VELIDHU

Area: 200m²

Procurement: Self designed and self-built

SAP: 104A Environmental Impact: 104A

CO₂ Emissions (t/year): – 0.67

Reduction: 110.2%

Air Pressure Test: 0.784 m³.h^-1.m^-2@50 Pa

LABC: Cornwall Council (ESconsult inc. Plan Check, Inspections, SAP Assessment, EPC and Air Pressure Test)

Velidhu is a self-designed, self-built family home in rural Cornwall, delivering exceptional thermal performance and carbon-negative credentials on a modest budget. Constructed for just £220,000, the 200m² dwelling achieves a SAP score of 104A and CO₂ emissions of –0.67 t/year, with an airtightness result of 0.784 m³/(h·m²) @ 50Pa. The design maximises passive solar gain through a dynamic sun space and twisted first floor, while a cantilevered master bedroom and sedum roof add architectural interest.

Built on a cast in-situ concrete raft using secondary aggregates, the superstructure features dual timber frames spaced 400mm apart to eliminate cold bridging and maximise sheep wool insulation. A breathable, triple-glazed envelope and MVHR system ensure year-round comfort with minimal heating demand. Rainwater harvesting, solar PV (pre-theft), and a fibre cement roof contribute to the home’s low-impact profile.

Ecological enhancements include bat-accessible cladding, swallow nesting zones, wildflower planting, and a biodiverse green roof. Future plans include a wildlife pond, owl box, and raised beds for food production. Velidhu exemplifies how hands-on self-build can deliver high-performance, low-carbon living with deep respect for nature and context.

The vision for Velidhu was to create a highly efficient, low-carbon family home in rural Cornwall that demonstrated what could be achieved on a modest budget through self-design and self-build. The brief focused on delivering exceptional thermal performance, affordability, and a strong ecological ethos while maintaining a contemporary, characterful design. The home needed to maximise passive solar gain, minimise energy use, and integrate seamlessly into its natural setting. Sustainability was a core priority, with the client aiming for carbon-negative performance, low running costs, and a lifestyle closely connected to nature through wildlife-friendly landscaping and renewable technologies.

The corner shaped plot made for an interesting design with the ground floor taking advantage of garden and a sun room orientated to take advantage of solar gains. The sun space can be opened to the lounge, kitchen/dining and playroom to provide free solar heating. The first floor has been twisted over the ground floor to enable the roof to face due south to maximise solar gains.  South windows and rooflights have been minimised to prevent solar overheating to the first floor.   Striking elements of the building include a dynamic cantilevered master bedroom to the first floor, which has no steelwork, an unheated ‘buffer’ solar sun space and a sedum roof to the lounge. The building is super insulated with sheep wool, the fabric is airtight, breathable and external joinery all triple glazed.  When there is no solar gain the house is primarily heated via an Air to Water Source Heat Pump (ASHP) via underfloor heating to the ground floor and secondary heating via a high efficiency wood burner, which has not been lit since moving in.  The first floor does not have any heating and relies upon recovered heat from a Mechanical Ventilation Heat Recovery System.  A 5000L rainwater harvesting system supplies water to WC’s, washing machine and outside taps.  The large mono pitched roof provides more than sufficient rainwater throughout the year, although the tank has a mains water back up the tank ran all summer long on rainwater.  The building is predominantly clad in locally grown western red cedar and locally sourced Trevillett stone.

The following provides a technical breakdown of the building services and performance of the buildings main components:

