A large window can still have too little ventilation opening
This calculator compares each housing room’s floor area with its recognized daylight window area and recognized ventilation opening area under Korean rules.
A quotation’s overall width and height may include fixed glazing and framing.
Treating that entire rectangle as openable ventilation area can hide a shortfall until after the window contract has been signed.
Daylight and ventilation need separate inputs and separate comparisons.
Homeowners reviewing window replacement, family members helping with a parent’s renovation, and small housing landlords changing room layouts can use the result to prepare specific questions for their architect and supplier.
Bring a floor plan and a window schedule, identify the shortfall, and request revised recognized areas before committing to work.
This is arithmetic using entered recognized areas, rather than a site inspection or individual permit assessment.
Scope: confirmed habitable rooms in Korean housing
The legal meaning of a habitable room
Building Act Article 2(1)(6) defines a habitable room by uses including residence, office work, work, assembly and recreation.
The Korean term is broader than an everyday family living room and can include bedrooms depending on their actual use and drawings.
Changing a room label does not settle applicability, and an entire dwelling’s supplied or exclusive area should not be entered as one room’s floor area.
Building Act Enforcement Decree Article 51(1) covers habitable rooms in detached and multi-unit dwellings, school classrooms, medical-facility patient rooms and accommodation guest rooms.
This tool implements only the housing portion of that scope.
Schools, patient rooms and guest rooms require additional use-specific review; shops and officetels are not automatically assigned the housing ratios here.
When use is uncertain, leave applicability unknown and check the building register, permit drawings and actual occupation with the responsible professional.
Compare daylight 1/10 and ventilation 1/20 separately
Daylight window minimum
Daylight minimum = floor area A / 10
Article 17(1) of the Rules on Standards for Evacuation and Fireproof Construction of Buildings requires the ordinary daylight window area to be at least one tenth of the room’s floor area.
Recognized window area is compared; the result does not calculate indoor illuminance or hours of direct sunlight.
Ventilation opening minimum
Ventilation minimum = floor area A / 20
Article 17(2) sets the ordinary ventilation window area at at least one twentieth of floor area.
Use the recognized area of openings that can actually serve ventilation.
A broad sheet of fixed glazing is not the same as a genuinely openable area.
Shortfall = max(0, minimum − recognized area).
Surplus = max(0, recognized area − minimum).
The actual area ratio is recognized area / floor area × 100.
Surplus in one independent review unit is not transferred to another room to cancel its shortfall.
Comparisons use unrounded numbers; formatting a small difference on screen does not change the underlying status.
Enter recognized areas with their evidence
- Floor area: enter the reviewed room’s area in square metres.
Align the boundary with your architect and do not mix pyeong, supplied dwelling area or the entire unit’s exclusive area.
- Daylight window area: use the area recognized for the room’s daylight calculation.
Check how the supplier’s outer-frame or glass dimensions were converted into the reviewed figure.
- Ventilation opening area: use a verified figure reflecting the opening configuration and restrictions.
Fixed portions, overlapping sashes, opening restrictors and product details need review.
The calculator supplies no invented recognition factor.
- Basis and date: record the drawing identifier, window-schedule revision, reviewer and calculation notes.
The date records when the evidence was actually checked; it does not select a historical version of the law.
Blank and zero mean different things
Leave an unknown area blank while waiting for drawings or a supplier’s reply.
Enter zero only when the absence of recognized area has been verified, such as a room with no openable ventilation portion.
A blank value pauses that comparison; a verified zero is compared with the ordinary minimum.
Each area supports up to 100,000 m² and six decimal places.
These are software input limits, not permitted building sizes.
Combining two rooms requires a verified sliding partition
Article 17(3) treats two habitable rooms divided by a sliding partition that can be opened at any time as one room when applying paragraphs (1) and (2).
Select the two-room mode, confirm that condition, and enter a basis and verification date.
The tool then adds the two floor areas and separately adds their daylight and ventilation areas.
