Need snow shoveled from roof

[DickR]

Originally Posted by Belmont Resident

.... There was a problem with the house holding water during the plaster curing time and dehumidifiers were brought in to solve this.....
....I would think that having the most insulation possible on the roof is the best option.

In both concrete and plaster curing, part of the water is tied up by chemical reaction and becomes part of the solid result. The excess water must be removed by evaporation. Ultimately, that water should be removed from the air by mechanical dehumidification or by ventilation. One should not expect or want all that moisture to go out through the walls.

Nearly all cases of ice damming at the edges of roofs are due to warmth getting to the roof surface. Much of the time this is due to heat carried by air leakage from conditioned space into the attic (vented attic) or the roof cavity in the case of a cathedral ceiling. Can lights in the upper floor ceiling are notable heat leaks, even those rated "air tight" (AT), and from a building science point of view are generally a bad idea in those locations. But any air leak that carries heat from conditioned space to the roof deck contributes to conditions that lead to ice damming.

More and more attention is being given to building science issues, and some builders have learned how to get it right, but sadly some still just build the way they've always done it. Insistent homeowners who prefer form over function also are part of the problem.

[Rusty]

Originally Posted by DickR

In both concrete and plaster curing, part of the water is tied up by chemical reaction and becomes part of the solid result. The excess water must be removed by evaporation. Ultimately, that water should be removed from the air by mechanical dehumidification or by ventilation. One should not expect or want all that moisture to go out through the walls.

Nearly all cases of ice damming at the edges of roofs are due to warmth getting to the roof surface. Much of the time this is due to heat carried by air leakage from conditioned space into the attic (vented attic) or the roof cavity in the case of a cathedral ceiling. Can lights in the upper floor ceiling are notable heat leaks, even those rated "air tight" (AT), and from a building science point of view are generally a bad idea in those locations. But any air leak that carries heat from conditioned space to the roof deck contributes to conditions that lead to ice damming.

More and more attention is being given to building science issues, and some builders have learned how to get it right, but sadly some still just build the way they've always done it. Insistent homeowners who prefer form over function also are part of the problem.

You have posted some very interesting info about roof insulation and venting.


When my cathedral ceiling was built they used foam baffles the full length of the ceiling before insulation was added. The baffles channel cold and hot air to the ridge roof vent for proper ventilation. On one side the baffle goes halfway in the ridge vent and then the other side overlaps that one.
I have never had any ice damming on my roof.

[songkrai]

Originally Posted by DickR

Insistent homeowners who prefer form over function also are part of the problem.

Yes, yes, and yes.

[BroadHopper]

Originally Posted by DickR

In both concrete and plaster curing, part of the water is tied up by chemical reaction and becomes part of the solid result. The excess water must be removed by evaporation. Ultimately, that water should be removed from the air by mechanical dehumidification or by ventilation. One should not expect or want all that moisture to go out through the walls.

Nearly all cases of ice damming at the edges of roofs are due to warmth getting to the roof surface. Much of the time this is due to heat carried by air leakage from conditioned space into the attic (vented attic) or the roof cavity in the case of a cathedral ceiling. Can lights in the upper floor ceiling are notable heat leaks, even those rated "air tight" (AT), and from a building science point of view are generally a bad idea in those locations. But any air leak that carries heat from conditioned space to the roof deck contributes to conditions that lead to ice damming.

More and more attention is being given to building science issues, and some builders have learned how to get it right, but sadly some still just build the way they've always done it. Insistent homeowners who prefer form over function also are part of the problem.

I was building one of the 'green' homes back in 2010. I had a lot of contractors dispute RBC 2010 codes and architect/engineer specifications mostly because they had a tried and true method of building. One of them was dehumidifying the space between the roof and plastic sheeting even during the addition of insulation. This particular build is a closed system where there are no air circulation under the roof. Many contractors walk away from the project. The home is into its 3rd winter without any problems. Roof has never been raked and there are many valleys and gables.

[dpg]

Lots of times ice dams occur not because the roof wasn't "raked" but because of issues with the attic space. Attics idealy need to be very well vented through the soffits and in the winter VERY COLD! An attic should preferably average the same temperature as the outside air. When it's this cold snow will not be as likely to hit the roof and begin melting which eventually forms an ice barrier. After $15,000 worth of ice damming issues two winters ago I became very educated in this subject. Most folks attribute ice dams to the gutters backing up which does happen however a home can still have "damming" even without gutters installed.