• MVHR system: A high efficiency (90%) Vent Axia Sentinel Kinetic Plus with Summer Bypass and Automatic Humidistat Boost Controller.  Mainly 180mmSpiral Wound Steel duct and PVC 150mm/125mm ducting, ProAir Oval ducting.  Lindab “Safe” Connection system and Zehnder Flat51 low profile ducting system.  Steel painted Adjustable Air Valves, Flexible sound attenuation.  Insulated Externals Ducting U vale of 0.038.  This system provides excellent indoor air quality (moisture, particulates, pollutants are filtered) and the rigid ducting is efficient and reduces noise levels.
• ASHP: Mitsubishi Ecodan 8.5kW – COP 3.17 (however due to efficiency of building it is running at just under COP 4)
• Cylinder: 300L pre plumbed Mitsubishi HU150-300FTC4ST with integrated hydraulic components and advanced self-learning controls, 2 zone controls.  Mitsubishi Electric’s fourth-generation controller includes intelligent, self-learning room temperature control as standard. This together with advanced weather compensation ensures the system delivers efficient, comfortable heating regardless of the season
• UFH: GF only (wet system at 150mm centres) The Wundafloor green system supply’s one digital programmable thermostat for each room meaning you only spend money on heating the areas you live in the most. Also with built in setback mode, your floors will never fall below a set temperature, preventing long and costly heat up times
• Towel rails: 2 no. electric towel rails to first floor bathrooms with built in programmable thermostats (not used for heating and not required for drying to MVHR maintaining a consistent 40-50% relative humidity in the house, installed as back-up).
• Wood Burner: Westfire Uniq 23 inset, 6.1kW output with dedicated air supply and Isokern insulated flue with Leca infill. Air pressure test revealed this installation is extremely airtight.  Unfortunately it is unlikely to ever be lit and has not yet been lit due to the excellent year round performance of the building
• PV 6kW: 24 x Shine Time 250w Mono blacks modules with Fronius IG TL 3.6 inverter
• Lighting: 100% dedicated low energy throughout inside and outside.  The GF total is 310W, 1^st floor 154W and outside is 51W (most of which are PIR), which totals 515W for the whole house.  Given that many of these lights are feature lights it will be extremely rare for these to all be on at once.  The whole house will therefore run on the equivalent to 5 x 100W light bulbs if everything is on at the same time, which is unlikely
• Rainwater harvesting tank: 5000L tank for flushing WC’s and washing machine
• Cooking/White Goods: AEG Induction Hob and AEG electric double oven (both A rated), AEG Fridge/Freezer (A+ rated), Bosch Dishwasher (A++ rated), Washing machine (A+ rated)
• Air Pressure test result:784 m³.h^-1.m^-2@50 Pa, which is the lowest the Cornwall Council Building Control Test Engineer (Adam George) has ever tested. During the test there were a couple areas of air leakage where the folding sliding door met the corner post in the lounge and a services duct in the kitchen.  These were sealed but never re-tested.  3 months later Ian discovered another 6” services duct under the utility cabinets which had not been sealed.  He is confident that with this sealed it would be less than 0.6 and fully passive house compliant.
• Treatment Plant. High performance Klargester BA package treatment plant provides environmentally safe treated effluent with low running costs (10-14p per day).

The basic principles employed during the design, specification and construction is to ensure that the building has low embodied CO₂ content.   Materials were selected that have not required a large amount of energy in their sourcing, processing or transportation.  The solutions include:                                                                                       

