Renewables for New Build Homes in Cornwall

The Cornwall Climate Emergency DPD, adopted February 2023, sits alongside the Cornwall Local Plan (Strategic Policies 2010-2030, adopted 2016) as the development management framework for the unitary authority. The two principal policies affecting new build renewables:

Policy CE1 (Net Zero Carbon Development): All new dwellings must achieve net zero operational carbon over a year, demonstrated through an Energy Statement at planning application stage. The Energy Statement must include: SAP 10.2 calculations for predicted regulated energy use, predicted unregulated energy use (appliances, cooking), proposed renewable generation capacity, and net carbon balance accounting. Where on-site renewable generation cannot fully offset operational carbon, off-site carbon offset contribution is required at the prevailing 'shadow carbon price' (currently £241/tCO₂e, indexed annually).

Policy CE2 (Sustainable Buildings): No fossil fuel primary heating systems in new dwellings — gas, oil, LPG, coal, anthracite all prohibited as primary heating sources. Secondary heating (wood stoves, biomass, point-of-use electric) is permitted but cannot be relied upon for SAP rating. Heating must be either: (a) electric heat pump (ASHP, GSHP, water source or exhaust air), (b) heat network connection where available, (c) direct electric (only acceptable for very low energy demand dwellings — Passivhaus or AECB Building Standard equivalent).

Compliance is demonstrated at planning, Building Regulations and post-construction stages. Cornwall Council's Climate Change team review Energy Statements at planning, with Building Control inspecting installation compliance.

The Future Homes Standard (FHS) is the next iteration of Building Regulations Part L (conservation of fuel and power) and Part F (ventilation) for new dwellings, consulted in 2019 with interim 2021 changes (the 31% CO₂ reduction step) and final standards due H2 2025 with implementation in mid-2026. The expected final FHS requires:

• 75-80% lower regulated CO₂ emissions vs 2013 Part L — typically requiring heat pump heating, high fabric efficiency, and 3-5kWp solar PV on a typical 3-bed house
• No new gas connections in new dwellings — gas heating ban nationally (Cornwall already there since Feb 2023)
• Heat pump or heat network as default — direct electric only acceptable in very small dwellings (under 50m² typically) or where heat demand is below 15 kWh/m²/year (Passivhaus territory)
• Higher fabric standards — walls 0.18 W/m²K (current 0.26), roof 0.11 W/m²K (current 0.16), windows 1.2 W/m²K (current 1.4)
• Improved airtightness — target permeability 5 m³/h/m² (current 8 m³/h/m²), typically requiring MVHR
• Compulsory solar PV on most new dwellings (final consultation language remains open)

For Cornish self-builders and developers, FHS will not introduce significant new requirements beyond the existing DPD — Cornwall is already ahead. The principal new element is the explicit solar PV requirement and tighter airtightness.

The cardinal mistake on new-build renewables is bolt-on retrofit thinking — designing the building first, then 'fitting the heat pump'. Properly integrated design starts with the renewables and works outward. Our pre-construction service:

• RIBA Stage 2 (Concept Design): Review architectural concept, advise on heating strategy, heat pump siting, MVHR plant location, solar roof orientation/pitch optimisation, cylinder room location, electrical riser positions
• RIBA Stage 3 (Spatial Coordination): Full mechanical schematic, MVHR ducting routes, pipe routes, electrical loads, structural penetrations identified for structural engineer
• RIBA Stage 4 (Technical Design): Final equipment specifications, SAP 10.2 modelling, Energy Statement preparation for planning
• RIBA Stage 5 (Construction): First-fix and second-fix installations, coordination with general contractor, commissioning
• RIBA Stage 6 (Handover): MCS certification, BUS grant administration (where applicable to self-builds), Building Control sign-off, owner training
• RIBA Stage 7 (Use): Year 1 review and optimisation

This integrated design approach typically reduces total install cost by 15-25% vs retrofit-thinking specification, while delivering 8-15% better SAP performance.

A FHS-compliant new-build 3-bed Cornish house (typical floor area 95-120m²) has a design heat loss of 2.8-4.2kW at the Cornwall design temperature. A 4-bed family home (140-180m²) typically 4.0-5.8kW. A 5-bed executive home (200-260m²) typically 5.5-7.8kW. These are dramatically lower than retrofit-of-existing-property figures (where 11-14kW is normal for a 3-bed). The implication: smaller, more efficient heat pumps that operate at lower flow temperatures (typically 35-40°C in normal weather) with higher SCOPs (4.2-4.8 routine).

Typical specifications:

• 3-bed FHS new build (115m²): 5kW Mitsubishi Ecodan PUZ-WM50VAA, 30°C design flow, SCOP 4.5, ~£3,500 product cost
• 4-bed family home (165m²): 7kW Vaillant aroTHERM Plus 75/6 R290 or 8.5kW Mitsubishi Ecodan, ~£4,800 product cost
• 5-bed executive (220m²): 9kW Vaillant aroTHERM Plus or 11.2kW Mitsubishi Ecodan, ~£6,200 product cost
• Ground source alternative (where land available): 6-8kW NIBE F1255 or Vaillant flexoTHERM with horizontal collector loop, 80-120m bore-hole — adds £6,500-£14,500 vs ASHP but delivers SCOP 4.8-5.3 and quieter operation

For developments at St Austell area (Higher Trewhiddle, Retallick Meadows, West Carclaze) and Newquay (Edgcumbe Green, Treloggan), we work directly with the developer's M&E consultant or as the lead M&E for self-build plots.

