IAQ IQ Winter, 2019-2020
©2020 Jeffrey C. May
Winter is here, and with winter can come ice damming.
Ice damming can cause expensive damage, including at the exterior. One new home I investigated was plagued by severe ice damming. The icicle that formed from snow melting above the attic furnace was so mammoth that when it fell, it demolished the deck below. I recommended that the homeowner stop the hot-air leaks and install insulation between the rafters above the furnace.
This past winter, we received several calls from hysterical homeowners who took a brief respite from manning the buckets in their living rooms and bedrooms. These callers had urgent questions about what to do to avoid mold. Whether or not mold grows depends on how long surfaces remain wet, what the surfaces consist of, and whether or not there is insulation in the framing cavities. In severe cases of ice damming, I recommend that walls and ceilings be opened up, insulation removed, and the cavities allowed to dry. Supplemental heaters can be used if needed.
If a musty smell develops from ice damming, that’s a sure sign that microbial growth has taken place. It does not necessarily mean, however, that people will be exposed to microbial allergens, which may or may not infiltrate a living space.
As a building professional, you will want to look very carefully at the exterior siding, to see if you notice cedar extractive stains. These stains on clapboards and shingles are caused by water flowing over cedar, which contains soluble tannins – similar to those in tea leaves. Ice-dam stains are often visible on cedar siding beneath the soffit, which in some cases may actually fill with water or ice.
Just keep in mind that extractive stains under windows at the lower level may be the result of water entry at trim or siding joints, due to improperly sloped window drip-cap flashings.
You may see stains from ice damming on the inside, at exterior walls and ceiling surfaces near the perimeter. A non-invasive moisture meter can be used to determine if a stain is still damp.
There are a few caveats to using such an instrument, however. In most cases, if the ice damming has taken place a month or more prior to your inspection, and there is no insulation in the framing cavity, the odds are that the stained area will be dry. On the other hand, if the cavity is heavily insulated with fiberglass, dampness could still be present.
Another confounder would be the presence of cellulose insulation, which contains water-soluble salts that act as fire retardants. Water that has flowed through cellulose insulation and has saturated drywall or wood will leave behind salts when it evaporates. These salts conduct electricity. Since most moisture meters measure the electrical properties of the substrate, dry wood and plaster that contain conducting salts may appear to be wet. (Corners with metal beads always register as wet.)
A third complication of using a moisture meter is the effect of temperature. As surprising as it may seem, you can put a moisture meter on the ice of a frozen lake and obtain a dry reading, because ice is a very poor conductor. This means that in winter, before using a moisture meter, you should always measure the temperature of the surface with an infrared temperature sensor, to be sure that the surface is above freezing.
One possible, urgent remedy for a potential ice damming crisis that I’ve heard works is to fill a panty hose leg or stocking with calcium chloride “Ice Melt,” and throw the hose or stocking up onto the roof, just above a gutter. Each stocking should be perpendicular to the gutter. The heat and chemical action of the calcium chloride will melt the ice jam and drain the water from the roof pond. Just caution the home occupant about collecting the melt-off, as the calcium could affect plant growth under the gutter or at the end of the downspout.
You may want to provide some hints to your clients to help them prevent ice damming in the first place. Installing “Ice and Water Shield” on the sheathing under the shingles is certainly part of the answer, as we all know. The material should extend about three feet beyond the interior wall. Since heat loss from the house is the obvious cause of ice damming, increasing attic insulation will also help minimize ice damming. More importantly, warm, moist air should be prevented from migrating into the attic; otherwise, all the insulation in the world is defeated. (Warm, moist house air flowing up into the attic also leads to condensation and mold growth on the attic sheathing, usually heaviest on the north-facing side.)
Improving attic ventilation may reduce ice damming but eliminating heat loss to an attic is most important.
On your inspections, check to be sure that the pull-down stairway is not warped, that there are no gaps around an attic door, or that a hatch is airtight. Older, “vented” recessed lights on the top floor, as well as leaky heat ducts, are also sources of warm air. Make sure that a bathroom exhaust vents directly to the exterior, and not into the attic or soffit. And if there are heating ducts in the attic and central humidification in the system, be sure that the ducts aren’t leaky and that any attic air handler is airtight to the exterior (including the filter holder).
This is a useful book for clients who have allergies, asthma or other environmental sensitivities, or for anyone who is concerned about the negative impacts that poor indoor air quality can have on human health. Look for Edition 2 in the fall of 2020.
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