Building a home to the Future Homes Standard (FHS) is fundamentally different from building to current Part L 2021 rules. The biggest changes are in services: gas boilers are replaced by heat pumps, at notional-level airtightness trickle-vent natural ventilation gives way to continuous mechanical ventilation (dMEV in the notional dwelling; MVHR where specified), the notional airtightness tightens to 4 m³/(h·m²), glazing holds at the 2021 notional 1.2 W/m²K (high-performance double or triple), and rooftop solar PV is mandatory. This guide walks through each change in practical detail, covering what builders need to do differently and what new skills are needed.
Heat Pump Installation
Almost every FHS house will be heated by a heat pump, typically an air source heat pump (ASHP); flats may instead connect to a heat network. For builders accustomed to gas boiler installation, this is a significant change in both the equipment and the construction process.
External Unit
- Concrete plinth or mounting frame: The external unit needs a level, stable base. A concrete plinth (typically 900 mm × 600 mm × 100 mm) is standard, with anti-vibration mounts
- Clearance: Allow at least 1 metre around the unit for airflow. Do not locate in enclosed corners, against fences, or where airflow is restricted
- Acoustic considerations: Avoid locating directly below bedroom windows or adjacent to neighbouring properties. Check local planning noise conditions
- Pipework penetrations: Refrigerant pipework and electrical cabling route between external unit and internal components, typically through the external wall at low level
Internal Components
- Hot water cylinder: 150–250 litres, typically located in a utility room or airing cupboard. Heat pumps cannot provide instant hot water like combi boilers
- Buffer vessel (if required): 50–100 litres, prevents short-cycling on smaller systems. Located adjacent to cylinder
- Controls: Heat pump controller, room thermostat, and potentially zone valves for multi-zone systems
Heat Distribution
Heat pumps operate most efficiently at low flow temperatures (35–45°C). AD L1 has required new and fully replaced wet heating systems to be sized for a maximum flow temperature of 55°C since 2021, well below the 70–80°C once typical of gas-heated homes. This requires differently sized emitters:
| Emitter Type | Flow Temperature | Builder Implications |
|---|---|---|
| Underfloor heating (UFH) | 35–40°C (ideal for heat pumps) | Screed or dry-system installation; coordinate with floor build-up |
| Oversized radiators | 40–45°C | 2–3× larger than conventional; heavier; larger brackets needed |
| Standard radiators | 70–80°C (NOT suitable) | Do not use: forces high flow temps, reduces heat pump efficiency |
Commissioning
Heat pump commissioning is more involved than gas boiler commissioning and typically requires a specialist:
- F-gas certification: Required for anyone handling refrigerant (checking charge, topping up, or decommissioning)
- Flow rate verification: Water flow through the heating circuit must match the heat pump's requirements
- Controller programming: Weather compensation curves, hot water schedules, and defrost settings must be correctly configured
- Performance recording: Commissioning data must be recorded for handover documentation and the Part L compliance evidence
Airtightness: Building to 4 m³/(h·m²)
Achieving the FHS airtightness target requires every trade on site to understand and respect the air barrier. It is not solely the responsibility of the drylining team or the membrane installer: any trade that penetrates the air barrier must seal its own work.
Identifying the Air Barrier
The air barrier must be a single, continuous layer throughout the building envelope, clearly identified on all construction drawings. Common approaches include:
| Construction Type | Air Barrier Layer | Sealing Method |
|---|---|---|
| Timber frame | Vapour control membrane (warm side) | Taped joints, proprietary grommets at penetrations |
| SIPs / closed panels | Factory-sealed OSB sheathing | Taped panel joints; site-sealed at junctions |
| Masonry cavity | Parged inner leaf or dedicated membrane | Continuous wet parge coat or taped membrane |
| CLT (cross-laminated timber) | CLT panels with taped joints | Proprietary tapes at panel junctions; membrane at interfaces |
Sealing Service Penetrations
Every pipe, cable, and duct that passes through the air barrier must be individually sealed. Best practice includes:
- Proprietary grommets for individual cables and small pipes, far more reliable than site-applied mastic
- Top-hat seals or flexible collars for larger pipes and ducts
- Service zones on the warm side of the air barrier to minimise the number of penetrations. Run electrical and plumbing distribution within the service void
- Pre-formed penetration sleeves for MVHR supply and exhaust ducts through the external wall
Mid-Build Testing
MVHR Installation
MVHR installation is a first-fix activity that must be coordinated with the structural, electrical, and plumbing programmes. Poor installation is the most common cause of MVHR performance problems.
