Deck Footing Options on Slight Slope

[harborremodel]

I'm doing design for a deck. The deck will sit over a slope that slopes down toward the house. The deck is attached to the house with a ledger board but then runs out 20' and meets the top of the slope. I'm wondering what the deck should sit on where it meets the slope. Should i dig down and pour footings? I live in the rainy northwest so i want the framing done right so it's not sitting in water and rotting.

 

[Snoonyb]

With a projection of 20' you'll also need an intermediate support with footings.

I suggest you find a local structural engineer and have him design, with calcs, the supporting member and footings.

 

[Sparky617]

Footings are a must and required depth varies by location. In areas with harder winters they can be 48" deep, in areas with mild winters 12". They need to go to solid, undisturbed sub-soil (clay in many areas) that must pass a test by the inspector to handle the load. The test is relatively simple, he has a rod with a T-handle and when he leans into the rod it can't sink very far into the ground.

I'd recommend bringing the footings up above grade and using a post bracket to get the wood up off the concrete. Doing this will greatly extend the life of your pressure treated posts. Oh, and Snoonyb's suggestions are all valid.

 

[bud16415]

My hot tub deck is 12x16 and in part as an experiment I built it free floating and not attached to the house with the ledger. I’m also on a slight slope but sloping away fron the house and live in a zone where conventional footings have to go down a min of 48”. With the deck able to float I left it an inch from touching the house. I didn’t have to calculate if the house had adequate strength to support a side of the deck and with the house being on a deep footing the rest could not be allowed to float, as the frost would rip it from the house.


I used the pre-cast concrete footings that posts sit into and I dug into the earth just far enough to leave a couple inches above grade. The sides of the footings are sloped and when the earth freezes they are stable from any movement except rise and fall. The deck has been in now for several winters and has a 6000 pound hot tub sitting on it and it moves up and down about a half inch when the weather drops as low as –30f. So far every spring it is back where it started and is level and tight. All my construction was PT wood I recycled and held together with guard dog deck screws.


My house is 150 years old with field stone foundation and some timber framing around the rim joist. I didn’t want to get into needing to calculate the house factor into the deck.


Local codes are all over the place and how they are enforced. I felt comfortable with a free standing deck as having no effect on the structure and if I had enough guys I could pick mine up and move it. So in that way it is not permanent.


The big question for me was how would it stand up to freeze/thaw cycles? At this point I don’t have any concerns of it failing. It is only about 3’ high at its highest point and if it was a taller deck like second floor height I would have likely planted the poles much deeper with deep footings.


I’m not saying this is the proper method only this is what I tried and had success with on a low deck and didn’t have to get into breaking the water shield of the house and dealing with that and also the excavation cost of deep footings.