Foreword
This is a private standard published by Trueinch. It is not an American National Standard.
What it is. This Part sets the checks, thresholds, climate rules, room hours and area rules for homes in the United States. The method that turns them into a True Inch Score is in Part 1, and the way the standard is kept is in the Procedures.
Where its values come from. The values come from three kinds of source:
Public codes, read in their own text: the International Residential, Building, Property Maintenance and Energy Conservation Codes; the HUD Code; the Fair Housing Act's regulations and guidelines; the 2010 ADA Standards.
Public summaries of paywalled standards: ANSI Z765, ASHRAE 62.2 and 55, NKBA.
Where no standard sets a level, our own measure, stated as such, with its reason in Annex F.
What to check before 1.0 is final. A value marked [U] in the research notes was not confirmed in a primary text. Each one is listed in Annex F and shall be confirmed before this edition leaves trial use.
Editions of the codes. The base edition is the 2021 I-Codes, with every 2024 change noted. The 2024 IRC renumbers Chapter 3, so both numbers are given (2021 / 2024).
Introduction
US buyers mostly judge houses, measured by a national standard (ANSI Z765), in climates that run from Miami's heat to Minnesota's cold.
What changes from India.
Mechanical ventilation and air conditioning are the norm, so natural ventilation counts for as much as the climate makes it worth (5.4).
Glass is low-e and double-glazed, so the defaults say so.
The codes differ by building type and by state, so this Part starts with three switches (4.1).
1Scope
1.1 This Part applies to dwellings in the United States and its territories:
Houses and townhouses under the IRC, including ADUs.
Apartments and condominiums under the IBC (group R-2).
Manufactured homes under the HUD Code (24 CFR 3280).
Existing homes: the IPMC's habitable-room rules overlay the checks.
1.2 It does not apply to hotels, dormitories, assisted living or boarding houses.
2Normative references
Codes
| Code | Edition and sections |
|---|---|
| ICC IRC | 2021, with 2024 changes: R302.5, R303, R304, R305, R307, R310, R311, R312, R314, R315; M1505; G2406; P2705; P2708 |
| ICC IBC | 2021: Chapters 10 and 12 (1011, 1015, 1031, 1202, 1204, 1208) |
| ICC IPMC | 2021 and 2024: Chapter 4 |
| ICC IECC | 2021 and 2024: R301 (climate zones), R402.1.2, R403.6 |
| HUD Code | 24 CFR 3280.106, .109, .404 |
| Fair Housing Act | 24 CFR 100.205, with the Fair Housing Accessibility Guidelines (1991) |
| ICC A117.1 | 2017: 1104 (Type B) and 1105 (Type C) |
| 2010 ADA Standards | Referenced for dimensions only. They do not cover private homes |
Measurement
ANSI Z765-2021, Square Footage: Method for Calculating.
Fannie Mae Selling Guide B4-1.3-05.
ANSI/BOMA Z65.4, for multi-unit residential.
Ventilation and comfort
ASHRAE 62.2-2025, Ventilation and Acceptable Indoor Air Quality in Residential Buildings.
ASHRAE 55-2023, Thermal Environmental Conditions for Human Occupancy: the adaptive model and elevated air speed.
Daylight. These are the basis for this Part's levels:
IES LM-83-23;
EN 17037:2018+A1:2021 and its UK National Annex.
Other references. These are the basis for this Part's levels:
ICC/ASHRAE 700-2020, the National Green Building Standard;
UK Approved Document F (2026), for the purge rate;
UK Approved Document M4(2) (2015, 2016 amendments), for bed clearances;
NKBA Kitchen and Bath Planning Guidelines, through public summaries.
Local overlays
California Residential Code (2022 and 2025), and Title 24 Part 6 Table 150.0-G.
New York City Building Code (2022), and New York Multiple Dwelling Law §§30–31.
3Terms and definitions
These add to Part 1 §3.
| Term | Definition |
|---|---|
| Habitable room | A room for living, sleeping, eating or cooking (IRC). Bathrooms, toilet rooms, closets, halls, storage and utility spaces are not habitable rooms. |
| Sleeping room | A room used, or labelled, as a bedroom. |
| Emergency escape and rescue opening (EERO) | An operable window or door from a sleeping room or basement that a person can get out through, as IRC R310 / R319 requires. |
| Finished area | Area suitable for year-round use, with finishes like the rest of the house, measured as ANSI Z765 says (§9). |
| Above grade, below grade | As ANSI Z765 says. A level is below grade if any part of it is. |
| Covered multifamily | An apartment building of 4 or more units, first occupied after 13 March 1991, where the Fair Housing Act's design requirements apply. That means every unit where there is an elevator, and ground-floor units where there is not. |
| Visitable | ICC A117.1 Type C: a step-free entrance, an entrance level with a toilet room, and a 36″ route. |
| SHGC | Solar heat gain coefficient: the share of the sun's heat a window lets through. |
| Window-pleasant hours | The hours a year when opening windows is pleasant, defined in 5.4. |
4Inputs, switches and defaults
4.1 Switches. Three inputs change which rules apply. Each comes from the plan where it can, and otherwise from a question.
| Switch | Values | What it changes |
|---|---|---|
| Building type | House or townhouse; apartment; manufactured home; existing home | Ceiling minimums, the 120 ft² room rule, escape-window scope, the fall threshold, guard heights, the area method |
| Jurisdiction | From the place | California and New York City carry their own rules (Annex B). Elsewhere the IRC 2021 applies, with 2024 noted |
| Fair Housing Act coverage | Apartments only: covered or not | When covered, its design requirements become gates. Otherwise they are graded references |
