Overbuilding?

[cbrian]

Hello. I am new to the forum, but have been reading over some of the material and thought I would post a question that has been bothering me. I live in Central Texas and plan on building a small lake house (24*32 w/ loft), on a somewhat sloped lot (5-6' drop over 32'). From everything I am reading I should drill down half-way to china, place columns half a mile wide, and make sure everything is reinforced with titanium. Like I say, I am in Central Texas, so snow loads and frost heaving just do not exist. I have seen everything from a 2-story house with 16"x16" pads with a couple of cinder blocks sitting right on the ground standing since the 1930's, to a "box house" with 3/4" thick walls that sat on dry stack rocks since the 1890's. Is this need to publish facts and figures way beyond what is needed just a legal out in the event something goes wrong, or are the 50% of the homes in the U.S. ready to fall in at any second? My plan was a simple a 2'-3' hole, 6" gravel, 6"x24"x24" reinforced pad, 12" form tube to make up the remainder allowing the tube 6" above grade to accept a 6"x6" treated post via galv. base, and 3- 2"x10" to make a girder, and overkill my joist to 2"x8" - 16o.c.

[flyingvan]

    You can always find old, old houses with some shoddy construction still standing---but for every one of those you see, there are dozens that failed long ago that are long gone.  Soils are highly variable and a single soft spot can wreak havoc.  All the building codes are a balance between what the UBC thinks is safe, tempered by big developer lobbies that want to keep cost down.  Many of the codes are designed around a 30 year old structure life span, which has made things challenging for fire departments (trusses fail quickly in fires)
    As far as your build goes----there are many options for how to do your foundation.  Foundations are pretty easy to do correctly and very difficult to repair or upgrade later.  As far as depth goes, the rule is 7' to daylight on a slope----There's a discussion somewhere in this forum that describes that better but I have to find it...basically you have to dig straight down so an imaginary horizontal line 7' or more out breaks the surface.  Steeper slope, deeper hole

[Squirl]

For pier foundations, sinking things deep is to counterbalance the leverage force when putting the weight of an entire house on piers.  In frost areas foundations already have to be deep so it is not any extra burden.  If you have little to no frost line you can do a full block foundation and perimeter footing cheaper, faster, and safer than a pier foundation.  I don't understand the obsession with pier foundations in areas without frost depths.

I have seen many citations to exceptions of the basic rules of building still standing, but in the end they are the exceptions not the rules.  What you don't see are the hundreds of houses built on bad foundations that were torn down long before any of us were even born.  Houses don't tend to just collapse, they get severely damaged and cost huge amounts of money and time to fix or people walk away from them and they are torn down.

I didn't see if you mentioned a center beam, so a triple 2x10 girder with two clear span floors can span 5'-6" according to span charts. So I would guess 14-16 posts each side.  By the time you add up the pt posts, the brackets, the added bracing required, the skirting, and the 2x10 beams, an unreinforced concrete block wall dry stacked with SBC would be stronger and probably faster and cheaper.

Footing thickness for a two story to code is 7".

If you would like to explore other options, I would be happy to write and discuss them with the process, and costs.  Due to the leverage, engineering concerns, I cannot give greater input on shallow sunk tall piers.

[MountainDon]

Not overbuilding; it's building to best practices.

There's some good info, great thinking and excellent advice in the two posts above.  In your virtually no frost depth you would be almost certainly ahead of the game if you dug a 12 inch deep perimeter trench, did full perimeter footing. On that either build a formed and poured stem wall or a block wall for a crawlspace. Something along those lines should last longer with less trouble, fewer repairs than anything built on piers, especially for something the size of what you propose.

[alex trent]

Let me preface with the fact that I got a lot of great advice on building on piers...from the guys who first tried to talk me out of it.  I appreciate the fact that they did that in spite of their "obsession" that this is a dumb way to build.

I agree that a full traditional foundation is easier and more trustworthy.  But, in some instances it is not the best choice.  When you have a steeply sloped site and do not want a ton of excavation for aesthetic or environmental reasons..or both they fit the bill.  And, if you want them, you have to be careful and "overbuild", so to speak.  My cabin is likely overbuilt, but I am happy to have done it as the cost and work in minimal if done at the start. Know your soils, build piers correctly, fasten posts correctly and brace correctly.  There is plenty of information on all of that...most on this site, so you can build and not be in th dark even though there is no code standard for things.

