Deep Energy Retrofits with Brian Butler and the Residential Green Building Committee

By Rose Brakesman

What better time to talk about Mass Save Deep Energy Retrofit than on a cold February evening with the Residential Green Building Committee. Brian Butler walked us through how Boston Green Building does a Deep Energy Retrofit (DER).

Some DER “rules of thumb”:

1.5 air changes per hour (ACH)

R5 windows

R10 basement slab

R20 foundation walls

R40 walls above foundation

R60 in the roof/attic

DER is documented and looks for a reduction in energy use between 50-90%, so the process starts with determining a baseline on energy use and a blower door test to document the number of air changes per hour (ACH) in an existing older house. Many of these houses are what Brian calls “gushers”, which are houses that leak air and energy at an alarming rate. One house that Boston Green Building is tackling for DER just went through a blower test and had 9 ACH. (DER is 1.5 ACH). 9 ACH is equivalent to leaving a two foot by two foot hole in the exterior wall year round!

Jokes abounded… “Did you leave the bathroom window open during the test?” Nope, double checked. Many older houses are just that leaky from gaps around the windows and doors, leaks where the basement meets the frame, and so on. This is the kind of house that can most benefit from a Deep Energy Retrofit and there are many like this.

Additionally, most of the current housing stock in Boston will still be here in 2050, so building better new homes won’t help nearly enough. Happily enough for Brian and his cohorts, it doesn’t look like they’ll run out of work anytime soon! Even nicer is the DER “guidebook”- the Mass Save Deep Energy Retrofit Builder Guide; this is more helpful than a long process of repeated submittal, revision, and re-submittal so that the guidebook streamlines the process. Hopefully more builders will jump on board and provide some DER competition!

After addressing the building envelope, there are typically additional complications and hazards that go along with “tightening things up.” One such issue is indoor air quality. In the original leaky building there’s a “stack effect” where supposedly “fresh” air starts in the basement (along with mold and mildew), then it moves upward through the house via temperature stratification. Once the building envelope is at 1.5 ACH or less, then there is no stack effect. Facilitated ventilation is required and that is a very good thing. Now stale air can be taken from one area of the house that will be moved through heat recovery ventilation (HRV). A high efficiency HRV unit is the best way to go and can have an efficiency of 90%, which means stale air at 72o is exhausted and fresh air is drawn in at around 65o.

In the end, Brian and Boston Green Building are “dragging poorly performing homes kicking and screaming into the 21st century and hopefully addressing all the issues to keep from killing the occupants.” Originally, only one utility company participated in Mass Save DER, but now there are six participating utilities. Conspicuously absent from the list is NStar….but there is some carbonated bottle shaking going on to hopefully bring them back on board.