The Theresa Passive House: A Blueprint for High-Performance Design in Hot-Humid Climates

The Theresa Passive House, nestled in Austin's historic Clarksville neighborhood, stands as a remarkable example of how architectural preservation can harmoniously merge with modern sustainable design. This 2100 square foot residence, completed in 2020, is not merely a renovation and addition to a 1914 Craftsman bungalow; it is a meticulously engineered dwelling that embodies rigorous targets in energy efficiency, indoor air quality (IAQ), thermal comfort, embodied carbon, and responsible materials sourcing.[1] These ambitious goals were established by the Passive House Institute U.S. (Phius), a leading authority in high-performance building standards.

Architectural Design, Building Enclosure, Building Science, Code, Dehumidification, Electrification, Environmental Design, Filtration, Healthy Home, Heat Pumps, High Performance Homes, HVAC, Indoor Air Quality, Mechanical Design, Passive House, Phius, Solar, VentilationPositive EnergyMay 28, 2025Theresa Passive House, high-performance design, hot-humid climates, residential performance, sustainable design, architectural preservation, energy efficiency, indoor air quality (IAQ), thermal comfort, embodied carbon, responsible materials sourcing, Passive House Institute U.S. (Phius), Phius certification, PHIUS 2018+ Source Zero, ASHRAE Climate Zone 2A, photovoltaic panels, battery backup systems, self-sufficiency, resilience, Forge Craft Architecture + Design, Hugh Jefferson Randolph Architects, Studio Ferme, integrated design process, building envelope, HVAC system, on-site solar panels, MEP (Mechanical, Electrical, Plumbing) engineering, Positive Energy, building science, human-centered design, net-zero energy buildings, heating loads, cooling loads, source energy, airtightness, energy modeling, continuous insulation, thermal bridges, air changes per hour (ACH@50 Pa), air leakage, Blower Door Test, high-performance windows, triple-glazing, low-emissivity (low-e) coatings, Solar Heat Gain Coefficient (SHGC), balanced ventilation, Energy Recovery Ventilators (ERVs), dedicated dehumidification, right-sizing mechanical systems, comfort, health, durability, passive survivability, Winter Storm Uri, University of Texas research, climate-specific standards, moisture management, key performance metrics, site energy use index (EUI), renewable energy production, wall assemblies, water control layer, air control layer, thermal control layer, vapor control layer, wood frame system, mineral wool insulation, unvented roof, Marvin windows, indoor pollutants, combustion products, Volatile Organic Compounds (VOCs), particulate matter (PM2.5), ASHRAE Standard 62.2, ventilation rates, Variable Refrigerant Flow (VRF) heat pump AC, Panasonic Intellibalance 1000 ERV, MERV filtration, heat pump hot water heater, climate resilience, extreme weather events, grid outages, source zero certification, community education, AIA Housing Award, Passive Project of the Year – Retrofit, Austin Green Awards, affordable multifamily housing, building envelope prioritization, mechanical ventilation with energy recovery (ERV) implementation, MEP systems integration, advanced air filtration, MERV ratings, active energy independence, photovoltaics, battery storage, MEP engineer collaboration, climate-specific MEP solutions, commissioning agent

Phius Market Penetration in the US: A Comparative Analysis with Typical Code-Built Houses

The adoption of Phius passive building standards in the United States, while demonstrating a robust upward trend, currently constitutes a small fraction of the overall construction market, which is predominantly characterized by buildings constructed to meet minimum code requirements. Phius certified buildings offer substantial advantages over typical code-built houses, most notably in their superior energy efficiency, which translates to significant reductions in operational energy consumption and associated costs. Furthermore, these high-performance buildings provide enhanced indoor air quality, increased durability, and a greater level of resilience against extreme weather events and power outages. The number of Phius certified projects and the total square footage of these projects have been steadily increasing across the US, reflecting a growing interest in and adoption of these advanced building principles. Moreover, the integration of Phius standards into the energy codes of several states and municipalities indicates a growing recognition of their value in achieving ambitious energy efficiency and sustainability goals. This report aims to provide a comprehensive, data-driven analysis of the current market penetration of Phius standards within the US construction sector, offering a comparative perspective against conventional code-compliant building practices and assessing the implications for the future of sustainable building in the nation.

