Three editions
2010, 2021 and 2026, each with its own method and its own table. Which applies depends on when the work was notified.
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Ventilation, design stage
Part F trickle vent calculator
Background ventilator equivalent area for System 1, under whichever edition of Approved Document F applies to the work.
The 2010 and 2021 editions do not size ventilators the same way. 2010 reads a dwelling total from a floor-area band crossed with the bedroom count; 2021 fixes an area per room and drops floor area entirely. The tool changes shape with the edition rather than blending the two. The 2026 edition carries the 2021 tables unchanged.
Everything is calculated on this device. When you download a report or save a file, any supplied contact and project details are sent securely to Briary and retained separately from anonymous Tool Insights; calculation values are not retained. Read our tool privacy information.
The awkward cases
Single storey, a leaky design permeability, a restricted façade and open-plan kitchens all change the answer, and each is handled explicitly.
Check a real schedule
Enter the equivalent area the window schedule actually provides and the tool says whether it is enough, and by how much it is short.
The dwelling AD F 2021
Rooms 4 ventilators
| Room | Number | Each | Total |
|---|
Not enough ventilators. Paragraph 1.57 wants at least
5 ventilators across the habitable rooms and
kitchens; the schedule has 0.
.
Open-plan kitchen and living room. Note 2 to Table 1.7 wants no fewer than
three ventilators, each of the habitable-room equivalent area, within the open-plan space.
Restricted façade. Under the 2021 and 2026 editions, note 1 to Table 1.7
says the table should not be used where the dwelling has one exposed façade or 70% of its
openings on one façade, and that expert advice should be sought. Under the 2010 edition the
full area is repeated at a low position, which the figure above includes.
The per-room minima govern. The sum of 5000 mm² per habitable room and
kitchen plus 2500 mm² per wet room exceeds the Table 5.2a dwelling total, so it is the
figure to work to.
Check a proposed schedule Optional
Use the equivalent area at 1 Pa from the product data, not the free area or the physical opening size.
Project and your details Needed for the PDF
The name and company are printed on the PDF report and are needed before it can be produced. Everything else here is optional and is printed only if you supply it.
Method, data and scope
The 2010 and 2021 editions of Approved Document F do not size background ventilators the same way. The 2010 edition reads a whole-dwelling equivalent area from Table 5.2a, a floor-area band crossed with the bedroom count, then distributes it subject to per-room minima of 5000 mm² in a habitable room and 2500 mm² in a wet room. The 2021 edition abandons the dwelling total and fixes an area per room in Table 1.7: 8000 mm² for a habitable room or kitchen, 4000 mm² for a bathroom, none for a utility room or sanitary accommodation, with the habitable and kitchen figures rising to 10,000 mm² in a single-storey dwelling.
The 2026 edition carries the 2021 ventilation tables unchanged. Only the paragraph numbering moved, and a new Table 1.8 was added limiting the design static pressure of ductwork.
This covers System 1 only, background ventilators with intermittent extract fans. Systems 2 to 4 size their ventilators differently. Extract rates, purge provision, internal door undercuts, commissioning and the interaction with open-flued combustion appliances all sit outside this tool.
Approved Document F is guidance, not the requirement itself. Other ways of meeting requirement F1 are available.
Help
How to use this tool
Start here, then keep the guide open alongside your work. Expand a section for the information you need.
Before you start
Have the bedroom count, the total floor area of all storeys, the room schedule and, if you are checking a proposal, the equivalent areas from the window schedule. Establish which edition of Approved Document F applies to the work before anything else: the 2010 and 2021 editions do not size background ventilators the same way, and the tool changes shape with the edition rather than blending them.
1. Choose the edition
The 2021 edition applies in England to work notified from 15 June 2022; the 2010 edition applies to earlier work and in Wales. The 2026 edition carries the 2021 tables unchanged, with paragraph renumbering and a new duct pressure table. The 2010 method reads a dwelling total from a floor-area band crossed with the bedroom count; the 2021 method fixes an area per room and drops floor area entirely.
2. Describe the dwelling
Bedrooms and total floor area across all storeys. Single storey up to the fourth storey above ground adds to the 2010 figure. A design air permeability leakier than 5 m³/(h·m²) at 50 Pa moves you to a different table under 2010. A dwelling with one exposed façade, or with 70% of its openings on one façade, is a case the 2021 table says should not be used at all.
3. Count the rooms
Habitable rooms excluding the kitchen, then kitchens, utility rooms, bathrooms and sanitary accommodation. Under the 2021 method each room type carries its own equivalent area and the total is their sum. Under 2010 the per-room minima are a floor: where they add up to more than the dwelling total from the table, they govern, and the tool says so.
4. Check the proposed schedule
Enter the equivalent area the window schedule actually provides. Use the equivalent area at 1 Pa from the product data, not the free area and not the physical opening size — they are different numbers and mixing them up is the most common error in this calculation.
What is outside this tool
System 1 only: background ventilators with intermittent extract fans. Extract rates, purge provision, commissioning, the interaction with open-flued appliances in Approved Document J, and the whole-dwelling ventilation rate are all separate questions. Ventilator positioning, height above floor level and control are outside it too.
PDF, saving and support
The PDF needs your name and company under Project and your details. It records the edition, the table used and the room-by-room build-up. Save inputs writes a .briaryvent file. For problems, email toolsuite@briary.co.uk with the tool name, browser and what you entered.
Tell us about your project
Send the location, project stage and current drawings. We will confirm the assessment route and information needed.