Deck footings

[dencinger]

Can concrete blocks be used as footings? We are looking to build a 19x13 deck that will only be 2 feet off the ground. we need to put footings at 48 inches in ground. This will be freestanding/floating. Permit not required when unattached and less than 30 inches.

 

[Greenman]

Does it freeze where ever you are? Any idea what the load bearing capacity of the soil is?
When you say footings at 48" are talking about the depth of the piers or the space between them?

 

[herm0016]

easier to dig a hole and fill it with concrete than to lay up block in a hole. 48 in deep i am assuming. use the metal brackets on top of the concrete and then your post.

 

[BoomerD]

easier to dig a hole and fill it with concrete than to lay up block in a hole. 48 in deep i am assuming. use the metal brackets on top of the concrete and then your post.

Yep. Normal cinder blocks have almost zero structural strength. Best os to dig a hole, use a form tube, stick a steel bracket in the top to connect your bottom 4x6 timbers. Alternatively, (not my choice) you can dig a hole, fill it with concrete, stick a 4x4 in the mud, and build on that...but I prefer the brackets. You can PROBABLY get by with concrete pier blocks in the center of the span...maybe.

 

[jmagg]

Op question contradicts itself.
Edit..
Learned today that any deck not attached is a floating deck.

 

[Greenman]

Op question contradicts itself.
Edit..
Learned today that any deck not attached is a floating deck.

The issue is we have no real idea of what he's asking, and apparently he doesn't much care as he's never been back.

 

[jmagg]

If he used a square auger bit, I suppose block would be ok as long as he started with a solid four and filled the top to accept the lag bolt.

 

[Greenman]

On a low deck, it's more about the bearing capacity of the soil rather than the type of foundation. Unless it's in the frozen north, then it's a whole different story. If I was building it around here I'd assume the ground could carry 1500 pounds per square foot. Using 40 pounds psf live load and 15psf dead load for the deck, I would need 10 square feet of bottom bearing pier to support the load. I don't know how it's figured where the ground freezes. I would assume skin friction piers but I have no idea what the freeze thaw cycle does to that, or how much of the pier counts as load bearing.

 

[Red Squirrel]

To do it "right" you should go 10 feet deep with sonotubes and pour a bunch of piers but that is hard and expensive work. That said if it's not attached to the house you can probably just leave it floating. It WILL move with the frost heave but it should ideally just move back to normal in summer. I'll be building my deck and the gas line passes where I would need to dig so rather than do it by hand I will just make it a floating deck. I'll lay it on top of patio stones. Not exactly the best way but I don't have enough height to use even deck blocks by the time I account for lumber size since the patio door is not very high off the ground and don't want the deck to be higher.

I did the same for my shed, I just made it floating, I did use deck blocks and did dig a little but to put them in the ground but I didn't go to frost level. I figure if it starts to shift too much I can just jack it up and add shims. The deck would be a bit harder to fix after the fact though as there would not be easy access to the beams once the deckboards are down. I won't dig or anything as I figure if I don't disturb the soil it's already packed down enough that it ideally won't shift too much.

If you were attaching it to the house then you do need to do piers going to frost level otherwise it might rip apart from the house and cause damage. Attaching to the house is also tricky as it's hard to tell where the joists are from outside, especially if the house is brick. You don't want to attach only to the brick as that's not structural.

 

[Greenman]

To do it "right" you should go 10 feet deep with sonotubes and pour a bunch of piers but that is hard and expensive work. That said if it's not attached to the house you can probably just leave it floating. It WILL move with the frost heave but it should ideally just move back to normal in summer. I'll be building my deck and the gas line passes where I would need to dig so rather than do it by hand I will just make it a floating deck. I'll lay it on top of patio stones. Not exactly the best way but I don't have enough height to use even deck blocks by the time I account for lumber size since the patio door is not very high off the ground and don't want the deck to be higher.

I did the same for my shed, I just made it floating, I did use deck blocks and did dig a little but to put them in the ground but I didn't go to frost level. I figure if it starts to shift too much I can just jack it up and add shims. The deck would be a bit harder to fix after the fact though as there would not be easy access to the beams once the deckboards are down. I won't dig or anything as I figure if I don't disturb the soil it's already packed down enough that it ideally won't shift too much.

If you were attaching it to the house then you do need to do piers going to frost level otherwise it might rip apart from the house and cause damage. Attaching to the house is also tricky as it's hard to tell where the joists are from outside, especially if the house is brick. You don't want to attach only to the brick as that's not structural.

Doing it right in the frozen North is a lot different than in sunny CA. We kind of need to know where the fellow lives.

 

[jmagg]

I'm in zone 5, and have built a few decks to code at 48 inch frost line depth and finished at 50lbs per sq ft framing. Guess the square auger bit joke didn't fly.

 

[Scarpozzi]

Is the ground sloped at all under the deck? You need to consider what would happen if the blocks get washed out slightly over time...it could make the deck wavy or sag in spots. If this happens, it will cause water runoff issues (decks should be slightly sloped in the direction of the boards unless you get fancy and do 45's.

I built a 16'X20' deck two summers ago. I'm glad I went 16 feet with it.... I just took 16 foot composite decking and ran it perpendicular to the side of the house...using hidden fasteners...then framed it in with finished boards. I ended up doing 2x8's with lots of cross supports and probably 12 piers because I didn't want it to move. It wasn't that bad because the frost line here isn't too deep. I really just went down 2 feet and held the structure together with galvanized carriage bolts.

I used Trex composite...Trex also made the hidden fasteners. This desk doesn't get direct sun after 2pm because my 28' high garage is right next to it... It's pretty awesome. Consider that if you have more than one place to build a deck... Build it in the shade for afternoon parties, flash some kind of BBQ gang sign with your hands and scream EAST SIDE!!!!!!

 

[Micrornd]

I used Trex composite...Trex also made the hidden fasteners.

Looks really nice. Kudos!

How big is the gap between boards using the Trex fasteners?
Have you had any mold issues or is that no a problem in your area?

 

[Mr.IncrediblyBored]

Please disregard the Squirrel. Sometimes the Wildlings forget only they have to deal with 8 feet of permafrost. Most of us south of the wall only have to dig 48 inches at most for residential footings.

 

[Scarpozzi]

Looks really nice. Kudos!

How big is the gap between boards using the Trex fasteners?
Have you had any mold issues or is that no a problem in your area?

Maybe 1/8" gap or more....I'd have to measure. These are the fasteners: https://www.diyhomecenter.com/trex-...3F_cCCLF85UJn81ZnvF9dBODS9ffr6kxoCZ8gQAvD_BwE

No mold here, but the deck gets morning sun and dries out. I put adhesive window flashing on top of the 2x8s and ledger to prevent them from getting water damage. And flashed under the siding, but that's not cause any issues that I can tell. If it were on the other side of the house, the deck might require scrubbing once a year to clean up mildew.

My father in law had someone build a deck for him using the same Trex decking. They didn't support the boards as much as I did, used traditional deck screws, and he pressure washed the deck too hard....it also gets direct afternoon sun. His deck looks 10 years older than mine and it's only 1 year older. I think the sun and pressure washer damage are worse than the poor construction. Just saying, my deck was pretty simple, but I took time and consideration into everything.