4.2 Defaults. Each default used shall be listed in the report as assumed.
| Input | Default |
|---|---|
| Ceiling height, where not printed | 9′0″ (SP-8 isn't scored) |
| Window sill and head | 36″ and 80″ |
| Window type | Single-hung: openable share 0.40, in the lower half. Casement 0.80, slider 0.40, awning 0.35, sliding door 0.45, fixed 0 |
| Glazing | Double-glazed low-e: visible transmittance 0.60; SHGC by climate zone (Annex B) |
| Door clear width | The leaf minus 2″ for a hinged door; half, minus 1″, for a sliding pair; minus 2″ at each side for a bifold, where its leaves fold; minus 1″ for a pocket door. A way in with no door hung in it (the open side of a porch) isn't held to a door's widths |
| Doors inside | Open by day for air, as their swings are drawn |
| Kitchen exhaust | A ducted hood at 100 cfm capturing half of what is cooked: ASHRAE 62.2's minimum |
| Bath fans | 50 cfm intermittent, as the code requires. They are off when smells are traced |
| Terrain | Suburban for houses; city for apartments |
| Surroundings | Open sky |
| Floor level | Houses: the ground. Apartments: unknown (ask) |
| Household | Bedrooms + 1: the primary bedroom holds 2 and each other bedroom 1. Or the owner's household |
4.3 Questions, in order of value. The report asks only what changes its result:
which way the front door faces, where the plan has no north arrow;
the building type, where it's unclear;
the floor, for an apartment;
Fair Housing Act coverage;
sill heights and window types;
floor-to-floor height, where there are stairs;
whether a fan or a ducted hood is fitted;
the fuel of any furnace or water heater drawn.
5Climate
5.1 Zone. The climate zone is IECC Table R301.1's zone for the place's county. Where the county is unknown, it is worked out from the typical year by R301.3 (Annex B).
5.2 The typical year. It is PVGIS's typical meteorological year for the place: hourly temperature, humidity, wind and irradiance.
5.3 Welcome and unwelcome sun.
w = cool sunny hours ÷ (cool sunny hours + hot sunny hours)
Cool is outdoor air at 20 °C or below; hot is 27 °C or above.
Sunny means direct normal irradiance of at least 120 W/m² (WMO's sunshine threshold), in daytime.
Expected values (informative; computed on the typical years before 1.0 is final):
Zones Expected w 1–2 0.1–0.35 3 0.4–0.6 4A/B 0.55–0.7 3C/4C 0.8 or more 5–8 0.75 or more
5.4 Window-pleasant hours. H_win counts the hours from 7 am to 11 pm in the typical year when all of these hold:
the outdoor temperature is within ASHRAE 55's adaptive 80% band, from the running mean outdoor temperature (outside a running mean of 10–33.5 °C, 20–26 °C is used);
the dew point is 17 °C or below;
the wind is 7 m/s or below;
it isn't raining, where the year records rain.
The natural-ventilation checks (AR-1, AR-2, AR-3, AR-6) take their weights × m:
f = H_win ÷ 5,840 (the waking hours of a year) m = 0.4 + 0.6 · f
The floor of 0.4 is there because a home must always be able to air out after cooking, cleaning or painting.
5.5 Usual wind.
The median 10 m wind speed, and the most frequent of 16 directions, over the window-pleasant hours of the three warmest months.
Where those hours are fewer than 100: 3 m/s from the year's most frequent direction.
6The checks
How to read the tables.
Levels follow Part 1 §6: minimum 50, medium 75, high 100. Zero is where the curve reaches 0 points.
"↓" marks a check where less is better.
"Kind" names the source's kind: code, standard, recommendation, convention or our measure.
6.1Space
SP-1 Room sizes (gate). Habitable rooms only. There are no grades: fit (SP-2 to SP-4) grades quality.
| Building | The gate fails when |
|---|---|
| House | A room is under 70 ft², or under 7′0″ in any horizontal direction. Kitchens are exempt. Floor under a sloped ceiling below 5 ft, or a furred ceiling below 7 ft, doesn't count (IRC R304 / R325) |
| Apartment | As for a house, and: no room of 120 ft²; an efficiency unit's living room under 190 ft²; a kitchen passage under 36″ (IBC 1208) |
| New York City | A room under 80 ft² or 8′0″ wide; no room of 150 ft² (NYC BC 1208) |
| Manufactured home | The HUD Code's room areas (24 CFR 3280.109) |
Kind: code.
SP-2 Bedroom fit. Each bedroom. The levels are discrete.
| Bedroom | Minimum | Medium | High |
|---|---|---|---|
| Primary | A queen (60×80″) with ≥ 24″ on both sides and at the foot, and a 36″ route from the door | A king (76×80″) with ≥ 30″ on both sides and at the foot, and a 60″ dresser with 36″ clear in front | A king with ≥ 36″ all round, the dresser with 36–42″, and a chair, a dressing area or a walk-in |
| Others | A twin (38×75″) with 24″ along one side, and a 36″ route | A full or queen with 24″ on both sides, or a twin plus a 48×24″ desk with 36″ for the chair | A queen with ≥ 30″ on both sides, and a desk or dresser with 36″ clear |
Kind: the bed sizes are a convention (ISPA). The 30″ clearance is a recommendation (UK Approved Document M4(2) §2.25: 750 mm); the 24″ and 36″ clearances are practice.
SP-3 Living and dining fit. The living space and the dining area. P is the design household.
| Space | Minimum | Medium | High |
|---|---|---|---|
| Living | Seats for P (an 84″ sofa and a chair). A 55″ TV at 1.2–2.0 × its diagonal (5.5–9 ft). A 30″ walkway that doesn't cross between the seats and the TV | Seats for P + 1. A 65″ TV at 1.2–1.6 × its diagonal (SMPTE/THX). 36″ walkways | Seats for P + 2, and a reading spot by a window. 42″ walkways |
| Dining | A table for P (24″ a place), with 32″ from its edge to a wall where nobody passes | P + 2 seats; 36″ where people edge past, 44″ where they walk past | P + 4 seats, or an extending table, with 44″ wherever people pass |
Kind: recommendation (NKBA's seating clearances) and convention. The two spaces are combined by their room hours.
SP-4 Kitchen capacity. The kitchen.
| Minimum | Medium | High |
|---|---|---|
| Range, sink, fridge and dishwasher all fit, with a landing area beside the cooktop and the fridge | NKBA landing areas at the sink, cooktop and fridge; usable counter ≥ 158″ [U]; dishwasher within 36″ of the sink | Usable counter ≥ 198″ [U]; island seating at NKBA's 32/36/44″; a pantry (SP-5) |
Kind: recommendation (NKBA). The aisles are in LY-5.