Code, Building Science, Electrification, Healthy Home, High Performance Homes, HVAC, Phius, Passive HousePositive EnergyMay 26, 2025Phius passive building standards, US construction market, code-built houses, energy efficiency, operational energy consumption, indoor air quality, durability, resilience, extreme weather events, power outages, Phius certified projects, square footage, sustainability goals, Phius certification programs, net-zero energy buildings, continuous insulation, airtight building envelope, high-performance windows and doors, heat- and moisture-recovery ventilation, minimal space conditioning systems, Phius CORE, Phius ZERO, Phius REVIVE 2024, deep energy retrofits, climate-specific standards, US building codes, decentralized regulatory framework, International Code Council (ICC), National Fire Protection Association (NFPA), model building codes, International Energy Conservation Code (IECC), Home Energy Rating System (HERS) Index, ENERGY STAR certification, building permits, single-family homes, multifamily projects, commercial buildings, market penetration of Phius, certification growth trends, energy savings, construction costs, indoor environmental quality, thermal comfort, natural disasters, factors influencing Phius market adoption, regulatory endorsement, decarbonization, training programs, professional certification, long-term cost savings, financial incentives, Qualified Allocation Plans, perceived higher upfront costs, familiarity with passive building principles, specialized materials, traditional construction practices, future outlook for Phius, zero-carbon built environment.

The Resurgence of Natural Building Materials in High-End Homes: A Building Science Perspective for Architects

The landscape of luxury residential architecture is undergoing a profound transformation, driven by an escalating demand for homes that embody both sophisticated elegance and profound environmental responsibility. This evolution is particularly evident in the growing emphasis on sustainable practices, personalization, and a deep, intrinsic connection to the natural world. By the end of this decade, it is anticipated that high-end homes will prominently feature biophilic design principles, seamlessly integrating elements such as optimized natural light, lush indoor gardens, and fluid indoor-outdoor living spaces. This is not merely a passing aesthetic trend but a fundamental redefinition of luxury, where well-being and ecological stewardship are as valued as opulence and exclusivity.

Natural Building Material, Indoor Air Quality, High Performance Homes, Healthy Home, Environmental Design, Code, Building Science, Building Enclosure, Architectural DesignPositive EnergyMay 26, 2025luxury residential architecture, sustainable practices, personalization, environmental responsibility, biophilic design, natural light, indoor gardens, indoor-outdoor living spaces, United Nations Sustainable Development Goals, Paris Agreement, net-zero energy buildings, carbon footprint, eco-friendly building materials, passive design strategies, smart home technologies, personalized climate control, AI-driven systems, sustainable materials, natural building materials, renewable resources, low carbon footprints, recyclability, biodegradability, greenhouse gas emissions, construction waste, energy efficiency, insulation, thermal properties, indoor air quality (IAQ), low-VOC compositions, breathability, durability, organic aesthetic appeal, wellness strategy, building science, building envelopes, moisture management, bulk water, vapor diffusion, air-transported moisture, deflection, drainage, drying, vapor pressure, vapor permeability, dew point, hygroscopic materials, hydrophilic materials, hydrophobic materials, capillarity, hygric buffering, vapor retarders, vapor barriers, cold climates, hot and humid climates, mixed climates, thermal performance, R-value, thermal mass, heat capacity, thermal conductivity, density, specific heat capacity, thermal inertia, air movement, natural ventilation, wind-driven ventilation, stack effect, volatile organic compounds (VOCs), off-gassing, formaldehyde, benzene, toluene, earthen homes, adobe, compressed earth block (CEB), rammed earth, compressive strength, seismic considerations, reinforcement techniques, foundations, moisture barriers, wall protection, code acceptance, hemp-based materials, hempcrete, hemp batt insulation, carbon sink, hemp hurds, lime-based binder, fire resistance, char layer formation, VOC neutralization, structural frame, shear strength, Cross-Laminated Timber (CLT), engineered wood, CNC technologies, load-bearing capabilities, strength-to-weight ratio, acoustic properties, sound absorption, floating floors, charring effect, fire ratings, prefabrication, climate-specific design, structural engineers, building science consultants, skilled professionals.

