Ventilation Survey: IAQ Assessment & Part F Compliance

Quick Answer: A ventilation survey assesses background and extract ventilation against Building Regulations Part F (2021) and identifies indoor air quality (IAQ) defects: missing trickle vents, undersized extract fans, blocked ducts, condensation risk, CO2 buildup. Cost £200–£500 for domestic survey, £600–£1,200 with CO2/RH data-logging. Critical for retrofit projects under PAS 2035:2023 — improving airtightness without addressing ventilation creates condensation and mould.

Summary

UK housing has shifted from leaky (Victorian/Edwardian) to airtight (post-2010 new-build, retrofitted older stock) without consistently updating ventilation strategy. The result: a national mould and condensation problem affecting an estimated 25–30% of dwellings. Awaab Ishak's death in 2020 from mould-related respiratory failure led to "Awaab's Law" amendments to the Housing Act 1988 and renewed focus on ventilation compliance.

A ventilation survey identifies the gap between Part F minimum requirements and what's actually installed. Common findings: missing or sealed-over trickle vents (replaced windows often omit them), kitchen extract running at low CFM, bathroom extract ducted into roof void rather than externally, no whole-house ventilation in airtight retrofits.

For trades, ventilation survey opportunities split into three: pre-retrofit survey (essential under PAS 2035:2023), post-condensation/mould remediation, and rental sector compliance (landlords need documented ventilation assessment). The survey + remediation work bundle generates good margins; survey-only is more modest.

Key Facts

• Building Regulations Part F (2021) — Background and extract ventilation requirements
• Background ventilation (whole-house) — Trickle vents minimum 2,500–8,000 mm² equivalent area per habitable room
• Extract ventilation rates — Kitchen 30 L/s intermittent or 13 L/s continuous; bathroom/WC 15 L/s intermittent or 8 L/s continuous; utility 30 L/s
• Whole-house mechanical — Continuous extract (dMEV) or MVHR (Mechanical Ventilation with Heat Recovery)
• CO2 thresholds — <800ppm good, 800–1,500 acceptable, >1,500 poor (CIBSE TM40)
• Relative humidity — 40–60% optimal; >70% mould risk
• Test equipment — Vane anemometer (£50–£200), CO2/RH data logger (£150–£500), airflow hood (£300–£800)
• PAS 2035:2023 — Specification for retrofit of dwellings; mandates ventilation assessment
• MVHR efficiency — 75–95% heat recovery typical; tested under EN 308
• Survey time — Domestic 1–2 hours on site; 2–4 hours with data logging period

Quick Reference Table

Detailed Guidance

Why ventilation matters more after retrofit

A leaky Victorian house has 15–25 air changes per hour (ACH) infiltration — accidental ventilation. Mould rare because moisture clears quickly.

Modern airtight retrofit (with insulation, new windows, sealed lofts) might have 1–3 ACH. Without engineered ventilation, that's not enough to remove cooking/showering moisture, CO2 from breathing, VOC emissions. Result: condensation on cold surfaces, mould on north-facing walls, headaches/poor sleep from high CO2.

This is the central retrofit error: airtightness without ventilation. PAS 2035:2023 explicitly addresses this — any retrofit improving airtightness must include ventilation assessment.

Part F (2021) — what compliance looks like

For existing dwellings (Part F1B), Building Regulations 2021 require:

Background ventilation:

• Trickle vents in each habitable room (lounge, dining, bedrooms)
• Minimum 2,500 mm² each for kitchen/bathroom
• Minimum 8,000 mm² in living/dining rooms
• Vents at >1.7m above floor

Extract ventilation rates:

• Kitchen: 30 L/s intermittent (when cooking) over hob, or 13 L/s continuous
• Bathroom: 15 L/s intermittent or 8 L/s continuous
• WC: 6 L/s intermittent
• Utility room: 30 L/s

For airtightness below 5 m³/h.m² @ 50Pa (most retrofits aim for this), whole-house ventilation is required (continuous MEV or MVHR), not just intermittent extract.

The standard survey process

1. Pre-visit information — Property age, recent works (insulation, windows, MVHR install), occupant numbers and habits, mould history, heating system
2. Walk-through — Each habitable room photographed, vents and extract fans noted
3. Measure extract rates — Vane anemometer or airflow hood at each extract; compare to Part F minimum
4. Measure trickle vent area — Each vent's free area noted; compare to Part F minimum
5. Visual inspection — Mould, condensation, water damage in each room
6. Test for blocked ducting — Smoke pen near ducted extract to verify external discharge
7. CO2 / RH logging (optional) — 7–14 day data log in bedrooms gives quantitative IAQ data
8. Report — Compliance assessment, defects, recommendations with costs

For a 3-bed semi: 1.5–2 hours on site, 2–3 hours reporting. With data-logging: deploy loggers (15 min), retrieve after 7 days (15 min), analyse data (1–2 hours).

Common defects found

Missing trickle vents: The #1 finding. Replacement windows (FENSA-installed pre-2010) often omitted trickle vents. Post-2010 installations should have them but many don't. Fix: retrofit trickle vents or alternative background ventilation (e.g. mechanical PIV).

Sealed-over trickle vents: Occupants close vents in winter to "stop the draught". Mould then appears. Fix: education + permanently-open vents (occupant can't close).

Undersized kitchen extract: Re-circulating cooker hoods (charcoal filter, no external duct) = zero true extract. Common in flats. Fix: ducted external extract retrofit.