SP-5 Storage. The home. Its points are the mean of two sub-checks.
| Sub-check | Minimum | Medium | High |
|---|---|---|---|
| Bedroom closets | Every bedroom has a closet ≥ 24″ deep, with ≥ 4 ft of rod per occupant | ≥ 6 ft of rod per occupant; the primary has ≥ 10 ft, or a walk-in | A primary walk-in (≥ 5 ft wide one-sided, ≥ 7 ft two-sided) with ≥ 14 ft of rod; others ≥ 6 ft each |
| The house | A coat closet anywhere; a pantry cabinet | A coat closet at the main entry; a linen closet near the bedrooms; a reach-in pantry | A walk-in pantry, and a drop zone or mudroom at the garage door |
Kind: convention and recommendation [U]. The UK space standard's built-in storage (1.0–4.0 m²) is the reference.
SP-6 Outdoor space. Applies where outdoor space is drawn. If none is drawn, the check isn't scored, and the report asks: "Is there a private patio, deck or balcony?". Answered yes, it is taken at the minimum until it is drawn; no, it scores 0.
| Home | Minimum | Medium | High |
|---|---|---|---|
| House | A private patio, deck or porch ≥ 54 ft² (5 m²), reached from a living space | ≥ 100 ft², ≥ 5 ft deep, with a door from the living space, dining area or kitchen, and a table for P | ≥ 200 ft², or a covered outdoor room seating P + 2 |
| Apartment | A balcony ≥ 4 ft deep that takes two chairs | 5 m² + 1 m² for each person beyond two, ≥ 1.5 m deep | Twice that, or a table for P |
Kind: our measure. The London Plan's size is the reference [U].
SP-7 Floor that is only for passing ↓. The home: halls, stairs and passage strips that can't be furnished, as a share of the floor. Open-plan walkways that are also living floor don't count. A space the drawing leaves unnamed counts where it is as narrow as a hall (1.5 m, 4′ 11″, or less) and opens into two rooms or more.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 35% | 20% | 15% | 10% | Linear |
Kind: our measure. Its anchors stay provisional: the reference set can't fix them (Annex A).
SP-8 Ceiling height. Gate and grades. Scored only where printed, or given by the owner.
Gate:
houses: under 7′0″ in habitable rooms and halls, or under 6′8″ in a bath or laundry;
a sloped room needs half its area at 7′0″, and floor under 5 ft is excluded;
basement obstructions down to 6′4″ are allowed.
apartments: under 7′6″;
New York City: under 8′0″.
Levels: minimum, the gate's value; medium, 8′0″; high, 9′0″.
Kind: code (IRC R305 / R313; IBC 1208.2; NYC BC 1208.2) and convention.
SP-9 Carry-in. Big pieces reach their rooms through every door and turn. The levels are discrete.
| Minimum | Medium | High |
|---|---|---|
| A 36″ fridge (36×31×70″), the range, and 27″ washer and dryer reach their places | Also an 84″ sofa (36″ deep, 32″ high) to the living space, and a queen mattress to every bedroom | Also a king or split-king box spring to the primary bedroom, and a 90″ sofa section |
Kind: our measure, with real US product sizes.
SP-10 Laundry. The home.
| Minimum | Medium | High |
|---|---|---|
| Room for 27″ machines, stacked or side by side, with the dryer able to vent outdoors and 36″ clear in front | A laundry room or closet for side-by-side machines (≥ 5 ft wide) with 42″ in front, on the bedroom floor or within 30 ft of the bedrooms | A laundry room with a ≥ 36″ folding counter and a sink, within 15 ft of the primary closet or the bedroom hall |
Kind: recommendation (NAHB's most-wanted feature; NGBS requires the dryer to vent outdoors).
6.2Daylight
DL-1 Window area (gate). Habitable rooms.
The gate fails when glazing (its windows' and its glass doors') is under 8% of the room's floor (New York City: 10%).
The adjoining-room rule applies first (IRC R303.2): a room may count an adjoining room's windows when at least half the common wall is open, and the opening is at least a tenth of the interior room's floor and 25 ft².
Wording: a failure reads "below the natural-light minimum". IRC 2024 and the IBC let electric light at 6 fc substitute, so it reads "confirm the alternative" for a new home. For an existing home under the IPMC, it is the code's requirement.
Kind: code (IRC R303.1 / R325.1.1; IBC 1204; IPMC 402.1; NYC BC 1205).
DL-2 How bright by day. Each habitable room.
The quantity, E50: the illuminance reached over half the work plane for half the daylight hours. It is the room's median daylight factor × the site's median diffuse horizontal illuminance, from the typical year.
| Room | Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|---|
| Living, dining, office | 15 lux | 150 lux | 300 lux | 500 lux | Log |
| Kitchen | 20 lux | 200 lux | 300 lux | 500 lux | Log |
| Bedroom | 10 lux | 100 lux | 150 lux | 300 lux | Log |
Kinds and sources.
Minimum: the UK National Annex to EN 17037 for dwellings (standard).
Medium and high: EN 17037's minimum and medium levels (standard).
Bedroom medium: LEED v5's sDA150 for spaces without visual tasks (standard).
Pairing and edition 1.1.
This check is paired with SN-2, unwelcome sun.
Edition 1.1 adds annual sDA300/50% (LM-83-23: 55% accepted, 75% preferred) as a cross-check.
DL-3 Depth and evenness. Each habitable room.
The quantity, E95: the illuminance reached over 95% of the work plane for half the daylight hours.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 5 lux | 50 lux | 100 lux | 300 lux | Log |
Kinds and sources.
Medium and high: EN 17037's minimum and medium second criterion (standard).
Minimum: our measure.
Fact shown beside it: the room's depth over its window-head height. A single-sided room deeper than 2.5 × the head height is noted.
6.3Sun
The mix. Sun = w · SN-1 + (1 − w) · SN-2, with w from 5.3.
SN-1 Welcome sun. The living space carries 0.6 and the bedroom with the most sun 0.4, following EN 17037's "at least one habitable room", with the living room preferred.
The quantity: the hours the room is in sun (Part 1 §5.3) on the 21st of the typical year's coolest month (21 January without it). Edition 1.1 averages the typical year's days with cool sunny hours: following the sun through every such day is some ten times a report's work in 1.0.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 0.15 h | 1.5 h | 3 h | 4 h | Log |
Kind and source. Standard: EN 17037's sunlight exposure levels. No US code or standard rewards sun in homes, and US daylight standards treat it as glare; this Part borrows the European levels and says so.
