The only thing you can’t retrofit is retrofit

Why early design matters more than you realise

Retrofit succeeds or fails long before anyone steps on site. When assessments and design are rushed or sequenced incorrectly, projects stall, funding unravels and the final result underperforms.

This article sets out why early design matters, what goes wrong when it is skipped, and how to structure a project so the promised performance shows up in real life.

The pattern we keep seeing

Well intentioned teams move quickly to “get work done” and then try to backfill compliance. It rarely ends well.

Typical failure points:

• Works start before assessments, moisture diagnostics and design are complete

• Designers are appointed after procurement or even after scaffold is up

• Compliance is expected to be “sorted afterwards” when it can no longer be evidenced

• Installers are asked to make site decisions that belong in design

The uncomfortable truth is simple. PAS 2035 cannot be reverse engineered, and TrustMark will not certify what was not designed.

PAS 2035 is a sequence, not a checklist

Think of it as four linked steps. Each one informs the next.

Assess → Design → Install → Verify → Lodge

• Assess: Whole house assessment, moisture and ventilation checks, evidence gathering and risk identification

• Design: Options appraisal, moisture safe details, sequencing, resident impacts, specification and drawings

• Install: Competent installation that follows the design, with records that prove what was done

• Verify: Commissioning, evaluation and post works checks so performance is evidenced

• Lodge: Submit the full design package, including drawings, assessments and installation records to TrustMark for certification.

Reverse does not exist. If key elements are installed first, many risks can no longer be measured or designed out.

The funding consequence

Funding and certification hinge on process.

No compliant process means no TrustMark certification. No TrustMark certification means funding is at risk.

Even when funding is not in play, the practical cost remains. Rework, programme drift, unhappy residents and reputational damage are all much more likely when design happens late.

What “starting too soon” looks like in the real world

Below are anonymised examples that mirror situations we meet across the UK.

Example 1: Windows fitted before design

A contractor replaced windows to meet a quick-win KPI. The reveal details for future EWI had not been designed. When insulation was later installed, cold bridges appeared around frames and internal condensation increased at the heads. The fix involved removing trims and refitting sections with tapes and extended cills. Time lost, budget burned, residents inconvenienced.

Example 2: Re-roofing without ventilation strategy

Roofs were stripped and re tiled as part of cyclical works. Eaves ventilation and underlay type were not coordinated with the planned loft insulation top up. After handover, damp patches appeared on the ceiling slopes. A ventilation upgrade and remedial works were added at extra cost. A short design check would have prevented it.

The approach that works

Early design protects funding, programmes and reputations. The following habits consistently deliver better outcomes.

What to do:

• Appoint the retrofit designer early so the sequence is locked in from day one

• Run clear assessments that cover fabric, moisture, ventilation and resident needs

• Set a defined design and risk strategy, including junction details and buildability notes

• Install to the plan, with photos and records as you go

• Verify performance, commission ventilation, capture resident feedback and close out issues

• Submit to TrustMark for certification

Practical sequencing tips

• If windows must be replaced early, design the final reveal now so tapes, cills and frame positions suit future insulation

• Coordinate roof remedial works and roofline extensions with the insulation and ventilation strategy so eaves, underlays and vents all align

• Decide on cavity extraction or refill before committing to EWI so you know what you are fixing to

• If heat pumps are in scope, complete fabric improvements and emitter checks first so flow temperatures can drop and comfort is maintained

A quick readiness checklist

• Do you have a documented assessment for each archetype, including moisture risk and ventilation?

• Are details for eaves, canopies, cills and services designed and coordinated?

• Will installers receive drawings and a simple “how to prove it” photo list?

• Is post works evaluation scheduled within three months of handover?

Design it right. Retrofit it right.

At Target Green, we support clients from the very start, so retrofit works first time. If you are planning works this year, talk to us early.

We will help you sequence assessments, design and delivery in a way that protects funding, keeps residents on side and achieves the performance you are aiming for.