A house is as much an expression of what you want as it is an engine where I live.eering plan that has everything thought out for you.  So, those of you who want (or need) to build houses on piers can relax a bit. Done right they will not crash and they have a lot of advantages in some situations. For me, the sloped site is one...the other is security...nice to above the grade

[AdironDoc]

I've often wondered the same thing.. "does it really need to be like this?" My builder has so rightly said, "It's the extra 10% that's the difference between acceptable and excellent". Plenty of cabins up here on posts/piers, even done to code, leaning or fallen.  In the end, it's gonna cost you either way. For something as fundamental as a foundation, I figure, it's worth the extra effort. It's worth the extra cost.

[cbrian]

I am not obsessed with post and pier, I am obsessed with saving money and time. To build any solid perimeter means tons of excavation on virgin ground, heavy machinery+steep slope=$$$. I have had it looked at many ways, and I am told 30k for a slab and retaining walls, 15-20k for cinder-block with crawlspace, or 50k for a walkout basement. Now take those numbers and the impact on my beautiful 2 acres of virgin land, and compare them to piers that I can do myself for about 1k and be done in a week. I want to do it right, but I definitely need to go with piers. I am not sure what part of the country some of you are from, but with the exception of bigger cities, every other house in Texas would'nt pass code, and many are sitting on concrete blocks right on the ground, at least in Central Texas. And next time your on the Texas Coast, take a look at the rows and rows of bay houses sitting on 6x6 piers 12' in the air. I understand that a Mercedes is a great car, but some of us have to drive an old chevy. I could spend 100k on my foundation, and one day 1,000 years from now it will be a tourist attraction, but I just want a little cabin on the lake that doesn't cost more than a new house in town. Any ideas where to get info on the proper depth, size of piers? Also, I believe I am correct in stating just because it is sloped the sheer force is no different than if the ground where flat, IF the structure is level.

[John Raabe]

I appreciate the comments of Alextrent above.

In many of the simple plans that I sell on the CountryPlans site I have included several foundation plans - pier and beam, crawlspace, slab, etc. It has been my intention with these to give owners options that they can explore and work out for their local situation. Not all of those foundation options are suited to every site and there are lots of conversations here on the forum about what is BEST!

But best is both local and personal - and not just an argument over codes or "best practice". Best practice, after all, is just an ever-changing collection of the opinions of the "construction industry", commercial builders, engineers and code officials, as to what is most likely to keep them out of lawsuits. Because of this CYA element it is understandably very conservative, but good general advice.

When I once asked my engineer "how long do we have to wait on fill dirt before it can be considered 'undisturbed' soil"? His answer, "after you run a glacier over it." That's good general advice.

[cbrian]

I guess I forgot to explain the plan I had so far. The main structure not considering porches is 24'x32', with a loft. My pier layout consists of 12" piers only under bearing walls, so outsides and middle (3 rows of 5). The span between piers will be 8' (actual 7') the bearing length, and 12' (actual 11') between rows joist width. I planned on a 2.5' deep hole with gravel base, 24"x24"x8" reinforced footer, and a 12' pier to make up the remainder, and coming 6" above grade with the pier. My girder would be 3- 2"x10" plywood sandwiched 32' x 3 girders. My floor joist would be 2x8 spanning 11' (carrying only floor load). So I have all my loads directly on the girder and into piers. My soil is 6"-8" of black loam then I hit a rocky hard chalk type layer that seems to go on forever. I have rock outcroppings 4'-5' high all around my build site. I have yet to find anyone who would tackle the job when I did want a traditional foundation, and after seeing all the rock and the hardness of the ground after a few inches I can't find anyone to even dig piers without the use of a huge drill machine that can't even get to my site, not to mention I don't want to disturb this piece of land to that extent. Any ideas on what to do? I feel like I am in some remote area of Alaska, shovel and pick time?

[cbrian]

If you have little to no frost line you can do a full block foundation and perimeter footing cheaper, faster, and safer than a pier foundation.  I don't understand the obsession with pier foundations in areas without frost depths.

How do you derive at that? A slope of 5'-6' drop over 32' and you say a perimeter footing is cheaper, faster, and safer? First of all you would have to hire and excavator at 200$ an hour to dig for a day or so, right there  your already more expensive, and already slower than a pier foundation. Then you say it is safer, safer how? My pier foundation will not be holding back tons and tons of soil, and my drainage for my pier foundation will be easier to achieve. With a full block foundation I will be not only holding back tons of soil, but also rock and water in heavy rain. My sight, while not the steepest, does show signs of slides, and cedar trees laid over from heavy rains. I want to be safe, do it right, and all with minimal impact. The question isn't why people are obsessed with pier foundations, the question is why when they seem the obvious choice some people won't except that fact.

