footer depth on 45 degree slope

[DIY man]

I have a question on the proper depth of a footer on a 45 degree slope. Local code (South central PA) states I need a 36" footer depth. My problem is that the footer is going to be dug on a 45 degree slope. I know/think the footer should be deeper but I couldn't find any formulas or charts telling me how deep.

From what I think I will need to go down 51 inches but that is based on me thinking it through and using basic math.

I'm looking for someone to either tell me I'm right, point me in the direction of a chart formula, or give me the answer.

Thanks in advance.

[Wgoodrich]

You have duplicate posts right now asking the same thing in two different forum subjects. This forum subject is your better choice to get your answers I am going to lock your post in the other forum subject so all your answers will show here for all to find.

When building on a slope you create what is called step footers. The 36" is your frost depth. You can go deeper but not shallower than the frost depth without changing the supporting strength of that footer keeping it equal. Step footers are done by digging deep on one end then going horizontal at that same elevation till it hits 36" deep. This happens as the hill goes down it may be 50" deep for say 5' before it gets within the 36" distance from the surface. Then you stop that step of the footer. Then dig straight down and start another deep part of the next step of the footer and going horizontal again till it gets within 36" of the surface and continue stepping down your footer as the hill goes down.

The above design is no different than you standing on the side of the hill with one foot higher than the other. Either foot can support your body equal to the other foot although at different elevations on the hill where you stand.

Hope this helps

Wg

[DIY man]

Thanks for the reply and no problem on locking the other thread. I intended to post it in this form only. I didn't realize I put it on another. I just thought I messed up submitting it.

I think I understand the concept of the step footer. I did a brief google search and will be looking into it later. Thanks. It would seem easier to just dig a really deep single hole and use more concrete than layering it. But then again this will be a rather large deck and I want to do it right one time.

[CR500]

I found some info a while back about footers for retaining walls when placed on a slope. Basically you sized the footer according to the wall, then there was a specification about the distance required when projecting a line horizontally from the footing to daylight.

I'm away on travel for another week or so but if you're interested I can try to find the info when I get back.

[DIY man]

Wgoodrich,
I now fully understand the step footer thing. Since my whole house is on a slope the foundation for the house and my recent addition was dug that way.
If you misunderstood my design for the deck it will be 28' wide at the house and 15 to 17 feet out depending on the location. I will have a beam at 13' out from the house being held up by 6x6 posts supported by single piers. That amounts to 4 posts 7' apart. I intended to just dig a separate hole for each pier. Diameter would depend on the weight the post needs to support.

So I do not believe I'm stepping into the step footer territory. At least I hope not. That's a lot more digging.

If I'm wrong please correct me. If I'm right I'l like some reassurance.

Thanks.

[Wgoodrich]

If you put it on posts the posts must be set below frost line declared in your area if your deck is attached to the house. If the deck is free standing with posts next to the house but deck not touching the house you don't have to dig below frost line for the deck. If your slope is what you say I would dig the posts below frost line measuring the depth at the post from finished grade at the post location. Now concerning our prior discussion, imagine you could sinke into the ground and see through the earth and see the bottom of each of those posts. There is your stepping of your footer. In this case the post stays the same depth only at its own location making each post to be lower in elevation than the post installed up hill. Step foundation does the same. Now you idea of digging down deep and diging the trench out to the end so the bottom of the hill at the end of that footer is still below frost depth as required would take a huge amount of concrete not necessary. I understand now you plan on using posts but just trying to help you picture how a step footer and post bottom depth dropping as the hill drops works. I advise digging to frost depth to help hold the deck from sliding down the hill.

Good Luck

Wg

[DIY man]

Thanks again,
I do finally have a pretty decent understanding on the step footer. I also can admit my limitations and if I build anything needing that much of a foundation, even on a flat chunk of land, somebody else is pouring the foundation and laying the block. I'm good to go with the rest of the framing and finishing, even the electrical. I'll skip the roof framing but I'll put on the shingles.

Back to the deck. Yes, I am going down to the frost line, 36 inches here on a flat surface. Yes the slope is 45 degrees which will just add to the fun of digging the holes and filling them with concrete. It will be attached to the house with ledger boards. I'm trying to avoid a whole lot of posts,

[Wgoodrich]

Ok I think we may have a problem here now. You said "I'll skip the roof framing but I'll put on the shingles." Now I have thought this over a while and I am quite sure if your skip the roof framing you are going to have a real hard time putting on the shingles when there is no roof. Just thought I would mention this little problem. Hee Hee Sorry I tried to resist but just couldn't let that one go without some ribbing.

Wg

[pushkins]

"sky shingle hooks" !!:evil2::evil2:

[DIY man]

Wow, 7 real posts before this thread went downhill. At least I got my origional question answered first. I googled the sky hooks but couldn't find any. Do they have a different name?

Seriously thanks for the help with this issue. I'm moving on to other problems now.