Energy retrofit of a Sears kit home in Concord, Massachusetts (2007)

Case Study

Concord Retrofit House
Location	West Concord, MA
Built	1916
Project data
Project date	2006-2007
Cost	$300,000
Project team
Architect	Building Science Corporation
Contractors	The Synergy Companies Fin's Tin (HVAC Contractor)
Consultants	Building Science Corporation

The objective of this project was to demonstrate that a 50% reduction in home energy use can be met today in existing housing. The project house was built in 1916 and is a typical example of American Foursquare -style Sears kit home. It is located in West Concord, Massachusetts, an area of the United States rated as a cold-to-very-cold climate zone. The house had never received any system upgrades and still retained its original wiring, plumbing and oil-fired boiler. The existing systems were in need of updating, including plumbing, electrical and heating. Using systems engineering techniques, the enclosure and mechanical systems were analyzed to determine the most cost effective ways to meet this goal. Care was taken to provide proper water management details as the additional insulation was added.

Existing structure

The mail-order Sears home is of a fairly simple Foursquare style design, with a footprint of 3,600 square feet, two stories, four bedrooms, 3.5 baths. In-keeping with the style, the building is crowned with a pyramid-shaped roof detailed with hip-gabled dormers.

The window-to-wall ratio is sparse, however each room in the house has at least two windows on at least two sides of the house. This fenestration means that natural daylight is available in every room during most daylight hours. The windows’ location on different sides of each room also promotes natural, cross-ventilation. While the original house enclosed 3,600 square feet, only 2,000 square feet were intentionally conditioned. The non-conditioned space included 1,000 square feet in the basement and an additional 600 square feet in the vented attic.

The bathroom and kitchen, which were in poor condition, were replaced during renovation. One of the second-floor bedrooms was converted to a bathroom and laundry room in anticipation of future occupants. Another full bath was added in the attic and the space was retrofitted for air conditioning. By the end of renovation, what was a four-bedroom, 1.5-bath house became a four-bedroom, 3.5-bath house with a fully conditioned basement to be used as an exercise and family room. Long-range plans called for four to five occupants.

Energy use reduction strategies

All of the renovations used systems engineering principles to ensure good indoor air quality and long-term durability while providing deep energy reductions:

• drainage plane (water-repellent materials designed to drain water—e.g., house wrap, building paper or taped facing on sheathing);
• air barrier (airtight continuous enclosure around conditioned space);
• thermal barrier/insulation (layer that controls heat flow by conduction between interior and exterior).
• vapor control (materials designed to control the movement of water by vapor diffusion, to prevent accumulation that can result in damage to the building);
• combustion safety (fossil fuel burning appliances using sealed combustion technology);
• air change (provision for dilution of interior air with outside air);
• pollutant removal at source (bath and kitchen exhaust fans).

Window replacement

To increase comfort within the home, the first step in the renovation was to replace the existing windows. The interior sash stops and sashes were removed. The whole opening was wrapped with a peel-and-stick membrane, leaving enough around the exterior to integrate with the new drainage plane. A new vinyl-clad wood-framed window was installed from the exterior into the pocket that was formed by wrapping the opening with membrane, so that no interior trim had to be changed. The sills were extended and exterior trim was wrapped back to the plane of the window. The exterior siding was butted to the trim.

Drainage plane continuity

Draining water away from the enclosure starts at the roof. The rooftop vents were removed, and the roof was stripped down to the original board sheathing. Two layers of foil-faced foam were installed followed by a new layer of plywood sheathing. The roof sheathing was covered entirely with ice and water shield and new shingles were installed. Care was taken to retain the depth of the original overhang which was achieved by furring out the fascia board. The original wall shingles had been covered with aluminum siding. The siding was removed and hauled away by a scrap metal contractor. The shingles were removed to expose the original board sheathing.

A corrugated house wrap was installed over the board sheathing and connected to the window wrap as well as the top and the bottom of the wall sheathing (with a continuous bead of caulk for air barrier continuity). Then, the two layers of two-inch polyisocyanurate were applied with the joints staggered and joined with adhesive construction tape. The insulation board was held in place with one-by-three furring strips screwed back to the board sheathing. Pre-primed cedar siding was then attached to the furring strips. This resulted in a three-quarter inch space (open at top and bottom) that allows drainage of water and ventilation to dry much of the remaining water.

Multiple mechanisms in the new assembly promote shedding of water. When rain hits clapboard siding, the majority of the incident water drains to the outside. The three-quarter inch ventilated space provides added protection (water is not “sandwiched” between the clapboard and the underlying structure, plus the space allows for ventilation drying). Any small amount of water that penetrates past the cladding is drained on the outside face of the insulating sheathing. Finally, any water that manages to get between the two layers of insulating sheathing is carried down the wall on the draining house wrap. Since the windows were installed back at the face of the house wrap/board sheathing, the rain is kept away from the face of the window, further increasing the long-term durability of the window.

The basement did not show any signs of ever having water leakage, but as a precaution, the interior face of the existing wall was drained at the bottom with a drainage mat that was turned up the wall from the d�oor. The drainage mat below the insulated slab will allow some water to be stored and will carry any excess water to an interior sump pit. This pit can be fi�tted with a sump pump in the future if there is any sign that the ground water level is changing.