[Squirl]

Most of the quoted price on other types of foundations is labor, not materials.

1k is a little low of an estimate for piers after you add in bracing, skirting, and girders.

A full perimeter footing on a sloped site can be stepped.  Here is a picture with UBC code citation.

http://www.naffainc.com/x/cb2/Struct/Footings%20and%20Slabs.htm



You should dig down a few inches to get past the vegetation layer of the top soil. 

Since cost is an issue to you I will run down the other type I proposed.

So a full perimeter foundation for a two story house has to be 12 inches wide as long as you don't have the worst type of soil. With 7" deep and 112 linear feet long that is around 2 yards on concrete. Even if you ordered 50% more at 3 yards for the step areas and overage that would be around $350 of concrete around here.  20 ft pieces or rebar where $7 when I bought them last year. So around $100 more in rebar.  So for $450 with almost no digging, as long as you can reuse the 2x8s from the forms for floor joists, you have a full perimeter foundation in a day or two.

Since you won't have unbalance fill pressing on the foundation you can use drystack concrete blocks without rebar or grout.
http://www.sakrete.com/products/detail.cfm/prod_alias/Surface-Bonding-Cement
They were $1.25 last year. Let say you were doing a 6 ft wall sloped over 32 ft.  It would take a little more time to plan out, but for rough estimates let's say that is 336 square ft of wall.  With the average 8x16 block taking .8 square ft. it would be around 420 blocks. Even if prices increased at to $1.50 that is $630.  SBC costs around $15 a bag and should cover 50 square ft.  So around $200 in SBC.  PT 2x4's and J bolts are cheap. $1.00 a bolt, $3 per 2x4. 

Even rounding up for unforeseen costs, I would estimate $1500 -$2000 in materials for a full perimeter foundation.  It might even be less work because you won't have to dig much of anything.

A 24x32 1.5 story building is a $30-$40K investment off the bat.  If there was a different option that was stronger and was comparable in both time and money, I would take the more stable option.

[John Raabe]

Nice work Squirl!

Very helpful analysis and estimation calculation.

[Squirl]

Also with a full perimeter foundation center beam posts can be on grade even in frost depth areas.  No digging.

[Squirl]

Sorry, I did not mean just your posting about pier foundations. You are the third or fouth from central Texas that has posted on this.  I just thought there were many misconceptions about traditional foundations and misunderstandings, especially in cost/benefit.  It appears that you have the understanding that you have to dig a very deep in a no frost depth area.  I have read the building code extensively and a few dozen other books on foundations, and have never seen that.  If there is a special provision that you have to go X feet deeper because of a slope, I don't know it.

Houses are heavy.  At 1500 square ft, I know it will be a cabin to you, but it is the size of a house to me.  The more points and wider area you distribute that much weight the more stable it is. 

As you can see I am more comfortable telling you something is good practice and OK that has been tested across millions of structures and has passed approval by hundreds of architects and engineers vs. something that hasn't.  I'm not saying that your pier design won't work, I am telling you about something else that almost definitely will.

[cbrian]

If a step foundation can be poured by hand I am sold. But like I say everyone I have spoken to will not touch my build, last guy said it would take a crane to pump concrete to the site, and he couldn't get a crane close enough if he wanted to, another said a bulldozer would need to do a weeks work to get to it. This area is restricted, I cannot tear it up, or bulldoze, and I would not want to if I could. Can a step perimeter foundation be poured by hand using sakcrete?!?! I know I want to keep the disturbance to the area at a minimum, last thing I need is someone digging up Indian remains, and my whole build being put off for who knows how long.

[cbrian]

If I can hand pour a perimeter step foundation, I assume I could rock that thing , yeah? That would be awesome! I have been collecting barn, and old house wood, mainly hand hewed beams, some true dimensional oak/pine lumber, and tons of 1"*12" planks. I have a trashcan full of old square nails. My entire cabin is being constructed from reclaimed wood, so a block wall covered with stone would really put the finish touch on it, much better than piers allowing you to see under the house.

[metolent]

My cabin is on a grade as well and I have a full perimeter stepped foundation with a pony wall on the back/low side.  I also elected not to even use piers on poured footers under my center beam; instead I used another full-length stem wall with access "cut-outs" to allow access across the entire crawlspace.

