Background
Ventilation
Calculations
Part F — equivalent area schedules.
Every habitable room needs adequate background ventilation to control moisture and indoor air quality. We calculate the correct equivalent area of background ventilators for your project so it meets Part F of the Building Regulations.
- Calculated to current Approved Document F
- Room-by-room equivalent area schedule
- Covers new builds, extensions & window replacements
Part F
Compliant
cm² EA
Equivalent Area
Fast TA
Design Stage
UKwide
Desktop Service
What are background ventilation calculations?
Background ventilation calculations determine the correct equivalent area (cm²) of background ventilators — typically trickle vents fitted in window frames or purpose-made wall ventilators — required in each habitable room of a dwelling to satisfy Part F of the Building Regulations.
Approved Document F sets minimum equivalent area requirements based on room type, floor area and the overall ventilation strategy for the dwelling. Getting these figures right at design stage means your window schedule and ventilator specification are correct before anything is ordered or installed.
Why does it matter?
As new dwellings have become more airtight to achieve Part L energy targets, controlled background ventilation has become the primary defence against condensation, damp and mould. Under-specified ventilators — or none at all — leave building control with grounds to refuse sign-off and leave occupants with a home prone to moisture problems.
Who needs this service?
Developers, architects, building contractors and window installers working on new dwellings, residential extensions, change-of-use conversions, and window replacement projects where building regulations consent is required.
Four reasons to get the calculations right.
Background ventilation is easy to overlook at design stage — and expensive to correct once windows are on order. Here is why it matters.
Part F Compliance
Approved Document F sets minimum background-ventilation requirements. Building control expects documented evidence that ventilators are correctly sized. Our compliance report is produced specifically for that submission.
- Accepted by all UK building control bodies
- Current 2021 edition of Approved Document F
Avoids Redesign & Delays
Getting equivalent areas right at design stage — before windows are specified or ordered — prevents non-compliance at building control and the abortive cost of sourcing replacement units with trickle vents.
- Resolved before window orders are placed
- No abortive window replacement costs
Healthier Homes
Adequate background ventilation reduces condensation, damp and mould — protecting both the occupants and the fabric of the building. Correctly sized ventilators are a straightforward, low-cost way to achieve this from day one.
- Reduces condensation and mould risk
- Protects indoor air quality
Window Replacements Too
Replacing windows can trigger background-ventilation requirements — particularly where existing frames had no trickle vents. We confirm what is needed for your project so you and your window installer know exactly what to specify and avoid a building control hold-up.
- Confirms requirement before windows are ordered
- Clear trickle-vent specification for installers
Right first time, every time.
Calculated to current Approved Document F, with a clear room-by-room schedule and compliance report ready for your building control submission.
Clear value up front
Design-stage advice and a fully documented compliance report are included — no hidden extras for interpretation or follow-up queries.
Calculated to Current Part F
All calculations follow the current Approved Document F (2021 edition). We keep up with changes to the guidance so your submission reflects the current standard.
Room-by-Room Schedule
You get a clear schedule setting out the required equivalent area for every room and ventilator position — exactly what your building control body and window installer need.
Design-Stage Advice
We review your plans and flag any rooms where the ventilation strategy needs revisiting before you place window or ventilator orders — saving abortive cost.
Pairs with SAP & Vent Testing
We carry out SAP calculations and ventilation testing in-house. Bundling the three services under one roof removes the coordination risk and compresses your programme.
Fast Turnaround
Background-ventilation calculations are typically turned around within a few working days of receiving your drawings. Tell us your deadline and we will work to it.
Nationwide Desktop Service
A fully remote, desktop service — no site visit required. We work on projects across England, Wales and Scotland from a single point of contact.
Four steps to your compliance report.
A straightforward desktop process. From receiving your drawings to delivering your compliance documentation, we keep it simple and fast.
Design Review
Send us your floor plans, room schedule and intended ventilation strategy. We review the project scope and confirm what Part F requires for your specific project type.