The Case for Dedicated Dehumidification In Sealed Attics

Modern building design increasingly embraces sealed attic construction as a strategy to enhance energy efficiency and improve air leakage control, particularly beneficial for the performance of HVAC ductwork. This approach, where the attic space is brought within the building's thermal and air control envelope, fundamentally alters the moisture dynamics compared to traditional vented attics. While offering significant advantages, sealed attics introduce unique moisture challenges that demand precise and active management to prevent long-term durability issues and maintain superior indoor air quality.

Building Science, Architectural Design, Building Enclosure, Dehumidification, Healthy Home, Filtration, High Performance Homes, HVAC, Indoor Air Quality, Mechanical DesignPositive EnergyMay 23, 2025Sealed attics, dedicated dehumidification, moisture control, energy efficiency, indoor air quality, HVAC systems, air leakage, building durability, condensation risks, mold growth, air barrier, thermal barrier, insulation, roof deck temperature, building codes (IRC), ASHRAE standards, unconditioned attics, conditioned attics, psychrometrics, vapor control, duct performance, latent load, sensible load, building science principles, dew point, hygric buffering, controlled ventilation, air sealing, maintenance issues, cross-contamination, volatile organic compounds (VOCs), pests, allergens, duct leakage, system strain, pressure balancing, wood framing, sheathing, building envelope, resilience, sustainability, dehumidifier sizing, condensate management, building science experts, MEP engineering.

Understanding "Ping Pong Water" and Navigating Attic Moisture Dynamics in Modern Roof Assemblies

The design of residential attics has undergone a significant transformation. Conventionally, attics were vented spaces with thermal insulation placed on the attic floor, separating the unconditioned attic from the conditioned living space below. However, contemporary building practices increasingly favor unvented, or "conditioned," attics where insulation is applied directly to the underside of the roof deck.[1] This shift is driven by several factors, including the desire to bring HVAC equipment and ductwork within the building's thermal and air barrier envelope to improve system efficiency and longevity, enhance overall building airtightness for energy savings, and create potentially usable conditioned or semi-conditioned space within the attic volume.[3]

Building Enclosure, Building Science, Dehumidification, HVAC, High Performance Homes, Healthy Home, Code, Architectural DesignPositive EnergyMay 23, 2025"Ping Pong Water" phenomenon, attic moisture dynamics, modern roof assemblies, unvented attics, conditioned attics, moisture control challenges, roof sheathing moisture, attic ventilation, airtightness, energy efficiency, solar radiation, thermal buoyancy, hygric buoyancy, OSB hygroscopicity, chemical potential of wood, sorption isotherms, hysteresis, OSB and mold susceptibility, roof assembly durability risks, sheathing degradation, rot, corrosion of metal components, "bound water, " climate zone dependence, spray polyurethane foam (SPF), open-cell SPF (ocSPF), closed-cell SPF (ccSPF), vapor permeability, air barrier qualities, water barrier, code requirements, active attic conditioning, supply air strategies, return air strategies, dedicated dehumidification, exterior insulation, vapor diffusion ridge vents, fibrous insulation assemblies, cellulose, fiberglass, mineral wool, air tightness, vapor control layer, hybrid insulation systems, architect design considerations, building science principles, interior humidity management, material compatibility, constructability, quality control, building codes, hygrothermal modeling, risk management, lifecycle costs.

