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Fawley Passive House: Passive House Certification Received!

It's official. Fawley Passive House has received the Passive House Classic certificate! This is the first project I have designed that has achieved this gold standard. The process has honed my skillset and stoked my passion for energy efficiency; demanding an in-depth assessment of the design to an incredible level of detail from start to finish.

A quick re-cap on the project:

Conceptually, the house is inspired by a nut, with a warm and soft inner environment protected by a tough outer shell. The nut opens over the entrance to reveal the warm inner within.

The house is south-east facing and takes advantage of an existing hazel tree which is located directly in front of the largest area of glazing to act as shading in the summer months, whilst allowing the sun through in the cooler months. Further shading is provided on the south-west and south-east elevations in the form of an overhanging roof that also shelters the main entrance, and frames a view towards the orchard.

The form is modest and simple with a rectangular plan and steeply pitched roof containing the first floor rooms. The roof alters in height on the west side to facilitate the overhang and achieve more space upstairs. A double height atrium creates a more open feel, reveals the structure, and brings light deeper into the plan.

The house employs a variety of natural materials including 80mm thick external wood fibre insulation and clay plaster applied directly onto additional wood fibre insulation internally. The structure is comprised of timber I-joists that are filled with blown cellulose (Warmcel). This breathable construction system was chosen because of the simplicity of the detailing at key junctions such as the eaves because the same layers are applied to the wall and roof enabling neat and consistent thermal bridge free detailing. Pro-passive OSB racking board and Tescon Vana tape are employed internally to achieve brilliant airtightness and vapour control. To protect the building from the elements, profiled steel roofing sheets and thermowood cladding are installed over a ventilation void that also conceals the rainwater pipes.

Passive House Certification

The route to achieving Passive House certification typically involves employing a certified Passive House designer to undertake the required PHPP calculations and advise on the design and construction of the house. There are two routes to becoming a certified Passive House designer: either undergoing training and passing an exam; or being the lead consultant on a certified Passive House building and writing a short report. This project provided me with the opportunity to become a Passive House Designer without going through the expensive training and exam route. With my background in environmental engineering, I was confident that I could undertake the calculations myself and offered the clients a low-cost fee in return for them giving me the opportunity to lead the project through the Passive House certification process.

And it all went perfectly. We received the certificate not long after the house was complete in early 2023. The house is now listed on the Passive House Database. Here are some facts and figures:

  • Treated Floor Area (usable floor space of the dwelling): 92m2

  • Annual heating demand: 17kWh/(m²a)

  • Heating Load: 10W/m²

  • Frequency of overheating: 0% - external blinds, overhangs, and trees help here.

  • Air pressure test: 0.1(n50) [1/h] (an incredibly good result!)

  • Renewable Primary Energy (a measure of all the energy demanded by the house and occupants over the course of a year per m2 floor area): 45 kWh/(m²a) - well within the target of 60 kWh/(m²a)

  • Renewable Energy Generation (how much energy is generated via solar panels in this case: 40 [kWh/(m²a)]

  • The energy balance works out that the house demands only 5kWh/m² of energy from the grid in a typical year, which equates to 460kWh. That's about 10% of the energy required to run an average detached home in the UK.

In addition to incredible airtightness and insulation, the house is equipped with the following technologies:

The brilliant clients have also signed up RIBA 2030 Climate Challenge, and have begun monitoring the energy consumption from January. We require 12 months of data to submit to the challenge, and I shall be undertaking embodied energy calculations using the PH Ribbon plug-in for the Passive House Planning Package.

As soon as you walk into a Passive house you can notice the cosiness

If you are looking to build a house, there are so many good reasons to make it a Passive House and GreenTrace Architect would love to help you get there!

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