Warm Homes Plan — Insight 01A: New build and retrofit must be designed as one energy system

What does the Warm Homes Plan actually change for asset owners and developers—and what should we do now?

The Warm Homes Plan is not only a retrofit programme. It is a redefinition of what “good housing” looks like: year-round comfort, lower bills, and clean heat—delivered through better standards, stronger consumer protection, and a clear push toward electrification. For developers, the implication is that solar, low-carbon heat and overheating resilience must be designed in from concept stage. For portfolio owners, the implication is that retrofit must move from “measures” to auditable performance outcomes. In both cases, energy can no longer be bolted on: fabric, ventilation, summer comfort, roofscape solar and services strategy must be treated as one system.

New homes: “solar by default” plus low-carbon heat changes design from day one

The Plan commits to bringing forward the Future Homes Standard and is clear that new homes should combine high energy efficiency, low-carbon heating, and solar panels by default. That is a sea change because it turns roofscape and servicing into core architectural decisions rather than late-stage compliance items.

What this means in practice:

• Roof geometry becomes energy-critical. PV yield depends on roof form, orientation, shading, and maintenance access. If PV is treated as an add-on, you risk planning pushback, visual clutter, and compromised performance.
• Plant and distribution space must be designed in early. Heat pumps and hot water strategies (especially in apartments) require space, noise control, access, and a coherent approach to external units and risers.
• Summer comfort becomes part of compliance reality. Better fabric without shading/ventilation strategy increases overheating risk—so passive measures must be designed in, not value-engineered out.

CWA has delivered housing where PV is integrated flush within the roof plane, showing how “solar by default” can be achieved without visual clutter or compromised roof detailing.

Retrofit: the Plan forces a shift from “measures” to performance

The Plan is explicit that homes must be comfortable year-round and recognises the risks created by poorly executed interventions (including damp/mould outcomes when insulation is added without ventilation strategy). The direction of travel is toward programmes that can evidence outcomes, not just count installations.

For building owners, this changes the retrofit brief:

• Fabric + ventilation must be designed together to avoid moisture risk.
• Controls and commissioning become central to whether households actually see the promised comfort and bill outcomes.
• Overheating risk needs to be assessed and designed out through shading, glazing control, and ventilation—particularly in top-floor flats and highly glazed homes.

Quality and consumer protection are now delivery constraints (and that’s good)

A major strand of the Plan is rebuilding trust: clearer standards, stronger consumer protections, and higher expectations of delivery quality. This is a direct response to historic failures where upgrades produced poor outcomes.

For clients, that means your programme needs:

• professional design responsibility,
• procurement and QA that you can audit,
• clear handover/operation requirements,
• and evidence-led performance checks.

EPC reform is not admin; it’s the steering wheel

The Plan signals reform so EPCs better reflect clean heating and provide more useful insight for decision making. For anyone managing rented stock or a development pipeline, EPC methodology is effectively a compliance and capex steering mechanism.

The smart posture now is to design solutions that:

• work under today’s EPC regime (but probably not aiming for A rating today as that locks you into gas!), and

• remain robust or preferably move up the table as metrics evolve toward electrification and whole-home performance.

  Essentially we are in a transition period and this makes squaring this circle difficult right now.

Delivery options (and when each is rational)

Most portfolios and pipelines now fall into one of four pathways:

A) New build: design-led compliance

Best when: you control the design early.
Key success factor: roof-integrated solar + plant strategy + summer comfort designed at concept stage.

B) Measure-by-measure retrofit (fast, but riskier)

Best when: simple typologies with good access and low governance friction.
Failure mode: unintended consequences and variable outcomes.

C) Whole-building retrofit packages (slower start, stronger outcomes)

Best when: blocks, estates, mixed tenure, damp/mould history, or known overheating risk.
Trade-off: more front-end diagnosis; fewer surprises.

D) Phased programmes (often the only realistic route at scale)

Best when: large portfolios where learning and repeatability matter.
Approach: diagnose → low-regret actions → sequence deeper works building-by-building.

The minimum dataset you need before you start

Before you commission contractors or lock budgets, confirm a minimum dataset. The questions differ slightly for new build vs retrofit:

New build (developer checklist)

• Roof form/orientation/shading constraints (PV yield + maintenance access)
• Planning/conservation constraints on roofscape and plant
• Heat pump + DHW strategy (space, noise, access, risers/communal options)
• Overheating risk and passive measures (glazing control, shading, ventilation)
• Electrical strategy (capacity, metering, future flexibility/storage readiness)
• Procurement/QA route (who owns performance and commissioning)

Retrofit (portfolio checklist)

• Typology + constraints (access, roof, external space, plant/risers)
• Fabric reality (thermal bridges, airtightness risk, existing defects)
• Ventilation strategy (current provision + post-upgrade requirements)
• Damp/mould history and moisture pathways
• Overheating risk (orientation, glazing, shading opportunities)
• Services baseline (heating/DHW approach, distribution, controls)
• Electrical capacity / reinforcement likelihood
• Governance (who approves, who pays, who benefits—especially mixed tenure)

Safe next step

If you own a portfolio or have homes in planning, don’t start with technology choices. Start with a whole-building brief that treats fabric, ventilation, summer comfort, roof-integrated solar, and services as one system and then choose the delivery route that matches your governance and typology.

For dense estates or campuses where communal solutions are in scope, our energy division has published a companion Insight on system pathways and delivery economics.