If the connection is unconfirmed, it pauses the combined result even when all areas have been entered.
An ordinary door, or merely occupying the same home, does not automatically justify combining rooms.
Groups of three or more, balconies, double-window arrangements and obstructions are not automatically recognized.
Number the reviewed rooms on your drawing to avoid entering a room or window twice in different review units.
Switching back to single-room mode excludes the second room from calculation; the TXT review explicitly identifies the hidden room as excluded.
Verify lighting and ventilation equipment exceptions independently
Daylight lighting exception
The proviso to Article 17(1) refers to lighting devices providing at least the illuminance in Annex 1-3 for the room’s use.
For residential reading, dining and cooking the annex gives 150 lx; other residential use is 70 lx.
The measurement plane is horizontal, 85 cm above the floor.
A bulb’s wattage or lumen output alone does not establish this exception.
Check the installation, use and supporting evidence separately.
Ventilation equipment exception
The proviso to Article 17(2) refers to installation of mechanical ventilation equipment and centrally managed air-conditioning equipment.
The tool does not decide whether a particular installation satisfies that provision.
Owning an ordinary fan, air cleaner or recirculating room air conditioner does not establish the exception.
Ask the architect or services professional which equipment and applicable conditions support the individual confirmation.
An exception under review pauses only its own comparison.
A confirmed exception requires its separate supporting basis and a verification date, then marks that ratio as not applied.
Reference minimum areas remain visible when known, while shortfall, surplus and actual-ratio comparison are left empty.
An exception does not turn the minimum into zero, certify equipment performance or issue an approval.
Missing exception evidence returns that item to pending; do not copy a daylight exception into the ventilation field without independent confirmation.
From drawings to a saved review
- Confirm the building use and reviewed room, then select housing applicability.
Keep it unknown while the relevant documents are missing.
- Enter floor, recognized daylight and recognized ventilation areas in m².
Use the same drawing revision and avoid filling unknown figures with guesses.
- For a combined pair, verify the freely openable sliding partition and document the basis.
Being in the same dwelling is insufficient on its own.
- Confirm area evidence, enter its basis and date, and review lighting and ventilation exceptions separately.
Supply an individual basis for each confirmed exception.
- Read the shortfalls and pending reasons, save the TXT review, and take it with the drawings to your consultation.
Recalculate after revised recognized areas are supplied and check that you are sharing the current file.
Worked examples: a 20 m² room and a combined pair
These are fictional arithmetic examples, not recognized areas for a real property or recommended window dimensions.
Ordinary-ratio comparisons assume confirmed applicability, recognized areas and evidence.
Fictional room areas and daylight and ventilation minima, recognized areas and shortfalls| Scenario | Floor m² | Daylight min / entered / short m² | Ventilation min / entered / short m² |
|---|
| Room A alone | 20 | 2 / 1.8 / 0.2 | 1 / 0.8 / 0.2 |
| Room A at both minima | 20 | 2 / 2 / 0 | 1 / 1 / 0 |
| A+B, partition verified | 30 | 3 / 3 / 0 | 1.5 / 1.5 / 0 |
Room A has 20 m² of floor, 1.8 m² of daylight area and 0.8 m² of ventilation area.
Its minimum areas are 2 m² and 1 m², so each shortfall is 0.2 m².
If room B has 10 m² of floor, 1.2 m² of daylight area and 0.7 m² of ventilation area, a verified Article 17(3) partition produces totals of 30, 3 and 1.5 m².
Both ordinary ratios are then exactly met.
Separate reviews, or an unverified connection, cannot use this combined result to remove A’s shortfalls.
For a 20 m² room with verified zero ventilation opening, the ventilation shortfall is the full 1 m² minimum.
Use the status to decide what to check next
- At or above ordinary area ratio: the entered area meets the arithmetic ratio.
Brightness, airflow, thermal performance, safety and permit conditions remain separate questions.
- Below ordinary area ratio: mark the affected item and missing m² on the drawing.
