When ice dams form at the bottom of roofs, water can enter and cause damage to walls and roofs. A roof’s snow melts and runs down to its bottom edge, where it freezes. An ice dam is a large block of ice that can cause water to back up beneath shingles and cause damage.
Ice dams cause structural damage to walls and roofs.
There are many factors that contribute to ice dams.
Older homes often lack adequate insulation, especially at roof-to-wall joints. Particularly susceptible to this problem are low-sloped roofs with short overhangs. The heat from the frame members warms the roof deck and melts the snow; the water then rushes beneath the snow to the overhang, where it is no longer heated by interior sources and freezes.
A common concern is air leakage through walls since air transports a lot of heat. This causes the same melting in the attic.
While ventilation equipment like furnaces, ductwork, and air conditioning are rarely found in attics these days, if you do, it probably leads to ice damming. In addition, installing air handling equipment in the coldest and hottest parts of the house can increase your operating costs by 25%.
It isn’t as important to seal pot lights because of the heat they produce, but it is extremely difficult. Due to the warm air passing through the lamps, unlike other air leaks, the situation is made worse.
Snow: this may be difficult to understand, but snow has an R value of between 1 and 2. In the winter, snow insulating the roof warms the attic, melting the snow inside. Ice does not develop immediately on the roof surface; instead, water is absorbed into the snow layer, which then freezes.
Wind and sun: the wind will blow snow off a roof, most evidently at the ridge, and when the sun warms roofing materials, the snow around it melts and forms an ice dam.
Identifying and preventing ice dams:
As some of these issues (such as snow, sun, and wind) cannot be avoided, installing a waterproof membrane underneath the final roof covering at the bottom edge of the roof will help prevent water damage from ice dams.
Thanks to this membrane, any water collected beneath the shingles will be safely drained off the roof.
The use of metal surfaces at the bottom of the container is another frequent approach, which makes any ice that forms easy to remove. It works, but it can be dangerous if it falls in a high-traffic area.
It seems that covering an entire roof with a waterproof membrane has gained popularity in the last 15 years or so; while it will undoubtedly reduce ice damming, it requires a substantial financial investment that could have been better spent on improving air sealing and adding insulation to minimize heat loss.
By ensuring that the roof pitch and overhang are sufficient for proper ventilation and insulation, thermal bridging can be avoided in new construction. With high-heeled trusses, the upper deck of the roof can be raised, allowing for more space for insulation.
Typical fibrous insulation, such as cellulose and fiberglass, has an R3-4 rating, while spray foam has an R6 rating. As a result of spray foam’s high environmental cost, we cannot recommend its use, except in extreme circumstances, as this might be.
For older homes with limited space over top of walls, replace a lower-R value per inch insulation with a higher-R value insulation such as spray foam. Around the perimeter, you would need to do a one- to two-foot stripe.