SN-2 Unwelcome sun ↓. Each habitable room.
The quantity: the room's solar heat through its glass on the 21st of the typical year's warmest month (21 July without it; edition 1.1: over its hot sunny hours), with the zone's assumed SHGC (Annex B).
Its unit: an equivalent share of west glazing. That is the room's gain ÷ the gain of 1 m² of unshaded west glass at the same site in the same hours, per m² of the room's floor.
In words: "this room takes the summer sun of a room with X% of its floor in west windows."
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 16% | 8% | 4% | 2% | Linear |
Kinds and sources.
Minimum: the IRC's 8% glazing, all of it facing west.
Medium and high: NGBS 703.7.1's east (4%) and west (2%) glazing budgets (standard).
Shading. An overhang drawn on the plan is modelled. NGBS Table 703.7.1(7) is shown as the guide.
6.4Air
How these checks are weighted. AR-1, AR-2, AR-3 and AR-6 rate natural ventilation, so their weights are × m (5.4).
AR-1 Openable area. Each habitable room, after the adjoining-room rule.
Gate: fails when openable area (what opens of its windows and glass doors: half of a sliding one) is under 4% of the floor (IPMC, existing homes: 3.6%; New York City: 5%).
For a new home with whole-house mechanical ventilation, a failure reads "relies on mechanical ventilation, confirm" and carries no penalty.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 0% | 4% | 5% | 8% | Linear |
Kinds and sources.
Gate and minimum: code (IRC R303.1 / R325.1.2; IBC 1202.5; IPMC 403.1; NYC BC 1203.5); ASHRAE 62.2 §6.5 for detached homes.
Medium: the strictest US code (New York City).
High: our measure.
AR-2 Fresh air. Each habitable room.
The quantity: outdoor air changes an hour with the windows open by their type's share, in the usual wind.
Shown beside it: the same in still air, from the stack effect alone.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 0.4 | 4 | 8 | 15 | Log |
Kinds and sources.
Minimum: the purge rate of UK Approved Document F (2026), a standard used as reference.
High: NIST's ventilative-cooling rates (our measure).
AR-3 Cross-ventilation. The home.
The quantity: the share of habitable floor, by room hours, in rooms with openings on two façades. Opposite façades count 1.0, adjacent façades 0.75, and a path through an open door 0.5.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 0% | 25% | 50% | 75% | Linear |
Kind and source. Recommendation: NGBS 902.1.5 (two operable openings on adjacent or opposite walls); IGBC's tiers.
AR-4 Wet rooms. Each bathroom, toilet room and the kitchen.
There is no gate fail for a windowless bath. ASHRAE 62.2-2025 requires a fan in new toilet rooms, and the IRC accepts one, so the report reads "needs a 50/20 cfm fan ducted outdoors, confirm".
It fails only where a fan is known to be absent.
California: every bath with a tub or shower needs a fan, whether or not it has a window.
Points: 50 for the code met (fans assumed), plus 25 × the share of full baths with an openable window, plus 25 if the range stands on an exterior wall (the shortest hood duct).
Kind: code (IRC R303.3 / R325.2, M1505; CRC R303.3.1), plus NGBS 902.1.1 for the bath window.
AR-5 Smells ↓. Bedrooms and the living space.
The quantity: the hours-weighted mean of the bedrooms' peak share of a kitchen release.
The conditions: windows shut, inside doors open, the hood at 100 cfm capturing half (US practice: cooling season, code hood).
Where the home cooks: its kitchen, or the kitchen of an open plan ("KITCHEN + FAMILY ROOM"), where the smell is released under the hood.
Shown with it:
the same for a WC towards the kitchen and dining area;
a WC or bath door that opens onto the kitchen, dining area or living space;
an open kitchen beside a bedroom door.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 100% | 44% | 22% | 11% | Linear |
Kind. Our measure, fixed on the reference set (Annex A, 7 October 2026). Its provisional minimum, 20%, left two in three of the set's homes short of it: the anchor was at fault, not the homes (Annex A.5). A bigger hood (300 cfm, capturing three-quarters) is offered as an improvement.
AR-6 A breeze you feel. The living space and the bedrooms.
The quantity: the air speed where people are (Part 1 §5.3: over the bed in a bedroom, over the seats in the living space) in the usual wind, with the windows open by their share.
No credit above 1.2 m/s. Above 0.8 m/s, the report notes a possible draught.
| Zero | Minimum | Medium | High | Scale |
|---|---|---|---|---|
| 0.05 m/s | 0.3 m/s | 0.6 m/s (+1.2 K) | 0.9 m/s (+1.8 K) | Log |
Kind and source. Standard: ASHRAE 55's elevated air speed in the adaptive model.
AR-7 The garage. Applies where a garage is attached.
Critical (cap): any door, window or opening from the garage into a sleeping room (IRC R302.5.1).
Gate: the way out of the home passes through the garage.
Shown as checks: a 1⅜″ solid or 20-minute self-closing door; ⅝″ Type X gypsum under rooms above; a CO alarm.
| Minimum | Medium | High |
|---|---|---|
| The code is met | The garage door opens into a non-habitable buffer (mudroom, laundry, hall), not into the kitchen or living space | No habitable room over the garage, and a two-door vestibule, or a detached garage |
Kind. Code (IRC R302.5–R302.6, R311.1, R315.2), with our measure for the higher levels.
6.5Layout
LY-1 Privacy at the entrance. Seen from the front door, with the doors drawn open. The levels are discrete.
| Minimum | Medium | High |
|---|---|---|
| No toilet in view from the front door or the main seating | Also no more than 10% of any bedroom's floor in view from the front door, and an entry zone (≥ 3.5 × 4 ft) with a coat closet | Also no guest bath door facing the living space, dining area or kitchen, and the front door doesn't open straight into the main seating |
Kind: our measure.
LY-2 Daily routes ↓.
Measured: each route's walked length and its narrowest point.
Gate: every bedroom reaches a toilet without passing through another bedroom (IPMC 404.4.3).
