Case Study Portfolio
Six UK Passivhaus and EnerPHit dwellings
These projects are the thesis case-study portfolio. The cards keep the evidence hierarchy visible while allowing a quick visual scan of typology, site EUI, A1–C4 WLC, B6 and sequestration.
Finding 01
Certification is not a WLC guarantee
All six cases sit within the Passivhaus / EnerPHit family, yet A1–C4 WLC ranges from 697 to 2,155 kgCO₂e/m².
Finding 02
Energy and carbon rankings decouple
Tigh Na Cladach has the lowest gross site EUI, while Harpenden has the lowest B6 and A1–C4 WLC.
Finding 03
Fuel, PV and materials dominate spread
ASHP/PV, gas exposure, material palette and biogenic sequestration explain much of the cross-case variance.
Finding 04
Retrofit advantage is portfolio-bounded
The retrofit group has lower mean A1–C4 WLC than the new-build group, but this is an analytical portfolio, not a population statistic.
Operational energy vs operational carbon
Site EUI on the X-axis against B6 annual carbon intensity on the Y-axis. Marker shape encodes type (new-build vs retrofit); colour encodes fuel profile.
Reading the chart. Low energy does not automatically mean low carbon. Two cases at similar EUI can sit at very different B6 intensities depending on fuel mix and on-site generation. Harpenden achieves low EUI and low B6 because of the ASHP plus 8.1 kWp PV combination. Carrowbreck has moderate EUI but the highest B6 because of gas-led space heating and DHW.
A1–C4 whole-life carbon intensity by project
Rank 1 = lowest A1–C4 WLC intensity. Optional percentage-difference labels reference Harpenden as the lowest-WLC case.
Gross vs net site EUI
The gap between gross and net bars is the on-site PV (or PV-plus-solar-thermal) credit. Carrowbreck has no credited PV inside the thesis boundary, so its bars are equal.
Project profiles
Pick two projects below to view a side-by-side comparison table.
Site EUI and source EUI
Source-to-site ratio
Higher ratios indicate greater dependence on grid-electricity primary energy. Cases with on-site PV reduce their effective ratio after generation is netted.
Gross vs net source EUI
Site EUI ranking
| Rank | Project | Type | Gross site EUI kWh/m²·yr |
Net site EUI kWh/m²·yr |
Δ from PV/solar kWh/m²·yr |
|---|
Interpretation. Tigh Na Cladach has the lowest gross site EUI in the portfolio. Harpenden has the lowest net EUI thanks to a large PV contribution. Carrowbreck and Larch carry the highest gross EUI. The ranking shifts substantially when on-site generation is netted.
End-use breakdown
| Project | Space heating | DHW | Lighting | Equipment | Cooking | Local fans | Pumps | Total |
|---|
Non-heating loads, especially equipment, lighting and DHW, often equal or exceed space heating in well-insulated Passivhaus and EnerPHit envelopes. End-use composition is therefore essential when interpreting site EUI.
Delivered electricity, gas and on-site generation
Gross vs net site EUI
PV offset ratio
Harpenden achieves the strongest net-energy improvement on its 8.1 kWp PV array. Zetland and Larch also show major PV benefit. Tigh Na Cladach has solar thermal contributing to DHW only, not PV; Carrowbreck has no PV credit inside the thesis boundary.
Net imported energy ranking
B6 annual intensity
B6 60-year intensity
B6 ND vs Decarbonised scenario
B6 as % of A1–C4 WLC
Net site EUI vs B6 annual intensity
Why these do not move in lockstep. B6 is governed by delivered energy, fuel type, system efficiency and on-site generation. EUI alone cannot predict B6: a high-EUI all-electric case with PV can achieve lower B6 than a low-EUI gas-fired case.
A1–C4 WLC intensity
A1–C4 total absolute
A1–C4 plus Module D (supplementary)
Module D credit is shown separately. It does not change the headline ranking.
A1–C4 ND vs Decarbonised
WLC ranking
| Rank | Project | Type | A1–C4 (kgCO₂e/m²) | Δ vs best | B6 share (%) | Sequestration (kgCO₂e/m²) |
|---|
Headline finding. Harpenden achieves the lowest A1–C4 WLC, driven by ASHP, PV and bio-based specification. Carrowbreck records the highest, driven by high B6 (gas plus elec) and conventional material specification. Retrofit cases as a group sit below new-build cases on portfolio mean, although the spread is wide and this is a six-case portfolio, not a statistical population.
Stacked lifecycle distribution
Upfront carbon waterfall
Net A1–A5 = product (A1–A3) plus transport (A4) plus construction (A5) minus biogenic sequestration credited under A1–A3.