FHS-compliant airtightness (5 m³/h/m² target permeability) is too tight for natural ventilation alone — the dwelling cannot meet Part F minimum ventilation rates without mechanical assistance. Mechanical Ventilation with Heat Recovery (MVHR) is the default solution for new builds: a continuous-running fan system that extracts air from wet rooms (kitchen, bathroom, utility) and supplies fresh air to habitable rooms (living, bedrooms), recovering 85-92% of heat from extract air via a counter-flow heat exchanger.

Typical product specifications:

• Zehnder ComfoAir Q350 — 350 m³/h, 91% heat recovery, sensorless control. Premium spec, £3,800 product cost.
• Vent-Axia Sentinel Kinetic Plus — 320 m³/h, 89% recovery. Mid-market, £2,400 product cost.
• Nuaire MRXBOX95-WH1 — entry-level whole-house MVHR, £1,650 product cost.

Ducting (typically 75mm semi-rigid in service voids, 125-200mm rigid trunks in plant room) must be designed in conjunction with the structural and architectural design from RIBA Stage 2 — adding ducting as an afterthought in Stage 5 is the single most common new-build M&E error. Plant room space requirement: typically 1.6m × 1.0m for the MVHR unit + service clearances.

SAP 10.2 (Standard Assessment Procedure) is the government's methodology for calculating predicted energy use, CO₂ emissions and EPC ratings for new dwellings. Every new build in Cornwall (and nationally) requires SAP calculations at:

• Design stage SAP — submitted with planning application and Building Regulations submission. Demonstrates compliance with Part L (FHS from 2026) and Cornwall CE1/CE2.
• As-built SAP — submitted at Building Control completion, reflecting actual installed equipment, including airtightness test results, commissioning data, and any specification changes during construction.
• EPC generation — produced from as-built SAP, lodged on the central register, attached to the property's title.

Energy Statement (Cornwall CE1) goes further: full demand profile, renewable generation capacity, carbon balance, contribution to off-site offset if any shortfall. We produce Energy Statements for self-build planning applications, costing £750-£1,400 depending on dwelling complexity. Developer-led developments typically have their own M&E consultants producing these in-house.

The key sensitivity in SAP 10.2 for new builds: airtightness testing result. A predicted permeability of 5 m³/h/m² that achieves 7.5 m³/h/m² on the actual blower-door test costs around 18% in EPC SAP points — turning an A85 design into an A77 build. Construction airtightness discipline is critical.

MCS (Microgeneration Certification Scheme) certification is required on new-build renewable installations for: (1) BUS grant eligibility (where self-build qualifies — see grant section below), (2) most warranty registrations from product manufacturers, (3) future ownership confidence (when the property is sold, the new owner's mortgage lender or buildings insurer will require MCS certification of the heat pump and solar PV).

MCS certification covers: MCS-certified installer (we are MCS-certified across heat pumps, solar PV, biomass and battery storage), MCS-certified products (every heat pump, panel, inverter and battery in our specification is on the MCS-approved product list), MCS-compliant installation (following MCS 3005 for heat pumps and MIS 3002 for solar PV), and a unique MCS certificate number lodged on the central MCS register. We register every install within 10 working days of commissioning.

The MCS heat pump installer must complete: design certification (heat loss calculation to MCS 3005-D), commissioning certification (flow rates, balancing, system pressures), handover documentation, and an annual performance check during the warranty period. We provide all of this as standard.

The Boiler Upgrade Scheme £7,500 grant has specific rules for self-build properties. To qualify, the self-build must: (1) be an owner-occupied dwelling (not for sale immediately on completion), (2) have a valid EPC at the time of BUS application, (3) have the heat pump installed by an MCS-certified installer, (4) have a deeded property title in the applicant's name. Developer-built homes sold to first occupiers do NOT qualify for BUS — the developer's installation is part of the build price, not a homeowner-funded retrofit.

For Cornish self-builders at Penwithick, Whitemoor or single-plot custom builds, BUS is an important component of the financial case. We administer the BUS application as part of our service: the £7,500 is paid directly to us by Ofgem on grant approval, and we deduct it from the final installation invoice. Typical timeline: grant application at install commissioning, payment received 6-10 weeks after.

Where the dwelling does not qualify for BUS (developer-led, plot already sold to multiple buyers, planning conditions etc), we structure the financial case on operational savings + sale value uplift instead, typically still showing strong economic returns vs gas-fired retrofit later.

Designing solar into a new build is dramatically simpler than retrofit: roof pitch optimisation (35-42° for Cornwall optimum), orientation (within 30° of south), shading clearance (no adjacent buildings, chimneys at minimum height/positions), structural reinforcement (purlin sizing adequate for panel load 18-22kg/m²), and integrated mounting (in-roof systems pour into the slate or tile bedding rather than retrofitting onto existing roof).

Our standard new-build solar specification:

• Panel count: Sized to FHS / CE1 carbon balance requirements, typically 3.5-5.5 kWp on a 3-4 bed dwelling (8-13 panels)
• Mounting: Viridian Clearline Fusion in-roof (premium, ~£1,950/kWp) or GSE in-roof trays (~£1,650/kWp). Conventional on-roof for budget developments ~£1,400/kWp.
• Inverter: Hybrid with battery integration — Fox ESS H1-6.0 or Solis 6kW hybrid. Premium dwellings: Tesla Powerwall 3 integrated 11.5kW inverter.
• Battery: Increasingly default rather than optional — 9.5-13.5 kWh for typical new build, supporting time-of-use tariff optimisation and self-consumption.
• Smart EV charging: Many developments now wiring for EV charger as default. Myenergi Zappi or Andersen A2 specification.

Integrated specification cost: typically 6-8% of dwelling build cost (around £18,000-£28,000 for a 3-4 bed) covers heat pump + cylinder + MVHR + solar + battery, fully delivering FHS/DPD compliance with future-proof headroom for EV adoption.