Within the last couple of decades, a few things (among many) have dramatically increased within the world of design and construction: 1) buildings are getting much tighter and more heavily insulated; 2) there have been more building moisture problems relating to these increases in envelope thermal performance; 3) our collective understanding of the principles of applied physics in buildings (“building science”) has developed, and; 4) our access to technology – including high-speed Internet, affordable cloud storage, and inexpensive hardware and software – has greatly increased. Stir all of this together, and we see both an increased need, as well as an increased opportunity, for monitoring the performance of our buildings, especially the parts of the buildings we can’t readily access – namely, the inside of our envelope assemblies (i.e. walls, ceilings, roofs).
In this article we’ll take a brief look at why monitoring building performance (defined for the sake of this article as hygro-thermal performance – heat and moisture) is important, some basic types of building monitoring, and important considerations when deciding what type of monitoring to install in your next building project.
Why Monitor Our Buildings?
The vast majority of all buildings, especially single-family residences, have never had any monitoring conducted inside their walls and roofs. So why is this important all of a sudden? We eluded to this point in the introductory paragraph: a combination of higher-risk assemblies, coupled with increased access to technology and understanding of how buildings work, have lead us to both the need and the ability to understand more clearly how our buildings operate.
Speaking to the “need” part of this, we have demanded greater thermal performance from our buildings in the last couple of decades. An awareness that began in the United States during the 1970s (during that era’s energy crisis) has come to greater fruition, and rightly so – as a populous with a rapidly-shrinking middle class finds itself choosing between food or medicine and heating fuel, and as a globe faces the implications of our buildings’ energy appetite as it relates to climate change, there is an increasing cultural awareness of the importance of energy conservation in the operation of our homes and businesses.
This leads to the development and rehabilitation of buildings that feature an increase of insulation and reduction of air leakage. However, unless the “whole system” of our buildings is considered, including HVAC (heating, ventilation, and air conditioning) and other mechanicals, moisture sources, and use patterns, this increase of thermal performance can lead to higher incidences of moisture damage, either through condensation or through reduced drying potential and/or detection of wind-driven rain or other bulk water intrusions.
More so than ever, we need greater control over how our buildings operate. But as much of the “action” happens in ways we cannot overtly detect, we need monitoring in our buildings to help understand what is happening. In its simplest form, this may be a thermometer and humidistat set up in the house that lets us know the temperature and relative humidity (RH), respectively. However, there’s a lot that can happen inside our walls and roofs that won’t be perceptible in the living room or kitchen, and that’s where in-cavity monitoring comes into play. When you elect to build out of straw and plaster, the need becomes all the greater. Here are some of the reasons why in-cavity monitoring may be a valuable tool for your next (or current) building:
- Quality control: ensure that dew points are kept out of the middle of your thick assembly, and that relative humidities are kept within acceptable levels.
- Risk mitigation: taking on a more innovative or risky challenge with your next assembly? Monitoring will help track your progress and allow you to intervene before an issue becomes a problem, or a problem becomes a crisis.
- Institutional knowledge: as straw bale builders – or builders of any thick-walled, vapor-open construction regime – we have a lot to learn about how vapor, liquid, and heat move throughout our building envelopes seasonally and over time. Building upon this knowledge empowers us to make informed decisions and improve best common practices in both design and construction.
- Marketing and education: what better way to secure the confidence of your clients, colleagues, or skeptics concerning the viability of your building systems than to show real-world, real-time data confirming their stellar performance?
- Policy and advocacy: as we continue to work within the world of codes, loan provisions, and other regulatory frameworks, having data that proves, for example, that vapor barriers are not required in cold climates to ensure well-performing wall assemblies, is a very powerful tool in helping to shape a regulatory landscape that will be more accommodating towards straw bale assemblies and other similar technologies.
Types of Monitoring Systems:
There are many different approaches to monitoring your buildings, and many different events and conditions to monitor. Just a very small sampling:
- temperature – indoor, outdoor, in-cavity
- relative humidity (RH) – indoor, outdoor, in-cavity
- indoor air quality – VOCs, radon, CO, CO2, etc.
- water quality – pH, hardness, metals, petrochemicals, etc.