Each route:
meets its minimum's conditions, or scores 0;
then follows a mirrored log curve of its length through the anchors below;
routes are combined by how often they are walked: night bath 3, groceries 1, laundry 1, serving 2.
| Route | Minimum | Medium | High |
|---|---|---|---|
| Garage or parking door → kitchen | Not through a bedroom or bath; ≥ 30″ wide; ≤ 50 ft | ≤ 30 ft, past a drop zone, laundry or pantry | ≤ 20 ft, through a mudroom, ≥ 36″ all the way |
| Each bedroom → nearest full bath | Not through the living space, kitchen or another bedroom; ≤ 30 ft | ≤ 20 ft, within the bedroom wing | The primary bath is en-suite, and every other bedroom is ≤ 12 ft away, or en-suite or Jack-and-Jill |
| Bedrooms → laundry | Carriable at ≥ 30″; ≤ 60 ft | The same floor; ≤ 30 ft | ≤ 15 ft from the primary closet |
| Kitchen → dining | ≤ 25 ft | ≤ 15 ft | Next to it, ≤ 8 ft |
Kind: our measure and recommendation (NAHB; Zillow's en-suite at 84%).
On a drawing. Each route is walked from where a person stands in its room, on the floor joined to the way in (a room's middle is often under its bed or its table, and a corner its furniture closes off is no way in or out); kitchen → dining ends at the dining table, where one is drawn or placed, and a route to a toilet room at the bathroom it opens into. A route the drawing's floor doesn't join up (something drawn across a doorway, an opening narrower than a person passes sideways) isn't scored, and the report asks about it.
LY-3 Zoning. The levels are discrete.
| Minimum | Medium | High |
|---|---|---|
| A bath guests can reach without passing through a bedroom | A powder room or full bath on the main living floor, its door not facing the living space, dining area or kitchen | Also a main-floor bedroom with a full bath (in a home on more than one floor), or a split-bedroom plan with the primary suite apart from the others (on one floor) |
Kind: recommendation (visitability, NGBS 612.3, AARP).
LY-4 Doors. Every door. The levels are discrete.
| Minimum | Medium | High |
|---|---|---|
| No two door leaves collide, and no leaf hits a WC, basin or tub | Also no leaf hits the placed furniture | Also no open leaf narrows a route below 36″ |
Kind: our measure.
LY-5 How the kitchen works. The kitchen. Where appliances aren't drawn, the furnishing's placement is used, and the report says so. The levels are discrete.
| Minimum | Medium | High |
|---|---|---|
| The work triangle is at most 26 ft, with no leg under 4 ft; aisles ≥ 36″ | Every leg is 4–9 ft; aisles ≥ 42″; no main route crosses the triangle; the dishwasher is within 36″ of the sink; landing areas are met | Aisles ≥ 48″; island clearances ≥ 42″ on its working sides; seating clearances of 32/36/44″ met |
Kind: recommendation (NKBA).
LY-6 Noise by layout (facts, not scored). Shown, never called "quiet" or "noisy":
bedrooms sharing a wall with the kitchen, living space, a toilet, the garage or a laundry;
a bedroom door opening onto the living space;
an air handler in the garage.
6.6Safety & access
SF-1 Widths and doors.
Gate:
the required way-out door is under 32″ clear (a leaf under about 34″), is not side-hinged, or is under 78″ high;
a hall is under 36″ clear.
For covered multifamily (Fair Housing Act), these are gates too:
any passage door under 32″ nominal;
a route under 36″;
a kitchen under 40″ clear (60″ in a U-shaped kitchen);
the FHAG's bath clearances.
| Minimum | Medium | High |
|---|---|---|
| The code is met | A visitable path (A117.1 Type C): doors on the entrance level ≥ 32″ clear (31¾″), the path 36″, the kitchen on the entrance level 40″ | Every passage door 32″ clear; halls 36″, with 42/48/42″ at 180° turns; one bath with a 60″ circle or a T-turn and 30×48″ at each fixture; the kitchen 40″ (60″ U) |
Kind: code (IRC R311.2, R311.6; FHAG 3, 4, 7) and standard (A117.1 1104–1105).
On a drawing. A width within the drawing's precision of a value (½″, across a door's jambs or a hall's walls) is taken as meeting it, as SF-3's stairs are.
SF-2 Step-free. Steps at the entry are often not drawn. The report asks: "Is there a step at the front door or the garage door?".
| Below minimum | Minimum | Medium | High |
|---|---|---|---|
| No WC on the entrance level | Two of the three visitability features: 32″ doors on the entrance level, a WC on the entrance level, a step-free entrance | All three, as A117.1 Type C: a step-free entrance; the entrance level with a WC, a lavatory and a room of 70 ft²; a 36″ path | Also a bedroom and a full bath on the entrance level, the bath with a 36″ curbless shower and a 60″ turning space |
Kind: standard (A117.1 Type C) and recommendation (NCIL, AARP, NAHB).
A home with a WC on the entrance level and only one of the other two features is a near miss, at 25 points (Part 1 §6.6). The step at the entrance, unknown on a drawing, is taken as there (most US houses have one) until the owner says otherwise, and the report asks. The rest of the medium level (the entrance level's 70 ft² room and lavatory, a 36″ path) is taken as met with the three features; the high level's shower and turning space aren't on a drawing.
SF-3 Stairs. Applies where stairs are drawn. If floor-to-floor height isn't printed, the riser assumes the ceiling height plus 12″ of structure, and says so.
Gate fails when:
the width is under 36″;
the riser is over 7¾″;
the tread is under 10″;
a winder is under 10″ at 12″ from the narrow end, or under 6″ anywhere;
headroom is under 6′8″;
a landing is under 36″;
a flight rises more than 12′7″;
there is no handrail at 4 or more risers.
| Minimum | Medium | High |
|---|---|---|
| The code is met | Riser ≤ 7″ and tread ≥ 11″ | Also handrails on both sides, and no winders or spiral |
Kind: code (IRC R311.7 / R318.7; IBC 1011.5.2) and recommendation (AARP, NAHB).
On a drawing, as Part 2-IN's SF-3 says: a stair is its flights and landings together; a few steps (fewer than 8 risers) and anything narrower than 600 mm aren't one; a width or going within the drawing's precision of the code's (½″ across, ¼″ in the going) meets it; and a riser steeper than 7¾″ on the treads drawn is asked about, never failed, a plan cutting a stair on its way up. Headroom, handrails and winders' narrow ends aren't on a drawing.
