Cathedral ceilings can add a unique and spacious impression to your home, but they can also be a source of condensation and moisture damage if not properly designed, constructed, and maintained. In this post, we will discuss some common causes of condensation risks in roofs, how to reduce this risk, and preventive measures for the maintenance of cathedral ceilings.
What Causes Condensation In Roofs?
Condensation is a natural process that occurs when water vapor comes into contact with colder environments such as colder air or colder surfaces. In most cases, this becomes visible when water droplets form on a surface of a building enclosure element – for example, in a roof system. When this happens, the water vapor may not only condensate but can also freeze and go unnoticed for an entire winter. When temperatures then get warmer again building owners of homes with a cathedral ceiling can be in for quite a surprise as the accumulated frozen condensation (ice) can melt over a rather short period.
Cathedral ceilings have a higher condensation risk and require special design and construction details.
Other than hiring an experienced design and construction team, there are a few things that homeowners can do to prevent and reduce condensation from occurring in their cathedral ceilings. The most important thing is to keep the roof well maintained from both sides. Moisture does not always enter the roof from the exterior, Interior humidity that makes it into the roof system can also cause condensation. It is important to take action if any amounts of moisture accumulation are detected. Even if only minor amounts are visible it is advisable to consult with an expert, such as a professional engineer. Experts can assess the issue, identify the cause, and in the end can determine if long-term problems are to be expected over time if no remedial action is taken.
How To Reduce Condensation Risk In Cathedral Ceilings
The condensation risk in cathedral ceilings is higher than in more common ventilated attics we find in the U.S. Cathedral ceilings have to balance moisture and water vapor drive from both directions. From the exterior there is obviously rain, which is a main shelter concern, and for which we install various types of shingles to drain the roof area from any precipitation. Pooling water, capillary action, and absorption of moisture can impact the various materials in a roof system. When sun hits a roof after rainfall, there is water vapor “driven” into the construction due to a vapor pressure differential that exists under these conditions. For that reason we typically provide a ventilation path to quickly dry the affected materials again.
A similar pressure difference exists in colder months, where the higher humidity ratio (actual water vapor content – not to be mixed up with relative humidity!) of the warmer interior air has a higher pressure than the colder exterior side of the roof. It is specifically the interior moisture that can get into the cathedral ceiling and then condensate along the underside of a cold exterior material layer, such as a roof’s sheathing.
To avoid problems, it’s important to take steps to reduce the risk of condensation buildup. The following are an outline of some tips for reducing the risk of condensation and preventing moisture damage – any modifications to a cathedral ceiling should be discussed with a professional expert.
- Make sure that your roof is properly maintained and any damage of shingles is quickly repaired. Moisture intrusion from the exterior is hard to “dry out”, specifically if you have a well insulated roof. It is actually the reduced energy that is lost in a well insulated ceiling, which saves you on cost, but also reduces the amount of moisture that can be “dried out” over time.
- Cathedral ceilings need to be sealed well on the interior side – those recessed lights need to be special lights and are probably not the cheap deal you found online. They need to be air sealed to prevent humid interior air to “puff” directly into the colder roof cavities. Not a place to save some bucks.
- Speaking of those recessed lights – they may sure look cool in your ceiling, but they may actually be cool, or better cold, if there’s not enough insulation left behind them to protect against condensation along surfaces that are below the dew point of the interior space. Avoid deep lights that dramatically reduce the insulation level in the well.
- Same as mentioned for lights is true for any interfaces that may open due to thermal expansion and contraction of materials across times of a day and seasonal changes in the longer term. Elastic joints/sealants are critical for details.
- Air sealing the underside of sheathing or air baffles with a closed cell spray foam blocks air infiltration, but can create a vapor retarding effect that will lead to condensation that can quickly form to ice under the right outside conditions.
Preventative Measures For Reducing the Condensation Risk in Cathedral Ceilings
While the condensation risk in cathedral ceilings is higher it is not impossible to prevent condensation from occurring over the long run. It is important to take preventative measures in order to reduce the risk. Condensation can not only damage the insulation and thus increase your energy cost, it can also cause structural damage and reduce the life time of the entire roof. There are a few things homeowners can and should do:
Air sealing ventilation baffles with closed cell spray foam creates a condensation risk in cathedral ceilings.
- If the roof is back-ventilated (many cathedral ceilings/roofs are), soffit and ridge vents need to be kept free from dirt, dust, and pollen accumulation to do their job.
- If the home is in a more humid climate, super-cooling the interior space (less than 65°F) can lead to summer condensation on the backside of the interior drywall (or wood paneling), not worth the (perceived) comfort.
- Periodically check for air leaks and drafts around joints and seams – if there are any, the amount of moisture that can move into the construction can be substantial and is not easy to remove.
As a home owner, you should be aware of potential long-term consequences (cost and damages) associated with initially minor visually annoying condensation traces you discover. They are not only the perfect breeding ground for mold but can lead to rot and other severe damage to structural roof components.
All In All
Condensation in roofs is a common problem that can cause serious damage to your home. However, there are measures you can take to reduce the risk of condensation in roofs. However, once you discover moisture issues in the building enclosure it is time to contact a professional engineer or a building science expert to identify cause, criticality, and possible remediation. Hiring and independent expert, who can act in your best interest and who will not use a site visit as a lead to be hired as a contractor, should be the first step to take action.