Recirculating Hoods and Indoor-Air Quality

Designing Healthier Homes by Eliminating Fossil Gas Appliance Emissions

Architects, as the primary designers of our built environment, hold a profoundly influential position in shaping the health and well-being of building occupants. Beyond the critical considerations of aesthetics, structural integrity, and energy performance, a deep understanding of the invisible forces at play within a building's envelope is increasingly paramount. This report aims to equip architects with the essential knowledge to proactively design for superior indoor air quality (IAQ), particularly concerning emissions from common household gas appliances. The decisions made during the design phase, from material selection to mechanical system integration, directly influence the indoor environment and, by extension, the health outcomes of those who inhabit these spaces. This effectively positions architects as critical guardians of public well-being within the built space, expanding their traditional role to encompass a vital public health responsibility.

Indoor Air Quality, HVAC, Electrification, Architectural Design, Building Enclosure, Code, Filtration, Healthy Home, High Performance Homes, VentilationPositive EnergyMay 22, 2025Designing healthier homes, eliminating fossil gas appliance emissions, indoor environmental quality, architect's role, indoor air quality, gas appliances impact on home health, combustion byproducts, hazardous air pollutants, synthesizing scientific findings, actionable strategies for architectural practice, pollutants emitted by gas appliances, health effects, design and engineering solutions, fundamentals of indoor air quality, source control, ventilation, filtration, temperature and relative humidity levels, building as a dynamic system, geographic site, local climate, physical structure, HVAC, construction techniques, contaminant sources, occupants' activities and behaviors, air exchange pathways, mechanical ventilation systems, infiltration, air pressure differences, building envelope, "Building Tight, Ventilate Right" imperative, energy consumption, pollutant concentration, energy efficiency, ventilation strategies, indoor air pollutants exceed outdoor levels, internal pollutant sources, "concentration trap", managing and removing internal contaminants, key pollutants from gas appliances, nitrogen dioxide, carbon monoxide, particulate matter, volatile organic compounds, moisture, respiratory irritation, asthma exacerbation, infection risk, decreased lung function, fatigue, chest pain, impaired vision, headaches, dizziness, confusion, nausea, DNA damage, mortality, transmission of airborne pathogens, organ damage, allergic reactions, cancer, dampness, mold growth, electric coil burners, high-dose exposure, pulmonary edema, diffuse lung injury, bronchitis, ambient air quality standards, carboxyhemoglobin, unvented gas space heaters, gas stoves, back-drafting, angia, poor ventilation, ultrafine particles, respirable particulate matter, cooking emissions, airborne particles, pathogens, respiratory aerosols, formaldehyde, benzene, unburned natural gas leakage, environmental tobacco smoke, automobile exhaust, sensory irritation, carcinogens, moisture load, human respiration and perspiration, bathing, washing, plants, pets, appliance selection, all-electric homes, electronic ignitions, proper appliance installation and maintenance, ducted range hoods, capture efficiency, airflow requirements, multi-family homes, whole-house ventilation strategies, tighter building envelopes, backdrafting risks, make-up air systems, targeted spot exhaust, bathroom fan, high-efficiency filtration, MERV-13, infectious aerosol exposure, cost-benefit analysis, air cleaning, indoor particle concentrations, semivolatile organic compounds, monitoring and alarms, carbon monoxide alarms, advanced IAQ monitors, PM2.5 sources, collaboration with MEP engineers, certified technicians, health impacts, continuous leakage, moisture byproduct, all-electric transition, building a healthier future, works cited, RMI, ASHRAE, EPA, LBNL, ventilation and air cleaning, envelope leakage, hazardous air pollutant emissions, residential ventilation requirements.