Bathroom extract into roof void: Extract terminates in loft, not externally. Causes loft condensation, can rot timbers. Fix: duct externally with insulated flexible.

MVHR not commissioned: New build with MVHR installed but never balanced/commissioned. Fix: specialist commissioning by qualified installer (NICEIC, BPEC).

Blocked extract ducting: Build-up of grease (kitchen), lint (utility/bathroom). Found in 30%+ of older installations. Fix: duct cleaning or replacement.

Data logging — when to use

CO2 and RH logging provides quantitative evidence. Best used for:

• Mould diagnosis — Distinguish condensation (high RH) from rising damp (lower RH but moisture present)
• Bedroom IAQ — CO2 builds overnight; >2000ppm peaks indicate undersized ventilation
• Pre/post retrofit — Compare conditions before and after ventilation upgrade
• Landlord/tenant disputes — Objective data on whether property meets habitable standard
• MVHR balance check — Verify supply and extract pairs in different rooms

Loggers run 7–14 days minimum to capture variation (weekday vs weekend, weather). Cost adds £100–£300 to survey.

Selling ventilation surveys

Three positioning approaches:

1. Standalone diagnostic (£250–£500): Aimed at homeowners with mould or condensation. Survey identifies cause and remediation. Often leads to retrofit work.

2. Retrofit ventilation assessment (PAS 2035 mandated, £200–£400): Required for any externally-funded retrofit (ECO4, Local Authority Delivery, GBIS). Cost passes to retrofit provider.

3. Landlord HHSRS compliance assessment (£200–£450): Housing Health and Safety Rating System hazard assessment. Documents ventilation adequacy for rental compliance. Aimed at portfolio landlords.

Each opens a different market and has different referral pathways.

Working with TrustMark / PAS 2035

PAS 2035:2023 mandates a "Retrofit Coordinator" oversight role and structured ventilation assessment for any whole-house retrofit. Tradespeople doing ventilation install need:

• TrustMark registration
• PAS 2030 qualifications for installer trade
• MCS certification (if MVHR with heat recovery)

For survey-only work, no certification is mandatory but BPEC ventilation qualifications add credibility.

Worked example — 3-bed terraced retrofit assessment

• Pre-visit information gathering: 30 min
• On-site survey: 2 hours
• 7-day CO2/RH data logger deployment & retrieval: 2 × 30 min
• Anemometer measurements: 30 min
• Reporting and data analysis: 4 hours
• Total time: 8 hours
• Rate £45/hr × 8 = £360 labour
• Data logger hire/use: £50
• Sub-total cost: £410
• 30% margin: £123
• Quoted price: £533 inc. VAT

If retrofit ventilation work follows (typical £2,500–£6,000 for MEV install in this house), survey cost is absorbed by the bigger job.

Frequently Asked Questions

How do I know if a house needs MVHR?

MVHR is appropriate when airtightness is very high (<3 m³/h.m² @ 50Pa) or where running cost of continuous mechanical extract is a concern. Most retrofit projects achieve 4–7 m³/h.m² — continuous extract (MEV) is adequate and cheaper. MVHR for full Passivhaus retrofit or where heating savings justify capital cost.

Can I do a ventilation survey without expensive kit?

Basic survey yes — vane anemometer £50, smoke pen £15. CO2/RH logger £150 used. Total kit cost £200–£300. Professional inspectors use higher-spec (calibrated) equipment for compliance reporting. For homeowner-facing diagnosis surveys, basic kit is sufficient.

Trickle vents seem to cause draughts — is that normal?

Slight cold air feel near trickle vents in winter is normal — by design. If clients complain, options: (1) close vents temporarily (not recommended, mould risk); (2) reposition vents away from sitting/working areas; (3) install humidistat-controlled vents (open more in high humidity); (4) install whole-house ventilation as alternative.

Does Part F apply to refurbishments?

Yes — Part F1B applies to existing dwellings and any work that affects ventilation. Replacing windows triggers trickle vent compliance. Major refurb triggers full Part F assessment. Listed building exemptions limited.

Will improving ventilation lose me heat?

MVHR recovers 75–95% of extract heat. Continuous extract (MEV/dMEV) loses heat — but the ventilation rate is low (~13 L/s), so total annual heat loss is small (£30–£100/year typical). Compare to heat saved by removing mould and damp problems (significant).

Regulations & Standards

• Building Regulations Part F (2021) — Ventilation requirements

• Building Regulations Part F1B — Existing dwellings

• PAS 2035:2023 — Specification for retrofit of dwellings

• PAS 2030:2023 — Installation of energy efficiency measures

• BS 5925:1991 — Code of practice for ventilation principles

• EN 308 — Heat exchangers test methods (MVHR efficiency)

• CIBSE TM40 — Health issues in building services

• HHSRS (Housing Act 2004) — Housing Health and Safety Rating System

• Awaab's Law (Housing Act amendments 2023) — Damp and mould response timeframes for social landlords

• Building Regulations Approved Document F (Volume 1)

• PAS 2035 Retrofit specification

• TrustMark — retrofit standards

• BPEC — ventilation qualifications

• CIBSE TM40 — Health issues in buildings

• thermal imaging survey — pairs with ventilation for retrofit

• damp survey what to expect — damp diagnosis companion

• epc energy performance certificate — energy survey context

• homebuyer snagging survey — broader inspection