I was another SCCG member who attended Scott’s demonstration yesterday. It was fun and instructive to see some of Scott’s “building science” tools in action: he used and explained a blower door, manometer, “duct blaster” system, infrared sensor and more. In addition, the homeowner who graciously allowed us to invade his home received some immediate value in return, as the following anecdote will illustrate.
Scott brought a “duct blaster” system, which finds and measures air leakage in a forced-air hvac system. The procedure is to seal all the registers and other normal outlets, then pressurize the duct system through the return-air register. The duct blaster was, however, unable to reach the normal test pressure, so we knew something was wrong.
First, we checked to make sure we hadn’t missed sealing a register somewhere. That wasn’t it – they were all well-sealed with cardboard and duct tape (as you would expect in a job performed by a group of professional contractors). Then Scott hooked up a smoke-generator (I think it belonged to the Fillmore back in the 60s). By introducing smoke into the ducts, we had a way to visually spot leaks. It was actually the homeowner who, from the underfloor area, spotted smoke pouring out of a hole in the floor plywood under a bathtub. How could the smoke get there?
It turns out that the standard drop-in type bathtub is installed right next to the return-air chase, which is just a vertical framed shaft to conduct air from the return-air register to the ducting below, ultimately connecting to the furnace. There is apparently no ducting or lining within the shaft, so the space under and around the adjacent bathtub became part of that return air system. Cut a big hole in the floor for the tub drain (love those plumbers with Sawzalls!) and voila! – most of the hvac system return air is coming not from the heated space inside the house, but from under the bathtub and under the house.
As someone who works with energy-efficiency standards and design, I knew the value of infiltration control, hvac duct sealing, proper insulation installation, etc. But there’s a lot more going on than energy efficiency. The building science concepts Scott teaches in his Cabrillo classes go way beyond energy efficiency to include all aspects of what makes buildings (especially homes) safe and comfortable for their inhabitants. Topics such as indoor air quality, ventilation, moisture control to prevent mold and mildew, appliance combustion and exhaust gas safety, and many other concerns are included in the “whole house” approach. Building science concerns look more like a LEED checklist than Title 24 documentation.
Even within the energy-efficiency arena, the building science approach is completely different. Energy standards like the state Building Energy Efficiency Standards (aka T24) are essentially prescriptive. That is, they assign an efficiency measure (R-value or its inverse, U-value) to standard building components like wall, floor and ceiling assemblies; window and door assemblies; duct and hot water pipe insulation, etc. Hvac equipment like furnaces and water heaters are judged by numbers that reflect their efficiency in converting fuel to heated air or water. Lighting and appliances are treated in a similar manner.
The big weaknesses in this prescriptive approach are twofold:
- Actual performance in the field is not considered. T24 standards acknowledge that real-world installed performance never equals bench-tested values. A large “fudge factor” is built into the standards to account for that discrepancy. That’s just an average value, however, and tells us nothing about the performance of an individual home or installed system. The building science approach is the final step – verifying the actual in-place performance of building components and systems.
- Energy efficiency is only part of the picture. What our clients want is not just lower PG&E bills, but safe, healthy, comfortable homes.
I expect that, within two or three more T24 revision cycles, field testing will become a required part of a home’s building permit inspection process. Whole-house concepts like those in the LEED standards will also be incorporated. We can get ahead of the curve by learning about these concepts and technologies now. Thanks again to Scott for sharing some building science with us.
Workshop led by Scott Milrod Construction
Review by Carey Casey of Casey Design Services