lateral bracing

Started by astidham, July 25, 2010, 09:12:22 AM

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John Raabe

#25
I think I will rewrite the article on pier and beam foundations. I have perhaps over promoted the idea. Properly done in well-drained soil I would disagree that pier and beam would be a substandard foundation. However, while I show some lateral bracing ideas, stock plans are not engineered for specific sites - that must be done locally and adds to the cost. There are remote sites where concrete is difficult to pour so at those sites it may still be the best way to go.

A concrete crawlspace or basement can be built prescriptively in most locations and would likely justify a higher resale value as well. Most of my plans have crawlspace and slab foundations as well, but owner-builders often go for the pier and beam for some reason (perceived initial cost savings?)

Soil and site conditions are most often the cause of foundation failure, not the type of foundation. A pier and beam foundation where piers are leaning is easy to blame for the failure, even when the real problem is freezing water under footings as it sounds like it was at the house you are crawling around under now. Going to a basement foundation and the good drainage you are sure to put in will solve the water problem and get footings down below frost. This will likely be the last foundation the house needs.
None of us are as smart as all of us.

hpinson

I have the Little House and 20x30 House plan sets (my memory is that) both provide an option of a full perimeter crawlspace foundation, a slab, and the piers. I have to admit that as a na├»ve viewer of the plans, my first strong inclination was towards the piers, as a labor and cost savings do-it-yourself sort of foundation for a very small structure (14x20).  It took a lot of reading here to understand and be convinced otherwise. 


JasonInOympia

Quote from: John Raabe on August 16, 2014, 04:40:15 PMInteresting and I agree, pier foundations and bracing for sideward forces should be reviewed by a local engineer - most especially when building in poorly drained soil, on steep slopes or (even worse) on fill. But just advising a standard concrete foundation over a pier system may not help.

Understanding the character of the soil and the building site before committing to a build is key.  Frost heave in expansive soils can be very persuasive, no matter what the foundation system used. If there is any question about the stability of the soil, it is worth a visit from a soils (geotech) engineer. There have and will always be houses that are built in soil that should not have buildings on them. Building on such sites can be expensive and is best avoided. This is a battle nature usually wins.

What are the soil conditions at the third foundation house and what are the engineers suggesting for a solution?


John Raabe-

This has been very informative. I am currently working on a 2 story cabin build with gamble roof in the Centralia area. I've already committed to pier and beam (to keep costs down as was implied during the conversation). I had planned on just using the entire 48" sonotube pier (+12" footer) and then going up with a 6x6 the remainder of the height needed on the backside, where the ground is lowest. My cabin site is on a gentle slop with the bottom of front joist only 1' from grade and the back being about 6' off grade. I wasn't that worried about drainage, until I read this conversation. It will definitely be on my mind now. 

I was planning on using diagonal bracing, but wasn't sure about what size I should use.  My geotech did his report already and said I have good compacted soil for construction and didn't seem to be concerned with my pier and beam foundation.

With a 6x6 pillar, a 3-2x10 constructed girder, and all piers being 8' apart on a 16x40 2 story structure, do you think 2- 2x6's is enough to transfer the lateral movement? Or should I step it up to 2x8's, or even 2x10's?

As for the pier depth, since I am now more concerned with lateral movement, do you think I should lower the pier down to 3' (+12" for footer) below grade and leave the remaining 1' above grade? That means I'd be using a 6x6 post for the remaining 5' or so on the back side.

JRR

I've never experienced Pier and Beam personally.  Standard footings and foundations walls have always suited my situation.  But I can understand the use of it on plots where the ground is uneven and unwieldy.  A number of locations are like that here in Georgia, think "granite all around".  In this case drilled anchor rods and reinforced concrete piers would be about the only reasonable solution.  But for me, I would re-think the posts .. the treated 6x6's, or whatever, .. that extend up from the piers.  I would not stop them at the floor joists, but would let them extend up high into the walls.. perhaps all the way to the roof framing.  The piers and posts would have to be located so as not to cross through door and window wall openings, and there may likely be a greater number required.  And the framing planning has to move from Platform to Balloon style, at least partially.  But think of the added wind and seismic resistance.  The underfloor angle bracing would remain.

If I'm wrong, let me down gently please.