Heat Pumps, Air Sealing and Teamwork Reimagine a Historic Rowhouse

# Project snapshot

# Constraints that shaped the design The retrofit faced multiple built‑in limitations: shared masonry party walls, small floorplates, little overhead or basement mechanical space, and strict historic‑district rules that prevented major changes to the front façade. Those constraints made routing ductwork, locating equipment, and achieving airtightness more difficult than a typical new Passive House project.

# How the envelope was tightened The team layered air‑sealing solutions to protect the masonry and control vapor. A fluid‑applied Visconn membrane was placed against the exterior brick as one continuous air barrier. Inside, Intello Plus, a variable‑permeability air and vapor control membrane, provided a redundant line of defense. Tapes, sealants, and careful detailing bridged transitions.

Insulation strategy used three materials: Rockwool, actual lamb's wool batts, and dense‑pack blown cellulose. Triple‑pane Optiwin windows were installed. The finish strategy favored natural materials and low‑VOC paints to improve indoor air quality. Designers ran thermal modeling and condensation‑risk analysis while selecting assemblies.

# Mechanical approach: compact heat pumps and ventilation

Every element of the energy‑recovery ventilator (ERV) design and installation required careful coordination to fit within space limits and to meet Passive House performance targets. The retrofit required zoning solutions across three stories and compact equipment placements because mechanical pathways were limited.

# Project team and workflow Longview Structures, a Lancaster‑based general contractor that self‑performs much of its work, led the construction. Jesse Pellman, Longview co‑owner, described the company as hands‑on and focused on craftsmanship and high performance. High Efficiency Solutions, led by Dustin Ebersole, handled the HVAC design and installation and was involved for more than 18 months.

Early and ongoing collaboration among the homeowner, general contractor, and HVAC contractor helped resolve tradeoffs between preservation rules, envelope strategies, and mechanical routing. Energy modeling and field testing were used to verify performance aligned with Passive House requirements.

# Practical lessons for similar retrofits

• Start coordination early: historic constraints and shared walls change basic assumptions about routing and equipment locations.
• Use redundant air‑barrier strategies when you cannot alter an exterior façade.
• Combine multiple insulation types to fit varying cavities and to manage hygrothermal behavior.
• Treat ventilation design and ERV installation as integral to HVAC sizing when heat pumps will be the sole source of conditioning.

The Lancaster project shows how close attention to air sealing, material choices, compact heat‑pump systems, and discipline in installation can bring a historic urban rowhouse close to Passive House performance while preserving character.