SF-4 Escape windows. A check with no grades.
Applies to:
every sleeping room, basement and habitable attic in IRC homes;
in apartments, only below the fourth storey, on floors with a single exit (IBC 1031).
Exempt: a room with an exterior door to a yard or balcony (California, IBC).
Fails (critical, cap) only if it fails under the kindest assumptions: a casement with a minimal frame, about 4″ off the width [S]. It fails when the net clear opening is:
under 5.7 ft² (5.0 ft² at grade);
under 20″ wide or under 24″ high;
or has a printed sill over 44″.
Otherwise it is "meets, assumed", or "check", where the default window type fails.
A window's type known (drawn, tagged, or given by its owner) is judged as it opens: a hung window's lower sash, a slider's one sash, a casement whole. One that fails so is critical: there is no kinder assumption left.
Manufactured homes: 20×24″, 5 ft², sill ≤ 36″.
Kind: code (IRC R310 / R319; CRC R310.1; IBC 1031.2; 24 CFR 3280.106, .404).
SF-5 Falls. A check, shown as a finding only when the sill is printed and the floor is known.
An operable sill under 24″, more than 72″ above the ground, with no fall-prevention device (IRC R312.2).
Apartments: a sill under 36″ (IBC 1015.8).
Guards: 36″ (IRC); 42″ (IBC; 36″ inside low-rise R-2 units).
New York City: window guards are the landlord's duty where children aged 10 or under live.
SF-6 Can it be called a bedroom? (fact). This sets the bedroom count used everywhere in the report.
Not a bedroom when any of these holds:
under 70 ft² or 7 ft;
a kitchen or a non-habitable space;
no window or exterior door;
reached only through another bedroom (IPMC 404.4.2), a cap;
a garage opens into it, a cap.
"Bedroom, confirm" when:
its escape opening rests on an assumption;
its heat or ceiling height is unknown.
Shown, not scored:
a closet is not required by the codes (the HUD Code requires one);
a septic permit can cap the bedroom count (Massachusetts, North Carolina): a question;
appraisals count below-grade bedrooms separately.
7Weights
7.1 Part weights. The defaults of Part 1 §7.3 apply.
7.2 Check weights within parts. Each check's weight is a share of its part. Where a check doesn't apply, it drops out and the rest share its weight.
| Part | Checks and weights |
|---|---|
| Space | SP-2 25 · SP-3 20 · SP-4 10 · SP-5 15 · SP-6 5 · SP-7 5 · SP-8 5 · SP-9 5 · SP-10 10 |
| Daylight | DL-2 70 · DL-3 30 |
| Sun | SN-1 w · SN-2 (1 − w), from 5.3 |
| Air | AR-1 10m · AR-2 25m · AR-3 15m · AR-4 15 · AR-5 20 · AR-6 10m · AR-7 5 (m from 5.4) |
| Layout | LY-1 15 · LY-2 30 · LY-3 20 · LY-4 10 · LY-5 25 |
| Safety & access | SF-1 40 · SF-2 40 · SF-3 20 (SF-4, SF-5 and SF-6 are checks) |
8Critical issues (caps)
Part 1 §7.4 applies to each of these:
A bedroom or living room with nothing to light it from outside, where the drawing shows windows elsewhere: no window, glass door or open side to the outside, or to a deck, a porch or a patio.
A bedroom the way in reaches only through another bedroom (IPMC 404.4.2); one the drawing's doors don't join to the way in at all is reached another way (a wing with a door of its own).
A sleeping room whose windows can't meet the escape size even under the kindest assumptions, and which has no exterior door (SF-4).
A door, window or opening from an attached garage into a sleeping room (IRC R302.5.1).
9The size check
The size check is shown beside the score and never mixed into it.
9.1 Houses, townhouses and ADUs: ANSI Z765-2021, from the plan.
Where to measure:
each level to the exterior finished surface, or to the party-wall centreline for a townhouse;
finished space next to unfinished space, to the unfinished face.
Above and below grade are reported separately. A level is below grade if any wall isn't wholly above the ground. Where the grade isn't drawn, the report asks.
Ceiling rules:
7 ft, or 6′4″ under beams and ducts;
a sloped room needs half its area at 7 ft;
floor under 5 ft is out.
What counts and what doesn't:
stair treads and landings count on the floor they descend from;
openings to below are excluded;
garage, porches, decks and balconies are listed apart;
finished area not connected to the house through finished space is "non-standard finished area".
Rounding. Measured to 0.1 ft, reported in whole ft².
The plan declaration: "based on plan dimensions only; may vary as built".
Counts by level. Rooms, bedrooms and baths are counted per level, to line up with the uniform appraisal format.
9.2 Apartments in apartment-style buildings.
The interior perimeter, which Fannie Mae requires for condos (the same as BOMA Z65.4's Inside Net).
The centreline, also shown where the party wall's thickness is drawn, since condo declarations often use it.
The report also says that the deed or the state's condo law may define the unit differently.
9.3 North Carolina. The NCREC heated-living-area figure is offered beside it.
9.4 Compared with the listing. Where a listed area is entered, the report shows the difference. Where a printed room size disagrees with the drawing, it shows that number's receipt.
10Facts shown, not scored
| Fact | Basis |
|---|---|
| Where the codes require smoke alarms (each sleeping room, outside each sleeping area, each storey) | IRC R314 |
| Where they require CO alarms | IRC R315 |
| A fuel-burning furnace or water heater drawn in a bedroom or bathroom | IRC G2406 |
| Noise by layout | LY-6 |
| The bedroom-label check | SF-6 |
| Glare | Rooms with more than 20% of their floor in direct sun for over 250 hours a year (LM-83-23; edition 1.1) |
Annex A (normative): Corpus anchors
The rule. The anchors of AR-5 were fixed on the TIS-US 1.0 reference set by Part 1 §6.4 on 7 October 2026, and are printed in the check. SP-7's stay provisional: the set can't fix them (A.4). They are fixed again on a larger set during trial use, and change only with a new edition.
