If your house foundation is brick or stone veneer, the deck ledger should not be attached to the house foundation. At times attaching the deck ledger will compromising the building envelop or require excess labour to reseal after. Or it may be impossible to tie into the existing envelope, making it impossible to reseal, making it better to build a freestanding deck beside the house. Which raised the question of deck footing next to a house? What distance should deck footing be from the house?
A freestanding deck footing next to a house should be as far away from the house as possible. The allowable joist overhang determines the distance between the house and the deck footing from the house. Deck footing for 2×6 and 2×8 joist should be 16″ (400mm) from the house. Deck footings for 2×10 and 2×12 joist should be 24″ (600mm) from the house.
There are several reasons for distance between the house and the deck footings. Space is both for ease of installation as well as strength of deck construction. There is no value having additional footing next to your house to prevent structural damage to the house if the footings beside the house create structural problems for both the deck and the house. The size of the deck and footing location will determine the level of impact on the house, but the correct placement will minimize impact regardless.
How close can deck footing be to house?
Hate to build a freestanding deck beside your house to prevent damage to the house, only to damage the foundation below. Here is why its best to keep a deck footing away from beside the house.
Keep the Deck Footing off the House Footing
The main reason to keep the deck footings away from the house is the house’s footings. Most houses’ foundations rest on a strip footing which is a minimum of three times in width as the foundation wall is. Commonly a house wall is 8″ (200mm) thick with the strip footing being 24″ (600mm) wide. The footing projecting 8″ (200mm) or more out from the house.
A deck footing next to the house will transfer the load of the deck unto the footing improperly. The load of the footing should bear on the centre of the footing, not the edge. Think of it like stepping into a canoe. Stepping into the centre of a canoe is safe, and the canoe will support you. But if you step unto the edge of the canoe, it will capsize. Footings are the same; the load applied to the centre is good, applied to the edge it can tilt and sink. Damaging the house foundation along with the deck footing sinking.
Compounding the required distance from the house is the deck footing size, both the house footing projection and also the deck footing size. Required deck footing size varies by soil bearing capacity. The firmer the soil, the smaller the deck footing can be. The load also impacts deck footing size, more load requiring a bigger footing.
Deck posts like house footings should bear on the centre of the deck footing. There is some play, but ideally, the deck post needs to be in the centre. The size of this footing varies, but in Calgary where I build decks, the deck footing needs to be 10″ (250mm) in diameter. Meaning the deck footing is projecting 5″ (125mm) closer to the house than the centre of the deck beam. Adding an additional 5″ (125mm) to the house 8″ (200) footing projection, the centre of the deck footing needs to be 13″ (330mm) from the house to not bear on the edge of the house footing.
Many jurisdictions require larger deck footing than Calgary, meaning the footing needs to be even further away from the house. Medicine Hat requires a 24″ (600mm) pad under the concrete column, with Winnipeg going even further. Click here for a chart of required Canadian deck footings sizes and greater discussion of deck footing requirements. But in short, to not damage the house footings, deck footings need distance between the footing and house.
Soil Bearing Capacity for a deck close to the house?
Last summer, I was building a deck in a new neighbourhood, and a chatty neighbour had just finished building his deck in the next yard. Not a huge deck but a nice addition to his home. Unfortunately, the ground around the house was still settling. The deck footings close to the house where sinking. His beautiful deck was buckling towards his house, as the footing sank. The wonderfully designed slope away from the house was reversing, and his deck now sloped towards the house. Even worse, it was sinking rapidly.
The destruction of his deck could have been avoided with footing placement. The house had been backfilled 2′ (0.6m) around the house after construction. The additional ground excavated for construction of the foundation. The backfill is often not compacted, meaning it still needs to settle for a few years before it can support a deck. The distance off disturbed and uncompacted soil may be increased with evacuation cutback to prevent wall collapse. But it is safe to assume that ground around a newly built house will not support a deck. Settle will occur, with a freestanding deck sinking near the house.
The farther away from the house, the deck footing is the greater the chance that it’s on undisturbed soil able to support the deck. Distancing from the house increasing the chances of the deck lasting.
Preventing House Foundation Damage with Deck Footing Placement
The closer you dig to the house, the greater the chance of damaging the foundation’s waterproofing. The foundation can be a waterproofing membrane or sealant applied to the concrete. Spade, post hole digger scrapping the foundation will compromise the waterproofing. Creating a bigger issue of a leaky basement.
Digging the deck footing a few inches away from the foundation prevents foundation damage with a few inches of dirt shielding the waterproofing. Speaking of digging holes.
Its easier to dig a hole with space between the house and footing.
When I am estimating the time to build a fence, I always double the time for post holes beside the house. Digging a hole in close-quarter slows down progress. Digging a deck footing a foot or more away from the house will take half the time than one closer. Moving the footing, the maximum distance away from the house will get you enjoying your deck quicker.
Wondering how many footing your deck will need? Here is a chart with the number of footing required for a freestanding deck. Half the footing number will be along with the house, the other half supporting the deck away from the house.
Number of Footing for a Freestanding Deck
|Size of Deck||Size of Deck Beams||Number of Footings||Footing Spacing|
|8’ x 10’||(2) 2×8||4||6’0”|
|10’ x 10’||(2) 2×8||4||8’0”*|
|10’ x 12’||(3) 2×8||4||8’0”*|
|12’ x 12’||(2) 2×6||6||6’0”|
|16’ x 16’||(3) 2×8||6||7’0”*|
|20’ x 12’||(2) 2×8||6||6’0”*|
|20’ x 14’||(2) 2×8||6||6’0”*|
|20’ x20’||3 beams (2) 2×8||9 (3 rows of 3)||6’0”*|
- Not Incised, S-P-F Beam Material
- *2×8 beam cantilevering 16″ (400mm) both sides
- Meet or exceeds Canadian Wood Council Requirements
The above link to Canadian Wood Council includes many charts of deck joist spans and beam requirements helpful in designing a freestanding deck.
An additional advantage of cantilevering
Overhanging joist reduces its spans. Smaller joist spans translate into less deflection and a firmer deck. A great reason to incorporate cantilevers into a deck design even without the concerns about the foundation.
In Conclusion of Footing by a House
Locating deck footings, the maximum distance from the house based off the allowable joist cantilever will be better for your deck and house. Along with making construction easier with space to work.
Additional Deck construction Articles
With a freestanding deck, the number of footings is twice as many as with an attached deck. Making cost and ease of installation twice as important. There are several options for deck footings varying in cost. Here is a link comparing five popular footings and their cost.
If a deck is not attached to the house, you have some options with footings. Either a freestanding deck with footings or a floating deck. Click here to read a comparison between deck designs.