How Much Weight Can My Deck Hold?

Full formula and methodology: How this calculator works →

How much weight can a deck hold?

A Canadian deck built to NBCC 2020 requirements must support a minimum 1.9 kPa (40 lbs/sq ft) live load. On a standard 10×12 ft (3m×3.6m) deck, this means the structure must handle up to 2,060 kg (4,540 lbs) of live load distributed across the deck surface. The dead load of the structure itself is additional.

Live load capacity only. Add snow load per your city and dead load of deck structure. Hot tub loads must always be verified by a structural engineer regardless of deck size.

Hot tub callout: A filled 6-person hot tub weighs 2,000–3,600 kg — far exceeding the 1.9 kPa distributed limit on any part of the deck. This load must always be transferred directly to the ground through dedicated posts and footings placed beneath the hot tub. Standard deck framing is not sufficient. See the beam load calculator for hot tub support beam sizing, and the circuit breaker calculator for the required 50A GFCI circuit.

What reduces deck capacity? Spans longer than the joist and beam size can support, deteriorated pressure-treated lumber, improper fastener spacing, posts shallower than the frost line, and ledger connections that have corroded all reduce effective capacity below the code-design values. An older deck should be assessed by a structural engineer before adding significant concentrated loads.

Canadian deck load requirements

The National Building Code of Canada (NBCC 2020) requires residential decks to be designed for a minimum 1.9 kPa live load — equivalent to 40 lbs per square foot. This load represents the weight of people, furniture, and objects that the deck may need to support in normal use.

In addition to live load, the structural design must account for:

• Dead load: Weight of the deck structure itself — typically 0.5–1.0 kPa for wood decking, joists, and beams
• Snow load: In Canada, decks must also carry snow load per NBCC 2020. In Ottawa, this adds approximately 1.9 kPa. Snow load often governs deck joist design in Canadian climates
• Concentrated loads: Hot tubs, HVAC equipment, planters with soil — any heavy concentrated load must be individually checked and may require additional framing

In Canada, decks must also be designed for snow load per NBCC 2020 — in Ottawa this adds approximately 1.9 kPa, often governing deck joist design over the live load. Use the snow load calculator to find the ground snow load for your city, then add it to the deck live and dead loads above.

All provinces follow the NBCC as their base code, but many municipalities have additional requirements for deck construction — guardrail heights, fastener types, and footing depths can vary. Check with your local building department before starting construction.

Deck joist sizing

Deck joists span between the ledger board (attached to the house) and the beam or rim joist at the outer edge. The required joist size depends on:

• Span: The clear distance the joist must bridge
• Spacing: The on-centre distance between joists (12, 16, or 24 inches)
• Load: Combined live load (1.9 kPa) + dead load + snow load
• Species and grade: SPF No. 2 is the standard for pressure-treated deck framing in Canada

Closer joist spacing (12 inches) allows smaller joists for the same span. Wider spacing (24 inches) requires larger joists. The deflection limit for deck floors is typically L/360 — the same as interior floors — to prevent a bouncy, uncomfortable deck surface.

Beam and post sizing

The deck beam supports the joists and transfers their load to the posts and footings. Beam size depends on its span (the post spacing) and the tributary area it serves (half the joist span on each side of the beam).

Posts transfer the beam load to concrete footings and ultimately to the ground. Post sizing depends on the axial load (compression from the beam) and the unsupported post height. Taller posts require larger sections to resist buckling under load — a 4×4 post is acceptable at 1.5m height but a 6×6 may be required at 2.5m.

Footings must extend below the frost line — the depth at which ground freezes. In southern Ontario, frost depth is approximately 1.2m. In Winnipeg, it exceeds 1.8m. Footings shallower than the frost line will heave in winter, causing the deck to move and potentially damaging the ledger connection to the house.

Hot tub structural requirements

A hot tub is one of the heaviest loads a residential deck can face. A 6-person hot tub typically weighs:

• Empty: 300–500 kg (depends on size)
• Water (1,500–2,000 litres): 1,500–2,000 kg
• Occupants (6 people at 80 kg each): 480 kg
• Total: 2,300–3,000 kg — all concentrated in a 2×2m footprint

This load is far beyond what standard deck framing is designed to carry on a distributed basis. The hot tub load must be transferred directly to the ground through dedicated posts and footings placed immediately below the hot tub corners. The structural framing in the hot tub area must be engineered independently — typically requiring doubled or tripled joists and beams, and larger footings.

Worked examples

Example 1 — Standard backyard deck (Ontario): 4m × 5m deck, joists spanning 4m at 400mm o.c., SPF No. 2.

• Design load: 1.9 kPa live + 0.5 kPa dead + 1.5 kPa snow = 3.9 kPa total
• Load per joist: 3.9 × 0.4m = 1.56 kN/m
• Required section modulus: check against 2×10 SPF No. 2 (S = 212,000 mm³)
• Result: 2×10 SPF joists at 400mm o.c. — verify deflection

Example 2 — Deck with hot tub (BC): Hot tub area requires dedicated structure.

• Hot tub total load: 2,800 kg = 27.5 kN over 2×2m = 6.9 kPa
• Dedicated posts required directly below hot tub corners
• Footings sized for 27.5 kN total (4 posts × approx. 7 kN each)
• Result: Engineer-designed independent support structure required

Deck joist span reference (SPF No. 2, 1.9 kPa live load)

Approximate values — verify against NBCC span tables and local requirements. Does not include snow load.

Deck footing depth by province — Canada

Deck footings must extend below the frost line — the maximum depth to which the ground freezes in winter. A footing shallower than the frost line will heave as soil expands when it freezes, pushing the deck structure up and potentially cracking the ledger connection to the house. Frost depth varies significantly across Canada:

Minimum depths are general guidelines. Always confirm with your local building department — municipal requirements sometimes exceed provincial minimums, and soil type (clay vs sand vs rock) affects required footing design.

Sonotube vs helical pier: Most residential decks use concrete-filled sonotube (cardboard tube) footings. In areas with deep frost or expansive clay soils (Winnipeg, Regina), helical piers are an increasingly common alternative — they screw into the ground below the frost line and resist frost heave without large concrete pours.

Frequently asked questions

Code reference

Based on NBCC 2020 residential construction requirements (Part 9) and structural design requirements (Part 4), CSA O86-19 (Engineering Design in Wood), and provincial building codes. Footing depths per local frost depth requirements. Always obtain a building permit and have structural plans reviewed by your local building authority.

Next steps after your deck load calculation

Once you have joist sizing, beam sizing, and load capacity from the calculator, here is how to move the project forward:

• Apply for a building permit: All new decks over 0.6m (2 feet) above grade require a building permit in every Canadian province. Submit your joist sizes, beam sizes, post spacing, and footing dimensions — most municipalities provide a deck permit checklist, and this calculator gives you the structural numbers to complete it.
• Size your footings correctly: Footings must extend below frost depth — see the footing depth table on this page for your province. For a typical deck with 3m post spacing carrying 1.9 kPa live load, a 400mm diameter concrete footing at the required depth is the common minimum.
• Check your ledger connection: A deck attached to the house via a ledger board must be bolted — not nailed — to the rim joist. Half-inch lag bolts or structural screws at maximum 400mm (16") spacing are required per NBCC Part 9. Improper ledger connections are the most common cause of deck failures in Canada.
• Get an engineer for hot tub or elevated decks: If your deck will support a hot tub, or is more than 1.5m above grade, most permit offices require engineer-stamped drawings. Use the numbers from this calculator as your starting point — your engineer can work from them directly and typically only needs to confirm or upsize from a pre-calculated baseline.