SHDF Wave 2 – Welwyn Hatfield
Measured across our retrofit programmes
- 2,493homes with a post-works EPC
- +11average SAP points gained
- D → Caverage band movement
- 99.6%finish at band C or better
Crawford & Co assessed and coordinated these homes. Figures cover every programme where works are complete and a post-works EPC has been lodged, September 2026, and are not specific to this project.
Overview
Working with the principal contractor for the local authority, Crawford & Co Surveyors delivered a complete SHDF Wave 2 package: 73 retrofit assessments and coordination of loft insulation and External Wall Insulation (EWI).
Approach: detailed property surveys established each home’s current performance and constraints; from these we produced customised retrofit plans specifying insulation type and thickness, addressing structural considerations and ensuring regulatory compliance.
Outcome: a coordinated, standards-compliant programme that improved energy efficiency, cut carbon and enhanced living conditions across the 73 units.
Jonathan
Project Manager
Strategy
Fabric
Wave 2 stock is diverse: house types vary street by street, each with its own construction and its own constraints, and each needs its own answer. Measures on this scheme were specified per property from the assessment — external or internal wall insulation, loft and room-in-roof insulation, and window and door improvements.
Pre-existing defects are the rule rather than the exception on this kind of stock: dampness, condensation and mould, cavity wall tie failure, roof slumping and spread, timber decay and lintel failure. Every one of those has to be resolved before insulation goes on.
Identifying them at assessment is what makes enabling works a planned item rather than a mid-programme surprise.
Service
Ventilation and airtightness are one decision, not two. Extract ventilation, and demand-controlled mechanical extract ventilation with humidity sensing where it is warranted, are designed in alongside the fabric measures so that a tighter home is also a drier one.
Heating and hot water measures are matched to the demand the fabric work leaves behind, so plant is sized for the improved property.
Renewables
Where a property suits it, solar PV is added after the fabric measures, so that generation offsets a demand already reduced rather than masking one that has not been. Roof orientation, structural capacity and the condition of the existing covering all decide suitability, and the assessment records that rather than assuming it.
Conservation areas, listed status, and bird nesting or bat hibernation seasons all shape what can be installed and when. On this kind of stock those are routine planning considerations, not exceptions.
Vital Statistics
Properties in scope: 73.
Crawford & Co scope: Retrofit Assessment, Retrofit Coordination, Retrofit Design.
Measures installed: External wall insulation, loft insulation.
Programme period: 2024 to 2025 (indicative).
Each assessment records the property’s construction and its modelled performance before and after the proposed measures — space-heating demand in kWh/m² per year, carbon in kg per year and estimated energy cost. Figures are held per property rather than averaged, and are available to the client in full.
Detailing
Compliance is designed in rather than checked at the end. Assessments are quality-checked by a coordinator before they reach design, measures are modelled against the scheme’s target, and documentation is assembled as the work proceeds so that TrustMark lodgement is a formality rather than a scramble.
Our retrofit condition report was developed in house and approved by both the scheme provider and TrustMark. The work behind it contributed to our managing director’s appointment to the BS 40104 steering group — the British Standard for retrofit assessment. Where PAS 2035 leaves a technical question genuinely open, we take it up with the standard’s authors rather than guess.
Further Data
Standards
PAS 2035 / PAS 2030
Comfort
A retrofit that lowers a bill but leaves a home stuffy or damp has not worked. Comfort here means even temperatures, humidity that stays under control, ventilation the resident does not have to think about, and daylight where the property allows for larger windows or roof lights.
Residents remain in occupation throughout, so assessment visits are designed to capture everything needed in one appointment.
Monitoring
Coordinators quality-check every assessment before it reaches design, and the scheme runs with a live view shared between client, designer and installers so that discrepancies surface in days rather than at handover. Regular review meetings with client, designer and installers run for its duration.
Post-completion documentation is prepared for TrustMark lodgement through secure data sharing.
A medium-term plan covers maintenance, ongoing performance monitoring and future upgrades, so that the measures keep performing after the programme closes.
Social Value
RafaSocial value leadDuring this project Rafa was on a university placement, funded directly from this contract.