Is PAS 2035 expensive?

Adds 5–12% to retrofit cost (coordinator + assessor + QA). Often offset by avoided remediation: damp from poor IWI typically costs £8k–£25k to fix later.

Can I do a partial retrofit without it?

Yes for single measures (e.g. loft top-up). Deep retrofit without PAS 2035 risks performance gap, moisture issues and lost grant eligibility.

Does PAS 2035 cover listed buildings?

Yes — Risk Path C with bespoke moisture and heritage controls. Some heritage retrofits also need conservation architect input alongside coordinator.

Does Builderr work to PAS 2035?

Yes for deep retrofits — coordinator-led with PAS 2030 installer network and BPE testing on completion.

Quick Answer

What is PAS 2035 and when does it apply to a London renovation?

PAS 2035 is the British Standard for whole-house retrofit of domestic buildings. It mandates a retrofit coordinator, holistic assessment, designed sequence of measures, moisture-risk management and quality assurance. Mandatory for all government grant-funded retrofit (ECO4, BUS via Home Upgrade Grant routes, Social Housing Decarbonisation Fund). Strongly recommended for any privately funded deep retrofit (>2 measures, EPC uplift >1 band, or pre-1919 solid-brick London stock).

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What it covers

Assessment (U-values, airtightness, ventilation, heritage constraints, occupant needs). Design (sequenced measures, fabric-first, moisture risk, ventilation strategy). Installation (PAS 2030 installers, TrustMark register). Evaluation (post-works testing, BPE — Building Performance Evaluation — for some schemes). Replaces the old measure-by-measure approach with whole-house thinking.

Risk levels

Risk Path A: standard housing, minor measures (cavity, loft). Risk Path B: more complex, exposed/heritage/HMO. Risk Path C: highest — listed, complex, deep retrofit. Each path mandates increasing oversight: assessor level, coordinator involvement, sample sizes for QA.

Why it matters in London

Most London housing stock is pre-1919 solid brick — Risk Path B/C. Moisture risk from incorrect IWI is the dominant failure mode in heritage retrofits. PAS 2035 mandates moisture risk assessment, hygrothermal modelling and ventilation upgrades — exactly the controls that prevent post-retrofit damp problems.

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