1. Reclaimed sheep wool: a by-product of wool based industries in our region. The material is waste and previously discarded. It is untreated and has no embodied energy in terms of processing and only limited transportation requirements all being sourced from within the region. The material also has benefits in terms of its hygroscopic properties enabling it to act in harmony with changes in atmosphere, humidity and the seasons in general. With regard to handling, the material is safe with no off-gassing present in proprietary insulation materials. Additionally there are no damaging fibres and therefore no irritation is experienced by site personnel.
2. I-Joists: Engineered timber joists made from small sections of timber and timber by products (see below). They offer many design and performance advantages over conventional structural products including a composition which resists shrinking and warping, an excellent strength to weight ratio straight and uniform dimensions. The joists also have FSC & PEFC Accreditation & Labelling, Life Cycle Assessment and ISO14001:2004 Environment Management System.
3. Timber: recognised as one of the most sustainable building materials, all timber has been specified carefully ensuring that the chain of custody is clear.  This protects against irresponsible sourcing and irreversible damage to delicate ecosystems. Where possible, we advocate the use of European timber (FSC & PEFC) together with locally sourced green timber such as western red cedar which was used for cladding, fascias, barges and soffits.
4. Timber by-products: such as the bitumen impregnated fibreboard to the roof (Bitroc), orientated strand board (OSB), and hardboard (air tightness layer) have also been incorporated in order to utilise further waste products.  Additionally, these products have lower chemical content in terms of adhesives and binders than composite materials such as chipboard and medium density fibreboard, both of which have reported harmful binders which can cause a health hazard when working with the materials.
5. External Joinery: High specification triple glazed windows were specified to help reduce heat loss.  Windows in locations that are harder to maintain were aluminium clad to reduce maintenance.
6. Wood treatments: have been selected which limits the amount of chemicals utilised within the building.  OSMO polyx hardwax-oil rapid for clear internal applications was selected because it incorporates natural wood wax oils which are solvent free. Impra Profilan Opac was used on all timber painted black and is a satin finish waterborne paint which does not contain biocidal components. Awarded the Blue Angel seal award for its environmental friendly aspects
7. Wall membranes: have been eliminated from construction. This serves to provide a breathing shell (vapour permeable) which is not susceptible to condensation build up and significantly reduces the risk of associated respiratory illness.  As it breathes the structural frame is less prone to decay and offers greater longevity
8. Floor membrane: Visqueen Eco Membrane: Manufactured from 100% post-use polyethylene, diverting more waste from landfill.
9. Green roof: consist of varieties of succulent called “sedum”.  These are extremely tolerant of dry conditions, have limited growth but also replenish themselves readily year-on-year.  This provides minimum maintenance and promotes a range of wildlife as well as looking spectacular year-round but especially in late spring during the main flowering season. This roof also assists the drainage of the building by slowing down/holding up the run off of water from the roof prior to entering a drainage system.
10. Green roof membrane: EPDM Membrane is the most environmentally friendly roof membrane compared to all other roofing systems and is re-usable.  The membrane is root resistant and exceeds the expected lifespan of the vegetation layer.
11. Rainwater goods: Lindab Rainline polyester coated steel rainwater goods were selected because of quality, durability, minimal maintenance, recyclability and it has the lowest CO₂ footprint of any other system.
12. Natural Stone: Quarried locally supporting local economy and minimising transportation/CO₂.
13. Bitroc: naturally emulsified bitumen impregnated fibreboard made from Scandinavian recycled chipped softwood together with waste newsprint to provide a breathable sheathing board to the external walls and roof.
14. OSB: Oriented Strand Board made from thinnings from managed plantations (FSC); the process utilises 95% of the wood, discarded bark being used for fuel in horticulture.  Used for internal racking walls and first floor sub-deck.
15. Glulam Beams: Small sections of timber from sustainable sources glue laminated to provide a larger structural grade timber.  Used for cantilever, around glass floor and over larger openings as lintels.
16. Celotex FF4000 (over slab insulation):  A+ BRE Green Guide, CFC/HCFC free with zero ODP and low GWP. CE marking compliance to BS EN 13165:2001and manufactured in accordance with quality management systems with BS EN ISO 9001:2000 and Environmental ISO 14001.  The lightweight nature of the insulation means that less fuel is used when transporting from factory to building site.  Celotex claim that 100 times more energy is saved than that used for manufacture.
17. Earthwool: insulation to acoustic walls and floors (where breathability is not required).  A+ Generic BRE Green Guide rating.  Made using recycled materials.  Made from rapidly renewable organic materials. No added formaldehyde binder.  No added dyes.  Up to 70% less embodied energy and recyclable.

The building has been designed to accommodate birds and bats.  The birds nest in the mono-pitched roofs and are regularly seen flying in and out of both ends.  The hand split shakes provides a good habitat for flies which many birds feed on.  The waney edge timber cladding has been designed to allow bats to access between laps.  Large protected soffit areas have been designed with rough sawn penny gapped soffit boards to allow swallows to nest.  The biodiverse green roof provides flora and fauna as well as habitats for insects, butterflies and bees.  A new Cornish hedge provides habitat for reptiles, small mammals and invertebrates.  The boundary hedges have been planted with 200 copper beach trees and numerous willow coppiced from the site, hazel and oak.  Fruit trees have been planted in front of the hedges and have already provided crops.  Wildflower seeds which are bee friendly have been planted around the treatment plant area and a bee hive is proposed in this are in due course.  An owl box is yet to be built but will be located on the store outbuilding gable and a wildlife pond is the next project.  Raised beds for growing food will also form part of the landscaping scheme.  The sun space also provides large planters with a timed irrigation system to grow food.

