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Condensation Sensor (Courtesy Structure Monitoring Technology)

Condensation Sensor (Courtesy Structure Monitoring Technology)

 Editors note – The first installment of this series was in TLS Issue #66, which covers the reasons why we should monitor our buildings and the types of monitoring systems available. In this installment Jacob guides us in our choice of a monitoring system.

What System Do I Need?

There is a large range in cost, convenience, and logistics with each of these systems. The best way to select the right system for you is to first understand what you need to monitor, and then understand what parameters govern your system. Some questions and considerations for any monitoring system are(though some of these are more relevant to DIY than off-the-shelf):

– What are you monitoring and where, and how many sensors do you need? Do you want to deploy a combined temp/RH sensor, or individual temp and RH sensors, or just one or the other?

– What is the operating environment in which your sensors are located, and what is the data range your sensors need to provide? This is a big one – if you need to get readings from really cold ambient temperatures all the way up to really warm temperatures, sensors go up in cost (same with RH – it gets more expensive to find sensors that give accurate readings at higher RH). If you go with off-the-shelf systems you need to look at the spec’s and ensure the sensors will read within the environmental parameters you are seeking to evaluate. Otherwise, your data will not be fully representative of the conditions you are analyzing (your RH sensor may cap out at 30% even though the conditions are actually 70%). Accuracy is another important feature (that also affects cost). Many sensors drop off in accuracy as you get to the far ends of their range. If you are doing research-quality testing, or even looking for data of sufficient quality to present to a code official, or at a conference, accuracy becomes all the more important than just for curiosity’s sake or QC. This is a crucial consideration.

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– How are the sensors wired, and what are they wired to? What are you thinking of using to receive the data? How will you analyze it? The answers to these questions will vary depending on whether you are a DIY tinkerer, a busy contractor, or a technophobe home-owner (or some wacky combination thereof). It will also be influenced by your budget.

– How do you plan on powering the sensors? Hard-wired to a power source, or battery (wireless)? If battery, what is the system life-expectancy? Can the batteries be changed? How long do you plan on collecting data?

– Are you mounting/installing the sensors in such a way that they are protected from damage, yet still connected to the regional atmosphere? This logistic can be a very important one – as anyone who has been involved with the chaos of a community bale-raising or rigor and pace of a professionally-contracted construction project can attest.

Humidity Sensor (Courtesy Structure Monitoring Technology)

Humidity Sensor (Courtesy Structure Monitoring Technology)

– Will the specific mounting and wiring regime allow environmental changes that will alter your data? For example, housings that could trap condensation, or lead wires that could conduct thermal energy to or from the sensor region. A fundamental principle of the scientific process is that we alter our subjects through observation; building monitoring is no exception, and we need to understand how we are altering the environment of the sensor by virtue of the system’s installation to accurately interpret the results.

– How will you know which sensors are providing what data, and where they are located in the building? How do those locations relate to differing environmental conditions (i.e. solar orientation, vertical location)

– Do you plan on retrieving the sensors for replacement/maintenance/repair/calibration?

– How will you calibrate the sensors for accuracy prior to installation? If they are off-the-shelf, how did the manufacturer calibrate the sensors, and do they have recommendations for “field calibration” prior to, during, or after installation?

– Do you plan on also recording interior and exterior temp/RH to give full environmental context? Seeing a 70F reading in a wall can mean something very different during the summer time than during the winter. Building data is often taken out of context, which can lead to inaccurate conclusions, and poor decisions.

– Will the building occupants allow needed resources for long-term testing (access, power, internet connection, etc.)? This is a particularly important question for designers, builders, engineers, researchers, and other professionals not living in the buildings they seek to monitor.

If you haven’t ever considered building monitoring, this may seem like an overwhelming undertaking. Don’t despair! Just as building a house can be quite overwhelming at times, ultimately it is your own goals and intended purposes as a builder, designer, researcher, or owner that will drive how you design your program. Also like building, the devil is in the details, and a clear understanding of goals will lay out the design, which will inform those details. So like any good design, start with developing a sense of what you are looking to achieve, the logistics, budget, and time frame influencing the project, and see what solutions fit those parameters.

Hopefully most of these questions will be easy to answer, or perhaps not necessary to ask. There are many resources available for support in answering these questions and more. Vendors of off-the-shelf products are terrific sources of support, as are the generous and brilliant members of our open-source natural building community with monitoring experience.

Roll sensor with stereo jack (Courtesy Structure Monitoring Technology)

Roll sensor with stereo jack (Courtesy Structure Monitoring Technology)

You may well have a building science expert in your community, or online, who can consult on the design and implementation of your system, and/or help analyze the results. I strongly recommend finding published studies of projects that have had sensors installed (see aforementioned CHMC studies for examples), whether in straw bale walls or otherwise, and read the sections where they discuss methodology and the construction of the testing environment. They will give many good clues and precedent of how to set up a rigorous sensing system. That’s a great place to start.

It is our responsibility as a community to empower ourselves with the knowledge we need to make buildings that will stand up to the challenges of the next century. The technology is here, the science is emerging, and our curiosity and ingenuity is an inexhaustible resource we can tap to aid in our quest for knowledge and understanding. So instead of staring at your walls and wondering what’s happening inside, install some sensors, monitor the results, and of course – share your data.

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 and New Frameworks Natural Building, LLC can be found here


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