New Forest, Low Energy House
Richard Chivers

Creating A House Nestled In The Forest Landscape

PAD studio as Architects

PAD studio complete decade-long study of first low-energy new build house

PAD studio has revisited their first private residential commission after a decade-long study to determine the long-term environmental impacts of low-energy design. The five bedroom family home is located in the sensitive New Forest National Park in southern England, in a highly protected Site of Specific Scientific Interest.

PAD studio was originally commissioned by clients Jenny and Julian Gray to build a new environmentally conscious home on a large 18 acre plot, set against the fringes of an ancient woodland. Designed to nestle into the landscape, the timber clad home features a simple rectangular form overlooking a natural swimming pond, flanked by a self-contained guest annex. Both the annex and main house feature large south-facing glazed elevations tempered with timber louvre shutters to maximise solar gain, and green roofing. 

photo_credit Richard Chivers
Richard Chivers

Driven by their clients desire to live harmoniously and care for the delicate surrounding ecosystem, PAD studio’s design approach includes sustainable systems including high levels of insulation, a ground source heat pump (GSHP) supported by mechanical ventilation heat recovery (MVHR), solar photovoltaic panels (PV), evacuated solar thermal panels (for water heating) and a rainwater harvesting system. The building is sealed for airtightness and benefits from a long concrete retaining wall, a slender spine which supports the buildings’ thermal mass strategy and hugs it into the rear earth berm (which contains the earth removed to form the swimming pond and basement).

Thanks to the clients’ diligence and care for the home and its surrounding environment, PAD studio has been able to monitor its energy and environmental performance since completion in 2009. PAD studio recently analysed data captured by Purmetrix in 2021-22, finding the New Forest House is 97% cheaper to run than a new home built to 2021 building standards. 

photo_credit Richard Chivers
Richard Chivers

Utilising a combination of an GSHP, PV array and solar thermal to provide energy for the space heating, water heating, fans, pumps and lighting, the regulated operational energy of The New Forest House performs as a net zero home with CO2 emissions ranging from -2.46 to -0.76 (Kg CO2/m2/year). Further, the embodied carbon value (including sequestration) of New Forest House is 43% less than the current RIBA 2030 Climate Challenge and 2021 Building Regulations. By using solar and ASHP technology, the home has used 110% less energy compared to if it was powered by gas.

Jenny and Julian lead a creative lifestyle and have an electric kiln in their pottery studio, electric tools in the wood workshop, an infrared sauna and EV car charger. Without these very specific additional activities,  which most homes do not have, the total operation energy would better the 2030 Challenge by 95% and Building Regulations by 97%, making the building and home owners lifestyle almost carbon neutral. Even with the pottery studio, workshop and sauna, New Forest House is still 42% cheaper to run (or more efficient) than a house built to the 2021 Building regulations.

photo_credit Richard Chivers
Richard Chivers

While the house features energy efficient systems, maintenance is ongoing and will be benefiting from battery energy storage in 2023, which the owners are currently waitlisted for. 

Ecological and wildlife enhancement was a key part of the client brief during the project’s development. As custodians of the protected site, the clients requested a home that reflected their ambition for living with the landscape. As the living roof was pioneering at the time, PAD studio sought out the advice of Dusty Gedge, a specialist in green roofs, and the native seed mix was grown specifically for the project and provides a new ecological habitat. The swimming pond is now a haven for insects, newts, and birdlife, including the protected Kingfisher species, which all enjoy the native planting set around the water’s edge. The clients have also rewilded vast sections of the site to improve native planting, which support local wildlife including New Forest donkeys and ponies which roam the plains. 

photo_credit Richard Chivers
Richard Chivers

Ecology & Wildlife Enhancement:

Ecological and wildlife enhancement was a key part of the client brief during the project’s development. As custodians of the landscape the clients requested a home that reflected their ambition for living with the landscape. Some key features that contribute to ecological and landscape enhancement are the earth berm, swimming pond and green roofs. Combined with considered land management a home with a deep connection to the environment has been created.

photo_credit Richard Chivers
Richard Chivers

The Swimming Pond:

The swimming pond is planted with local and indigenous species to its edges. The pond is inhabited by several different species of dragonflies and damselflies, newts (palmate mainly)1, toads plus pond skaters, water boatmen and ramshorn snails. During the summer, the birds use it as a source of water and bathing. Occasionally grass snakes swim across the surface. There is a kingfisher that visits and evidently picks out newts. Kingfishers are vulnerable to hard winters and habitat degradation through pollution or unsympathetic management of watercourses. Kingfishers are amber listed because of their unfavourable conservation status in Europe. They are also listed as a Schedule 1 species under the Wildlife and Countryside Act offering them additional protection.2 Last summer there were nightjars flying above the pond at dusk to catch insects. They are nesting either on the site or very nearby. Bats are frequently seen bats on warm evenings doing the same thing. 1

photo_credit Richard Chivers
Richard Chivers

Green Roofs:

In this particularly rural and diverse location green roofs may not be considered to increase biodiversity but they have replaced the habitat which would have otherwise been lost by the footprint of a building with a tiled roof. The house features an extensive green roof planted with sedums which are drought tolerant, only watered twice in the 13 years since installation. On the annex an intensive green roof provides a deeper substrate which is planted as a kitchen herb garden with boarders of grasses and sempervivums. The sedum, grasses and other plants provide food sources for birds, insects, and the residents. The substrate acts like a sponge slowing water run-off, provides additional insulation from heat loss and solar heat gain and protects the roofing membranes from UV degradation.

photo_credit Richard Chivers
Richard Chivers

The Meadow:

The meadow flowers around the house are left to grow and seed which attracts many butterflies and moths. At least 2 wild bee nests have been discovered near the house and there is also a beehive. The meadow flowers are also a great source of nectar for the bees.

photo_credit Richard Chivers
Richard Chivers

Heathland:

The once shoulder height bracken has almost been eliminated from the heath enabling the heather and bilberry to thrive once again providing another source of nectar. Voles, shrews, and mice are frequently seen, a favourite amongst the local birds of prey. There are common lizards, slow worms, and grass snakes too - and the occasional adder.

photo_credit Richard Chivers
Richard Chivers

Earth Berm:

The berm provides a rich, protected grassland edge immediate to the house. Voles have established nests in the berm, mainly on the north side of the house. In addition is conceals the house, lessening its impact on the landscape, insulating its northern elevation, and acting as an acoustic barrier to the nearby motorway.

photo_credit Nigel Rigden
Nigel Rigden

Lowland Peat Bog:

The lowland peat bog is kept clear of scrub and there are now well-established areas of sundew (insectivorous plants), bog asphodel, cotton grass as well as sphagnum - it's a valuable carbon sink as a lowland peat bog. The two New Forest ponies we have on site take out the coarse grass which allows other flowering plants to take hold.

photo_credit Nigel Rigden
Nigel Rigden

Woodland:

In the woodland, ancient rides have been opened by taking out principally young birch trees from the edges so the sunlight can get down to the woodland floor. The woodland rides create places for rich, diverse plant life such as violets, bluebells, and wood sorrel attracting butterflies, moths, and other insects. Dense holly scrub is selectively cut back for the same reason consequently revealing many different types of fungi that has been hidden for many years waiting for its time.

photo_credit Nigel Rigden
Nigel Rigden

Regulated & Unregulated Energy:

There are two categories of for measuring operational energy use. Regulated Operation Energy covers space heating, water heating, fans, pumps and lighting, the core elements for the building to function. Unregulated Operation Energy which is personal electricity use by the home owner which includes home appliances, EV car charging, gyms, saunas, pools, workshop tools, all the elements that the home owner might use at the property depending on their lifestyle. The RIBA 2030 Climate Challenge is a framework launched in 2019 provides several targets for buildings including operational energy, water, carbon and wellbeing. PAD studio has committed to designing all buildings to meet or exceed these targets since 2020. The RIBA considers both categories of regulated and unregulated operation energy in its final assessment meaning that the home owners lifestyle also impacts the buildings total operational energy.

photo_credit Nigel Rigden
Nigel Rigden

Regulated Operation Energy:

In a straight comparison the electrical energy costs (without any offset of PV array) of the air source heat pump (ASHP) which provides space heating and hot water to The New Forest House is 57% cheaper to run with its ASHP than the same home installed with a gas combi boiler (at 90% efficiency) using 2023 Energy Price Guarantee (EPG) rates set by the UK government and Ofgem’s assessments. The 2023 GB average rates are 36p/kWh for electric and 11p/kWh for Gas. The yearly costing equating to £1,315 for the ASHP and £2,063 for mains Gas. This has been calculated with energy data collected from the house. The New Forest House benefits from a large Solar Panel, Photovoltaic (PV) array of 20 panels generating an average of 9,500 k/Wh/yr measured on site through data collection. The equivalent of £3,420 of mains supplied electricity at the EPG rates.