Equivalent-Area Calculation
We calculate the required background ventilator equivalent area (cm²) for each habitable room and wet room in the dwelling, following the Approved Document F methodology.
Schedule of Vents
You receive a clear room-by-room schedule of the required equivalent area per ventilator position — ready to share with your window supplier or installer for accurate specification.
Compliance Report
We produce a compliance report documenting the calculations and confirming Part F compliance — formatted for your building control submission.
Transparent guide pricing.
Send us your floor plans and a brief project description and we will give you a fixed-price quote — calculation, schedule and compliance report included.
Priced on project scope — dwelling count, room schedule and project type. Send us your drawings for a fixed-price quote.
- Calculated to current Approved Document F
- Room-by-room equivalent area schedule
- Compliance report for building control
- Design-stage review & advice included
Prices vary with dwelling count, room schedule complexity and project type. Contact us for an accurate fixed-price quote.
Part F is only one piece.
Background-ventilation calculations sit alongside SAP, ventilation testing and air pressure testing. We carry out all four in-house.
SAP Calculations
Part L energy compliance for new dwellings. Pairs directly with background-ventilation calculations — the ventilation strategy feeds both assessments.
Find out moreVentilation Testing
BPEC-accredited Part F ventilation testing — the on-site measurement that confirms the installed system is delivering the design flow rates.
Find out moreAir Pressure Testing
Part L air tightness testing for new builds and conversions. The airtightness result directly affects the ventilation strategy — the two assessments work together.
Find out moreGet your background ventilation calculations quote
Takes 60 seconds. No obligation. Send us your drawings and we will confirm the scope and quote the same day.
Background ventilation questions.
Everything you need to know about equivalent area, Approved Document F requirements, and when background-ventilation calculations are needed.
Still Got a Question? Ask Us What is "equivalent area" in background ventilation?
Equivalent area is a measure — in cm² — of how much air a ventilator allows through under a standard test pressure. Approved Document F specifies minimum background-ventilation requirements in equivalent area, so every trickle vent or background ventilator needs to meet the figure calculated for that room or dwelling.
Which rooms need background ventilation?
Approved Document F requires background ventilation in habitable rooms (living rooms, dining rooms, bedrooms) and in rooms containing a bath, shower or WC. We calculate the required equivalent area room by room and produce a schedule for your building control submission.
Do extensions need background ventilation calculations?
Yes, where new habitable rooms are created as part of an extension, the extension will need to satisfy Part F. We confirm the exact requirement for your project based on room usage, floor area and the ventilation strategy.
Does replacing windows trigger a background-ventilation requirement?
It can. Replacing windows in a dwelling can trigger a requirement to provide background ventilation in the replacement units — particularly where the existing windows had no trickle vents. We confirm what is needed for your specific project so you and your window installer know exactly what to specify.
When in the design process should I commission background-ventilation calculations?
At design stage, before windows and ventilators are specified or ordered. Getting equivalent areas right early prevents costly last-minute redesign or non-compliance notices from building control.
How do background-ventilation calculations relate to SAP calculations?
SAP calculations (Part L) and background-ventilation calculations (Part F) are closely linked — both feed into the overall ventilation strategy for a new dwelling. We carry out both in-house, which avoids the coordination issues that arise when they are done by separate consultants. See our SAP calculations page.
What documents do you need from me to run the calculations?
Floor plans and a room schedule — we need room type, floor area and the intended ventilation strategy. For window replacements, existing window schedules are helpful. We will tell you exactly what to send at quote stage.
Do you cover new builds as well as replacements and conversions?
Yes. We calculate background-ventilation requirements for new dwellings, residential extensions, change-of-use conversions, and window replacement projects — wherever Part F applies.
Do you cover all of the UK?
Yes — background-ventilation calculations are a desktop service and can be delivered for projects anywhere in England, Wales and Scotland. Send us your drawings and we will quote.