Major Thermal Bypasses
Don’t worry about the cracks around your windows until you’ve sealed all of the big holes in your house
First, a bit about my writing: I write in longhand, whenever I have some spare time. Between audits, at lunch, after the gym, when stopping for a coffee. Then I type the notes up. The thing is that I find a lot more spare time in my walking-around day than at the home or office. To say there is a bottleneck getting these notes into electronic form is a disservice to good-flowing bottles everywhere. This is by way of explaining an upcoming sentence.
Secondly, “major thermal bypasses” is building-geek speak for holes in your house — holes through which you are losing an abnormal amount of heat. More formally, they are areas in standard construction where flaws in the building enclosure allow air to escape, bypassing the thermal control layer.
Thermal bypasses: the what and where
The building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. includes those elements of the building (the floor, walls, and roofs) which separate the comfortable interior from the potentially uncomfortable exterior. Especially today, when it is 98°F out … in Maine. (<--- That was the sentence).
BLOGS BY ERIC NORTH
A huge part of an energy auditEnergy audit that also includes inspections and tests to assess moisture flow, combustion safety, thermal comfort, indoor air quality, and durability. is inspecting the building envelope for problems. And thankfully, as builders have standardized their building practices, they've been considerate enough to standardize how and where they make giant holes in the building envelope. Thanks, guys!
Thermal bypasses and the home buyer’s dilemma
As I mentioned, thermal bypasses are inadvertent holes in the building envelope. If one were to conceive of a perfectly insulated and airtight house (with an appropriate level of fresh ventilation air … no suffocating), it would be very simple. Make it like a box.
Wait, you want to get inside?! OK, we’ll add a door. And you want to see the ocean view you paid an extra $100K for? Well, they have a really lousy R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. compared to walls, but I suppose we can add a few windows. And a cathedral ceiling and recessed lights and a hot tub and a finished room over the garage and a zero-clearance fireplace and a giant hole in the wall for fresh air. (Wait a minute...)
You see where this is heading. Home buyers have wants and needs, and they are most often at cross purposes with the aim of having an easily defined building envelope. And the harder the building envelope is to define, the harder it is to keep the uncomfortable outside away from the comfy interior.
List of thermal bypass locations
When developing their housing certifications, Energy Star put together their list of common thermal bypasses. Thankfully, the good folks at the Department of Energy have collected this info in one place: the Energy Star thermal bypass list:
- Kneewalls like those found in Cape Cod style houses
- The ceilings over porches
- Attic hatches
- Zero-clearance fireplaces (I love these, because the leaks are entirely enclosed and not evident to the naked eye)
- Garage ceiling joists attached directly to the building framing
- Attic stairs built into exterior walls
- Bathtubs and showers built into exterior walls
- Cantilevered floors like those found in Garrison houses.
And the hits just keep on coming. Check out Energy Star’s list of thermal bypasses and take a look around your house. Fixing one of these issues can be a real heat saver and money saver.
- Erik North
Jan 30, 2013 6:13 PM ET