Duct Routes and Installation
- Rigid or semi-rigid ducting: Preferred over flexible for lower pressure drop, better hygiene, and longer service life
- Short, straight runs: Minimise bends, as each 90° bend increases pressure drop and fan energy consumption
- Route through floor voids and ceiling spaces: Plan routes to avoid clashes with joists, steelwork, and other services
- Protect during construction: Cap open duct ends to prevent debris ingress during the build. Clean ducts before commissioning
- Acoustic attenuation: Install duct attenuators on supply branches to bedrooms to prevent noise transfer from the central unit
Commissioning
MVHR commissioning requires measured airflow at every supply and extract valve, adjusted to match the design specification. Common issues include:
- Unbalanced airflow between supply and extract (causes pressurisation or depressurisation of the dwelling)
- Incorrect boost rates in kitchens and bathrooms
- Blocked or kinked duct runs reducing airflow to individual rooms
- Filters not installed or installed incorrectly
Fabric and Insulation
The FHS notional fabric U-values broadly carry over from the 2021 uplift, so a builder already delivering 2021-uplift fabric is most of the way there. The notional values remain well ahead of the limiting backstops:
| Element | Limiting Value (Backstop) | FHS Notional | Builder Impact |
|---|---|---|---|
| External walls | 0.26 W/m²K | 0.18 W/m²K | Full-fill cavity or insulated frame, as per 2021 uplift practice |
| Ground floor | 0.18 W/m²K | 0.13 W/m²K | Below-slab PIR or beam-and-block insulation, as per 2021 practice |
| Roof | 0.16 W/m²K | 0.11 W/m²K | Deep joist-level mineral wool or warm-roof rigid board |
| Windows | 1.6 W/m²K | 1.2 W/m²K (unchanged from 2021) | High-performance double or triple; heavier units and deeper frames where triple is specified |
| Doors | 1.6 W/m²K | 1.0 W/m²K | Insulated composite or timber doors |
Triple Glazing
The 1.2 W/m²K notional window is achievable with high-performance double glazing, so triple glazing is a choice rather than a requirement. Where it is specified, the units are heavier than double-glazed (typically 30–40 kg/m² versus 20–25 kg/m²) and builders should plan for:
- Stronger window fixings and wider frame profiles to carry the additional weight
- Two-person handling for larger units; manual handling assessments should be updated
- Deeper reveals to accommodate the thicker glazing units (typically 44–52 mm versus 24–28 mm for double)
- Careful air barrier detailing around window frames. The window-to-wall junction is a critical airtightness and thermal bridge location
Solar PV Installation
Solar PV must be installed on most FHS homes. Key considerations for builders:
- Structural loading: Panels add approximately 12–15 kg/m² to the roof. Verify roof structure is designed to carry the additional load
- Mounting system: Rails or integrated mounting brackets fixed to rafters through the roof covering. Weathertight sealing at every fixing point
- DC cabling: Route from panels to inverter location (typically near the consumer unit). DC cabling carries fire risk, so route through fireproof conduit where required
- Inverter location: Typically internal, near the consumer unit. Allow space for the inverter and ensure adequate ventilation for heat dissipation
- Coordination with roofing: Ideally install PV mounting rails during the roofing programme to avoid re-accessing the roof. Some integrated PV-tile systems replace conventional roof tiles entirely
Digital Records and the Golden Thread
The Building Safety Act introduces the Golden Thread, a comprehensive digital record of building information created during construction and maintained throughout the building's life, for higher-risk buildings. For an ordinary new dwelling the record-keeping duty comes from Part L instead: design-stage and as-built BREL reports, signed by the assessor and by the developer, supported by photographic evidence of build quality. The information worth capturing on an FHS home is much the same:
- As-built drawings showing actual construction details, not just design intent
- Product data sheets for every installed component (heat pump, MVHR unit, windows, insulation, etc.)