Air barrier continuity

For an air barrier to be eff�ective, it needs to wrap all six sides of the “conditioned cube,” and all components need to be connected in a continuous manner. The new slab was connected to the basement walls with spray foam that extended from the new basement slab to the rim sill, directly under the fi�rst �floor. The corrugated house wrap became the air barrier at the exterior wall above grade, helped by the two staggered layers of foam sheathing installed over it. At the roof-wall interface, the air barrier was transferred back to the interior at the sof�t where the housewrap was adhered to the board sheathing and then connected with spray foam to the top plate of the second �oor wall. It was continued with more spray foam to the interior side of the roof board sheathing. Thermal Continuity The insulation followed the same path as the air barrier to wrap all six sides of the cube. Starting at the basement, the existing slab �oor was covered with 2 in. of XP.S The existing basement walls were covered on the inside with 4 in. of closed cell spray foam. The exposed sills at the basement were sprayed from the inside as well. Then theexterior above-grade walls were �lled with cellulose, using the traditional method of making small holes in theexterior sheathing. The two 2-in. layers of polyisocyanurate were installed over the whole exterior wall. The roof vents were sealed, and the wall-roof intersections were lined from the inside with building paper to provide a temporary dam for the application of spray foam from the interior. Two additional 2-in. layers of polyisocyanurate were then installed on top of the roof deck. Vapor Di�usion Pro�le The roof assembly with its layers of insulation, plywood roof deck, and self-adhering membrane is impermeable. The exterior walls of the house were rendered vapor impermeable by the addition of the exterior foil-faced polyisocyanurate insulating layers. However, the thermal resistance of the insulating sheathing is suf�cient to stop any condensation on interstitial surfaces that might otherwise occur. A small area of the basement wall was left exposed above grade, allowing the concrete and stone structure to dry to the outside.

Mechanical System Upgrades

The draft hood water heater was inef�cient and vented through the masonry chimney, so it also was removed. A low-mass condensing boiler was chosen to provide space heat and hot water, and connected to the air handlers described below. A well-insulated storage tank provides domestic hot water. Three zones are tapped from the boiler, one for each air handler and one for the hot water storage tank. One air handler located in the basement serves the basement and �rst �oor. One central return for that air handler is located on the �oor of the �rst fl�oor central hallway. The other air handler, located on the conditioned attic level, serves the second �floor and the attic. One return is on the ceiling of the second

Energy reduction retrofits

An R-60 insulation value was achieved in the attic space by adding four inches rigid foam on the exterior and five inches of high density sprayed polyurethane foam to the underside of the roof sheathing. Roof insulation: Two layers of 2” polyisocyanurate rigid insulation Air Sealing: Airtight drywall approach; low expanding foam sealant around windows, sealants and adhesives used between framing components vWindow Specifications: Doubleglazed, Low-E, argon-filled: U=0.33 wWall Insulation: R-41 with blown cellulose cavity insulation and 4” of rigid foam on the exterior Foundation: Conditioned basement xFoundation Wall Insulation: R-20 walls with 4” high density sprayed polyurethane foam ySlab Insulation: R-10; 2” XPS insulating sheathing under the slab Drainage Plane: Taped foil-faced polyisocyanurate Radon Protection: Passive system installed Infiltration: 2.5 in2 leakage area per 100 ft2 envelope

PROJECT PROFILE Project Team: Building Science Corporation Address: West Concord, Massachusetts 3,600 ft2 two-story, 4 bedrooms, 31/2 bath single family home To be completed October 2008 Cost of renovation: $100/ft2 Annual utility costs: Gas before: $2,400/year Gas after: $858/year Electric before: $960/year Electric after: $471/year Total annual utility savings: $2,031/year

Window Specifications: Double glazed, Low-E, argon-filled: U=0.33 Wall Insulation: R-41 with blown cellulose cavity insulation and 4” of rigid foam on the exterior Foundation: Conditioned basement Foundation Wall Insulation: R-20 walls with 4” high density sprayed polyurethane foam Slab Insulation: R-10; 2” XPS insulating sheathing under the slab Drainage Plane: Taped foil-faced polyisocyanurate Radon Protection: Passive system installed Infiltration: 2.5 in2 leakage area per 100 ft2 envelope

MECHANICAL DESIGN Heating: 92% AFUE sealed combustion gas boiler in conditioned space Cooling: 13 SEER split system in conditioned space Ventilation: Supplyonly system with outside air to return; run at low speed with an ECM motor Filter: MERV 13 Return Pathways: Transfer grilles at bedrooms Ducts: Sheet metal trunk and flex runouts in conditioned space DHW: 0.8 EF side-arm storage tank Appliances: ENERGY STAR dishwasher, refrigerator, range, clothes washer, clothes dryer Lighting: Energy Star CFLs Site Generated Power: None

ADDITIONAL FEATURES • Large overhangs with crown molding to accommodate additional exterior foam • Front porch • Maintenance-free fiber cement siding and trim • Very high efficiency faucets, shower heads and toilets • Plan minimizes water run-off

External links

• Building Science Digest