# The code numbers behind the Sheets.

> Each Sheet sets its code notes for the job's US state or Canadian province. These are the model-code numbers it starts from (the IRC in the US, the NBC in Canada, with Ontario's differences) and the local figures we found. Towns amend the codes, so confirm with your building department before you dig or frame.

## 1. How deep footings go (frost depth)

Footings for [decks](https://studsheet.com/sheets/deck), [deck stairs](https://studsheet.com/sheets/stairs), [additions](https://studsheet.com/sheets/addition) and [concrete piers](https://studsheet.com/sheets/concrete) go below the frost line, and in the US at least 12″ below undisturbed ground either way (IRC R403.1.4). Each jurisdiction sets its own depth (IRC Table R301.2), so most of these are one town's figure, as an example of the area.

| Where | Depth | What the figure is |
|---|---|---|
| **Minnesota** | 42″ in southern counties (Hennepin, Ramsey) to 60″ in northern ones (St. Louis) | State rule, Minn. R. 1303.1600 |
| **Massachusetts** | 48″ | Statewide, 780 CMR 51 |
| **New Hampshire** | 48″ | Durham, for example |
| **Michigan, Illinois, Iowa, upstate New York** | 42″ | One county or town in each, for example |
| **New Jersey** | 36″ in the north and center, 30″ in the south | Ask your town's construction office |
| **New York City** | Set by the NYC Building Code | Ask the NYC Department of Buildings |
| **Colorado** | 36″ | Littleton, for example |
| **Virginia** | 24″ | City of Fairfax, for example |
| **Ontario** | 1.2 m (47¼″) | Ontario municipal deck guides |
| **Alberta, Nova Scotia** | 1.2 m | Alberta's deck guidance and Calgary; Halifax |
| **Manitoba** | 1.8 m (70⅞″) | Manitoba's deck guide and Winnipeg |
| **British Columbia** | About 457 mm (18″) on the south coast; 610–760 mm around Squamish–Lillooet; deeper north | Municipal footing guides |

## 2. Stairs, handrails and guards

For [inside stairs](https://studsheet.com/sheets/istairs), [deck stairs](https://studsheet.com/sheets/stairs), [concrete steps](https://studsheet.com/sheets/concretesteps), [steel and spiral stairs](https://studsheet.com/sheets/steelstairs) and [railings and guards](https://studsheet.com/sheets/railing). US numbers are the IRC 2021 (the 2024 IRC keeps them under new section numbers: stairs R318.7, guards R321); Canada is the NBC 2020 Part 9 for stairs in a house.

| | United States (IRC) | Canada (NBC 2020) |
|---|---|---|
| **Riser** | 7¾″ (196 mm) at most | 125–200 mm (4.9–7.9″) |
| **Tread or run** | Tread at least 10″ | Run 255–355 mm (10–14″) |
| **Riser and tread differences** | ⅜″ at most within a flight | 5 mm between steps next to each other, 10 mm across the flight |
| **Headroom** | 6′ 8″ | 1950 mm (6′ 4¾″) |
| **Handrail height** | 34–38″ | 865–1070 mm |
| **Handrail needed** | 4 or more risers | Inside: more than 2 risers. Outside: more than 3 |
| **Guard needed** | A drop of more than 30″ within 36″ of the edge | A drop of more than 600 mm (23⅝″) |
| **Guard height** | 36″ (34″ along the stairs) | 900 mm; 1070 mm (42″) outside where the deck is more than 1.8 m up |
| **Openings in the guard** | A 4″ sphere can't pass; 4⅜″ on the stairs; 6″ in the triangle under the stair's bottom rail | 100 mm (Ontario: 150 mm in the triangle at the stair) |
| **No-climb zone** | None | 140–900 mm above the floor where the drop is more than 4.2 m. Ontario: at any height |

New York and Virginia allow 8¼″ risers and 9″ treads, and some towns ask for 42″ guards. Quebec houses of 2 storeys or fewer follow municipal bylaws; StudSheet uses the NBC numbers there until checked.

## 3. Basement wall insulation

When you finish a [basement](https://studsheet.com/sheets/basement), the energy code sets the wall insulation. In the US it's the IECC 2021 (Table R402.1.3), by climate zone; your county sets the zone.

| US climate zone | Basement walls |
|---|---|
| 0–2 (Florida, Hawaii, the Gulf Coast) | No minimum |
| 3 | R-5 continuous **or** R-13 between studs |
| 4, except the Pacific Northwest coast (New Jersey is 4A) | R-10 continuous **or** R-13 between studs |
| 4 Marine (coastal Washington and Oregon), and 5–8 | R-15 continuous **or** R-19 between studs **or** R-13 plus R-5 continuous |

California enforces its own energy code (Title 24): ask your building department.

**Canada:** the NBC 2020 (9.36) sets an *effective* value for the whole wall, studs included: RSI 1.99 (R-11.3) in zone 4, RSI 2.98 (R-16.9) in zones 5 and 6, and up to RSI 3.97 (R-22.5) in zone 8 without a heat-recovery ventilator. **Ontario** (2024 OBC with SB-12): most packages need R-20 continuous, or R-12 plus R-10 continuous, over the full height of the wall. **Quebec:** total RSI 2.99 (R-17).

## 4. When a retaining wall needs a permit

For [garden and retaining walls](https://studsheet.com/sheets/retaining):

- **United States:** the IRC exempts walls 4 ft or less from the bottom of the footing to the top, unless they hold back a surcharge (a driveway, a slope, a building) (R105.2). A wall retaining more than 48″ of fill, or more than 24″ with a surcharge, needs a design (R404.4). Towns vary: in New Jersey terraced walls are added together.
- **Canada:** the NBC sets no general height; provinces and cities do.
  - **Ontario:** a wall over 1.0 m next to public property, a building's entrance or a public area is a "designated structure": permit, professional drawings and guards.
  - **Calgary:** 1.2 m or more, with walls within 1 m of each other counted together.
  - **Alberta:** any wall that holds up a building's foundation, or over 1.2 m next to public areas.
  - **Burnaby:** over 1.2 m, engineer-sealed.
  - **Halifax:** over 1 m on a serviced lot.
  - **Montreal area:** 1 m in Baie-D'Urfé and Terrebonne; boroughs differ.

## Questions

### How does StudSheet know my state or province's rules?

Set the job's US state or Canadian province (or switch any Sheet between US feet and inches and Canadian metric). The Sheet then uses that place's frost depth, stair and guard numbers, basement insulation, bag sizes (80 lb in the US, 30 kg in Canada), utility locate (811 in the US, the provincial service in Canada) and lead-paint year (before 1978 in the US, before 1990 in Canada).

### Do StudSheet's code notes replace my building inspector?

No. Towns, counties and municipalities amend the IRC, NEC, NBC and provincial codes. The notes give you the model-code numbers and the local figures we found, so you plan the job right; the building department has the final word, and every Sheet says so.