Clearing Up the Gray Areas

To see the article as it appeared in print, please go to Clearing Up the Gray Areas.

How Envelope Remote Conditions Monitoring (ERCM) can influence modern building practices

A sample graph of results from an Envelope Remote Conditions Monitoring system (photo: www.OmniSense.com)

Nate Gusakov

A large part of modern high-performance building design and practice is driven by hypothetical scenarios. We design our heating loads based on the assumed 15 or 20 coldest nights of a theoretical year for a given location; we insulate at least four feet below ground level for when the soil freezes that deep, having no idea what percentage of the time it actually does; we run ourselves through all sorts of mental and physical contortions (vapor barrier locations and types, interior-exterior insulation ratios, double stud walls, etc.) to avoid thermal bridging and condensation in the building assembly.

Let’s explain that last one a little more: At the highest level of building design we use advanced hygrothermal analysis modeling programs like WUFI or DELPHIN to predict how heat and moisture will flow through and around a certain building assembly or component (for more on these, check out: https://journals.sagepub.com/doi/full/10.1177/1744259120988760). The programs are very specialized, very complex, and take a lot of time and expertise to model even a relatively small detail. As a result, much of modern building practice (and even state codes) uses rules of thumb like ‘a 1200 ft2 home needs two tons of heating capacity’, or ‘you need 60% of your total roof insulation on top of the sheathing plane’, or ‘wall assemblies must achieve R-20 cavity insulation plus R-11 continuous.’ Each of these might be excellent advice or guideline in certain specific situations, but with the huge variation in individual building designs, location microclimates, occupational uses etc., there is bound to be a lot of gray area in the real world.

Especially in renovations (which are SO important – 80% of the building stock that we’ll be using in 50 years is already standing, so we had better take care of what we got!), there are often decisions made about building assemblies that fall squarely in a gray area from a building science perspective. With building code also being less clear and stringent about renovation requirements, I have seen budget or sequencing concerns steer decisions away from ‘building science best practice’ to ‘building science bare minimum’ many times. Assessing condensation potential and risk is one of the most troublesome parts of defining ‘building science bare minimum.’ For large commercial projects, advanced modeling may be used at significant expense, and everyone will hope that the models got it right. For small commercial or residential projects, we are usually back to rules of thumb and gray areas. Fortunately, there is technology available that has the capacity to push our understanding forward by leaps and bounds in the next ten years. I will borrow a phrase already used by manufacturing and industry, and call it Envelope Remote Conditions Monitoring, or ERCM.

ERCM consists of placing small self-contained sensors in various locations of the building assembly. Each sensor is a little box that screws into any component of the building, usually into wood framing or plywood sheathing. The basic sensors that I am using (made by OmniSense, www.omnisense.com) will measure temperature, relative humidity (RH), absolute humidity, dew point, and wood moisture equivalent (WME, via the installing screws). By way of the magic of Wi-Fi and small battery technology, these little buggers will send data for all of the above parameters for about 15 years to a central hub located somewhere in the building, and that hub will then send it to whoever wants to monitor the data online. ‘Alarm’ email notification thresholds can be set for each of the parameters, and all of the data is searchable for any given time period. What does all of this mean from a practical perspective? A recent installation offers a good example: A local residential renovation that I am consulting for ran into budget and design constraints. As a result, there are portions of an un-vented roof assembly receiving an over-roof with exterior insulation, but not enough to achieve a 60/40 ratio. This section of roof is squarely in the gray area for possible condensation risk. Will it cause a problem? Probably not, but it is hard to tell. The homeowner is completely aware of all the factors involved, and so to help ease everyone’s minds I installed remote sensors at the peak of said roof, above both bathrooms and in the center of the house to capture and relay data. The sensors above the bathrooms represent the likely worst-case scenario locations due to the point source of bathroom moisture. The central sensor will serve as a control as it is above the ‘dry’ living room. I have alarm thresholds set for RH and WME (I’ll be notified via email if RH registers above 70% or WME above 15% in any of the locations), and at any point I can log in and look at the graphed results over time. Not only is it fascinating to see the building envelope conditions react to weather and job site events, I will be able to alert the homeowner and builder long before any potential issues are present long enough to cause real damage.

For this one project, the information provided by the ERCM system will offer a reduction in worry; peace of mind that possible risks will not create unseen problems in the future. If the data from this one system is added to a growing pool of similar data from other ERCM installations, then we will be talking about real and significant furthering of our building science understanding. Instead of relying on hypothetical modeling to ‘see’ the behavior of a building assembly over time, we will be able to look at the real thing, clarifying the current gray areas with more and more black-and-white pixels of real-world data.

Nate Gusakov is the founder of Green Mountain Enclosure Consulting, LLC (www.GMECx.com)