Navigating the HVAC Refrigerant Transition and the Promise of Hydronic Systems for Future-Ready Architecture

The global heating, ventilation, and air conditioning (HVAC) industry is undergoing a significant transformation driven by the phasedown of high-Global Warming Potential (GWP) refrigerants, primarily Hydrofluorocarbons (HFCs). This shift, mandated by international agreements like the Kigali Amendment and domestic legislation such as the U.S. American Innovation and Manufacturing (AIM) Act, presents both substantial challenges and unique opportunities for the Architecture, Engineering, and Construction (AEC) industry.

Heat Pumps, HVAC, High Performance Homes, Indoor Air Quality, Electrification, Building Enclosure, Architectural Design, CodePositive EnergyMay 22, 2025HVAC refrigerant transition, high-Global Warming Potential (GWP) refrigerants, Hydrofluorocarbons (HFCs), Kigali Amendment, U.S. American Innovation and Manufacturing (AIM) Act, supply chain disruptions, refrigerant costs, technical training, mildly flammable refrigerants, hydronic systems, air-to-water heat pumps, ground source heat pumps, water as heat transfer medium, building performance, global HVAC refrigerant landscape, Montreal Protocol, ozone-depleting substances (ODS), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), HFC phasedown, U.S. ratification of Kigali Amendment, HFC consumption reduction, global warming mitigation, low-GWP technologies, HFC Allocation Program, Allocation Framework Rule, GWP limit of 700, R-410A systems, refrigerant leak detection, refrigerant reuse, reclaimed and recycled HFCs, leak repair, recordkeeping, reporting, labeling, automatic leak detection (ALD) systems, reclaimed HFCs for servicing, cost of compliance, A2L-class refrigerants, R-454B, R-32, refrigerant flammability, safety protocols, certified HVAC technicians, ACCA A2L training, ASHRAE Standards, UL Safety Standards, refrigerant types comparison, R-22, R-290 (Propane), R-744 (CO2), R-717 (Ammonia), AEC industry challenges, project timelines, supply chain constraints, refrigerant shortages, material scarcity, A2L safety training, regulatory compliance and enforcement, EPA regulations, state-level regulations, equipment availability and compatibility, refrigerant recovery machines, hydronic system types, radiant systems, baseboard heating, chilled beam systems, snow melt systems, AWHPs principles, AWHPs benefits, GSHPs principles, GSHPs advantages, ground loop, ground temperature stability, GSHP design considerations, GSHP energy savings, Investment Tax Credit (ITC), Inflation Reduction Act (IRA), technology neutral homes, renewable electricity sources, building envelope performance, HVAC system sizing, thermal insulation, high-performance glazing, air leakage, whole building design, commissioning, thermal performance, airtightness, passive building principles, Phius (Passive House Institute US), continuous insulation, thermal bridging, condensation prevention, super-insulation, minimal space conditioning system, moisture management, dew point temperature, latent loads, dedicated outdoor air system (DOAS), dehumidification, smart controls, material selection for radiant cooling, wall design for hydronics, floor design for hydronics, ceiling design for hydronics, building physics, heat transfer processes, moisture dynamics, indoor air quality, economic benefits of hydronic systems, operational cost reductions, energy efficiency, high-efficiency circulator, VRF system comparison, DX unit comparison, water source heat pumps, lifespan of hydronic systems, maintenance costs, environmental impact of hydronics, decarbonization, solar thermal, geothermal energy, strategic design for sustainable HVAC.

Rethinking Moisture Control: The Primacy of Air Tightness Over an Outdated Fixation on Vapor Barriers in Building Envelope Design

For decades, the architecture and construction community has engaged in a persistent debate surrounding the role and necessity of vapor barriers in building envelope design. This discussion, while touching on critical aspects of moisture control, has often been characterized by an overemphasis on the ability of specific materials to resist vapor diffusion, sometimes to the detriment of addressing more significant moisture transport mechanisms. Within the building science community, however, the principles governing moisture movement are largely considered settled science. It is well-established that air leakage, rather than vapor diffusion, is the predominant pathway for moisture transport through most wall assemblies.

