Floor live loads for houses in Canada (NBC 2020)

The National Building Code of Canada (NBC) 2020 is the model building code published by the National Research Council of Canada. Division B Part 4 covers structural design by an engineer: Subsection 4.1.3 sets out limit states design and the load combinations, 4.1.4 dead loads, 4.1.5 live loads due to use and occupancy, and 4.1.6 to 4.1.8 snow and rain, wind and earthquake.

Article 4.1.5.3 and Table 4.1.5.3 give the minimum specified uniformly distributed live load for each use of floor or roof, in kPa (1 kPa = 1 kN/m²). Table 4.1.5.9 gives concentrated loads, and floors are designed for whichever has the worse effect. The table below lists the uniform loads.

Most houses fall under Part 9 (Housing and Small Buildings), where joists, rafters, beams, lintels and footings are usually sized from the Part 9 span tables, which already allow for the loads. Article 9.4.1.1 lets you design a Part 9 member to Part 4 instead, and that is when the values on this page apply directly. Where floor framing is engineered but the walls and footings below are taken from Part 9, the floor's Table 4.1.5.3 live load must not exceed 2.4 kPa (9.4.1.1(2)).

Ontario, British Columbia, Quebec and Alberta publish their own building codes, which build on the NBC; the other provinces and territories adopt the NBC, sometimes with amendments. Check the code in force where the house is built.

Values in Table 4.1.5.3 are minimums: where the intended use gives a higher load, use it (4.1.5.1(1)). One- and two-way floor slabs take no reduction for tributary area (4.1.5.8(1)), and roofs designed for the 1.0 kPa minimum take none either (4.1.5.8(2)).

In the NBC, partitions are a dead load, not a live load. Where partitions are shown on the drawings, use their actual weight (4.1.4.1(2)). Where they are not, use a partition weight allowance based on the expected weight and position of the partitions, but at least 1 kPa over the area of floor considered (4.1.4.1(3)).

The weights and allowances used must be shown on the drawings (4.1.4.1(4)). Where the allowance would reduce another load effect, such as uplift, leave it out (4.1.4.1(5)).

In most of Canada the roof is governed by snow, not by the 1.0 kPa roof live load. Article 4.1.6.2 gives the specified snow load S from the 1-in-50-year ground snow load Ss and rain load Sr for the location (Subsection 1.1.3 and the climatic data in the code), the importance factor Is, and factors for roof shape, wind exposure, slope and drifting. Part 9 houses use the simpler formula in 9.4.2.2. Look up the values for the building's location rather than using a typical figure.

A two-storey wood-frame house. Second-floor joists span 4.0 m from each exterior wall onto an interior bearing wall on the ground floor, so the wall's tributary width is 4.0 / 2 + 4.0 / 2 = 4.0 m. The roof trusses span from exterior wall to exterior wall, so the interior wall carries no roof or snow load. Ground-floor storey height 2.7 m. The same method works for an ICF house with a wood-frame second floor.

Assumed values (check them for the actual build-up): floor dead load 0.6 kPa (joists, subfloor, finishes and ceiling); partitions not fixed on the drawings, so the 1.0 kPa allowance of 4.1.4.1(3); interior stud wall 0.5 kPa of wall area; live load 1.9 kPa (Table 4.1.5.3, residential areas, Div. A 1.3.3.3.).

Factored loads, NBC 2020 Table 4.1.3.2.-A. Case 1: 1.4D = 1.4 × 7.75 = 10.9 kN/m. Case 2: 1.25D + 1.5L = 1.25 × 7.75 + 1.5 × 7.60 = 9.7 + 11.4 = 21.1 kN/m. Case 2 governs. Its companion snow load (1.0S) is zero here because the roof does not bear on this wall. Use 21.1 kN/m to check the studs, the top and bottom plates, and a beam or lintel under the wall.

Service load: D + L = 7.75 + 7.60 = 15.4 kN/m. Use it for deflection checks under Table 4.1.3.4 and, with the soil's allowable bearing pressure, to size a footing.

Where the wall continues to a footing, add the ground floor's own tributary load and the basement wall. For a member carrying more than 20 m² of residential floor, 4.1.5.8(4) allows a live load reduction for tributary area; it is not applied here.

• Using the US 40 psf (1.92 kPa) or a European 1.5 kPa for a Canadian house. The NBC value is 1.9 kPa.
• Treating partitions as live load. In the NBC they are dead load, with an allowance of at least 1 kPa where they are not shown on the drawings.
• Designing a roof for 1.0 kPa and forgetting snow. Check the snow and rain load of 4.1.6 for the location; it usually governs.
• Using 1.9 kPa for an exterior balcony or deck. Exterior balconies take 4.8 kPa, and so do roof terraces used by people.
• Missing the 9.4.1.1(2) limit: an engineered floor over Part 9 walls and footings must not carry more than 2.4 kPa live load.
• Checking deflection with factored loads, or the wall with service loads. Keep factored and unfactored totals apart.