes two tensioning bolts are used on long straps. They are used in new roofs and also in an older roof to correct a sagging section of roof.