Ask the supplier for the revised recognized area and dimensions before deciding whether a whole window must be replaced.
- Pending: applicability, floor or recognized area, partition conditions, exception review or evidence is missing.
An independently verified result for the other item can remain available.
- Confirmed exception: the ratio is not applied for this review.
This is not an equipment certificate or administrative approval.
- Outside supported scope: obtain a use-specific review for classrooms, patient rooms, guest rooms or another unsupported use.
The saved review retains room inputs, whether a hidden second room was excluded, evidence dates, exception bases and pending reasons.
Check the drawing version against actual site conditions before sharing it.
Inputs are not stored on a server, so download any required review before closing the browser.
Review any personal information you have put in free-text notes before sharing the file.
Practical use during replacement and room subdivision
Compare equivalent replacement quotations
Two similarly priced windows can allocate fixed and openable portions differently.
An unchanged external size does not guarantee unchanged ventilation opening area.
Ask each supplier to use the same recognized-area basis before comparing proposals.
Expanded balconies, obstructions and double-window arrangements require architectural review beyond a simple product rectangle.
Review the rooms after subdivision
A new partition can change which room a window belongs to and how each space is classified.
Enough window area for the original open dwelling does not establish enough area for every newly divided room.
A proposed sliding partition still needs confirmation of the freely openable condition and drawings.
Structure, substantial alteration, escape, smoke exhaust and fall protection require separate checks.
Sufficient daylight window area does not establish sufficient direct-sunlight hours or perceived brightness where orientation, nearby buildings or shading differ.
Opening area also does not predict actual outdoor airflow, wind direction, CO₂ concentration, mould prevention or health safety.
Do not present an area-ratio result as a comfort certificate or construction approval.
Frequently asked questions
Does fixed glazing count as ventilation area?
Separate light-transmitting glass from openings that actually serve ventilation.
Enter independently verified recognized areas for daylight and ventilation.
Can I enter half of a sliding window’s total area?
The tool does not apply a universal 50% factor.
Use an area verified for the frame, overlap, opening limits and actual configuration.
Can a bedroom be a habitable room?
Yes, the legal term covers rooms used for residence and is broader than a family living room.
Confirm the actual use and applicable drawings.
Does any door allow two rooms to be combined?
Article 17(3) concerns two rooms divided by a sliding partition that can be opened at any time.
Ordinary doors and groups of three or more are not automatically combined.
Does owning an air conditioner remove the ventilation-window ratio?
A recirculating air conditioner alone does not establish the exception.
Verify the equipment and conditions in the proviso to Article 17(2) and record the individual basis.
Can brighter lights replace the daylight-window requirement?
An Annex 1-3 lighting exception exists, but this tool does not measure or approve it.
Verify residential reading/dining/cooking 150 lx or other residential use 70 lx on a horizontal plane 85 cm above the floor.
Does the tool reconstruct old permit rules?
No.
The law snapshot was checked 2026-10-26 and uses the Rule and Decree effective 2026-10-06.
An evidence date does not automatically apply historical provisions or transitional rules.
Can I sign a contract when both ratios are met?
The result confirms only the entered-area arithmetic.
Verify recognized areas, site dimensions, exceptions and separate safety, design and permit requirements with your architect and supplier before deciding.
Official sources, dates and the next contract check
Sources were checked on 2026-10-26 using direct current-law search, article and annex calls to the National Law Information OPEN API.
The Rule and Decree versions took effect on 2026-10-06; the Building Act definition version took effect on 2026-02-27.
Annex 1-3 itself displays an amendment date of 2012-01-06.
These are Korean 2026 rules, not internationally applicable building standards.
Open your floor plan and window schedule, then verify both recognized areas for each room.
Save the shortfalls and unresolved points and ask your architect or supplier about revised dimensions, partition eligibility and lighting or ventilation exceptions.
Recheck amendments and the rules applicable to the individual permit immediately before contracting.