A.1 The reference set. The US plans of the Trueinch corpus, rebuilt at the current format: 157 plans, 72 of them real (builders' and listings' plans, read by the product) and 85 generated (homes drawn by the corpus's generator in four drawing styles and rendered clean, at low resolution, photographed or as a phone picture, then read like any upload). A plan is a page of its drawing, as the product reads it: 9 of the 157 are a house's upper floor or basement or a building beside it (a garage, a pool house), and count for the rooms the checks judge in them. Each is placed at one of five sites in turn; a plan with a north arrow faces as it says (18), and the rest with the top of the drawing to each way in turn (139).
| Site | Climate zone | Plans (real + generated) |
|---|---|---|
| Kansas City | 4A | 32 (15 + 17) |
| Houston | 2A | 32 (15 + 17) |
| Phoenix | 2B | 31 (14 + 17) |
| Chicago | 5A | 31 (14 + 17) |
| Seattle | 4C | 31 (14 + 17) |
A.2 How it was measured. Every plan through the plan's own facts and the airflow network (SP-7 and AR-5), and a sample of 12 (6 real, 6 generated), spread through the set so that it meets every site and every facing, through every engine but the 3D breeze, for the standard-anchored checks: the light model and the overcast daylight take most of a house's work. AR-6, which the 3D breeze measures, is left out of the yardstick. AR-5 is measured where a plan has a kitchen, its own or an open plan's, and a bedroom (132 of the 157). The facts are kept, so the anchors can be fixed again without the engines (scripts/score/reference.py anchors).
A.3 The yardstick. On the sample, the standard-anchored checks leave 29% of the rooms and plans they judge short of their minimum, 50% short of their medium and 68% short of their high:
| Check | Judged | Short of the minimum | Of the medium | Of the high |
|---|---|---|---|---|
| SP-2 | 32 rooms | 6% | 6% | 19% |
| SP-3 | 16 rooms | 56% | 56% | 69% |
| SP-4 | 10 plans | 0% | 10% | 50% |
| SP-8 | 5 plans | 0% | 0% | 0% |
| SP-10 | 12 plans | 58% | 75% | 92% |
| DL-2 | 67 rooms | 34% | 58% | 85% |
| DL-3 | 67 rooms | 27% | 73% | 97% |
| SN-1 | 21 rooms | 5% | 10% | 19% |
| SN-2 | 67 rooms | 52% | 64% | 70% |
| AR-1 | 67 rooms | 25% | 37% | 66% |
| AR-2 | 59 rooms | 2% | 7% | 30% |
| AR-3 | 12 plans | 58% | 67% | 100% |
| AR-4 | 10 plans | 0% | 60% | 90% |
| AR-7 | 2 plans | 0% | 50% | 100% |
| LY-2 | 9 plans | 44% | 100% | 100% |
| LY-3 | 10 plans | 60% | 100% | 100% |
| LY-5 | 10 plans | 40% | 80% | 80% |
| SF-1 | 11 plans | 0% | 100% | 100% |
| SF-2 | 12 plans | 100% | 100% | 100% |
| SF-3 | 2 plans | 0% | 100% | 100% |
A.4 The anchors.
| Curve | Zero | Minimum | Medium | High | Short of the minimum: provisional → fixed | Judged |
|---|---|---|---|---|---|---|
| AR-5, kitchen → bedrooms | 100% | 44% | 22% | 11% | 64% → 29% (scaled) | 132 plans |
| SP-7, floor only for passing | 35% | 20% | 15% | 10% | 3% (provisional) | 156 plans |
AR-5 was 50%, 20%, 10% and 5%. Its zero would have been 110%: a share's is never past 100%.
SP-7 stays provisional. 103 of the 156 plans (66%) have no floor only for passing as their drawings name it: an open plan's walkways are its living floor, which the measure leaves out. Matching the yardstick would put the minimum at 3% of the floor, and make any hall at all the fault rather than how much of the floor it takes. SP-7 needs a measure of circulation the set can fix: the floor the walks between the doors take, which furniture can't.
A.5 AR-5: the home or the anchor. Under the provisional anchors, the US demo home's first finding was that cooking smells reach its bedrooms at about a third of the kitchen's strength (32%, and 27% with the engines as corrected for this edition). That is what a house with its inside doors open and its windows shut does, and the anchor was at fault, not the home:
The physics. The hood takes 100 cfm (47 l/s) out, and half of what is cooked with it. The other half mixes into the kitchen, and the kitchen's warmth from the cooking turns its air over through every open doorway and open side: a doorway 3 K warmer than the hall carries some 160–180 l/s each way, over three times what the hood draws. The hall and the open bedroom doors carry it on within the 20 minutes of cooking. A hood that captures more, a kitchen that can be shut, or the bedrooms' doors shut keep it out of them.
The set. The bedrooms of half the set's homes get 29% or more of the kitchen's strength at the peak, and 85 of 132 (64%) got more than the provisional minimum of 20%, against the standard-anchored checks' 29% short of theirs.
Fixed on the set, the minimum is 44%: the demo home's 27% is between the minimum and the medium, as a home at the set's middle is, and is no longer a finding. A home whose bedrooms get more than 44%, as three in ten of the set's do, is short of it, and is told so.
Annex B (normative): Climate
B.1 Computing the zone from a typical year (IECC R301.3), where the county is unknown. HDD uses base 18 °C; CDD uses base 10 °C.
| Zone | Thermal rule |
|---|---|
| 0 | CDD10 > 6,000 |
| 1 | 5,000 < CDD10 ≤ 6,000 |
| 2 | 3,500 < CDD10 ≤ 5,000 |
| 3 | CDD10 ≤ 3,500 and HDD18 ≤ 2,000 |
| 4 | CDD10 ≤ 3,500 and 2,000 < HDD18 ≤ 3,000 |
| 5 | 3,000 < HDD18 ≤ 4,000 |
| 6 | 4,000 < HDD18 ≤ 5,000 |
| 7 | 5,000 < HDD18 ≤ 7,000 |
| 8 | HDD18 > 7,000 |
The moisture letter:
Marine (C), when all of these hold:
the coldest month's mean is between −3 and 18 °C;
the warmest month is below 22 °C;
at least 4 months are above 10 °C;
summer is dry.
Dry (B): annual precipitation P (mm) is below 20(T + 14), 20(T + 7) or 20T, for 70% or more, 30–70%, or 30% or less of the rain falling in April–September. T is the annual mean in °C.
Moist (A): otherwise.
