Warm House, Wet Attic

Winter time. It evokes visions of snow, cold winds and hunkering down beside by a nice warm crackling fire. Most of us also notice the air is dryer. The frigid winter air can not retain as much moisture as the temperate air of summer. We find our lips get chapped and our sinus become dry and uncomfortable.

The air inside our homes during those cold winter months is perceived to be dryer as well, especially because the heat is running. And to some extent the air is dryer, but don't forget we heat our homes and warm air holds more moisture than cold air.

During winter with the home all buttoned up we continue bath, breathe and cook. Moisture, moisture and more moisture. On top of all that many people run humidifiers just to add a little more water into the air.

Where do you suppose all that water goes?

The other natural principal to remember is warm air rises, but more importantly is attracted to cold air. Eventually some of that warm moist air inside the cozy conditioned envelope of the homes interior diffuses into the cold attic.

What happens to warm moist air when it cools?

Condensation!

Condensation in the attic during the winter is a fairly common phenomenon and can be mild to acute. Attic ventilation is supposed to get rid of the moisture that eventually ends up in the attic, but can be over whelmed.

Most often condensation occurs because the homeowners are over humidifying the home. Humidification increases the relative humidity (RH) inside the conditioned space of the home. Higher RH can lead directly to issues such as mold growth, dust mites and other microbial growth.

The two photos show condensed moisture inside attics on the roof deck.

The first photo is from a home built in the 1950s. No insulation was present in the walls and the attic was minimally insulated. Moisture is condensing predominately at the soffit area. This is likely due to a greater amount of heat and moisture able to travel through the upper portion of un-insulated exterior walls and condense on the coldest portion of the roof. The interior of the walls may quite possibly look similar.

The second photo, which ironically was taken while writing this blog, is the direct result of over humidification and quite possibly inadequate attic venting. The homeowners run room humidifiers in each bedroom every night while sleeping.

Generally indoor RH should be maintained at 25 - 60%. Lower is better and generally healthier because of the decrease in incidence of microbial growth. Most people can not detect any difference in RH in this range. In other words if you walked into two separate rooms with a RH of 25% and 60% you could not discern which room had the higher RH or vice versa.

Humidification should be done sparingly and monitored closely. Watch for signs of high RH such as condensation on windows. Check you attic for frost or condensed moisture on roofing nails and buy a humidity monitor (Hygrometer).

Over time a condition such as the ones shown above can become detrimental to the home and its occupants.