Materials + rough costs
Footings + concrete
Permit + guard reminders
Ontario Deck Building Calculator
A deck looks innocent on paper — until you start counting posts, concrete, hardware, stairs, and railings. This calculator gives you a realistic planning picture before you buy lumber (or start debating composite vs. wood like it’s a religion).
Planning tool only. Your municipality has final say on permits, setbacks, and details. If you’re attaching a ledger to your house, treat it like a structural connection — because gravity never takes a day off.
How to use this calculator (without making it a weekend project)
Enter deck length, width, and height above grade. Toggle stairs and footing type. The right column updates with materials, costs, and a few common Ontario compliance flags.
- 1Start with size (length × width). The big cost drivers show up fast.
- 2Set height. At ~24″ above grade, guard/permit conversations usually begin.
- 3Choose footing system. Concrete adds up quickly, and frost depth isn’t optional.
Style note: The calculator below sits inside a safe wrapper so your WordPress theme doesn’t mess with
fonts, spacing, or placeholders.
Estimate deck materials, footings, stairs, and guard requirements
Planning a deck in Ontario is one of those projects that looks “simple” right up until you start adding up the material, the posts, the concrete, the stairs, the railings… and then you remember there’s a building department involved. This calculator helps you build a realistic materials-and-cost picture before you start shopping (or arguing about composite vs. wood).
Enter your deck length, width, and height above grade and the calculator will estimate the framing, decking, footings (including concrete), and key compliance flags that commonly trigger permits and guard requirements. It’s a planning tool — your municipality always gets the final say.
Deck Building Calculator
Calculate materials, costs, and Ontario Building Code compliance
Length
feet
Width
feet
Height Above Grade
inches
Include Stairs
Number of Steps
steps
Auto-calculated from height (7.5″ per step), editable
Post Height (grade to deck)
inches
Height of post from ground to bottom of deck
Decking Board Price (per linear foot)
$
Framing Lumber (per board foot)
$
Concrete (per cubic meter)
$
Waste Factor
%
📋 Permit Requirements
Required if deck is over 24″ high OR over 108 sq ft area.
🔨 Ledger Board
Must be lag screwed or bolted to house (NOT nailed). Use staggered ‘W’ pattern for fasteners.
📐 Joist Spacing
Standard spacing: 16″ on center. Use 2×8 minimum for spans up to 12 feet.
Estimated Total Cost
$0
0 sq ft deck
🛡️ Guards (Railings)
Guards mandatory for decks 24″ or higher. Minimum 36″ (915mm) high with maximum 4″ spacing between balusters.
🏗️ Footings
Must extend below frost line (4+ feet in Ontario). Standard: 36″x36″x12″ pad with 12″ sono tube. Alternative: BIGFOOT system.
🪵 Materials
Pressure-treated lumber required within 6″ of grade. Use galvanized or stainless steel fasteners (G-185 coating).
If the totals feel higher than expected, that’s normal — decks are “simple” right up until you count posts, beams, hangers, bolts, concrete, railings, and the joy of digging below frost. This tool is meant to help you plan a realistic range and understand which components are driving the cost.
Before you build, confirm requirements with your local municipality (permit triggers, setbacks, guard rules, and inspections). And if you’re attaching a ledger to your house, treat it like a structural connection — details matter, because gravity never takes a day off.
Mini FAQ (quick answers)
Plain-language deck answers — the stuff that usually comes up before you even buy the first 2×10. This is guidance only; your local building department has the final say.
Permits
Guards & stairs
Footings & ledger
QWhen do I usually need a permit for a deck in Ontario?▾
Two common triggers are height and size. Many municipalities require a permit once the deck is about
24" (600 mm) above grade or if it’s a larger structure (especially if attached to the house).
Best move: call your building department before you dig — it’s cheaper than “surprise rework.”
QWhy does 24" matter so much?▾
Around 24" above grade is where guards (railings) often become mandatory.
Once guards are involved, the deck becomes a bigger safety item, which usually means permits and inspections enter the chat.
QDo I always need railings, and how tall should they be?▾
If your walking surface is high enough, guards are required. Minimum heights vary by deck height and local interpretation,
but 36" (915 mm) is a common baseline for many decks. Openings typically need to pass the “4-inch / 100 mm ball” test.