The following provides a technical breakdown of the building services and performance of the buildings main components:

• MVHR system: A high efficiency (90%) Vent Axia Sentinel Kinetic Plus with Summer Bypass and Automatic Humidistat Boost Controller.  Mainly 180mmSpiral Wound Steel duct and PVC 150mm/125mm ducting, ProAir Oval ducting.  Lindab “Safe” Connection system and Zehnder Flat51 low profile ducting system.  Steel painted Adjustable Air Valves, Flexible sound attenuation.  Insulated Externals Ducting U vale of 0.038.  This system provides excellent indoor air quality (moisture, particulates, pollutants are filtered) and the rigid ducting is efficient and reduces noise levels.
• ASHP: Mitsubishi Ecodan 8.5kW – COP 3.17 (however due to efficiency of building it is running at just under COP 4)
• Cylinder: 300L pre plumbed Mitsubishi HU150-300FTC4ST with integrated hydraulic components and advanced self-learning controls, 2 zone controls.  Mitsubishi Electric’s fourth-generation controller includes intelligent, self-learning room temperature control as standard. This together with advanced weather compensation ensures the system delivers efficient, comfortable heating regardless of the season
• UFH: GF only (wet system at 150mm centres) The Wundafloor green system supply’s one digital programmable thermostat for each room meaning you only spend money on heating the areas you live in the most. Also with built in setback mode, your floors will never fall below a set temperature, preventing long and costly heat up times
• Towel rails: 2 no. electric towel rails to first floor bathrooms with built in programmable thermostats (not used for heating and not required for drying to MVHR maintaining a consistent 40-50% relative humidity in the house, installed as back-up).
• Wood Burner: Westfire Uniq 23 inset, 6.1kW output with dedicated air supply and Isokern insulated flue with Leca infill. Air pressure test revealed this installation is extremely airtight.  Unfortunately it is unlikely to ever be lit and has not yet been lit due to the excellent year round performance of the building
• PV 6kW: 24 x Shine Time 250w Mono blacks modules with Fronius IG TL 3.6 inverter
• Lighting: 100% dedicated low energy throughout inside and outside.  The GF total is 310W, 1^st floor 154W and outside is 51W (most of which are PIR), which totals 515W for the whole house.  Given that many of these lights are feature lights it will be extremely rare for these to all be on at once.  The whole house will therefore run on the equivalent to 5 x 100W light bulbs if everything is on at the same time, which is unlikely
• Rainwater harvesting tank: 5000L tank for flushing WC’s and washing machine
• Cooking/White Goods: AEG Induction Hob and AEG electric double oven (both A rated), AEG Fridge/Freezer (A+ rated), Bosch Dishwasher (A++ rated), Washing machine (A+ rated)
• Air Pressure test result:784 m³.h^-1.m^-2@50 Pa, which is the lowest the Cornwall Council Building Control Test Engineer (Adam George) has ever tested. During the test there were a couple areas of air leakage where the folding sliding door met the corner post in the lounge and a services duct in the kitchen.  These were sealed but never re-tested.  3 months later Ian discovered another 6” services duct under the utility cabinets which had not been sealed.  He is confident that with this sealed it would be less than 0.6 and fully passive house compliant.
• Treatment Plant. High performance Klargester BA package treatment plant provides environmentally safe treated effluent with low running costs (10-14p per day).

U-Value Summary – Constructed

Walls                                0.10

Mono Pitched Roofs       0.12

Sedum Roof                     0.13

Ground Floor                   0.09

Roof windows                 1.0

Windows (Tilt & Turn)    0.9 average (some are 0.75)

Doors:

Folding Sliding   0.82

Glazed External 0.85 average

In order to provide carbon negative power during the construction phase 6kW of Solar PV panels were installed once the roof was complete.  Unfortunately they were stolen from the roof a couple of months later, together with power tools and majority of hand tools causing a physical and emotional set back forcing Ian and his family to sell their home and live in a caravan on site for the remaining year of the build.  The caravan was single glazed and un-insulated, but did have some heating!  Ian’s wife saw this as an adventure, but not quite like staying in a static caravan while holidaying in the south of France with 2 young children!