by Skander Spies
The last few weeks in western Montana have been some of the wettest in history. If you have ever had a roof leak, mold problem, or flooded basement, then you probably already know that wood and water don’t always mix. Often in the process of making buildings more energy efficient, we have the opportunity to address issues related to water. This post is about how our integrated package of insulation, air sealing, and mechanical services often includes preventing liquid water and airborne moisture vapor from damaging your building.
(Re)Move the Moisture
Looking at an attic bid this afternoon, I immediately noticed there wasn’t any attic ventilation at all. The roof is the primary water management system for the house. As such, they are exposed to brutal temperature extremes, high winds, rain, snow, hail, and UV. To put it simply, the life of a roof is hard. Attic ventilation is designed to allow outdoor air to remove moisture from the attic space, as well as reduce the temperature difference across the roof sheathing (remember, they contribute to ice dams). Removing this moisture is important not just to protect the sheathing but also to prevent condensation in the insulation.
Attic insulation prevents conductive heat loss from the house to the air in the attic. The more insulation you add, the colder the attic air gets- great, unless there is moisture in that air. If there is, the warm air carries the moisture up and into contact with the cold roof sheathing where is condenses. Good ventilation will carry that moisture and condensation away before it turns into liquid water and before it causes problems. Generally, warm air leaks from the house up into the attic because hot air rises and traditionally attics aren’t air sealed. Even having a properly sealed attic won’t always prevent moisture from getting into the attic air so having good ventilation is essential for preventing long term problems. In general, you never want to have unconditioned, un-vented space. Attics can be vented with soffit vents, gable vents, ridge vents, or dedicated surface mount vents. We can coordinate with a roofer to ensure that any upgrade properly addresses both heat loss and proper ventilation.
Down and Dirty
Does your floor ever feel cold or damp in the winter? This is the problem:
Your crawlspace or basement is a common area for moisture to penetrate your home often bringing other pollutants like dust and radon. Similar to an attic, conventional construction lets outside air into the crawlspace to prevent moisture buildup. Unfortunately, that lets heat out in the winter and if you have air conditioning, it can promote moisture damage in the summer. We’ve done several crawlspace upgrades recently, and our clients have been pleased to find how low impact the improvement process is. For existing buildings, it’s usually easiest to add insulation and a vapor barrier; making the crawlspace just like another part of the living space. This also has the bonus of providing storage space for the occupants. Unlike an attic, it’s not always possible to determine where the moisture is coming from so the products and systems we use have to be more specialized.
Dam Ice on the Roof?
One of the most common issues behind a roof leak is an ice dam. Ice dams can also be a good indicator of energy loss through your attic. Ice dams form when the roof sheathing is heated by the building below, melting any snow that has accumulated. The liquid water then drips to the edge of the roof which is cold so the water re-freezes. Through the winter, ice and water shrink and swell with repeated freezing and melting. This can buckle shingles and/or damage the roof sheathing underneath, causing water leakage that looks like a roof problem. Other factors like low slope roofs or roof valley intersections can also amplify these problems, but most of the time the key issue is in temperature differences in the roof sheathing and heat loss through the attic. Learn more about how we air-seal and insulate attics here. You can also check out a great article about ice damming, here.