Business Details
21 Years
experience
Sustainable Architecture & Passive House Design
Since 2005, Onion Flats (OFA) has established itself as an award-winning architecture practice dedicated to advancing sustainable, high-performance building solutions. Our team combines decades of hands-on experience in architecture, construction, and development with specialized credentials in Passive House and LEED certification. We deliver innovative architectural design and sustainability consulting grounded in practical expertise, focusing on energy efficiency, resilience, and community impact. Our integrated approach spans Passive House projects, Deep Energy Retrofits (DER), and modular construction, ensuring clients achieve cost-effective, low-carbon outcomes. Recognized for pioneering LEED Platinum developments and Net-Zero-ready buildings, we maintain a commitment to education, equity, and replicable design strategies.Our sister company, Onion Flats Development, complements our architectural services through design-build experimentation. We prioritize client collaboration, technical excellence, and mission-aligned solutions tailored to regional needs. Our work includes Phius-certified projects, the first LEED Platinum duplex in the U.S., and groundbreaking awards from ULI and Green Building United. By combining academic rigor with field expertise, we guide clients through complex sustainability challenges while maintaining a focus on healthy, affordable built environments. Our leadership in high-performance design continues to shape industry standards across the Northeast and beyond.
Services
Architectural Design
Passive House Certification
Deep Energy Retrofits
LEED Certification
Modular Construction
Sustainability Consulting
Net-Zero Building
Building Envelope Analysis
Affordable Housing Design
Historic Renovation
Details
- Year established: 2005
Highlights and features
- We offer over 25 years of experience in sustainable architecture and construction.
- Our team includes in-house Passive House Certified Consultants and Tradesmen.
- We pioneered the nation's first LEED Platinum duplex and Phius-certified projects.
- We provide integrated design-build solutions through our sister company JIG, Inc.
- We develop proprietary DER feasibility tools in partnership with RMI.
Associations and certifications
- PHIUS Certified Consultant
- PHI Certified Designer
- LEED AP
- CPHC
- CPHD
What people say
Seasoned professionals
Sustainable design leaders
Passive House experts
Award-winning projects
Client-focused solutions
Services
Deep Energy Retrofits
Our Deep Energy Retrofits reduce energy consumption by 80% or more through comprehensive building envelope upgrades. We specialize in pre-manufactured DER solutions for multifamily housing, combining Passive House principles with scalable retrofit strategies. Our team provides feasibility analysis, design, and construction administration to transform inefficient buildings into high-performance assets.
Passive House Design
We deliver Phius-certified Passive House projects that achieve superior energy performance while maintaining occupant comfort. Our services include thermal modeling, air-tightness testing, and material selection to meet rigorous international standards. Our architects hold multiple Passive House certifications and have completed award-winning projects across residential and commercial sectors.
LEED Certification
Our LEED Accredited Professionals guide projects through certification for sustainable commercial and residential developments. We implement low-tech, cost-effective materials to maximize environmental impact while ensuring compliance with USGBC standards. Our portfolio includes the nation's first LEED Platinum duplex and multiple award-winning green buildings.
Modular Construction
We provide modular construction consulting with expertise in panelized building systems and off-site fabrication. Our team offers site suitability analysis, manufacturer selection, and financial modeling for modular projects. This approach reduces construction timelines while maintaining high-performance standards through integrated Passive House principles.
Sustainability Consulting
Our sustainability consulting covers energy modeling, carbon reduction strategies, and lifecycle analysis for new and existing buildings. We specialize in affordable housing solutions that balance environmental performance with cost-effectiveness. Our team develops customized strategies aligned with client goals and regulatory requirements.
People
Timothy McDonald
Principal Architect
Licensed architect in four states with 20+ years leading sustainable design teams. Co-founded OFA and JIG, Inc., integrating design and construction for high-performance buildings. Certified Passive House Consultant and LEED AP with teaching and nonprofit leadership experience.
Howard Steinberg
Principal Architect
Registered architect with 30+ years in Mid-Atlantic construction. Co-founder of OFA and JIG, Inc., specializing in sustainable development. Certified Passive House Designer and LEED AP known for strategic project leadership and technical excellence.
Kara Haggerty Wilson
Design Director
Certified Passive House Designer with expertise in affordable housing and energy modeling. Guides teams toward resilient, cost-effective solutions while maintaining focus on client sustainability goals through collaborative design processes.
Dan Addis
Project Manager
Manages diverse project types including Passive House commercial developments and historic renovations. Provides hands-on coordination and field support to ensure project success from design through construction completion.
Jeannette Penniman
Project Manager
Certified Passive House Consultant with experience across education, residential, and historic retrofit projects. Focuses on equitable design solutions and leads teams through complex certification processes for high-performance buildings.
Questions
What architectural services do you specialize in?
We specialize in Passive House design, Deep Energy Retrofits, LEED certification, modular construction, and sustainable building consulting for residential and commercial projects.
Are you certified in green building standards?
Yes, our team holds multiple certifications including LEED AP, PHIUS Certified Consultant, and PHI Certified Designer for international Passive House standards.
What geographic areas do you serve?
We primarily work in Philadelphia, Boston, and the Northeast United States, with project experience across North America.
Do you offer consulting for existing buildings?
Yes, we provide Deep Energy Retrofit consulting, building envelope analysis, and sustainability strategies for existing structures to achieve net-zero performance.
Can you help with modular construction projects?
Our team offers modular consulting services including design, manufacturer selection, and financial analysis for panelized construction projects integrating Passive House principles.
What awards has your firm received?
We've received the ULI Willard Rouse Award, Green Building United Groundbreaking Award, and International Passive House Award for innovative sustainable design.