Building EnclosurePositive EnergyMay 22, 2025Vapor Barriers, Air Barriers, Building Envelope, Building Science, Moisture Management, Dehumidification, Durability, Resiliency, Air tightness, vapor barriers, moisture control, building envelope design, moisture transport mechanisms, air leakage, vapor diffusion, air barrier systems, historical context of vapor barriers, evolution of vapor barrier science, bulk water intrusion, capillary action, air-transported moisture, defining air barriers, defining vapor retarders, air permeance, water vapor permeance, dew point temperature, energy efficiency, indoor air quality, building durability, acoustic control, continuity of air barrier, dedicated dehumidification, climate-specific vapor control, reservoir claddings, solar-driven inward vapor drive, ventilated rainscreen, "smart" vapor retarders, moving forward with air tightness, recommendations for architecture and construction, building codes and standards, quality assurance/quality control

Breathing Easy: The Case for a National Indoor Air Quality Code in the United States

The United States faces a significant, yet largely unregulated, public health challenge: the quality of the air inside its buildings. Americans spend approximately 90% of their time indoors , breathing air that can be two to five times, and occasionally more than 100 times, more polluted than outdoor air. Despite this reality, the nation lacks a comprehensive federal code specifically governing indoor air quality (IAQ), relying instead on a fragmented system of state regulations, voluntary guidelines, and limited occupational standards. This regulatory gap results in inconsistent protection and contributes to a silent epidemic of health problems—ranging from asthma and allergies to cardiovascular disease, cognitive impairment, and cancer—and imposes a substantial economic burden through healthcare costs and lost productivity, estimated in the tens to hundreds of billions of dollars annually.

CodePositive EnergyMay 1, 2025Indoor Air Quality (IAQ), national IAQ code, public health, building codes, regulations, ventilation, filtration, source control, pollutants, health effects, respiratory illnesses, allergies, cardiovascular disease, cognitive impairment, economic burden, healthcare costs, lost productivity, EPA recommendations, ASHRAE standards, WHO guidelines, implementation challenges, legislative action, phased implementation, research, workforce development, public-private partnerships, Clean Air Act, National Ambient Air Quality Standards (NAAQS), Model Clean Indoor Air Quality Act (MCIAA), California Title 24, Occupational Safety and Health Administration (OSHA), General Duty Clause, Particulate Matter (PM), Volatile Organic Compounds (VOCs), carbon monoxide (CO), radon, nitrogen dioxide (NO2), ozone (O3), formaldehyde, mold, biological contaminants, asthma, COPD, sick building syndrome, structural codes, fire codes, electrical codes, plumbing codes, information asymmetry, market efficiency, negative externalities, energy efficiency, MERV 13 filters, monitoring protocols, maintenance, schools, healthcare facilities, workplaces, cost-benefit analysis, financial assistance, tax incentives, utility programs, stakeholder engagement, building industry, public health advocates, labor unions, environmental organizations, consumer advocacy groups, government agencies, international models, European Union, Canada, South Korea, Japan, Singapore, air changes per hour, carbon dioxide (CO2) sensors, commissioning, verification, education, public awareness campaigns.

The Damp Deception: How a Well-Intentioned Code Change is Fostering Mold in New Homes

The promise of a new home often includes visions of a healthier, more energy-efficient living space. However, a subtle yet significant regulatory shift in U.S. building codes, particularly affecting hot-humid climate zones, may be inadvertently undermining this very promise. Before 2021, residential ventilation requirements were often loosely enforced; homes were typically required to have a ventilator, but the actual volume of air exchanged was not mandated to be measured. This frequently led to systems being ineffectively installed or even "sabotaged" by HVAC contractors, rendering them inoperable or improperly configured from the outset. Consequently, many homes, even in that period, did not achieve consistent fresh air exchange. Compounding this, most residential HVAC systems lacked any form of supplemental or dedicated dehumidification, a feature that building science experts have increasingly recognized as crucial, especially for high-performance homes in moisture-laden environments.

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