Tweet
I live in a high snow load area. It may not be highest in the US but its right up there for the Northeast. The town next to me has 140 lb/ft2 ground snow load which if my conversion is correct is 683 kg/m2. All the roofs are sloped in that town. The older camp owners still have to get the roofs raked as they were not designed for the snow load I am not aware of any new flat roofs as the risk of frozen roof drains is too high. There are some flat roofs in the area with slightly lower snow load but they usually have some slight pitch that leads to scuppers on the low side of the roof. The normal approach if its a heated building is install roof drawings with tapered foam in the roofing system to pitch to the drains. The drains go through heated spaces so that they are always above freezing. The problems usually occur when the building owner does not maintain the drains and let them fill up with leaves or other debris or the building ceases to be heated. In both cases the roof stops draining and the snow on the roof turns into ice during freeze thaw cycles until they exceed the capacity of the roof and then it fails. The other strictly commercial system is a so called inside out roof where the membrane is applied to the deck which is equipped with drains. The roof is them covered with blocks that are insulation on the bottom with a concrete coating on top.Its pretty rare.
The term ice damming in the northeast of the US is pretty well only applied to sloped roofs. Typical construction is unheated attic space under a sloped roof with the roof running past the exterior walls for some distance as an overhang Snow on the roof melts faster than on the overhangs as heat leaking out of the house raises the attic temp somewhat higher than the outside. The water runs down the roof until it hits the overhang that is not heated by the attic and it freezes. The water then dams up and backs its way up the roof under the shingles. There are couple of solutions. Electric heat tape applied to the shingles o the ovehangs is the quick fix, buts it ugly and the heat tape have a limited life Installing ice and water shield from the lower edge of the roof up several feet doesnt stop the damming but it stops the water from getting back inside. Installing soffit vents and ridge vents to equalize the temperature between the attic and the outside also works. The last newer technique is a cold roof where the roof deck is a stress skin panel with the insulation sandwiched between a plywood facer on either side. The entire roof stays the same temp so no ice damming. This also can be done by spraying foam on the inside of the roof deck but there is some conductivity through the rafters.
I can speculate that putting tilted panels on a flat roof will cause icing issues but its really not the panels fault and I dont see how a panel could be modified to prevent it. The issue with ice damming is melt water drainage. Fix that and the ice doesnt form. The snow on the panel will melt faster than the snow piled on the roof. The reality is that unless the panels are vertical, certain snow conditions will cause snow to stick to stick to them and cover them for several days after the storm and the owners will not want the hassle of shoveling them off anyhow. What is usually used in unattended buildings with occupancy in winter conditions are vertical panels on the walls. The snow reflects the sun on the panels and it cant build up on them as they are vertical. Obviously no use in summer. Panels are cheap so I would just install them flat on the roof, uses good drainage design and if you need winter PV integrate vertical panels into the design for winter use on a separate MPPT channel.
The term ice damming in the northeast of the US is pretty well only applied to sloped roofs. Typical construction is unheated attic space under a sloped roof with the roof running past the exterior walls for some distance as an overhang Snow on the roof melts faster than on the overhangs as heat leaking out of the house raises the attic temp somewhat higher than the outside. The water runs down the roof until it hits the overhang that is not heated by the attic and it freezes. The water then dams up and backs its way up the roof under the shingles. There are couple of solutions. Electric heat tape applied to the shingles o the ovehangs is the quick fix, buts it ugly and the heat tape have a limited life Installing ice and water shield from the lower edge of the roof up several feet doesnt stop the damming but it stops the water from getting back inside. Installing soffit vents and ridge vents to equalize the temperature between the attic and the outside also works. The last newer technique is a cold roof where the roof deck is a stress skin panel with the insulation sandwiched between a plywood facer on either side. The entire roof stays the same temp so no ice damming. This also can be done by spraying foam on the inside of the roof deck but there is some conductivity through the rafters.
I can speculate that putting tilted panels on a flat roof will cause icing issues but its really not the panels fault and I dont see how a panel could be modified to prevent it. The issue with ice damming is melt water drainage. Fix that and the ice doesnt form. The snow on the panel will melt faster than the snow piled on the roof. The reality is that unless the panels are vertical, certain snow conditions will cause snow to stick to stick to them and cover them for several days after the storm and the owners will not want the hassle of shoveling them off anyhow. What is usually used in unattended buildings with occupancy in winter conditions are vertical panels on the walls. The snow reflects the sun on the panels and it cant build up on them as they are vertical. Obviously no use in summer. Panels are cheap so I would just install them flat on the roof, uses good drainage design and if you need winter PV integrate vertical panels into the design for winter use on a separate MPPT channel.
Comment