Membranes…Interior Air-Control Strategies That Can Work

This article first appeared on the Green Building Advisor Website.

I’m from Minnesota, one of the few areas in the lower 48 that still regularly uses polyethylene sheeting as a vapor retarder, we’ve become very good at detailing these interior membranes for use as an air barrier.  (The practice is also very common in Canada and Alaska.)  The average blower door test I conduct for new homes in my market has now moved below 2 ACH50, most achieving these scores only using an interior air control strategy.  I don’t recommend using poly in most cases, instead I suggest moving to a class II vapor retarder, (smart, variable, and responsive vapor retarders), these products can also be used for air control.  Installing the two products is similar, so, what are the tricks to an effective interior air barrier installation?

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Northern Built Pro’s Top 5 Blog Posts for 2023

Happy New Year!  2023 was a good year for the Northern Built Pro website with 45 new blog posts, many first appearing on the Green Building Advisor website, and some that ended up in a couple trade magazines, Fine HomeBuilding and Journal of Light Construction.  I wrote a few that were directly for manufacturers of building materials, including Rockwool, Andersen Windows and Doors and Sashco.  I am looking forward to partnering with a few additional manufacturers in 2024.  A teaser to one that I am currently writing an article about, TimberHP.

These are the top 5 blog posts that were written and published in 2023.

5.  The Diminishing Return of Insulation

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An Airtight Home, What Do the Blower Door Numbers Mean?

I recently had the opportunity to attend a BS and Beer meeting in Kansas City, MO where the meeting took place in a home under construction.  The home was being built by Aarow Building (Jake Bruton) of Columbia, MO (they recently opened an office in Kansas City).  The home is a single level, slab on grade with around 3,250 square feet.  At the time of the meeting, the home was just finishing the mechanical, electrical, and plumbing systems and about to move to the insulation phase.  A perfect time for a mid-build blower door test.

The purpose of a mid-build blower door test is to confirm that the home is on track to meet the air tightness metric (Jake informed me that all his new homes are contractual bound to achieve 1 ACH50 or less) and to find any missed opportunities in the air sealing of the home.  The mid-build testing can be simple, get the home to negative or positive 50 Pascals of pressure and record the CFM rate, this type of testing is called “single point”.  If you feel the CFM rate (or the calculated air changes per hour at 50 Pascals number) is too high, set the fan on “cruise control” and go find the air leak locations.  There’s no need to perform multi-point testing this early in the build, (a type of blower door testing where CFM rates are measured at progressively lower pressure points, usually starting at 60 Pascals), save that type of testing for the final blower door test. Continue reading “An Airtight Home, What Do the Blower Door Numbers Mean?”

Why You Need Blower Door Testing

This article first appeared in issue 304 of Fine Homebuilding Magazine.

I bought my first blower door in 2009, back when new construction was in a downturn and energy auditing and weatherization projects were on the rise.  I took a 40-hour energy auditing training course at a local college which included hands-on training on how to use a blower door.  It took many tests before I became comfortable in its operation and understood the information it was providing.  Though one of the more expensive tools I own, I’ve been able to keep it busy and add this specialized testing to my business’s income stream.

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Construction Design-Wind Washing

Wind: The natural movement of air relative to the planet’s surface.

Washing:  A method of cleaning.

Wind Washing:  Cleaning using air?

Well, not quite.  Wind washing with regards to insulation is the ability of air movement to degrade the effectiveness of an insulation.  We will get to that in a little bit.  First a quick lesson on how fibrous insulations works.

A close-up of Rockwool ComfortBatt showing the fibers and small air pockets.

We use insulation to slow the movement of heat through our building assemblies.  Heat will move in three ways, conduction (heat moving when objects are in contact with one another), convection (heat transferred by moving air), and radiation (heat moving through spaces).  Fibrous insulations forces heat to move through fibers and small pockets of air, which slows heat movement in both radiation and conduction and prevents heat transmission by way of convection. Continue reading “Construction Design-Wind Washing”

Construction Materials-Airtight Electrical Boxes

Working as a residential electrician back in the late 1990’s, I remember learning of a new electrical box that we were asked to use on all exterior walls and in the ceilings of unconditioned attic spaces.  At the time, they were called “vapor tight” boxes.  These boxes were designed to reduce air movement through wall or ceiling cavities by sealing the electrical box to the wall or ceiling air barrier and also to seal the electrical wires where they enter the box.  Air will contain at least some water vapor, by air sealing the electrical box, we were also reducing the amount of water vapor that could potentially enter a wall or ceiling.   The name “vapor tight” was at least partially correct.

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Construction Design-Service Cavity

This post was first published at

There are many methods used to make a home airtight, it all comes down to one simple rule, continuity.  Continuity is easily attained when there’s nothing that penetrates the air barrier.  No electrical boxes, plumbing drains and vents or ducts that need to extend from inside a building’s envelope to the outside.  Of course, there are times when different things need to extend from inside to outside, like the need for an outside water faucet.  But there are also many occasions when different systems end up outside that don’t need to be outside.  For example, forced air heating and cooling ducts that leave the conditioned space of the home simply because there was no space to keep them hidden inside the home.  Planning a service cavity can help keep most mechanicals inside the building envelope. Continue reading “Construction Design-Service Cavity”

Construction Design-Randy’s Dream Design

Guess what?  I just won the lottery!  (Not really, but for the purpose of this blog, let’s pretend.)  I’m looking to build myself a new home.  I have choices.  I could build a McMansion with plenty of space I don’t need and will never use.  I could concentrate only on the interior finishes and how the house looks.  If you’ve ever read my blog, you already know what direction I’ll take.  The house won’t be big, a couple thousand square feet is plenty for me, maybe a rambler with a second story over part of it built on a slab, no basement or crawlspace.  Being a BS* guy, I would make an invest in the stuff that is hidden, those pesky control layers I often talk about.  It would be based on the Pretty Good House concept. Continue reading “Construction Design-Randy’s Dream Design”