Back to architect homeSample retrofit brief — mock data

Sample — 1930s semi-detached retrofit (mock)

EPC C → B target · fabric-first + ASHP + solar · ROI north star

Archetype

1930s cavity semi-detached

EPC target

C → B

Floor area

92 m²

Confidence

Medium-low — many estimated fabric assumptions

Loft: 150 → 300 mm target

Glazing: ~24% floor area (south + west) — Part O early review

Plant: ASHP + MVHR with summer bypass · 6.5 kWp PV + 10 kWh battery planned

Download this mock brief as JSON, Markdown, or PDF — planning aid only, not a certified export.

Evolving Home · Architect brief

Sample — 1930s semi-detached retrofit (mock)

RetrofitNorth star: ROIefficient electrified

For your 92 m² retrofit (EPC C) · M23 2LN — ROI north star

Generated 09/07/2026, 08:26:38

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.

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.

Assumptions ledger (compact)

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

Project assumptionsEstimated
For your 92 m² retrofit (EPC C) · M23 2LN — 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
Year built not confirmed — heritage and construction assumptions provisional
Evidence gapsMissing
No blower-door test scheduled — airtightness target is design intent only
Questions for SAP / HEM assessorEstimated
Confirm notional vs actual specification path

Consultant handoff preview

Live previewPreview only

Project assumptions

·For your 92 m² retrofit (EPC C) · M23 2LN — 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

·Year built not confirmed — heritage and construction assumptions provisional
·No blower-door test scheduled — airtightness target is design intent only

Questions for SAP / HEM assessor

·Confirm notional vs actual specification path
·Overheating screening method for primary living rooms
·Renewable contribution accounting if PV included later

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

Retrofit-specific risks

Moisture risk

Solid walls and internal insulation need hygrothermal review — never assume dry lining is low-risk.

Traditional / solid-wall construction

Breathable approaches and ventilation strategy must align with wall build-up.

Resident in place

Staged works and disruption sensitivity affect sequencing and cost.

Heritage constraints

Listed or conservation-area limits may block external insulation — document alternatives early.

PAS-style evidence prompts

Role clarity for assessor, coordinator, and installer — planning aid only, not formal PAS compliance.

Glazing risk: LowThermal mass opportunity: MediumSolar potential: MediumCooling load flag: Low

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.

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

5–10 kW (indicative peak, not SAP/PHPP)

Annual demand band

4025–6325 kWh/yr space heating/cooling demand band

Overheating basis

Moderate — confirm with orientation and glazing schedule

PV indicative range

3.7–6.4 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

Staged retrofit sequence

Demo planning view

1
1. Verify first
Moisture survey, EPC lodgement check, asbestos/damp flags before fabric changes.
2
2. Low-regret fabric
Loft/top-up, draught reduction, targeted glazing — avoid trapping moisture in solid walls.
3
3. Ventilation strategy
Plan MVHR or balanced ventilation before major airtightness gains.
4
4. Heating transition
Right-size ASHP after fabric improvements; avoid oversizing on pre-improvement loss.
5
5. Solar / storage / flex
PV and battery after demand profile is understood; label export assumptions.
6
6. Post-works monitoring
Smart meter or sensor upload to improve Evidence Grade — planned capability.

Verify first

Loft depth and access — measure before insulation target
Cavity wall fill suitability — borescope or pilot holes
Suspended timber floor — ventilation path and moisture risk
Asbestos / damp survey before invasive fabric works
Existing heating emitters sized for future ASHP loads

Staged retrofit prompts

Whole-dwelling assessment before measure selection (PAS 2035-style prompts — not PAS certification)
Ventilation strategy after airtightness improvements
Resident-in-place phasing and disruption windows
Post-works monitoring and commissioning evidence

Evidence ladder

Recommendations sharpen as facts move from estimated → known. Score confidence bands reflect the same honesty.

Known

Client-stated floor area, confirmed build type

Estimated

U-values from archetype; glazing ratio from concept drawings

Missing

Blower-door result, loft depth, wall construction confirmation

What improves confidence: site survey, EPC lodgement, blower-door test, measured post-occupancy data (planned).

Compliance-adjacent checks

Flags for professional review — Evolving Home does not sign off Part L, Part O, SAP, PHPP, or HEM.

Issue	Why it matters	Who verifies	Evidence	Next action
Part L / energy performancePart L	Fabric and plant choices affect notional vs actual performance path.	SAP / HEM assessor or regional equivalent	assumed	Lock U-value targets and confirm assessment route at technical design
Ventilation strategyVentilation	MVHR requires airtightness QA and summer bypass planning.	Ventilation designer / assessor	assumed	Document intended ventilation route and extract strategy
Heating plant sizingHeating	Heat pump sizing must follow fabric-first heat loss, not rule-of-thumb.	Heating engineer / MCS installer	assumed	Align with Air-source heat pump sized after heat loss — low-temperature distribution…
Moisture & solid-wall retrofitMoisture	Solid walls need breathable or verified safe insulation strategy.	Retrofit coordinator / moisture-risk assessor	partial	Confirm wall build-up and monitoring plan before insulation install
Design intent onlyDesign intent	Evolving Home does not lodge SAP, PHPP, or HEM files.	Qualified assessor	assumed	Export intent pack and schedule formal modelling

Client meeting one-pager

Plain EnglishPlanning aid

Share with clients before consultant appointments — highlights intent, risks, and decisions without certification language.

For your 92 m² retrofit (EPC C) · M23 2LN — ROI north star

Stage investments by payback confidence; electrify heating only after fabric targets are set. This brief ranks pathways for your stated priority — it does not replace accredited energy modelling.

Top risks to discuss

Overglazing risk — Large unshaded south glazing increases overheating before heating load drops.
Thermal bridge detailing — Junctions at balconies, corners, and extension ties need explicit psi-value strategy.
Occupied retrofit sequencing — Plan phased works to limit dust, noise, and heating outages while residents remain in place.

Client decisions

Residents stay during works — phased rooms and disruption windows
EPC starting point (C) — agree target band and measure priority with client
Plant change: heat pump air — confirm radiator/emitter upgrade scope
North-star priority: roi — shapes pathway ranking in this brief

Consultant verification next steps

Book SAP / HEM assessor early — confirm notional vs actual specification path
Schedule overheating screening for primary living rooms and high-glazing façades
Verify wall construction and moisture risk before insulation specification
Agree resident-in-place phasing with contractor before tender