The 9,500 k/Wh/yr of energy produced by the PV array covers the total regulated energy demand of the house which includes space heating, water heating, fans, pumps and lighting. All essential demands for the building to function. With the PV panels the ASHP has no annual energy cost. The surplus energy (equivalent to £2,105 of national grid electric) produced by the PV array is used for additional demands of the occupants life style, the unregulated operational energy. Utilising a combination of an ASHP and PV array to provide energy for the space heating, water heating, fans, pumps and lighting the regulated operational energy of The New Forest House performs as a Net Zero home with CO2 emissions ranging from -2.46 to -0.76 (Kg CO2/m2/year). This figure reduces as the national electrical grid has been de-carbonised. Since the house was constructed in 2010 the national electrical grid has been decarbonised through the introduction of sustainable energy sources. The carbon impact factor of the national grid by approx. 68% from 0.43 to 0.136 unlike gas which has remained the same at 0.21. When the ASHP was installed in the New Forest House in 2009 and without the any installation of an onsite PV array the ASHP would have had a 51% bigger carbon impact than the use of a gas combi-boiler. The clients decision was on the investment in future technologies and on the basis that the electrical grid would become less carbon intensive in the future which it has. With the de-carbonisation of the electrical grid over the last 13 years the carbon impact of the heat pump has been reduced by about 65% (based on a comparison between 2012 SAP and SAP 10.2 methodology).

photo_credit Nigel Rigden
Nigel Rigden

Gas Alternative:

If the clients had chosen gas as the main source of energy for space heating, water heating, fans, pumps and lighting the house would have a CO2 emissions of 6.62 (Kg CO2/m2/year). That’s 7.38 to 9.08 (Kg CO2/m2/year) more CO2 than using the ASHP & PV array combination.

Using gas could free up the electrical energy produced by the PV array and used towards the less predictable unregulated energy demand of an occupants lifestyle the home owner would be subject to global supply and cost fluctuations. On gas the home would have produced in excess of 110% more CO2 over the last 13 years than the current ASHP & PV array.

photo_credit Nigel Rigden
Nigel Rigden

Unregulated Operation Energy:

Unregulated operational energy is subject to the demands of our lifestyle and life’s associated modern technologies. The operation energy target (<35 kWh/m2/year) in the RIBA 2030 Climate Challenge includes both regulated and unregulated energy. The New Forest House has an actual assessment total for operational energy demand of 24 kWh/m2/year. This 13 year old house betters the RIBA 2030 Climate Challenge operational energy target by 9% based on the current lifestyle demands of the home owner and 2021 Building regulations by 42%. The current home owners have particular lifestyle choices that would specifically impact the unregulated operation energy demand such as an electric kiln in the pottery studio, electric tools in the wood workshop, infrared sauna and EV car. Without the very specific additional activities (pottery studio, wood workshop, infrared sauna, and EV car) which most home do not have the total operation energy would better the 2030 Challenge by 95% and Building Regulations by 97%. Making the building and home owners lifestyle almost carbon neutral. Even with the additional pottery studio, workshop and sauna New Forest House is 42% cheaper to run (or more efficient) than a house built to the 2021 Building regulations. If we exclude the additional items which most homes do not have then The New Forest House is 97% cheaper (or more efficient) than a house built to the 2021 Building regulations.

photo_credit Nigel Rigden
Nigel Rigden

Embodied Carbon:

The embodied carbon value (including sequestration) of The New Forest House (359 KgCO2e/m2) is 43% less than the current RIBA 2030 Climate Challenge and 2021 Building Regulations (625 KgCO2e/m2) targets. The Sequestered Carbon of The New Forest House is -55 KgCO2e/m2. The embodied carbon is especially low for a house built 13 years ago with a frame, basement and retaining walls built in concrete. However, it should be considered that the RIBA Climate Challenge revised their embodied carbon target figures in 2021 from 300 KgCO2e/m2 up to 625 KgCO2e/m2. Meaning The New Forest House would have exceeded the 2030 target by 20%. As a further comparison a greater perspective our recently completed project The Clay Retreat has an embodied carbon figure of 159 KgCO2e/m2.

photo_credit Nigel Rigden
Nigel Rigden

Water:

Water to the house is supplied on-site by an existing well that was reconditioned. The well is fitted with a UV filter. The well was used to slowly fill the natural swimming pond once the building was completed.

photo_credit Nigel Rigden
Nigel Rigden

Team:

Client: Jenny & Julian Gray
Architecture & Landscape: PAD studio
Environmental services: EDP Ltd
Structural engineer: AWA Engineering   
Data capture: Purrmetrix 
Data analysis: MESH Energy  
Photographer: © Richard Chivers 

photo_credit Nigel Rigden
Nigel Rigden
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