Onion Flats
Onion Flats Architecture is a Philadelphia-based sustainable architecture and design-build firm founded in 1997, specializing in Passive House, LEED-certified, and Deep Energy Retrofit projects for affordable housing developers, CDCs, private developers, and institutional clients across the Mid-Atlantic, Northeast, and New England.
- Company typePrivate
- Founded1997
- HeadquartersPhiladelphia, United States
- Headcount11–50
- GTM typeB2B
- OfferingServices
What Onion Flats does
Onion Flats Architecture (OFA) is a Philadelphia-based sustainable architecture and design-build firm founded in 1997 that specializes in high-performance, energy-efficient buildings using Passive House (Passivhaus) standards, LEED certification, Deep Energy Retrofit (DER) methodologies, and prefabricated panelized construction. The firm holds multiple category-defining credentials, including Pennsylvania's first certified Passiv Haus (Belfield Townhomes, 2012) and the nation's first LEED Platinum duplex (Thin Flats Phase 2, 2009), and was awarded the 2014 International Passive House Award from the Passive House Institute. Its technical approach combines superinsulated building envelopes, thermal bridge-free construction, airtightness, balanced ventilation with heat recovery, and on-site solar PV integration, with demonstrated outcomes of up to 95% Energy Use Intensity reduction on DER projects.
The firm operates offices in Philadelphia, PA and Manchester, MA, and serves four primary customer segments: affordable housing developers and Community Development Corporations (CDCs), private market-rate developers, institutional clients (theatres, universities, civic organizations), and government/emergency management agencies. Its project portfolio spans single-family and multi-family residential, mixed-use developments, and master planning, with marquee projects including Thin Flats Phase 2, Belfield Townhomes, the Hano Homes DER (ten Boston duplexes, completed 2025), and unbuilt large-scale net-zero communities such as Morris Steel (692 units) and Vine Street (209 units). OFA generates revenue through project-based professional services fees for architectural design, construction documentation, construction administration, sustainability/Passive House consulting, and DER feasibility studies.
The go-to-market motion is sales-led and relies heavily on thought leadership through industry conferences (Greenbuild, NESEA, ULI), academic lectures at top-tier universities (Harvard GSD, MIT, UPenn, Columbia), published articles and case studies, and direct engagement with developers, CDCs, and institutional buyers. Strategic partners include Rocky Mountain Institute for decarbonization research, Sustainable Comfort Inc. for performance testing, Haycon for general contracting, Spacebox for modular emergency housing, and Resonant Energy for solar integration. The firm is privately held with no disclosed institutional investment or funding rounds.
Onion Flats firmographics
Firmographics- Name
- Onion Flats
- Legal name
- Onion Flats Architecture
- Website
- https://onionflats.com
- Company type
- Private
- Founded year
- 1997
- Operating status
- Operating
- Headcount range
- 11–50 employees
- Short description
- Onion Flats Architecture is a Philadelphia-based sustainable architecture and design-build firm founded in 1997, specializing in Passive House, LEED-certified, and Deep Energy Retrofit projects for affordable housing developers, CDCs, private developers, and institutional clients across the Mid-Atlantic, Northeast, and New England.
- Ownership category
- akta.pro rank
Where Onion Flats is headquartered
LocationHeadquarters
- HQ city
- Philadelphia
- HQ country
- United States
- HQ region
- North America
Offices2 records
Markets served
Onion Flats business model
Business model- GTM type
- B2B
- Offering type
- Services
- Cost components
- Personnel, Operations, Marketing or Sales, Technology or R&D, Others
Revenue model
- Architectural Design Services: Full-service architectural design for residential (single-family, multi-family), commercial, and institutional projects. Revenue generated through project-based fees for design, construction documentation, and construction administration.
- Sustainability Consulting: Passive House and LEED certification consulting, energy modeling, and sustainability advisory services for third-party developers and organizations.
- Passive House Consulting: Consultant architect and passive house consultant services for projects in other locations, as demonstrated by multi-family project in Madison, WI.
Go-to-market motion1 record
Distribution channels1 record
Marketing channels6 records
Onion Flats product offering
Product offeringCore offering
Onion Flats Architecture is a Philadelphia-based sustainable architecture and development firm that provides full-service architectural design, sustainability consulting, Deep Energy Retrofit (DER) services, and prefabricated construction for residential, commercial, and institutional projects. The firm specializes in Passive House and LEED-certified high-performance buildings, with a particular focus on affordable housing and decarbonization of existing building stock through envelope retrofits and Net-Zero energy design.
Product overview
Onion Flats Architecture is an architecture and development firm offering architectural design services and sustainability consulting, specializing in high-performance, energy-efficient buildings. Their core offerings include architectural design services, sustainability consulting (Passive House and LEED certification), Deep Energy Retrofits (DER), and prefabrication services. The firm's portfolio spans single-family homes, multi-family residential projects, and institutional/mixed-use developments, with notable projects including Thin Flats Phase 2 (nation's first LEED Platinum duplex), Belfield Townhomes (first Passive House in Pennsylvania), Hano Homes Deep Energy Retrofit (Passive House-targeted Boston project), Morris Steel and Vine Street (unbuilt Net-Zero energy communities), and Grape Flats (LEED Platinum affordable housing). They also provide Passive House education through lectures and workshops at universities and conferences.
Differentiator
Problem solved
Functional benefit
Products and services
- Architectural Design Services
Quantifiable outcome
- 95% reduction in Energy Use Intensity (EUI) achievable through Deep Energy Retrofit
- +5 more outcomes
Companies that use Onion Flats
Customer profileNamed customers8 records
Segments4 records
Ideal customer profiles4 records
Onion Flats technology and API
TechnologyTechnology focussed No
API detail
- Has API
- No
- API docs
- API detail
Core technology
AI maturity
App detail
Feature4 records
Onion Flats partnerships and signals
Strategic signalPartnerships
Six partnerships are on record, tiered core and minor.