In-use carbon (B-modules)
Sequestration vs A1–A3 product
Bio-based specification (Harpenden, Larch) shows substantially larger sequestration credits, displayed as negative values per RICS WLC v2 convention.
End-of-life (C1–C4)
Bio-based cases (Harpenden, Larch) show somewhat higher end-of-life intensity associated with the release pathway of stored biogenic carbon.
New-build vs retrofit, group means
Δ Retrofit minus New-build
Read with care. The retrofit group has lower mean A1–C4 WLC and lower upfront carbon than the new-build group, with marginally higher end-of-life intensity. Interpretation is portfolio-bounded across the six cases and should not be read as a statistical claim about the UK building stock.
Upfront A1–A5 (excluding sequestration) vs benchmark targets
Whole-life embodied carbon (A–C, excluding B6/B7) vs RIBA / GLA
Compliance status
| Project | Type | LETI 2030 upfront | GLA upfront | NZCBS upfront | RIBA WL embodied | GLA WL embodied |
|---|
Scope notes. LETI 2030 and NZCBS targets are largely new-build oriented; some upfront targets exclude biogenic sequestration; RIBA and GLA whole-life targets typically exclude B6 and B7. Compliance flags here therefore reflect the published scope of each framework rather than an absolute pass/fail in all jurisdictions.
A1–C4 WLC: ND vs Dec
WLC reduction percentage under Dec scenario
B6 ND vs Dec
B6 share of A1–C4 under ND vs Dec
All-electric cases show stronger B6 sensitivity to grid decarbonisation. Gas-involved cases retain a higher residual B6 because grid decarbonisation does not reduce gas combustion emissions. Decarbonisation changes magnitude but does not change all rankings.
Integrated performance matrix
Confidence labels.
H high
M-H medium-high
M medium
L-M low-medium
L low.
BPE-class evidence on operational and carbon metrics is not equivalent to lower-confidence comfort, IAQ or governance evidence; ratings are kept visible to avoid implicit aggregation.
Operational vs whole-life carbon ranking decoupling
Four of six cases change rank between gross site EUI and A1–C4 WLC. This is the core visual argument: operational ranking, B6 ranking and whole-life carbon ranking are related, but not interchangeable.
Thesis Findings
Eight thesis findings, robustness classification
These findings summarise the cross-case synthesis. Robustness labels refer to the evidential strength available inside this six-case analytical portfolio.
Finding 7.1 · Robust
3.1× WLC range
Certified Passivhaus-family dwellings still show a 3.1× A1–C4 WLC range. Certification alone does not constrain lifecycle carbon.
Finding 7.2 · Robust
Retrofit advantage
EnerPHit retrofits achieve a lower mean WLC than the Passivhaus new-build group in this portfolio.
Finding 7.3 · Robust
Fuel configuration drives B6
B6 ranges by 8.3×. Gas, all-electric, ASHP and PV combinations explain more than fabric standard alone.
Finding 7.4 · Robust
Material palette drives upfront carbon
Bio-based specifications create large sequestration credits; mineral-led specifications do not.
Finding 7.5 · Conditional
Decarbonisation reshapes the profile
All-electric cases show strong B6 reduction under decarbonisation, shifting attention toward embodied carbon.
Finding 7.6 · Conditional
Overheating risk remains visible
BPE evidence indicates overheating risk cannot be inferred from certification alone.
Finding 7.7 · Conditional
MVHR commissioning is an IAQ lever
IAQ confidence is strongest where BPE evidence exists; non-BPE cases should not be overclaimed.
Finding 7.8 · Fragile
Post-handover accountability gap
Certification provides a strong design/construction floor, but evidence weakens after handover.
Stakeholder Recommendations
From case-study evidence to decision guidance
These cards translate the dashboard into decision pathways for technical examiners, designers, housing providers, clients, policy stakeholders and researchers. They do not replace the thesis argument; they make its implications easier to communicate.
Clients and owner-occupiers
“Specifying Passivhaus is necessary but not sufficient for lifecycle carbon performance.”
- Ask for WLC options at concept stage, not after certification design is fixed.
- Prioritise low-carbon heating, PV readiness and material palette alongside fabric performance.
- Check whether PV, solar thermal and gas are treated consistently in the carbon boundary.
Evidence basis: A1–C4 WLC range of 3.1× and B6 range of 8.3× across certified / near-certified cases.
Designers and consultants
“Operational optimisation and lifecycle optimisation are related, but not the same design problem.”
- Use PHPP / dynamic modelling for energy, then test the material and services specification through WLCA.
