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Building Science-Window Condensation

As I write this blog, a good portion of the nation is experiencing very cold temperatures with high winds.  I’m currently sitting at -9°F with a windchill or feels like temp of -38°F.  Chatting with a good friend in Kansas City recently, he was impressed by the below zero temperature readings.  (He was actually begging me to stop sharing and keep the nasty weather in Minnesota.)  Because of the weather, I’ve been receiving emails and DMs on Instagram about how people’s houses are reacting to this weather extreme.  Window condensation has been one of the more frequently asked questions, so I figured I’d cover that topic in a blog post.

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Building Science-Natural Air Leakage

This blog first appeared on the Green Building Advisor website.

When conducting a blower door test, one of the ways we express the findings is with air changes per hour at 50 Pascals (ACH50).  As an example, a new home is blower door tested and found to be 2.75 ACH50, this means the entire volume of air inside the home is exchanging with the outside air 2.75 time per hour at the test pressure of 50 Pascals.  When discussing blower door testing with builders and homeowners, it can be hard for them to relate to the ACH50 number other than they know the home needs to be less than a certain level of air tightness to meet current code requirements.  Expressing the tightness as natural air leakage can sometimes be helpful.  How can we calculate the natural air change rate?  Well, there’s a formula:

ACH50/n-Factor = ACHnat Continue reading “Building Science-Natural Air Leakage”

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Building Science-Tight Homes and Negative Pressures, When Should We Be Worried?

This post originally appeared on the Green Building Advisor Website.

A couple years ago I was asked to perform a blower door test on a new home.  The home was small with a footprint of only 1130 square feet.  When the test was completed, the test report indicated an air leakage rate of 91 CFM at the test pressure of 50 Pascals, .33 ACH50.  Completely unexpected for this code-built house.  (I actually measured the volume of the home again and ran the test two more times before I was convinced I had an accurate test.)  The contractor contacted me some time later and indicated the homeowners were noticing air coming through the exterior light switches when the dryer was operating.  The dryer was producing close to the same negative pressure as my blower door every time it was being used, a negative pressure of about 50 Pascals.  Is this a problem?

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Building Science-Pyrolysis

This post originally appeared on the Green Building Advisor website.  www.greenbuildingadvisor.com

Pyrolysis [pahy-rol-uh-sis] noun

The chemical decomposition of wood by the application of heat alone in the absence of oxygen.

I used to perform risk assessment inspections for a couple small, local mutual insurance companies.  These companies would insure properties that were considered “high risk”, most were rural, some were accessible only by boat, ATV or snowmobile and they were often a long way from the nearest fire department.  Many had solid fuel burning appliances, usually a woodstove or fireplace.  Part of my job was to make sure that the woodstove or fireplace had the proper clearances to combustibles, proper floor protection, and that the stovepipe and chimney systems met the requirements of the manufacturer and/or code.  Most installations were safe, but every once in a while, I would find a home in danger of burning down. Continue reading “Building Science-Pyrolysis”

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Building Science-Ice Dams

This year seems to be a good (or bad depending on how you look at it) year for ice dam problems in my area, the intensity of ice dams seems to change year to year.  I was recently on an ice dam diagnostic with an insulating contractor and a general contractor, the home was built in the early 1990’s and there is evidence there have been issues from the beginning.  We spent a couple hours testing this home, I’ll get into what we found in a bit.

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Building Science-Existing Construction Improvements

This three-part series first appeared on the Green Building Advisor website and has been condensed into one post.

An unconditioned and uninsulated crawlspace, an unsealed and uninsulated forced air heating system, and an uncovered dirt floor, which by the way has a sewage leak.  If this were your home and you wanted to make improvements, where would you start? Continue reading “Building Science-Existing Construction Improvements”

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Building Science-Wintertime Interior Humidity

As I write this post at the end of November, our outdoor temperature is 28°F with an outdoor humidity of 75%.  Inside my home, the temperature is 70°F with a humidity level of 21%.  Slightly uncomfortable humidity levels for my family.  During last year’s polar vortex, when the temperatures reached nearly -40°F, my indoor humidity dropped to 9%, much too dry.  Knowing what I know about building science, I will not operate a humidifier.  This post will explain why. Continue reading “Building Science-Wintertime Interior Humidity”

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Building Science-Three Way Buildings Leak Air

I have talked many times about blower door testing, air sealing and air leaks in this blog, on the Green Building Advisor’s website, and more recently, in the pages of Fine Homebuilding Magazine.  Most of what I’ve written deals with testing a home or techniques used in air sealing a home.  This time I’m going to discuss the mechanisms that cause air to leak, there are only three of them, but first a little science. Continue reading “Building Science-Three Way Buildings Leak Air”

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Building Science-A Benefit of Exterior Insulation

I’m a big fan of exterior insulation.  It’s rarely used in my area, mostly because the State of Minnesota has eliminated that code requirement.  It has to to with our wide use of polyethylene sheeting as a vapor retarder on the warm in winter side of a wall assembly and then adding a low permeance plastic insulation product as exterior insulation.  These plastic foams would be the choice for most contractors, lower cost and easy to source.  Very slow vapor movement in either direction when a wall assembly becomes wet.  This posting isn’t going to get into the foam insulations, but more into what exterior insulation can do for a home. Continue reading “Building Science-A Benefit of Exterior Insulation”

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Building Science-An Interview with Gary Nelson

I think most of us know of this man, one of the founders of The Energy Conservatory and designers of the Minneapolis Blower Door.  I recently had the opportunity to chat with Gary.  My intent with the interview is a little different from other interviews that have featured Mr. Nelson.   I wanted to ask questions from a practitioner working in the field point of view. Continue reading “Building Science-An Interview with Gary Nelson”