Does Your Air Barrier Work in Both Directions?

first_imgFurther investigation ideasThe really neat thing about the project is that we used the same house to test two different systems. In the end, though, this was only one house, and it wasn’t finished. It would be nice to see this work extended to more houses with more configurations.One obvious test that would be nice to see is the difference in air leakage for housewrap and taped sheathing after the cladding and drywall are installed and the house is finished. There’s a huge difference between positive and negative pressure air leakage before cladding and drywall, but how big would it be at the end?Another set of experiments to pursue would be looking at the effect of different cladding types. Then look at the effect of the different methods for putting air gaps between cladding and sheathing: furring strips, wrinkled housewraps… RELATED ARTICLES Airtight Wall and Roof SheathingBlower Door BasicsQuestions and Answers About Air BarriersAll About Water-Resistive Barriers Do you want a good air barrier on your house? Of course you do. No one who knows anything at all about building science believes that old myth that a house needs to breathe. We want airtight houses, but then we want mechanical ventilation to bring in fresh air from outside (well, at least as fresh as you can get from your outside).The air barrier’s job is to minimize the amount of air that crosses the building enclosure between conditioned and unconditioned spaces. Does all of the air moving across the building enclosure always go the same way? No. It goes both ways. The amount of outside air that leaks in is matched by the amount of inside air that leaks out. (Sometimes the air leaking in or out is intentional, and we call that ventilation.)Once you understand that air can move both ways, it’s clear that you’d want an air barrier that works in both directions. Right? But when we test homes for air leakage, we pretty much always test them in only one direction: from outside to in. We put the house under negative pressure with a blower door and then measure the air flow through the fan, which tells us how much air is leaking in through the building enclosure. The air leakage test resultsWhen the house was ready to be tested with housewrap, we ran single-point blower door tests in two configurations – positive pressure and negative pressure, both at 50 Pa relative to outdoors.After the first test, the builder removed the housewrap and taped the Zip Wall seams. They had the house ready for the taped-sheathing test 10 days after our first test, so we came in and retested the house, as before.The results for both tests are below. The ACH50 results are based on the house volume of 52,113 cubic feet. A research project comparing housewrap to taped sheathingA couple of years ago, I did a little research project† for Huber Engineered Woods. (Disclosure: They were Energy Vanguard’s client and paid for this work.) They wanted to find out how air leakage through their Zip System wall sheathing compared to housewrap. Our objective was to test the same home for both infiltration and exfiltration with two different air barrier conditions:House sheathed with OSB; housewrap installed according to manufacturer’s instructions to serve as air barrier.House sheathed with Zip System wall sheathing and roof decking. All seams and openings taped as specified in manufacturer’s instructions.The builder framed the house as normal. They used Zip Wall sheathing and Zip Roof decking but left the walls untaped for the first test. They installed housewrap over the walls and sealed according to the manufacturer’s instructions. They set all windows and doors and sealed the house to the point where we could do the blower door testing. They also taped the Zip Roof decking and sealed all penetrations since the ceiling drywall was not in place. Allison Bailes of Decatur, Georgia, is a speaker, writer, energy consultant, RESNET-certified trainer, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard. Putting the results in perspectiveEven with the housewrap, this house was very tight, having infiltration and exfiltration rates of 1.36 and 2.40 ACH50, respectively. As we observed, the builder had taken great care to seal the housewrap completely, and that effort showed in the results.In a typical installation, the bottom edge of the housewrap is left unsealed. Seams are often taped poorly or left untaped. Numerous rips and tears keep the housewrap from lying flat. Sometimes siding installers cut the housewrap in the corners because the housewrap doesn’t lie flat there. If this house had the typical amount of extra leakage sites that these problems introduce, the initial test would have shown significantly higher leakage.Also, since this was a large house, much of the wall sheathing did not break over studs or plates (see photo below). Many of the seams that fell over open areas in the framing showed large gaps, as shown in the photos below. These gaps can allow a lot of air through, and that’s probably why the exfiltration result was so much higher than the infiltration result in the housewrap test.With the house under positive pressure, air from inside moved out through those gaps, blowing the housewrap out like a balloon. Once outside the sheathing, the air finds holes in the housewrap and escapes. Of course, with cladding installed, the housewrap wouldn’t be able to expand as much. With the house under negative pressure, the housewrap was pulled into the gaps, sealing the sheathing almost as well as the tape did in the second test.Still, even with such a low starting point for the air leakage rates, the taped Zip Wall sheathing performed significantly better – 20% for infiltration and 56% for exfiltration – than the housewrap used as the air barrier. Because the housewrap installation was better than normally observed in the field, these improvement numbers can be taken as a lower limit of how much better Zip Wall sheathing will perform compared to houses that rely on housewrap, at least when comparing houses of similar wall complexity. In smaller houses where all or most of the sheathing breaks over studs and plates, the effect may be less pronounced. TakeawaysAs I wrote in 2010 (before Huber ever contacted us), housewrap is not an ideal air barrier. If the builder takes great care, housewrap can perform well as an air barrier, but the typical installation leaves a lot of holes. What this research shows, at least for a house without cladding, is that housewrap works better for buildings under negative pressure than for those under positive pressure.The key takeaway from this initial work is that if you’re looking for really high levels of airtightness, you should seal the sheathing when you use housewrap. Taped sheathing‡ products, like the Zip System or taped foam board, will probably have lower air leakage than homes with housewrap and unsealed sheathing. I’ve written in the past about how housewrap is far from ideal as an air barrier. It can be a great drainage plane, however, and that should really be its primary purpose when you use it on the outside of a house. (As some unfortunate homeowners in Kentucky found out recently, trying to build a house without any kind of drainage plane leads to trouble.) Footnotes† I say it was a “little” research project because it wasn’t a scientifically rigorous study whose results establish a general truth. It’s one quick look at a particular phenomenon and it deserves more study. I worked on the project with Al Landers, PhD (now retired), Allen Sealock, and Danko Davidovic, PhD. Danko is a real building scientist with a degree from one of the best places to study building science: Penn State.‡ Tape is quite the controversial topic in building science circles, and some people don’t trust it. Joe Lstiburek, PhD, PE, is not one of those people. “Residentially we now use tapes on wood sheathings and foam sheathings  to provide water management and air management. So how well do these systems actually work? Now? Real well. In the early days? Not so good.” Read his article, Stuck on You. The first test showed an enormous difference between the negative pressure (infiltration) and positive pressure (exfiltration). The exfiltration rate was 77% higher than the infiltration rate. (The results are shown in the “% change 1” column above.)The second test showed marked improvement in both the infiltration rate (20% lower) and exfiltration rate (56% lower). (The reuslts are shown in the “% change 2” column above.)last_img read more