With only degree-days available, a place is marine when it is zone 3 with CDD10 ≤ 2,500, zone 4 with CDD10 ≤ 1,500, or zone 5 with CDD10 ≤ 1,000.
B.2 The assumed SHGC, unless the owner gives one:
| Zone | SHGC | Source |
|---|---|---|
| 0–3 | 0.25 | IECC R402.1.2's limit for new homes |
| 4, except marine | 0.40 | IECC R402.1.2's limit |
| 4C and 5–8 | 0.40 | The code sets none; this conservative value covers heat |
A typed or tagged SHGC replaces it, and the report says which was used.
B.3 Local overlays:
| Jurisdiction | Changes |
|---|---|
| California | A fan in every bath with a tub or shower; an exterior door may stand in for an escape window; kitchen hoods by Title 24 Table 150.0-G; the accessible-housing chapter (11A) from 3 units |
| New York City | 8′0″ ceilings; 80 ft² rooms, 8′0″ wide, one of 150 ft²; 10% glazing and 5% openable; window guards where children 10 or under live |
Annex C (normative): Room hours and the design household
Hours a day per person:
| Room | All hours (Air, Space) | Waking hours (Daylight, Sun) |
|---|---|---|
| Bedroom | 9.0 | 1.0 for an adult, 2.0 for a child |
| Living, family or great room | 3.5 | 3.5 |
| Kitchen | 1.1 (1.5 for the main cook) | 1.1 |
| Dining, if separate | 0.5 | 0.5 |
| Office, den or flex room | 1.0, or 5.0 when someone works from home | The same |
| Bathroom | 0.5 | Not scored |
| Laundry | 0.1 | 0.1 |
| Garage | 0.05 | Not scored |
| Outdoor living | 0.25 | 0.25 |
Room weight = its hours × the people who use it:
a bedroom: its occupants (the primary 2, the others 1);
a shared room: the design household, P.
The design household:
P = bedrooms + 1;
a studio, P = 1;
the owner's household replaces it when given;
when onboarding says someone works from home, the office (or the bedroom with the desk) takes 5.0 h.
Basis: BLS American Time Use Survey 2025 (sleep 9.03 h; TV 2.6 h; food preparation 0.71 h), EPA's NHAPS time spent in each room, and Building America's 16.5 h at home. The mapping of activities to rooms is a judgement, and is published as one.
Annex D (normative): Furniture and clearances
| Piece | Size (W × D, or as stated) |
|---|---|
| Twin bed | 38 × 75″ |
| Twin XL | 38 × 80″ |
| Full | 54 × 75″ |
| Queen | 60 × 80″ |
| King | 76 × 80″ |
| California king | 72 × 84″ |
| Nightstand | 18 × 16″ |
| Dresser | 60 × 18″ (36″ clear in front) |
| Desk | 48 × 24″ (36″ for the chair) |
| Sofa | 84 × 36″ (sectional piece 90″) |
| TV | 55″ and 65″ |
| Dining | 24″ of table edge per place (30″ at the head) |
| Fridge | 36 × 31 × 70″ |
| Range | 30″ |
| Dishwasher | 24″ |
| Washer and dryer | 27 × 30″ each |
Clearances:
| Where | Clearance |
|---|---|
| Bed sides and foot | 24 / 30 / 36″ (minimum / medium / high) |
| Dining | 32″ to a wall where nobody passes, 36″ to edge past, 44″ to walk past |
| Kitchen aisles | 36 / 42 / 48″ |
| Toilet, and also lavatories and bidets | 15″ from centreline to a side wall or obstruction, and 21″ clear in front (IRC P2705) |
| Shower | At least 30 × 30″ and 900 in² (IRC P2708) |
Annex E (normative): Conformance plans
The conformance plans are reference plans with their expected scores and tolerances (Part 1 §11). They are published with the reference set.
Annex F (informative): Sources, and what to confirm
The research notes behind each number:
I: US codes, measurement, accessibility and safety;
J: US households, climate, green and health standards;
K: method;
the research.
To confirm before 1.0 leaves trial use:
NKBA counter frontage (158″ and 198″), landing areas and closet conventions;
the London Plan's outdoor sizes;
ASHRAE 62.2-2025's toilet-room fan rule and whole-dwelling rate;
ASHRAE 55-2023's metabolic range and its air-speed table;
the final ANSI Z765-2021 text;
the UAD 3.6 policy;
the expected w and window-pleasant hours by zone, computed on PVGIS typical years;
the frame deductions behind SF-4's kindest assumption, against manufacturers' net clear tables;
SP-7's anchors, on a measure of circulation the reference set can fix (Annex A).
Annex G (informative): Where the codes disagree, and what this Part does
| Topic | The disagreement | What TIS-US does |
|---|---|---|
| Natural light | IRC 2024, the CRC 2025 and the IBC let electric light replace windows; the IPMC and NYC don't | DL-1 reads "below the natural-light minimum, confirm the alternative" for new homes. For existing homes and NYC, it is the code's requirement |
| Door widths | IRC 32″ clear at the egress door only; FHAG 32″ nominal at every door; A117.1 31¾″; AARP 36″ | 32″ clear, taken as the leaf − 2″ |
| Ceilings | IRC 7′0″; IBC 7′6″; NYC 8′0″ | By the building type and jurisdiction switches |
| Room area | IRC 70 ft²; IBC adds a room of 120 ft²; NYC 80 and 150 ft²; HUD Code 150 ft² living area | By the switches |
| Glazing and openable area | 8% and 4% (IRC, IBC); 3.6% openable (IPMC); 10% and 5% (NYC) | By the switches |
| Escape | IRC sill 44″; HUD Code 36″; the IBC needs none at the 4th storey and above, or with two exits | By the switches |
| Fall threshold | 24″ (IRC); 36″ (IBC) | By the switches |
| Kitchen clearances | 36″ (IBC, IPMC); 40″ (FHAG, A117.1); 42/48″ (NKBA) | Gates by code; levels by NKBA |
| Toilet-room windows | ASHRAE 62.2-2025 requires a fan in new construction; the IRC accepts a window | A fan is assumed; a window is a bonus |
| Kitchen exhaust | 100 cfm (62.2); 200 / 300 cfm (Indoor airPLUS); 400 cfm with make-up air (NGBS) | Scored at the code minimum; better hoods are offered as improvements |