QHow deep do footings need to go?▾
Footings typically must bear on undisturbed soil and extend below local frost depth.
Frost depth varies by region and soil, so use the depth your municipality requires.
Translation: “Close enough” is how you get a deck that moves like a trampoline in spring.
QLedger attached or free-standing: which is safer?▾
A properly flashed and bolted ledger can be great — but it’s also where many failures happen (water + rotten framing).
If your wall condition is questionable (brick veneer, weird framing, poor access for flashing), a free-standing deck can be the safer option.
QComposite decking: do I need tighter joist spacing?▾
Often yes. Many composite products want 12" o.c. depending on board direction and product.
Always check the manufacturer’s span requirement — it’s not a “builder opinion” issue, it’s a warranty issue.
QCan I use deck blocks instead of frost footings?▾
Sometimes for very low, free-standing platforms — but many municipalities won’t accept blocks for elevated or attached decks.
If you want fewer headaches, assume real frost footings unless your building department says otherwise.
QWhy are fasteners and hardware a bigger cost than people expect?▾
Because exterior decks need corrosion-resistant connectors (PT-compatible), plus hangers, post bases, bolts, screws,
and all the “small stuff” that isn’t small when you buy it.
Reality: Hardware is the silent budget thief of deck projects.
QWill this calculator match exactly what my inspector wants?▾
It’s a planning tool — great for early budgeting and material takeoff — but inspectors may require adjustments for spans, soil bearing,
setbacks/zoning, and attachment details. Use the numbers as a starting point, not a stamped drawing.
Ontario Deck Code FAQ
Click a question to reveal the answer.
1) Do I need a building permit for my deck if it’s over 24" (600 mm) above grade?
Usually yes. In Ontario, guards are required once the walking surface is more than 600 mm above finished grade, and most municipalities require a building permit for elevated decks. Confirm with your local building department.
2) Do I need a permit if the deck is under 24" but larger than ~108 sq ft (10 m²)?
Often, yes—especially if it’s attached to the house. Many municipalities use 10 m² and/or 600 mm as common triggers, but attachments can still require a permit. Confirm locally.
3) Do I need a permit to replace deck boards only (no framing changes)?
Typically no if it’s maintenance only (decking surface boards) and you’re not changing structure, size, height, stairs, or guards. Structural changes usually trigger a permit.
4) How close can my deck be to the property line (setbacks / zoning)?
That’s zoning, not Building Code, and it varies by municipality. Check your local zoning/setback rules before you dig footings.
5) Can I build a deck in an easement / near a septic bed / over a utility line?
Usually not advisable. Easements and utilities can restrict structures, and septic systems need clearance for function and future replacement. Get locates and confirm restrictions with the municipality/utility.
6) What drawings do I need for a deck permit application (site plan, framing plan, sections)?
Commonly: a site plan (deck location to lot lines), framing plan (joists/beam/posts with sizes/spacing), footing details, guard/stair details, and ledger/connection details if attached. Your municipality often has a checklist.
7) How deep do deck footings need to be in Ontario (frost depth)?
Footings typically must extend below local frost depth and bear on undisturbed soil. Frost depth varies by region/soil—use your municipality’s required depth.
8) Can I use deck blocks / patio stones instead of frost footings? When is that allowed?
Sometimes for very low, free-standing platforms. Many municipalities do not accept deck blocks for elevated decks or decks attached to a house. Verify locally.
9) What diameter sonotube do I need for a typical deck post?
There’s no single code diameter—load, soil bearing, post spacing, and deck size matter. Use your municipality’s prescriptive details/tables or an engineered design.
10) How far apart can deck posts be spaced?
Post spacing depends on beam size, number of plies, species/grade, joist span, and loads. Use municipal prescriptive tables where available, otherwise engineer it.
11) Can I use helical piles in Ontario, and do I still need a permit/engineering?
Helical piles are common, but permit requirements still apply if the deck triggers a permit. Some municipalities require pile specs and/or engineered layouts.
12) Do I need a concrete pier/sonotube plus a pad footing, or is a pier alone acceptable?
Often a widened base is required to spread loads and reduce frost/uplift issues. Whether a straight pier is acceptable depends on your local approved details and soil conditions.
