New Case Study: Belmont Modern Home

A Modern Mid-Century Home in Belmont

This modern high performance home in Belmont was built in two phases, beginning with an addition to an existing 1960s-era house. The home’s two bifurcated wings informed the decision to phase the project so that the owners could live in part of the home with their three children during construction. The design kept a similar footprint and created two distinct wings with a connector in between. This central corridor is the home’s formal entry point and provides a dramatic perspective overlooking the abutting Mass Audubon sanctuary beyond.

Inside or out, this home blends and flows into its surroundings, outfitted with large glass doors, generous windows and oversized sliders at several key connection points. The triple glazed Schucco windows and doors allow wonderful views regardless of the season. ZeroEnergy Design (ZED) carefully framed views of the outdoors from each space of the home, taking advantage of the scenic conservation areas and gardens surrounding it.

In keeping with the Passive House principles, the home is incredibly energy efficient with a Predicted Energy Use Intensity (pEUI) of 3.5kBtu/sf/yr. The super insulated envelope has a concrete slab has 4” of EPS below with an R-value of 17. The above grade walls are R-44 and the roof is R-66. The home’s air tightness exceeds .05cfm/ft2, which measures the air leakage in relation to the surface area of the building envelope. For context a typical new construction is about 3 ACH50 or less. This home tested about six times tighter than that - at 0.37 ACH50.

To optimize thermal comfort, state-of-the-art Zehnder ERVs supply all the living spaces with filtered fresh air year round. This feature enables recovery of 90% of the energy from the conditioned air as the stale interior air is exhausted out. The ERV, combined with the exterior insulation on the walls and roof, significantly reduces the energy needed to heat and cool the home.

All of the home’s appliances are electric. Mitsubishi heat pumps supply the heating and cooling; electric induction cooktop and laundry facilities take care of the cooking and cleaning and electric heat pump water heaters take care of the rest. 42 Roof-top mounted solar panels keep the electricity running and supply a powerwall for emergency back-up.

ZEN Associates worked with the architects and clients to seamlessly integrate the indoor and outdoor spaces with expansive views and oversized sliding doors. We worked to protect existing mature plantings around the home and the new plantings enhance the modern aesthetic of the home.  The use of native plants and thoughtful design brings the outdoors-in creating an organic feel to the new spaces. An interesting story from the build is that during excavation, an underground stream was discovered at the foundation level. We were able to divert it around the house and guide the natural water flow out over boulders from the excavated areas to the wetland in the backyard.

PROJECT TEAM

ZeroEnergy Design
Architecture & Mechanical Design

Auburndale Builders
Contractor

ZEN Associates
Landscape Architecture and Construction

MORE: Case Study

Montage
Furnishings

Nat Rea Photography
Photographer

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

Green Building Advisor Features ZED's Stephanie Horowitz on Zero Energy Homes

Green Building Advisor posed a simple question to ZED’s Stephanie Horowitz: “Is Zero Energy the Answer?” Horowitz joined a handful of experienced industry experts in submitting short essays on this topic, exploring the challenges, opportunities, and shortcomings of zero-energy homes. Many of the entries focus on rooftop photovoltaic (PV) systems, which generate electricity at home, heating systems and insulation, and the role homes play in the global picture of carbon emissions.

Article Link: Is Zero Energy the Answer? (subscription required)

Newton Net Zero, one of ZED’s super-insulated, net zero energy homes. EUI: 0.4kBtu/sf/yr | 0.19 ACH50

Hempcrete Comes to Cape Cod

Get a first look at this ZED consulting project (energy + HVAC design) in Harwich Port, MA where a hempcrete house is being built, one of the first of its kind in the country. ZeroEnergy Design provided the energy consulting and mechanical design for this forward-looking, carbon sequestering home. 

What is Hempcrete?
Hempcrete is a cutting edge biocomposite building material made from the chopped stalk of the hemp plant, a lime-based binder, and water. The result is a healthy, resilient and carbon beneficial building material that can be used to create a building’s thermal envelope, and which looks a bit like concrete. But unlike concrete, hempcrete actually sequesters carbon dioxide; a recent study showed that hempcrete can sequester 19 pounds of C02 per cubic foot. This progressive material is incredibly useful for: 1) reducing a building’s operational energy requirements with a well insulated, thermally broken, airtight enclosure, 2) sequestering carbon in the material itself, and 3) providing healthy indoor air via thermal mass and moisture absorbing behavior. 

