Cambridge MA

NESEA Pro Tour at Multifamily Gut Rehab in Cambridge

On Friday May 19th, ZED joined Northeast Sustainable Energy Association (NESEA) in leading a BuildingEnergy ProTour of a 3-unit triple decker in Cambridge that underwent a gut rehab after a fire in 2020. The project was developed by Homeowners Rehab Inc (HRI) and now provides three apartments for low-income residents.

Erika DeRoche of ZED kicked off the tour with a 45-minute overview of the project, which was then followed by a three-stage tour of the basement, exterior, and interior of one unit. Erika DeRoche from ZED, Deliandro Cruz of Alpha Smart Builders and Nate Wickman of New Ecology, Inc. hosted each station, talking about the finer points of this ambitious energy efficient renovation. Attendees were able to hear about design decisions around HVAC, Domestic Hot Water and Fire Protection systems, as well as the wall and flooring assemblies, all of which prioritized resident comfort and sustainability.

We are incredibly proud of this project and the work of all of our partners and collaborators that made it come together so successfully. Our hope is that this type of retrofit - all-electric, no combustion on site, high efficiency systems and super-insulated envelope - will serve as an example of not only what is possible for this building typology, but also what should become the norm for future projects.

Learn more about this project: Columbia Street Residences

More images from the tour here.

Inside an Air Barrier Inspection

Location: Inman Square, Cambridge, Massachusetts

Services: PHIUS+ Energy Consulting and Mechanical Design for a New Modern Single Family Home

ZED recently visited a site in Cambridge to check out the progress of the home’s air barrier. ZED’s Jordan Goldman, who provided energy consulting and mechanical design for the three-story, single family house, led the site visit along with representatives from ZRE Development (Owner) and GRS Construction (Framer). Site visits like this during construction are important both for catching any errors before the building enclosure is complete and for educating builders about proper technique going forward in the process.

Jordan walked the interior and exterior of the home, paying particular attention to the many tricky areas where air leakage typically occurs. A home’s air barrier is intended to limit uncontrolled air leakage into and out of a building’s thermal envelope. ZED’s design is for the air barrier to be continuous, which means that the system has no discontinuities, particularly as it transitions from one assembly to another (e.g. from wall to roof). ZED typically installs the air barrier at the sheathing layer, where it’s easy to maintain continuity across the envelope. Exterior rigid insulation will protect the air barrier from the outside and the framed wall cavity protects the air barrier from meddling hands on the inside.

Example of an air barrier:

Thermal Envelope:
The basement slab, foundation walls, above-grade walls, ceilings, roofs and any other building element assemblies that enclose conditioned space or provide a boundary between conditioned space and outdoors or uninsulated spaces.

Click to Expand this typical wall section, components of which exist at this project.

The largest component of this Cambridge home’s air barrier is the green ZIP System sheathing that wraps the whole exterior of the house, but there are other components that we will explore below:

Exterior: Green ZIP sheathing with integral air barrier. All seams of the ZIP must be taped, as well as any nails that have been overdriven (such that the nail head pulls through the green face of the ZIP) - with tape or liquid flashing.

Exterior: The roof edge detail has 4” of continuous insulation wrapping over the roof edge with the fascia board fastened to the structure underneath. A self-adhered membrane will be installed over the roof sheathing, turning down over the wall to tie into the ZIP sheathing.

Exterior: All exterior wall penetrations have to be water tight and air sealed. Water-tightness occurs at the outer surface of the foil-faced polyiso; air-tightness occurs at the ZIP sheathing. ZED recommends installing conduit / wires / pipes / ducts that will penetrate the building envelope now so that they can be easily air-sealed to the ZIP sheathing.

Interior: The slab vapor barrier turns up at the perimeter and is taped to the foundation wall. The foundation received a primer for proper tape adhesion.

Bonus: Jordan surfing the window well!

Exterior: Semi-rigid mineral wool insulation at foundation wall. Foil-faced polyiso foam board insulation should meet the kickout flashing from above and meet the mineral wool from below. Cut edges of polyiso should all be wrapped in tape.

Exterior: Windows are aluminum clad triple glazed windows, fully air-sealed at the exterior window face. ZED recommends a different sill prep for doors than windows, since water infiltration is more of a liability at the door sill. Lift/slide doors (see left) will lead to a freestanding deck.

Interior: Rim joists need insulation. Mineral wool batt is recommended for ease of installation.

Bonus: PV panels spotted on the neighbor’s roof!

Backstage at a Blower Door Test

Building diagnostics and commissioning is standard procedure at ZED, which includes blower door testing at key stages in the construction process. Blower door testing is a crucial aspect of putting together the building envelope correctly, helping ensure an airtight home. An airtight air barrier not only prevents cold or warm air from getting in, but also moisture, dust, pollen and other contaminants to entering the home.

What does a typical air barrier look like?

We perform blower door tests at multiple points during construction to ensure success. At our Columbia Street Residences project in Cambridge we had to do this initial test without a completed air barrier in the basement but were in range of our target. New Ecology performed the test and found approximate air leakage to be 2.6 ACH50.

How a Blower Test Works
The blower door test is used to quantify the amount of air leakage through a building’s enclosure. A blower door fan is temporarily sealed into an exterior door or window, while all other exterior openings are closed, as well as all mechanical exhaust devices shut off. When the blower door fan is turned on, it creates either a positive or negative pressure differential between inside and outside. This in turn forces air through any penetrations in the building enclosure it can find, which is what the blower door test measures. This air leakage results measurement called ‘air changes per hour,’ or ACH50.

Air Leakage (ACH50)
Air changes per hour (ACH) is calculated using a blower door at a standard pressure difference of 50 pascals (a unit of pressure) between inside the home and outside. A building's ACH50 therefore tells us that at the pressure of 50 pascals, air leaks from the building at a rate of X times the volume of the building per hour. For example, a leaky building might be 15 ACH50, while a high performance building is typically 1 ACH50 or less. The Passive House standard requires 0.6 ACH50 or less.

Architecture: ZeroEnergy Design
Mechanical Design: Ripcord Engineering
General Contractor: Alpha Smart Builders

Renovated Paul Rudolph House in Dwell, Energy by ZED

A Paul Rudolph House in Cambridge, Massachusetts, is featured in Dwell magazine after Ruhl Studio Architects renovated the much-loved mid-century home to accommodate the needs of the new homeowners and greatly improve the energy efficiency. As a consultant to Ruhl Studio Architects, ZeroEnergy Design provided energy consulting and mechanical design for the project. The envelope updates and new HVAC system help ensure increased thermal comfort, healthy indoor air, and a smaller operational carbon footprint for the home.

MORE: DWELL