- Sustainable Comfort, Inc.coreTesting and consulting partner for blower door testing, air sealing guidance, and high-performance building certification. Instrumental in achieving Hano Homes air tightness results of 0.27 cfm50/sf.
- HayconcoreGeneral contractor and construction partner for Deep Energy Retrofit projects. Partnered on Hano Homes and Brian J Honan projects, including window/door installation and blower door testing capabilities.
- RMI (Rocky Mountain Institute)coreStrategic partner for deep energy retrofit projects, providing research, analysis, and implementation support for building decarbonization initiatives.
- Tierney Development Services, LLCminorDevelopment consulting partner for affordable housing projects including Brian J Honan and Hano Homes DER projects.
- Maloney PropertiesminorProperty management partner for Brian J Honan Apartments project in Boston.
- U3 VenturesminorDevelopment partner for OEMNY Emergency Housing prototype project with Spacebox.
Scale indicators8 records
Recent moves6 records
Expansion highlights5 records
Onion Flats competitors and assessment
Company assessmentDirect peers
- Interface Studio Architects: Philadelphia-based architecture firm with comparable size and a strong portfolio in community-oriented, sustainable urban infill and mixed-use projects. Directly comparable on location, scale, and design philosophy around socially conscious, high-performance architecture.
- Bright Common: Philadelphia-based sustainable architecture practice focused on Passive House, LEED, and net-zero residential design for the Mid-Atlantic. Closely mirrors Onion Flats' service mix and customer base.
- KieranTimberlake: Philadelphia-headquartered firm widely recognized for high-performance building research, prefabrication (e.g., the Loblolly House), and sustainability-led design. Direct peer in mission, regional base, and integrated design-build approach.
- HMFH Architects: Cambridge, MA-based architecture firm focused on affordable, supportive, and educational housing with deep energy efficiency and Passive House experience. Directly comparable for serving CDCs and LIHTC-funded affordable housing in the Northeast.
- Lake|Flato Architects: San Antonio-based firm widely recognized for sustainable, regionally responsive design with extensive experience in residential and mixed-use projects. Comparable as a mid-size practice with a sustainability-led identity and national recognition.
- Leddy Maytum Stacy Architects: San Francisco-based architecture firm recognized nationally for net-zero energy, Passivhaus, and affordable-housing projects (including several HUD/CNCA awards). Comparable niche as a sustainability-driven, mid-size practice serving affordable and supportive housing.
- Union Studio Architecture & Community Design: Providence, RI-based architecture practice with an explicit focus on community-oriented, sustainable, and affordable housing design. Comparable mission, geographic service region, and client base.
- VIA Architecture: Seattle-based sustainable architecture firm with strong Passive House and net-zero multi-family experience. Comparable mid-size, sustainability-led practice serving urban infill and affordable housing.
Emerging players
- Steven Winter Associates: Building-science and Passive House consulting firm providing energy modeling, certification, and DER advisory services. Overlaps with Onion Flats' sustainability-consulting line and shares the same client base of affordable-housing developers pursuing Passive House certification.
Broad incumbents
- Handel Architects: Large, well-established multi-family and sustainable urban architecture firm with a national footprint and deep Passive House / sustainability credentials. Overlaps on high-performance multi-family and Net-Zero residential, but at much greater scale.
Market position
Strengths5 records
Weaknesses5 records
Competitive moat4 records
Key risks5 records
Key highlights7 records
Customer concentration
Onion Flats social profiles
Digital presenceOnion Flats compliance and trust
Trust signalCompliance7 records
Onion Flats financial estimates
Financial estimateRevenue estimate
Valuation estimate
Onion Flats leadership team
Management profileNumber of profiles
Profiles1 record
Onion Flats funding detail
Funding detailFunding overview
Funding rounds
Investors
Funding detail is available on the Subscription and Enterprise plan.Contact sales →
Onion Flats M&A and investment
M&A and investmentM&A
Investments
M&A and investment is available on the Subscription and Enterprise plan.Contact sales →
Frequently asked questions about Onion Flats
What does Onion Flats do?
Onion Flats Architecture is a Philadelphia-based sustainable architecture and development firm that provides full-service architectural design, sustainability consulting, Deep Energy Retrofit (DER) services, and prefabricated construction for residential, commercial, and institutional projects. The firm specializes in Passive House and LEED-certified high-performance buildings, with a particular focus on affordable housing and decarbonization of existing building stock through envelope retrofits and Net-Zero energy design.
Is Onion Flats a public or private company?
Onion Flats is a private company. It is classified as founder individual operated bootstrapped and is currently operating.
When was Onion Flats founded?
Onion Flats was founded in 1997. It employs 11 to 50 people.
Where is Onion Flats based?
Onion Flats is headquartered in Philadelphia, United States, in the North America region.
How does Onion Flats make money?
Three revenue lines are on record. Architectural Design Services are the primary driver. The others are sustainability Consulting and passive House Consulting.
Who are Onion Flats's main competitors?
Direct peers on record are Interface Studio Architects, Bright Common, KieranTimberlake, HMFH Architects, Lake|Flato Architects, Leddy Maytum Stacy Architects, Union Studio Architecture & Community Design and VIA Architecture. Steven Winter Associates is listed as an emerging player. Handel Architects is listed as a broad incumbent.
Does Onion Flats have an API?
No public API is recorded for Onion Flats.