2. LVL STRUCTURES IN FLOORS, WALLS, ROOFS AND IN SPECIAL APPLICATIONS 2.3 ROOF STRUCTURES Tall and slim LVL-P beams are ideally suited for thermally efficient roof structures. LVL-P rafters provide long span lengths and simple detailing for pitched or ridge roofs in residential buildings. Multiple span LVL-P purlins in hall constructions can be installed on site or as components of roof elements produced offsite. Large and robust LVL-C roof panels are fast to install, they work effectively in diaphragms, and they make it possible to create roof overhang eaves that have a light appearance without supporting beams. 2.3.1 Beam & rafter roofs LVL-P roof rafters are available in a wide range of sizes for different span lengths of pitched or ridge roofs. Energy efficiency requirements for roof structures set the minimum U-value at 0.09-0.15 W/mK depending on the country. With conventional mineral wool or wood fibre insulation this means that the insulation thickness needs to be ~250-450 mm. To provide adequate ventilation space between the insulation and roof covering in cold roofs, the rafters should be at least 100 mm taller or a separate batten structure is needed. In some countries a warm roof without a ventilation gap is the preferred solution depending on the climate and building physics design. LVL-P rafters provide an easy solution with minimum cold bridging. The rafters have good load-bearing capacity and stiffness, enabling wide rafter spacing, e.g. c/c 1200 mm. Ends of the rafters can be notched at the roof overhang section. This can be done on site with normal woodworking tools, or for faster installation the rafters can be ordered from the supplier with ends ready machined. Figure 2.27. LVL-P rafters in a mono-pitch roof structure. Figure 2.28. LVL-P rafters in a ridge roof structure. Metsä Wood Metsä Wood 66 LVL Handbook Europe
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