Building Code + Mass Save Update | Youthbuild Boston and more!

Many new homes are still being designed with two furnaces, one in the basement and one in the attic. Some have an attic only furnace in order to maximize living space by reducing utility room size when homes are built on slabs. Most always high efficiency condensing units are installed in attics. They cannot operate in cold attics due to condensate freezing and other issues. Thus, builders have traditionally been “semi-insulating” attics or building insulated boxes for high-efficiency furnaces. Both of these approaches severely limit the ability to get a HERS 55 or lower.

First, boxes should almost never be used. It leaves a portion of the duct system in a cold attic that has to be modeled as such. This costs HERS points. It is far better to bring the entire system inside conditioned space by making a thermal barrier and aligned air barrier along the attic roof deck and gable walls. Herein lies the challenge!

Spray foaming the roof deck is one effective approach because it creates an all-in-one thermal and air barrier that is aligned and very effective. However, this is typically most expensive and requires at the least a layer of closed cell foam to prevent moisture intrusion. More often, “net and blow” with cellulose or fiberglass is used under the roof deck as an effective thermal barrier. This can be a good approach. However, these materials do notcreate an air barrier.

In order to have an effective air barrier in an attic, it is necessary to have a continuous and complete air barrier on both sides of the blown-in insulation. Six-mil polyethylene simply does not work as an interior air barrier. Blower door testing using poly has proven this. It must be a rigid board that can be well sealed.  In order to make an effective exterior air barrier, it is necessary to seal the edges of the roof-vents under the sheathing from the baffles at the eaves all the way to the ridge. The goal is to make the blown-in insulation cavities air-tight. These measures will contribute significantly to a better HERS score!
One last note is that it is important to have air barrier work prepped or done before the HVAC equipment is installed in areas where access will be blocked once it is in place.

We at Ace Energy Services and 3ACH50, Inc. are pleased to be working with Youthbuild Boston located at 27 Centre St, Roxbury, to build a highly energy efficient and green home at 23 Ruskindale Road in Boston. Our goal is to make the home as energy efficient and green as the budget will allow. The preliminary HERS Rating is the range of 38-41 with the current design.

Most importantly on this project, we will be passing along our knowledge of building science, energy efficiency, and green building to a new generation of emerging professionals. More on the Ruskindale Road project once construction starts in October.

The MA Residential New Construction program that pays incentives to participating builders and HERS Raters has gone into effect July 1st.

The new program is the Blended Savings Approach (BSA.) There will no longer be fixed Tier levels and fixed payment for high-efficiency equipment. Rather, the amount paid will be based on a predetermined rate per MMBTU and/or kWh overall savings above a new MA reference home.

The new MA reference home is a higher bar due to increased energy efficiency of new homes over the last several years. However, now that reference home and rebate formula has been finalized, we (HERS Raters) can begin to provide builders with estimated rebate amounts.