- electrical usage – per appliance, per circuit, cumulative
- heating energy fuel consumption – space, central, domestic hot water
The list goes on from there. For the purposes of this article, we will restrict our focus to temperature and RH. There are many different ways to monitor your buildings, each with their advantages and disadvantages. A few basic categories include:
DIY sensors: many builders and researchers have built their own simple moisture content (MC) monitoring systems using either simple off-the-shelf sensors, or field-constructed wood-block sensors. In the former, sensors are placed in field-constructed perforated PVC housings with lead wires run through the wall to the surface where they can be read by the appropriate meter. In the latter – perhaps the simplest and least expensive approach – small blocks of soft wood are installed in the walls with stainless screws connecting lead wires to the surface, where they can be tested remotely with a wood moisture meter to assess the MC of the blocks – the idea being that the adjacent straw will be of a similar, or at least proportionally equivalent, MC. These systems are simple, inexpensive, and relatively easy to deploy. However, they require manual reading and logging – which may sound good in design but is difficult to keep up with and access for analysis after the fact, especially in clients’ buildings. They also require deployment in the midst of construction, which can be a big logistical challenge (many a lead wire has been mislabeled or completely lost between the bale installation and project completion). Examples of these can be found in the CHMC publications “Technical Series 00-103: Straw Bale House Moisture Research” (http://www.cmhc-schl.gc.ca/odpub/pdf/62573.pdf?lang=en) and “NHA 6408: Straw Bale Moisture Sensor Study” (http://www.cmhc.ca/publications/en/rh-pr/tech/96-206.pdf), or in The Last Straw article “Homemade Straw Bale Moisture Meters” (Spring 1998).
- Data loggers: a step up in convenience and accuracy are imbedded data loggers. In this system, a calibrated sensor is installed in a building cavity, and a small data logger stores data point readings for future retrieval and analysis. Compared to the DIY approach, this takes a lot of pressure off of having to walk over to each sensor with your moisture meter on a regular basis to capture the data, giving a more complete picture of what is happening. The sensors are also more accurate and are calibrated to ensure greater precision in the readings. If you are looking for more than just a red flag if the RH numbers are in the danger zone, this will be important (more on that in “Considerations” below). These systems are more expensive, however – while very basic systems can stay in the hundreds of dollars (US), you should expect to spend over a thousand for a more comprehensive system. Part of what drives the cost is the software and communications hardware required to retrieve the data from the data loggers and for analysis of that information. Data is only useful if it can be consumed in a meaningful way! This points to another downside: while some more expensive systems may be automated, most systems require you to either extract the data logger from the assembly, or to connect to the data logger through remote wiring and download the data for analysis. While the capturing of data will be consistent, its retrieval and analysis is still a manual activity, which can be hard to keep up with over time and in remote client buildings. Like the DIY sensors, these systems are generally designed to be installed during construction, unless other provisions for post-construction installation are made. One popular manufacturer of data loggers is Onset Computer Corporation, which creates the HOBO data loggers line (http://www.onsetcomp.com/products#dataloggers). Another is Omega Engineering, Inc, which offers the OMEGA product line (http://www.omega.com/products.html).
- Remote monitoring systems: perhaps the simplest-to-use of all are remote monitoring systems. Similar to data loggers, these systems feature calibrated, accurate sensors that are installed in the assembly during construction (unless other provisions are made). However, instead of manually retrieving the data with a communications interface and analyzing using proprietary software, these loggers automatically send their data to a cloud-based database for storage, and allow analysis via the web through a browser-based interface. This means that both graphical and numerical data analysis is available simply by logging onto a website. While this convenience may seem luxurious, it can sometimes make the difference between accessing the data and not, which certainly justifies its use. These systems are not cheap, however, and the convenience of having all the data stored and access remotely comes at a price – generally in the form of a monthly or annual subscription fee on top of any up-front hardware and activation costs. While there are a number of such systems for general building environments (i.e. “smart” thermostats or other building monitors that allow you to monitor the indoor temp and RH from your smartphone), in-cavity systems are relatively new to the market. One such system is the OmniSense monitoring system (http://omnisense.com). We are in the process of developing a similar system designed specifically for post-construction installation into straw bale, cellulose, and other insulated vapor-open building assemblies. Our SmartWand system incorporates a series of temp/RH sensors mounted into a housing, or “wand”, that is installed into a wall or ceiling after construction (but ideally before finishing) at the same time electrical rough-ins are being installed, greatly simplifying and reducing risk in deployment. Each “wand” then sends its sensors’ data to an interior unit, which also collects indoor temp/RH, which is then passed up to a cloud server for web-based access. An outdoor sensor is also connected to the system, to place the in-cavity data into full environmental context. More information can be found at buildingsensors.com; we expect to have these systems available on a limited basis in 2015.
What System Do I Need?
We’re going to cover the remainder of this topic in our next issue. Stay tuned…
Jacob Deva Racusin is co-owner of New Frameworks Natural Building, LLC, offering services in green remodeling, new construction, consultation, and education featuring natural building technologies. A BPI-certified contractor and Certified Passive House Consultant, Jacob is the co-author of The Natural Building Companion, and lives with is family in Montgomery, VT. Jacob can be contacted at firstname.lastname@example.org and New Frameworks Natural Building, LLC can be found here www.newframeworks.com.[/restrict]