There are three default footing spacing in Canada, 4’ (1.2m),6’ (1.8m) and 8’ (2.4m) provided by the Canadian Wood Council. A good start in figuring out a deck’s footings. The biggest controlling factor is the size of the beam. The larger and stronger the beam is the larger the footing space can be. Personally, I prefer a bigger beam requiring fewer footings. Of course, the beam is supporting joist, the length of the joist and the load they support contributes to the beam and footing requirements.
Quick Attached Deck Footing Chart
|Size of Deck||Beam Size||Number of Footings||Footing Spacing|
|8’ x 10’||(2) 2×8||2||6’0”|
|10’ x 10’||(2) 2×8||2||8’0”*|
|10’ x 12’||(3) 2×8||2||8’0”*|
|12’ x 12’||(2) 2×6||3||6’0”|
|16’ x 16’||(3) 2×8||3||7’0”*|
|20’ x 12’||(2) 2×8||3||6’0”*|
|20’ x 14’||(2) 2×8||3||6’0”*|
|20’ x20’||2 beams (2) 2×8||6 (2 rows of 3)||6’0”*|
- Not Incised, S-P-F Beam Material
- Flush hangered beam material must match Joist Depth
- *2×8 beam overhang 1’
- Meet or exceeds Canadian Wood Council Requirements
There is some exception by deck design and shape. A simple, attached rectangle deck will require the least amount of deck footings. Where an odd-shaped freestanding deck will require additional footings to support all the joists.
There are several factors affecting deck footings spacing. Which may change the number of footings you need. Always better to build to or exceed local code.
Let’s look over some of these factors to ensure that your deck is built to last. Quick references, easier to upgrade beam then adding footing, layout footing evenly for best results, but keep in mind the end use of the deck and adjust footings as required.
More Beam Less Deck Footings
Increasing the depth or number of plies of a beam will allow you to increase the footing spacing. For example, the difference between 6’ spacing and 8’ for an 11’ deep joist is a 2×8 two-ply instead of 2×6 beam. Often this is the deciding factor for footing spacing. More beam means less footings.
Whenever given a choice, I would rather increase the beam size and reduce the number of footings. Saving both time and money in building the deck. Increasing the footings spacing by 2’ for less than $20. A concrete footing will cost that and more.
Limited Space for Beam Depth
There are some rare situations where it is more advantageous to increase the number of footings not the depth of the beam. With a very low-level deck, where you are fighting for inches, 2” (50mm) may make all the difference in the deck’s construction. It may be better to dig an extra footing.
Before pouring the additional concrete, is it possible to add an additional ply to the beam? Allowing you to keep the same beam depth but increase the strength, increasing the span. The Canadian Wood Council allows substituting a third ply 2×8 instead of a two-ply 2×10. The same with 2×12, replacing with a three-ply 2×10 beam. Something to consider.
I look further into ways to lower deck beams close to the ground. If you would like to read some other possibility, click here.
Symmetrical spacing of deck footings
The footings can support more, and the deck will look better with symmetrical spacing of the post and footings. With a 14’ deck, it is better to evenly space the footings 7’ apart instead of 8’ and 6’. Even space will reduce the span of the beam, increasing the deck’s strength while looking more intentional in design.
Overhanging the beam past the footing will reduce their spacing.
The IRC allows deck beams to overhang the post, one-quarter of the backspan. Meaning two footing spaced 8’ apart can support a deck 12’ wide. The beam overhanging each footing by one quarter, 2’. Minimizing the required footings.
A word of caution, with beam overhang. It may be called the International Residential Code, but local code will overrule this at times. In Edmonton, Alberta, a deck beam can only overhang one and a half times the nominal depth of the beam. Meaning in Edmonton you can only overhang a 2×8 beam 12” regardless of the backspan. But in Kingston, Ontario, a 2×10 beam can overhang a maximum of 2’ (600mm) with a 1/6 backspan but a 2×8 16” (400mm). Similar in Calgary, where the limit is 2’ (600mm) also but regardless of beams depth.
Soil Bearing requirements for deck footings
The size of deck footings is determined by soil bearing capacity. Firmer soil requiring both smaller and fewer footings. This is important in a deck designed, but ultimately the spacing of the footing is determined by beam strength, not soil bearing. If the beam is strong enough but the soil is not as a general rule, the decking footing size will be increased.
Many jurisdictions have prescribed footings size and depth accounting for standard soil bearing in the area. In Calgary, where I build decks its 10”(250mm) diameter for all decks. Only requiring soil bearing calculation when involving engineering. If that the case the engineer will take care of the footing spacing also as it will affect their calculations.
Extreme Deck loads require smaller footing spacing.
Some situations require closer footing spacing. One extreme is hot tubs. Hot tubs put a lot of weight on a deck and require additional footings. Both to support the extra weight and distribute the weight evenly. Often its better to build the footing and beams to support the hot tub separate from the main deck. Considerably increasing the number of footings but safely supporting the hot tub.
Footings for deck point loads.
If there are extreme point loads on a deck, like a pergola post, it is often better to reduce and adjust the footings spacing to place the footing directly below the additional load. A footing can support a much greater weight directly applied then pushing down at a distance.
You can hold a heavier weight much longer centred on your body then outstretched arms. Footings are the same, placing the point load directly above, increasing the load the footing can support.
Deck Stairs Footings
Long runs of stairs also require footings on the ground. Two additional footings to support the stairs are a good idea. For lower decks, less than 2’ (0.6m), a treated sleeper or concrete pad is sufficient as frost heave will have minimal impact.