- Report gross and net operational energy separately so PV benefit is not hidden.
- Do not let excellent U-values obscure high B6 or high upfront carbon choices.
Evidence basis: Tigh Na Cladach, Larch and Harpenden show ranking shifts between gross EUI, net EUI, B6 and WLC.
Housing providers and local authorities
“EnerPHit retrofit can be a strong lifecycle-carbon pathway when paired with low-carbon systems.”
- Prioritise deep retrofit where the existing structure can be retained and upgraded.
- Screen retrofit options using A1–C4, B6 and comfort evidence together.
- Use Harpenden and Zetland as contrasting retrofit pathways: PV-heavy ASHP versus electric-led/post-heater configurations.
Evidence basis: Retrofit mean A1–C4 is lower than new-build mean in this portfolio.
Policymakers and standards bodies
“Operational targets alone cannot detect whole-life carbon divergence.”
- Pair operational-energy thresholds with upfront and whole-life carbon disclosure.
- Keep benchmark scope notes visible: new-build versus retrofit, sequestration, B6/B7 exclusions and Module D treatment.
- Avoid treating Module D credits as a substitute for lower A1–C4 burdens.
Evidence basis: Benchmark tab separates LETI, GLA, RIBA and NZCBS scope assumptions.
Supply chain and programme delivery
“Repeatability depends on services integration, commissioning and low-carbon material access.”
- Make ASHP/PV/controls coordination explicit in design risk registers.
- Track MVHR, DHW and occupant-facing controls through handover and POE.
- Procure bio-based or lower-carbon assemblies early enough to avoid late substitutions.
Evidence basis: Cross-case spread is shaped by fuel, PV, DHW, materials and delivery conditions, not certification alone.
Researchers and examiners
“The weak point is not the energy data; it is the variable confidence in comfort, IAQ and governance evidence.”
- Read comfort and IAQ conclusions with the confidence labels, not as equivalent to BPE-grade energy evidence.
- Separate PHPP overheating indicators from CIBSE TM59 dynamic overheating assessment.
- Use the matrix tab to audit where evidence is strong, medium or limited.
Evidence basis: Integrated Matrix keeps H/M/L confidence labels visible across non-energy dimensions.
Cross-Case Synthesis
What the dashboard is meant to prove visually
This synthesis is intentionally short. The full evidence remains in the interactive tabs.
| Thesis argument | Dashboard evidence to inspect | Most relevant tab |
|---|---|---|
| Passivhaus / EnerPHit is necessary but not sufficient. | Certified-family cases differ by 3.1× on A1–C4 WLC. | Overview; Whole-Life Carbon |
| Operational energy and lifecycle carbon are not interchangeable. | Site EUI, B6 and WLC rankings do not match. | Overview; B6 Operational Carbon |
| PV changes net energy and B6, not gross demand. | Gross vs net site/source EUI and PV offset ratio. | PV and Net Energy |
| Retrofit performs well in this portfolio. | Retrofit group has lower mean A1–C4 and upfront A1–A5. | New-Build vs Retrofit |
| Benchmark compliance depends on scope. | LETI/GLA/RIBA/NZCBS targets use different module boundaries. | Benchmarking |
| Evidence confidence must remain visible. | Comfort/IAQ/governance confidence varies by case. | Integrated Matrix |
Master data table
Optional data upload
Drop an .xlsx, .xls or .csv file here, or
The uploaded data is parsed against the same internal schema. Required columns include
project, tfa_m2, site_eui, net_site_eui, b6_annual, b6_60yr, wlc_a1c4, wlc_a1c4_dec, net_a1a5, sequestration. Embedded canonical thesis data is never overwritten unless you click Use uploaded data.
Method notes and scientific caveats
- The six cases form an analytical case-study portfolio under critical realism. They are not a statistically representative sample of the UK housing stock.
- All intensities use thesis-specific TFA denominators; Harpenden has a known PHPP/public TFA of 151.4 m² versus IES/WLCA TFA of 172.44 m²; this is surfaced in the project profile and data table.
- PV reduces net imported energy and B6 only where credited inside the thesis system boundary. Solar thermal (Tigh Na Cladach) is not equivalent to PV.
- Module D is reported as supplementary information per EN 15978 and is not added into A1–C4 headline totals unless explicitly toggled on.
- Decarbonised scenario results follow Table 6.11 / 6.12 and must not be conflated with non-decarbonised baseline results.
- Comfort, IAQ and governance evidence varies in strength across cases; PHPP overheating frequency is not equivalent to a CIBSE TM59 dynamic overheating assessment.
- Reference study period is 60 years across all whole-life calculations.