Recently my friend Jim Hammel and I went to do the final testing to verify a new Energy Star home. Duct blaster, blower door, digital manometers, flow hood, gas-leak detector, combustion analyzers. The particular house we tested performed very well because the builder understands the importance of building performance. Some of the other builders in the development where this house stands? Not so much.
How exactly do I know this? Because I see this sign posted on a phone pole right at the development’s entrance: “Roof Shoveling. Same Day. 530-2244. Fully Insured.”
Ice Dam Ice
“Why shovel a roof?” Well, it could be about snow loads. We get a lot of snow here in Syracuse, N.Y., and each year a couple of roofs collapse under it. The ones that go down are pretty much always older homes in disrepair. Roofs of new homes must be engineered to withstand substantial loads of 40 pounds per square foot.
The sign on the pole might just as well say “Caution: Poor Building Performance Ahead.” The roof-shoveling sign is there because the snow on these homes melts high on the roof and runs down to the eaves where it is colder and then the water freezes. Icicles form. More water runs down and freezes. An ice dam forms, the icicles grow, melted water backs up under the shingles, the roof leaks, the icicles fall off and hit the person when he rings the front doorbell, and so on.
And no, the snow does not melt on the roof to this degree because there is inadequate attic ventilation. It melts because warm air from the house is able to move into the theoretically unconditioned attic and warm the roof from underneath. Think of an electric blanket under your sheet. You can imagine what happens with an HVAC system or ductwork in the attic.
Stop the warm air at the ceiling plane and the ice dams don’t form, and you get just enough charming icicles to make your house look like a Christmas card.
How do I know this? Because we routinely fix ice dams by air sealing the house at the attic plane, and we never see the problem fixed by adding ventilation.
The rule of thumb is that 98% of new homes are in need of energy/performance-related retrofits on the day the buyer takes title. Such is the case with new homes that need their roofs shoveled. The opportunities for remodelers are as plain as the ice on the roof, and the opportunities are not in chopping off ice with a hatchet (or even trying to cut it off with a chain saw). Those particular measures can have unintended consequences. Ask me how I know.