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    10-Step Guide to Passive House Design

    Welcome to our guide on Passive House Design.

    These 10 steps help create energy-efficient homes through the design process.

     


    Orientation

    In Passive House Design, harnessing solar gain efficiently is paramount, and it all begins with orientation. Ideally, buildings should face North-South to optimise solar exposure. This principle not only influences the site layout and access arrangements but also guides the design of roads and infrastructure in larger projects.

    However, site constraints or contextual factors may pose challenges to achieving an ideal orientation. In such cases, an innovative design approach at the early stages can prove invaluable.

     


    Shape

    The proportions of a building play a significant role in its energy efficiency. Aim for an optimal ratio of building volume to surface area, as heat loss primarily occurs through the building’s exterior. Generally, larger buildings tend to have a better ratio.

    Commence with an efficient building form, considering the necessary space standards. A larger façade facing south can be advantageous, as it maximises solar gain and minimises heating requirements.

     


    Insulation

    At the outset of the design process, it’s essential to contemplate the necessary insulation levels for the walls, roof, and floor. A Passive House incorporates a thicker building envelope to minimise heat loss. Adopting this fabric-first approach yields long-term benefits, curbing energy consumption and reducing utility bills – all while contributing to environmental conservation.

    Planning the building with realistic thicknesses from the outset facilitates an efficient workflow through the RIBA Stages.

     


    Layout

    When devising the layout for your building, exploring various options is often the most effective approach. Aim for a larger open-plan living space to the south, capturing solar gain without the risk of overheating. It’s advisable to arrange spaces efficiently, clustering rooms with water supplies and extract requirements to minimise service runs.

    Optimising the use of the building’s insulated volume, including utilising roof space, is crucial. To mitigate heat loss in winter, consider incorporating a sheltered entrance, porch, or vestibule area, ensuring that external access does not open directly into a large living space.

     


    Services

    In a Passive House, the design of services takes on greater significance compared to a traditional dwelling due to its extreme air-tightness. A Mechanical Ventilation Heat Recovery (MVHR) system becomes essential, supplying the house with a continuous flow of warm, fresh air.

    Early planning of the ventilation strategy is crucial, encompassing considerations for air-flow paths and ducting routes. Each space should be categorised as supply, extract, or transfer. Optimally, reduce the amount of services by centralising the MVHR unit (whilst remaining in close proximity to the thermal envelope) and by planning compact routing of the ducts.

    Incorporating the MVHR system into the design early on is imperative, as it requires space on floor plans and within sections, usually within ceiling voids. Subsequent design considerations should include acoustics and sound absorbers, insulation to services, electrical efficiency, filters, and frost protection.

    Simultaneously, when designing services, it’s vital to contemplate the heating strategy for the building, encompassing the distribution and supply of space heating, hot water heating, and storage.

     


    Fenestration

    The design of fenestration plays a pivotal role in a building’s performance. Prioritise glazing on the south elevation while constraining it on the north, east, and west elevations.

    Solar gain for each window is calculated using the Passive House Planning Package (PHPP). This solar gain is then compared to the heat loss through each window, determining the energy balance throughout the year. Windows, besides providing natural light, should be designed with natural ventilation in mind.

    On warm summer days, cooling the building through natural ventilation is ideal. Achieve this by incorporating opening windows, ideally on different facades, leveraging the differential air pressure around the building. Thoughtful planning of natural ventilation paths and considering the use of stack ventilation significantly enhance operational efficiency and comfort levels.

    To optimise thermal efficiency, windows should be located within the insulation layer, with meticulous installation details. Recognising that windows often constitute the weakest points of the thermal envelope, careful attention is necessary to prevent heat loss, condensation, and mould growth.

     


    Solar Shading

    In conjunction with orientation and fenestration design, solar shading plays a crucial role in optimising the energy balance of a building. Large, high-performance windows on the south elevation effectively heat the property during winter. However, without solar shading, these same windows can contribute to overheating in the summer.

    Implementing solar shading over south-facing windows helps mitigate overheating during summer months when the sun is high, while still permitting the lower winter sun to penetrate the building.

    Managing shading is more straightforward on the south elevation due to the varying positions of the sun throughout the year. Contrastingly, controlling solar shading on east and west elevations is challenging due to the lower sun positions.

    A strategic approach includes the use of deciduous trees, which shed their leaves in autumn, providing effective seasonal shading.

     


    Triple-Glazing

    At the core of Passive House Design lies the essential feature of high-performance triple-glazed doors and windows. In a Passive House, meticulous attention is dedicated to the building fabric, encompassing a highly insulated building envelope and an air-tightness barrier. It is paramount that the specification and installation of triple-glazed components meet the highest standards, recognising them as the most vulnerable points in the façade.

    Tailoring the performance of triple-glazed components involves considering climate zone-appropriate U-values and G-values for the glass, spacer U-values, frame U-values, and install U-values. Fortunately, there is a comprehensive resource—the Passive House Component Database.

     


    Air-tightness

    Ensuring the air-tightness of a Passive House is paramount, necessitating achievement of less than or equal to 0.6 Air Changes per Hour—far surpassing typical Building Regulations. During construction, it is advisable to conduct three air pressure tests to verify the air-tightness of the building’s fabric before the final touches are applied.

    Integrating membranes into the walls is often mandatory, guaranteeing their seal at junctions and with fenestration. Meticulous detailing and the use of tapes and grommets at penetrations are essential to maintain a continuous, single-layer airtight envelope.

    Typically, the recommended placement for the air-tight layer is as a diffusion barrier on the warm side of the insulation.

     


    Cold Bridges

    A cold bridge represents a vulnerability in the building façade, where cold is transmitted through the building fabric—commonly observed around doors, windows, and fixings on the façade. The infiltration of cold into the internal environment not only diminishes thermal comfort but also fosters condensation, leading to mould growth and an unhealthy living space.

    Effectively mitigating cold bridges involves meticulously insulating and detailing building junctions, employing straightforward and approved methods. Crucial considerations encompass roof-to-wall details, wall-to-floor details, intersections, external attachments, MVHR and other service penetrations, as well as window and door installations.

    In a Passive House façade, insulation must maintain continuity, acting as the thermal jacket. The performance of a thermal façade can be evaluated using a thermal imaging camera.

     


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