13) Can I attach a deck ledger to brick veneer, or do I need to fasten into the rim joist?
Brick veneer is not structural. Ledger loads typically must transfer into structural framing. If the connection is questionable, a free-standing deck is often the safest route.
14) What fasteners are acceptable for the ledger (lag bolts vs through-bolts) and spacing?
Fastener type and spacing depend on deck loads and structure. Many municipalities specify minimum sizes and spacing. Through-bolts are often preferred where possible. Use corrosion-resistant hardware.
15) Do I need flashing over/behind the ledger, and what type?
Yes. Flashing is critical to prevent water intrusion and rot. Use durable, compatible flashing that directs water out and away—don’t rely on caulking.
16) When is a free-standing deck required (instead of ledger-attached)?
Common triggers: masonry/veneer walls, questionable house framing, inability to flash properly, or municipal requirements. Free-standing decks reduce risk of water damage to the house.
17) What joist size do I need (2×8 / 2×10 / 2×12) for my deck span?
Depends on span, spacing, species/grade, and loads. Use municipal span tables or an engineered design—especially for longer spans or heavy loads (hot tub, roof, etc.).
18) What’s the typical joist spacing—12" vs 16" vs 24" on-center—and when do I change it?
16" o.c. is common. Composite and thinner decking often require 12" o.c. 24" o.c. is less common and must match span tables and decking manufacturer requirements.
19) How do I size the beam (built-up beam, ply count) for my deck width and post spacing?
Beam sizing is driven by tributary width, post spacing, species/grade, and number of plies. Municipal beam tables can help; outside the tables, engineer it.
20) Do I need blocking/bridging between joists, and where?
Often yes—commonly at beam lines, guard post locations, and where joists need restraint to prevent twisting. Your local deck guide may show typical requirements.
21) What connectors are required (joist hangers, post bases, hurricane ties), and which ones are “must use”?
Use rated connectors where joists bear without full bearing, at ledger connections, and at posts/beam connections. Use exterior-rated, PT-compatible hardware.
22) When are guards required—does the 24" (600 mm) rule apply everywhere?
The 600 mm rule is commonly enforced in Ontario, but inspectors and municipal guides are the final word. When in doubt, design for compliance.
23) What is the minimum guard height—36" (900 mm) vs 42" (1,070 mm)—and what triggers the taller one?
Guard height requirements change with deck height above grade. Many municipalities enforce 900 mm at lower heights and 1,070 mm at higher decks—confirm locally.
24) What is the maximum opening between balusters/pickets (the “4-inch / 100 mm ball” rule)?
Openings typically must not allow passage of a 100 mm (4") sphere. Special rules can apply at stair triangles and other conditions.
25) Are horizontal rails allowed, or does Ontario require “non-climbable” guards?
Rules focus on safety performance and openings; some inspectors apply “non-climbable” interpretations. If you want fewer headaches, choose a clearly non-climbable guard design.
26) Can I use glass panels for guards, and what safety glazing requirements apply?
Yes, but use approved safety glazing and compliant installation details. Building departments may request product specs and structural details.
27) When do deck stairs require a handrail (and on which sides)?
Handrail requirements depend on number of risers and stair configuration. Municipal guides provide the clearest local interpretation—follow them.
28) What are the allowed riser height and tread depth for exterior stairs?
Ontario sets ranges for riser and tread dimensions and requires consistency. Use your local approved guide/OBC requirements for the exact numbers enforced in your area.
29) Do I need a landing at the top/bottom of deck stairs, and what size?
Often yes, especially at doorways and certain stair configurations. Minimum landing sizes are typically tied to stair width and safe footing requirements.
30) What fasteners are required for pressure-treated lumber (galvanized vs stainless), especially near the ledger/hangers?
Use PT-compatible fasteners/connectors (hot-dip galvanized or stainless where needed). Avoid standard zinc fasteners—they corrode quickly with modern PT lumber.
Important note (because frost always wins)
This calculator is meant to help you plan a realistic range. Final design should match local requirements for setbacks, spans, soil conditions, attachment details, and inspections. If your deck is attached to the house or elevated enough to need guards, assume permits and inspections are part of the job.