Whole-House Retrofit & PAS 2035 Explained

Whole-house retrofit and PAS 2035 — why a plan beats piecemeal measures.

The difference between a retrofit that transforms a home and one that quietly causes damp is almost always planning. PAS 2035 — the UK's retrofit standard — exists precisely because piecemeal, uncoordinated measures cause unintended consequences. This article explains the whole-house approach and the framework that underpins it.

A house is a system: its fabric, airtightness, ventilation, heating and moisture behaviour are interdependent. Change one in isolation and you change the others — often for the worse. Insulate a wall without addressing ventilation and you can cause condensation; draught-proof without insulating cold spots and you concentrate mould at the junctions. Whole-house retrofit means understanding the building as a whole and planning the measures to work together, in the right order.

What PAS 2035 is

PAS 2035 (Retrofitting dwellings for improved energy efficiency — specification and guidance) is the overarching UK standard for domestic retrofit, sitting alongside PAS 2030 (which covers the installation work itself). It was introduced after widespread evidence that poorly-coordinated retrofit — particularly under earlier funding schemes — was causing damp, mould and underperformance. It mandates a whole-dwelling, risk-managed approach rather than bolting on single measures.

Key PAS 2035 roles

Role	Responsibility
Retrofit Assessor	Surveys the dwelling — condition, occupancy, energy, moisture risk
Retrofit Coordinator	Oversees the whole project; manages risk; ensures the standard is met
Retrofit Designer	Specifies the measures and details (incl. moisture/ventilation)
Retrofit Installer	Installs to PAS 2030
Retrofit Evaluator	Checks the outcome against the design

The retrofit assessment and risk pathways

PAS 2035 starts with a proper assessment of the whole dwelling — its construction, condition, exposure, occupancy and existing moisture issues — not just an EPC. It then assigns a risk pathway (with more rigorous requirements for higher-risk buildings, such as traditional solid-wall or heritage construction), and requires that moisture risk specifically be assessed and managed throughout. This is a deliberate shift from 'install the measure' to 'understand the building, then design safely'.

The Medium-Term Improvement Plan

A central PAS 2035 concept is the Medium-Term Improvement Plan (MTIP): even if a homeowner only funds some measures now, the whole-house end state is designed first, so that today's works don't preclude or compromise tomorrow's. This avoids 'lock-in' — for example, installing a heating system sized for an un-insulated house, then insulating later and being left with oversized, inefficient plant; or insulating a wall in a way that makes a future airtightness or ventilation upgrade impossible.

Fabric first

Whole-house retrofit follows a 'fabric first, plant last' logic: reduce the heat demand through insulation, airtightness and good detailing before sizing the heating system. A heat pump fitted to a leaky, poorly-insulated house has to be large and runs inefficiently; reduce the demand first and the plant shrinks, cutting both capital and running cost. This sequencing is covered in depth in the fabric-first article in this guide.

Why this is the RetrofitIQ approach

Common questions from clients.

Do I have to follow PAS 2035 for my retrofit?

PAS 2035 is mandatory for retrofit delivered under most government-funded schemes, and is best practice for any retrofit. If you're paying privately you're not legally bound by it, but its whole-house, moisture-managed, risk-assessed approach is exactly what prevents damp and underperformance — so following its principles (assessment, whole-house plan, moisture risk management, proper ventilation) is strongly advisable regardless of funding.

What is a whole-house retrofit plan?

It's a coordinated design for improving the entire dwelling — fabric, airtightness, ventilation and heating — as one interdependent system, even if the works are carried out in phases. It establishes the end state first (a Medium-Term Improvement Plan), so each measure is compatible with the others and you avoid lock-in, such as installing oversized heating before insulating, or insulating in a way that prevents a later ventilation upgrade.

Why is piecemeal retrofit risky?

Because a house is a system: changing one element affects the others. Adding insulation without ventilation can trap moisture; draught-proofing without warming cold spots concentrates mould; oversizing heating before insulating wastes money. Uncoordinated measures are the main reason retrofits cause damp and underperform — which is precisely why PAS 2035 mandates a whole-house, risk-managed plan instead.