Material Attributes
Lime in the application of hempcrete uses about 80% less energy to calcine than when used in concrete. As an ‘air set’ material, the lime in hempcrete reabsorbs the CO2 that is driven off in calcining.

Hempcrete is resistant to mold growth, deters pests and won’t burn. The vapor permeable property of hempcrete also helps regulate building humidity, while its matrix structure provides excellent sound absorption.  

In addition to being a non-toxic and biodegradable material, hempcrete can be used to reduce construction waste by replacing drywall, which represents about 10% of building construction debris. Furthermore, hemp is a rapidly renewable resource with the greatest CO2-storing potential of any other insulation building material.

The Cape Cod Hemp House
The Cape Cod Hemp House exemplifies future focused, healthy, low carbon, net positive energy design. As this progressive home takes shape, we take a closer look at the carbon sequestering envelope, all-electric systems, and renewable energy sources that contribute to its net-zero energy makeup.

Envelope
The home's super-insulated envelope begins with 12 inch-thick walls with continuous hempcrete on the exterior and spray applied to a wood frame with bamboo wall lathe. The interior will be finished with a plaster coat. The roof includes hempcrete, wood sheathing, building wrap, and metal roofing. Triple pane windows round out the super insulated, airtight building enclosure.

Workers prep and spray hempcrete insulation between the 12 inch-thick exterior walls.

Systems
High efficiency systems in the home include air source heat pumps, a heat pump hot water heater, and energy recovery ventilation. Rightsized air source heat pumps provide heating and cooling matched with the thermally improved building enclosure. Balanced heat and energy mechanical ventilation systems provide constant fresh air while also managing humidity levels. A heat pump hot water heater efficiently provides domestic hot water. 

Renewables
The all-electric home’s consumption is offset with clean energy production on the roof from a 15kW solar electric system with a whole-house backup battery. The photovoltaic array is expected to offset 120% of the total annual energy consumption, resulting in a net positive energy house. 

A Future for Hempcrete
While builders continue to see value in hempcrete, one of the limitations to its wider use is availability. Facilities capable of processing hemp into hempcrete are mostly in Europe and some regulatory challenges still exist in growing hemp itself, particularly in the U.S. But once more forward-thinking producers and builders start utilizing hemp for construction, it could lead to many more eco-friendly, high performance buildings.

MORE:  CAPE COD HEMP HOUSE

The interior side of the exterior envelope includes bamboo lathe with hempcrete inside the cavity.

High-production European spray-applied hempcrete system. When completed, this project will be the first in North America to employ this system.

Forbes PROFILES Zero Energy Architecture LEADER

Noted author and expert on small/prefabricated houses, Sheri Koones, profiled ZED and interviewed Managing Director, Stephanie Horowitz, for Forbes.

Horowitz described how the firm’s commitment to making energy efficiency, health, and comfort baseline attributes for all projects, allows it to instead use the design time to create spaces that are beautiful, functional, and durable.

She also discussed ZED’s Lincoln Farmhouse and Dartmouth Oceanfront projects, while sharing that changes in the building codes were necessary to bring energy-efficient homes into the mainstream.

Full article is linked below.

MORE: ZED - LEADERS IN ZERO ENERGY ARCHITECTURE

Hollis Montessori Goes Net Positive

The Hollis Montessori School celebrated their tenth anniversary with a transition to renewable energy. As the first Certified Passive House elementary school in the U.S., the building already has an exceptionally efficient enclosure paired with high performance systems (for heating, cooling, hot water, lighting, and ventilation). The new installation of a 56.8 kW photovoltaic system completes the vision developed by the board of directors. The system is expected to offset all the energy demand of the high-performance building, with extra energy available for use for the other buildings on the school campus. The building is now net positive energy, and contributing to the goal of net zero energy for the entire campus.

ZED provided Passive House Consulting and Mechanical Design for the project.

MORE: HOLLIS MONTESSORI CASE STUDY