Building Science

The House of Horrors

I set aside an hour to write a blog post before I headed off to Michigan for Thanksgiving.  45 minutes of that hour was taken up speaking to an acquaintance with a residential construction nightmare story.  I’ll share his quick story in the 15 (now 14) minutes I have before my wife picks me up for our family trip.

This individual had plans drafted up for an energy efficient home with promised good indoor air quality.  The builder, it appears, didn’t reference those plans too carefully.  A ground source heat pump (a.k.a. geothermal) was installed to heat and cool the home located in the Chicagoland area.  This can only work if the walls are extremely well insulated.  Although the plans called for rigid foam insulation on the exterior of the sheathing along with superior cavity insulation, all he got was some blown-in cellulose in 2×4 (not 2×6) walls.

That missing rigid foam insulation is causing two problems.  The first is related to heat transfer.  The foam insulation is there to help prevent thermal bridging.  When you have insulation only between studs, heat will often be transferred through the wood studs.  Remember: drywall is in direct contact with the wood framing.  The wood framing is in direct contact with the sheathing.  The sheathing is in direct contact with the cold weather.  Thermal bridging is when all that great insulation gets bypassed, leaving cold spots on the wall in the winter time.  Thermal bridging also occurs in the summer time, but in the opposite direction.

The second problem caused by the lack of rigid foam insulation on the exterior of the sheathing is that the ground source heat pump was sized based on the additional R value it provides.  Without it, the home is colder in the winter, and warmer in the summer.  Now he is looking for ways to supplement the heating and cooling because the geothermal system isn’t cutting it.

Time doesn’t permit me to go into all of the other problems we discussed.  Here are some of my favorites:

  • Bathroom exhaust fan dumping humid air into attic, not the outdoors
  • Exhaust fans allowing cold attic air to dump down into the bathroom
  • Improper weeps at the base of the brick facade
  • Only a feeble attempt at zoning the HVAC system that greatly missed the mark
  • Batt insulation with the kraft paper facing the wrong direction (visible mold growth discovered)
  • No humidifier installed, which is needed in the winter because of the air leakage
  • R-13 walls where R-30 was in the design

Well my time is up.  Have a great Thanksgiving!  I know I have so much to be thankful for!

By Ian Cull

I'm I.A.N. the Indoor Air Nerd. I'm a speaker and consultant on indoor air quality issues. To learn more about me, click "about" at the top of this page.

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