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The Eyes have it: Bosch adds new camera to smart home lineup

first_imgInternet of Things Makes it Easier to Steal You… Why IoT Apps are Eating Device Interfaces Tags:#Bosch#camera#IFA 2016#ifttt#Internet of Things#IoT#Nest#smart home#smoke detector Follow the Puck David Currycenter_img Small Business Cybersecurity Threats and How to… Bosch reaffirmed its commitment to the smart home at IFA 2016 in Berlin, where it announced three new devices and integration with IFTTT, one of the largest Internet of Things (IoT) platforms.It comes two years after Bosch launched the Home Connect app, an attempt to make the German manufacturer a hub for other smart devices. That has had limited success, and Bosch appears to be moving away from a lead role, instead integrating with popular platforms.See Also: Will keeping an eye on the driver save autonomous cars?The IFTTT integration works for almost all of Bosch’s smart home devices launched before 2016, meaning you can finally connect your dishwasher to the Amazon Echo or Philips Hue lights.The three new products at the IFA conference include a 360 indoor camera, a smoke detector and air quality monitor, and a camera for the front door that also acts as a porch light.Bosch’s indoor camera has a clear advantage over Nest Cam or Netatmo Connect, it can see the entire room. Users will be able to place the camera anywhere, and still get a clear shot of the entire room. Instead of turning the device off by the wall, users can press a button and the camera retreats into the cylinder, providing privacy when you need it.The smoke detector, Bosch Twinguard, uses air quality monitoring to recognize false alarms. The built in tracking could be useful in countries where air quality is not great, like China and India, alerting homeowners to volatile organic compounds.Bosch gunning for Nest?Bosch Eyes, the front door camera, is another two-in-one. It detects when someone is outside the door, but also works as a porch light for late night callers. Users can connect the camera to any IFTTT supported device, like Philips Hue, to receive an alert when someone is at the front door.The first two devices from Bosch are clear attempts to take away some Nest marketshare. Both devices improve on Nest’s own devices, the smart thermostat and smoke detector. Considering Nest’s turbulent last year, it could be a smart move to try and grab new customers, who don’t want to pay +$200 for a two year old device. Related Posts last_img read more

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