Building on a Slope

[fraggin]

So I took 4 days to get some work done. I got a road cut through and picked out a spot and pulled some measurements. I want to build near the top of a hill. I measured the slope and at 24', there is a 5' drop. I did not want to do any grade work, I want to build with minimal impact. My question is what method is the best for building on this kind of slope?

[glenn kangiser]

My choice would be concrete footings with sonotube piers to about 18" above ground then diagonal braced wood posts from there to the beams.  The top beam could mount directly on the top row of concrete piers with a vapor break between the wood and concrete.

[fraggin]

What size sonotubes would you reccomend?

[glenn kangiser]

I'm not an engineer but if I was doing it in a non-engineered non-permit application I would use big enough to add about four 1/2 inch vertical rebar with  hooks on the bottom into the footing and 3/8 cage ties (circle ) wrapped around every 12 inches then about 3 of them in the top 6 inches, with my anchors in the middle of that - probably 10 to 12 inch diameter.  In the bottom would be about an 18" to 24" square footing to spread the weight with 4 rebars crossed in the bottom. 

This may be overkill but I have worked on engineered ones similar to this.  This can vary depending on your soil conditions.  If in doubt or permit required you may need an architect or engineer to design it.  Just an idea of what might work - no guarantees.

[glenn kangiser]

Old discussion

http://countryplans.com/smf/index.php?topic=614.0

[glenn kangiser]

Finally found a pix - this one has minimal bracing and I would recommend more but it has been there for years.





More on this discussion.

http://countryplans.com/smf/index.php?topic=1312.0

[poppy]

My site has the same slope as yours and I am using a pier/post design.

I think a good rule of thumb for concrete pier size is 1" dia. for every 1' in span between them.  I am using 12' spans, so 12" piers (Sonotubes are great).

I believe that 12" out of the ground for a reinforced concrete pier is a good distance unless you don't want to use any PT lumber for beams or posts; in that case, 18" might be better.  Keep in mind that if you use a beam on pier design with joists on top of the beam, then the upper side of the building is pretty high and then add the slope for the low side.

I am not going to use a moisture barrier on the ground, because I believe the slope opens it up enough on the low side so that air circulation is adequate.

Depth of pier and base size is all dependent on soil type and frost line.  No one can give you a proper depth and bearing surface area without that info.  (I continue to be bewildered by the number of questions about foundation design when no site conditions are given.)

For absolute minimum site impact I am using a pin pier design (poppy's pin pier plan detailed in another general forum thread)

As others have already said, bracing is critical.

Another important question, how big is the house/cabin?

[fraggin]

I plan on building 16X24 based on the Victoria Cottage plans.
The soil location is east texas. The soil type is sandy down to about 36" then red clay.
Frost line is no issue as the winters are very mild. I was going to put more info into my first post that I did, but earlier, I was just trying to get a quick answer as I was still on site and speaking with someone who is helping me with the project.

I actually spent Thurs-sunday doing site prep. I put in a 36" culvert in a ravine, and I burned 3 gallons of gas in my chainsaw clearing half a mile of road to the site and about 12 ours on a tractor. I didn't expect to get so much done, but ambition willing, things fell into place.

I'm somewhat confused on the methods used for post and beams where connectors are used. At my parents lake house, I've seen a few houses go up using the post and beam method, but I have never seen anyone use simpson ties or connectors. The traditional method in this area seems to be digging a deep hole, pouring in some gravel, then dropping in a 6x6 PT post, then pouring cement in the hole. I've read that this method is not reccomended because the concrete corrodes the wood? Is this correct? Are we talking 30 years? 50? Just curious. Maybe we're just that far behind the times in the construction industry around here.

[glenn kangiser]

It could last a long time and it might not. 

The thing is that the post mounted on top of the concrete where it can dry will last longer with less chance of problems.  There are different grades of treatment also.  I have a lot of treated boat dock timbers that have lasted a long time and some that are rotted inside the treated shell. 

In any case - it is repairable and not the end of the world either way you go if there is at some time in the future, a problem.

[fraggin]

I pulled some strings, and got someone to help me go to the site and pull some strings....   

Anyway, Here's a pic of the 5' drop of elevation on the highest corner.

[poppy]

There is a free foundation plan for a 16' wide cottage over in the Plan Support section that may give you some more ideas.

I would think that some E. Texas folks will weigh in on this project; they can help you more than I.

In general on a sloped site, I would be concerned with drainage patterns.  I think you are ahead of the game somewhat because if I understand your location, the cabin will be near the top of the slope.  I have read that having the top of the building higher than the top of the slope is a good idea.  In any case water run off towards the foundation should be avoided if possible.

Another concern I would have is soil creep when adding a significant load to soil on a slope.  Again the Texas folks should be able to shed some light there. I would think that a shallow pier would work well on a level site, but the slope adds several more factors that create the need for good anchorage to mother earth.