BackBeta — Guided retrofit (1-2-3)

Retrofit / extension

Pick a goal, confirm fabric context, then export your design-intent pack.

Carried in:ROI96 m²EPC DTemperate UK

3 · Your pack

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Glazing risk: LowThermal mass opportunity: ExcellentSolar potential: MediumCooling load flag: High

Beta — Planning viewretrofitefficient electrified

Preference-aligned pathway "Efficient Electrified" — readiness not evaluated; preference order only (score unchanged).

Envelope targets

walls: U ≤ 0.15 W/m²K (concept target) Source
roof: U ≤ 0.12 W/m²K (concept target) Source
airtightness: ≤ 1.0 ACH @ 50 Pa (design target) Source
glazing: Balance g-value and Uw by orientation; avoid overglazing south façades Source
floor: Confirm existing floor U-value before extension junction design Source

Risk flags

[medium] Overglazing risk — Large unshaded south glazing increases overheating before heating load drops.
[medium] Thermal bridge detailing — Junctions at balconies, corners, and extension ties need explicit psi-value strategy.
[medium] Occupied retrofit sequencing — Plan phased works to limit dust, noise, and heating outages while residents remain in place.
[high] Existing overheating signal — Upgrade measures must not worsen summer comfort — consider shading and ventilation first.

This pack is design-stage decision support from Evolving Home. It is not a SAP calculation, PHPP balance, HEM assessment, or Energy Performance Certificate. A qualified On Construction Domestic Energy Assessor (or PHPP consultant) must produce the authoritative compliance model for Building Regulations and/or Passive House certification.

Passive House (PHPP) certification and UK Building Regulations (SAP/HEM) are separate workflows. This brief supports early design intent only.

Research & sources

Linked, not compliance proof

Indicative quantity ranges

Planning bands only — not SAP, PHPP, or HEM model outputs. Verify with qualified assessor.

Peak heat loss

7–12 kW (indicative peak, not SAP/PHPP)

Annual demand band

4872–7656 kWh/yr space heating/cooling demand band

Overheating basis

Elevated — high south/west glazing or existing overheating signal; Part O / comfort screening advised

PV indicative range

3.8–6.7 kW roof PV indicative range (subject to shading and roof area)

Ventilation assumption

Whole-house MVHR when airtightness target ≤ 1.5 ACH50

Confidence

Low — north-star and defaults only; pathway: efficient electrified

Indicative bands are planning aids — see how we test score assumptions on our validation benchmarks page. Not SAP, PHPP, or certification output.

Consultant handoff preview

Live previewPreview only

For your 96 m² retrofit (EPC D) — ROI north star. Illustrative pack contents — not a lodged SAP, PHPP, or HEM file. Pro exports include versioned assumptions from your saved project.

Project assumptions

·For your 96 m² retrofit (EPC D) — ROI north star
·Recommended pathway (preference-ranked): efficient electrified — unknown
·Climate profile: Temperate (UK)
·Occupied retrofit — phased sequencing and dust/noise constraints apply

Envelope & glazing

·walls: U ≤ 0.15 W/m²K (concept target)
·roof: U ≤ 0.12 W/m²K (concept target)
·airtightness: ≤ 1.0 ACH @ 50 Pa (design target)
·glazing: Balance g-value and Uw by orientation; avoid overglazing south façades
·floor: Confirm existing floor U-value before extension junction design

Evidence gaps

·Site location not confirmed — climate and orientation assumptions provisional
·Solid-wall construction — moisture-risk review before insulation specification
·Year built not confirmed — heritage and construction assumptions provisional
·No blower-door test scheduled — airtightness target is design intent only
·Battery / thermal storage sizing not locked — solar readiness is design intent only

Questions for SAP / HEM assessor

·Confirm notional vs actual specification path
·Overheating screening method for high-risk façades and summer comfort
·Renewable contribution accounting if PV included later
·Which PCDB product categories apply to heating and MVHR?
·What air permeability target is assumed for Design SAP / HEM?
·Are thermal bridge psi-values from accredited details or bespoke calc?
·What evidence will be collected for as-built sign-off?

Questions for PHPP consultant

·Thermal bridge Psi-values for preferred junction details
·Heating/cooling load after fabric specification locked
·Ventilation summer bypass strategy with MVHR

Consultant handoff pack

Planning aid only

Demo export from current planning view. Sign in and save to unlock Pro persisted exports.

Filenames include mode + north star + date. Multi pack exports four scenarios for the same site inputs.

Practice workspace

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Practice inquiry

Evolving Home · Architect brief

Retrofit — EPC D · roi

RetrofitNorth star: ROIefficient electrified

For your 96 m² retrofit (EPC D) — ROI north star

Generated 30/08/2026, 04:35:27

Design brief summary

Preference-aligned pathway "Efficient Electrified" — readiness not evaluated; preference order only (score unchanged).

Envelope targets

walls: U ≤ 0.15 W/m²K (concept target)
roof: U ≤ 0.12 W/m²K (concept target)
airtightness: ≤ 1.0 ACH @ 50 Pa (design target)
glazing: Balance g-value and Uw by orientation; avoid overglazing south façades
floor: Confirm existing floor U-value before extension junction design

Risk flags

[medium] Overglazing risk — Large unshaded south glazing increases overheating before heating load drops.
[medium] Thermal bridge detailing — Junctions at balconies, corners, and extension ties need explicit psi-value strategy.
[medium] Occupied retrofit sequencing — Plan phased works to limit dust, noise, and heating outages while residents remain in place.
[high] Existing overheating signal — Upgrade measures must not worsen summer comfort — consider shading and ventilation first.

Passive House (PHPP) certification and UK Building Regulations (SAP/HEM) are separate workflows. This brief supports early design intent only.

Assumptions ledger (compact)

Key assumptions, evidence gaps, and verification hooks for consultant handoff.

Project assumptionsEstimated
For your 96 m² retrofit (EPC D) — ROI north star
Project assumptionsEstimated
Recommended pathway (preference-ranked): efficient electrified — unknown
Project assumptionsEstimated
Climate profile: Temperate (UK)
Project assumptionsEstimated
Occupied retrofit — phased sequencing and dust/noise constraints apply
Envelope & glazingEstimated
walls: U ≤ 0.15 W/m²K (concept target)
Envelope & glazingEstimated
roof: U ≤ 0.12 W/m²K (concept target)
Envelope & glazingEstimated
airtightness: ≤ 1.0 ACH @ 50 Pa (design target)
Envelope & glazingEstimated
glazing: Balance g-value and Uw by orientation; avoid overglazing south façades
Envelope & glazingEstimated
floor: Confirm existing floor U-value before extension junction design
Evidence gapsMissing
Site location not confirmed — climate and orientation assumptions provisional
Evidence gapsMissing
Solid-wall construction — moisture-risk review before insulation specification
Evidence gapsMissing
Year built not confirmed — heritage and construction assumptions provisional