Residential or agricultural buildings usually sport conventional roof coverings like shingles, slate, roll asphalt roofing, or wooden shakes. When these supplies attain the top of their typical five-to-20-year lifespan, metallic roofing is a sexy and sensible possibility.
Preliminary issues
Earlier than a re-roofing challenge, evaluate zoning and code restrictions to make sure the chosen roof coverings meet native rules. Completely different neighborhoods, communities, and areas might have particular pointers. For roofs with slate or wooden shakes, removing is critical. Slate, although heavy, is recyclable and in excessive demand. Wooden shakes, being cumbersome and uneven, create an unsuitable floor for metallic roofing, inflicting a wavy look.
Structural evaluation
Evaluating the bodily situation of the construction is a crucial first step. Inspection
will be completed from the attic area or by eradicating current shingles. Any broken areas needs to be repaired to satisfy present constructing codes.
Metallic roofing over current shingles
Metallic roofing will be put in over current shingles if the construction’s useless load capability permits it. One layer of shingles sometimes weighs between 1.1 and 1.45 kg/m2 (2.4 and three.2 lb/sf) and two layers weigh round 2.3 to 2.7 m2 (5 to six lb/sf). Most trusses are designed for a complete useless load of 4.5/m2 (10 lb/sf). Metallic roofs add solely 0.4 to 0.7/m2 (0.8 to 1.5 lb/sf).
Situation of current shingles
If current shingles are broken, cut up, or waterlogged, it could point out underlying structural points. In such instances, shingles needs to be eliminated, vital repairs made, and the brand new metallic roof put in over artificial underlayment or 14-kg (30-lb) felt. If shingles stay, set up underlayment after which 51 x 102 mm (2 x 4 in.) purlins or 25 x 51 mm (1 x 4 in.) furring strips to connect the metallic panels. Panels shouldn’t be put in straight over the shingles. Over time the shingle look can telegraph via the panel, and working fasteners via the shingles might trigger the fasteners to dimple the panel floor or not seal correctly to the panel.
Set up strategies
When utilizing uncovered fastener panels, set up a vapor barrier (ideally artificial underlayment) earlier than attaching the panels. Use fasteners lengthy sufficient to penetrate plywood or OSB or 25 mm (1 in.) into dimensional lumber, keep away from overdriving fasteners to stop dimpling the panels, and pay attention to current shingle imperfections.
Underlayment will be positioned straight on outdated shingles or purlins, offering further moisture safety. Underlayment can bleed asphalt on sizzling days, probably staining the metallic roof, so artificial underlayment is advisable because it avoids this challenge. Nevertheless, 14-kg (30-lb) felt can’t be used below standing seam roofs with out an extra slip sheet to stop tearing from thermal motion. Ice and water shields needs to be used alongside eaves and valleys to stop moisture infiltration.
Connect 51 x 102 mm (2 x 4 in.) purlins or 25 x 76 mm (1 x 3 in.) furring strips flat on the roof and fasten into trusses or rafters with two fasteners at every connection. Purlins needs to be spaced a most of 610 mm (24 in.) on middle horizontally up the roof slope. Guarantee valleys are crammed strong, 305 mm (12 in.) from the middle on either side to help valley flashing.
Standing seam panels observe the identical suggestions as uncovered fastener panes; many require a strong substrate. That is achieved by eradicating the shingles and putting in over the present decking with new underlayment, or by filling areas between purlins with inflexible insulation or fiberboard, including insulation worth. Don’t fasten metallic roofing on to insulation; use purlins for attachment to trusses or rafters.
Fasten metallic panels to purlins per specified patterns, contemplating native wind uplift resistance necessities. Design wind velocity, roof peak, slope, form, location, and constructing use all affect the uplift design. Eaves, ridges, hips, and gables want extra fasteners or nearer purlin spacing for elevated wind resistance. Seal aspect laps with butyl sealant tape for optimum weather-tightness.
Including insulation between purlins reduces noise from rain and offers condensation safety by shifting the dew level temperature. Use a vapor barrier on the nice and cozy aspect of the insulation to attenuate condensation throughout the attic area. Keep away from extreme insulation that might bulge the metallic roofing.
Steve Maule is the engineering supervisor at Fabral Metallic Wall and Roof Techniques, the place he has labored on their engineering group for greater than 18 years. Steve has a Bachelor of Science (BS) in Mechanical Engineering from Penn State College and has spent his profession constructing his experience within the metallic cladding trade.