- Commissioning records for heat pump, MVHR, solar PV, and electrical installation
- Airtightness test certificates (both mid-build if conducted, and final)
- Photographic evidence of key construction stages, particularly air barrier continuity, insulation installation, and service penetration sealing
- Homeowner handover documentation covering operation of heat pump, MVHR (filter replacement, boost controls), and solar PV monitoring
Skills and Training
| Skill Area | Certification / Competence | Notes |
|---|---|---|
| Heat pump installation | F-gas certification (refrigerant handling) | MCS certification recommended for quality assurance |
| MVHR installation | No specific qualification mandated | BPEC or equivalent training recommended; commissioning requires airflow measurement equipment |
| Airtightness | No formal certification (yet) | ATTMA or equivalent training strongly recommended |
| Solar PV | Part P electrical competence | MCS is one route to demonstrating competence and is needed for export tariffs; DC wiring requires specific training |
| Triple glazing | Standard fenestration skills | Additional manual handling training for heavier units |
| Digital records | No formal certification | Familiarity with digital record-keeping platforms |
Builder Preparation Checklist
Frequently Asked Questions
What is involved in installing a heat pump for a new build?
Installation involves: a concrete plinth for the external unit with adequate clearance, refrigerant pipework between external and internal units, a hot water cylinder (150–250 litres), emitters sized for 45°C flow temperature(oversized radiators or UFH), a dedicated electrical circuit, and specialist commissioning to verify refrigerant charge, flow rates, and controller settings.
How do you achieve 4 m³/(h·m²) airtightness on site?
You need a continuous, identifiable air barrier throughout the envelope. Key steps: identify the air barrier layer on all drawings, seal all joints with proprietary tapes and membranes, use grommets for every penetration, conduct mid-build airtightness tests before finishes are applied, and ensure all trades understand the air barrier location and their responsibility to maintain it.
What does MVHR installation involve for builders?
MVHR is a first-fix activity. It requires: a central unit location with acoustic separation from bedrooms, 80–120 metres of ducting through floor voids or service zones, supply valves in every habitable room, extract valves in every wet room, two external wall penetrations, and commissioning with measured airflow at every valve. See our Ventilation & Part F page for more detail.
What are the Golden Thread digital record requirements?
The Building Safety Act Golden Thread applies to higher-risk buildings, not to new homes generally. For an ordinary new dwelling the duty comes from Part L: the BREL report plus photographic evidence of build quality. The pack most builders keep is the same either way: as-built drawings, product data sheets, commissioning records for heating, ventilation, and renewables, and airtightness test certificates.
What training do site teams need for FHS construction?
Key training areas: heat pump installation (F-gas certification for refrigerants), MVHR duct installation and commissioning, airtightness techniques (air barriers, proprietary sealing), solar PV mounting and DC wiring (Part P), handling triple-glazed units where they are specified, and record-keeping. Many developers are investing in training programmes now ahead of the deadline.
Related Pages
Ventilation & Part F
MVHR requirements, airtightness interaction, and HEM's ventilation modelling under the FHS.
Part L Changes
Detailed breakdown of fabric specifications, U-values, and heating requirements.
Architect Design Guide
Form factor, glazing, thermal bridges, and design strategies that affect on-site construction.
Developer Compliance & Cost Guide
Cost impact, procurement planning, and transitional strategy for FHS projects.