As for cost, it sounds like my site is a bit closer to civilization than yours with better access, but I had quotes of 4k-5k for the foundation.  They had the site cleared and footings dug and ready for inspection in a day and my site had quite a few trees.  After inspection the next morning, they poured the footings.  Waited for it to cure and got the forms/rebar ready for the stem walls.  After several more inspections and the pour, the framing for the floor started.  I recall the foundation taking about a week (2-3 guys), which was mostly dedicated to waiting for the concrete to set up and inspections.  They were a great crew - they didn't use a pumper truck and instead "wheelbarrowed" and "bucket brigaded" concrete down to the farthest section to avoid the added expense of calling in a pumper truck.  Unreal.

Good luck...



This is a shot of the center stem wall. 

[alex trent]

I like the step foundation idea and see where that could work....sometimes.

But we are still getting lost in the cost ( which is miscalculated in the frenzy to prove "you can build a foundation as cheap" ) and the weight of the house and other stuff that has little to do with what a person wants in a house and what can reasonably be done in a given area. .  You need more than an engineer to figure that out.

For a small house, on a steep slope and minimizing the environmental impact (in several ways) pier and post is still the best bet...if you do it right.  And, of yeah, it happens to be what some people want. The constant naysayer barrage is getting old and in my opinion is and boring and counterproductive.

[AdironDoc]

Can't speak to building on grade but my 20 x 40 was quoted $5k for post/pier. I paid $7k and went full pwf. Poured was impossible as camp is 2 miles into the sticks. Glad I have the storage and looking back, I'd change nothing.

[UK4X4]

I'm 2 years into my planning and it seems to change every few months as I talk to more people and engineers- every one has diferent ideas on what works best !

every area is diferent- every soil- angle of the land -frost -rain -water runoff etc etc etc.

It seems that every plot needs to be assesed individually and a suitable design chosen for that land-

a wrong choice of foundation based simply on cost down the road could be a complete faliure.

Perimeter foundations are true and tested - my house in the UK has one- its on clay soil but no frost- its 113ish years old this year

It spreads the load over a great surface area and is mechanicly sound when the walls are added.

Post and beam have issues with height/ soil conditions/ wind load etc etc

The ones you see on the coast of TX often have a perimeter grade beam and 20-30ft deep steel piles below what you see at surface

Fema has a whole bunch of info on pile /post foundations- I have a link arround here somewhere

Footings size, depth and x bracing makes or breaks a pier foundation - lacking in thought on any one may cause you heart ache down the road.

Start with the soil - type and structure- water running through ? bed rock etc

I think I'd start at the loads roof-attic-floor-walls

That will give you the total weight........the position of the supporting beams will divide up that weight
Calculate what beams you need to support those loads
then you have to work out the weights per post
Then you look at what size of piers you need to support that weight.

There are multiple worked examples arround here...if you can find them !

US geological survey gives you basic soils in your area, and provides a free report- that gets you a start on theoreticly what your soils can support
lots of TX is clay- which gives its own problems with expansion due to water

If I have a few mins later I'll point you too one

This one is based on sizing the beams- the software calculated the weights per post.....although you can do manually as well

http://countryplans.com/smf/index.php?topic=10511.0

[MountainDon]

.....Texas Coast, take a look at the rows and rows of bay houses sitting on 6x6 piers 12' in the air.

I type/think too slow for UK4x4   He beat me on some, but I spent the time so here it is....


Just a FYI, the only comparison that can be made between the typical owner-builder pier foundation and the pilings that are used in coastal areas is that both place the building up off the ground. It is normal for coastal pilings to be designed by an engineer after soil analysis. Owner-builder piers are usually done by a guess. Residential pilings can range from 20 feet to 60 feet in length with considerably more piling below the surface than above. Pilings are frequently 12 x 12. In part these requirements are why coastal homes tend to be uber expensive; it's not worth the foundation cost to build a cottage.

[alex trent]

Everybody is right (well almost).  Goes to show a lot of ways to skin this cat.

But in making example for or against important to compare same stuff.  A beach house on the outer banks of NC with three stories and 4,000 sq feet is not the same as a 600 sq. foot single story in a much less wind threatened area (ok, in this climate, there may be no such thing).  But the formidable pilings they rest on are not exactly any prototype for a cabin or a small house, which do with a lot less.  Not a bunch of rubble to be sure, but can still be built right.  If the soil bearing capacity is worrisome, take a sample and find out...if you cannot or will not do that, likely you are on the road to problems there or someplace else.

[Don_P]

TX, lake, hard chalklike layer just under A soil horizon, local contractors quoting high foundation prices.

Caliche

[MountainDon]

Caliche

Caliche is actually a 4 letter word, even though it doesn't appear to be at first. 

I believe it is used or can be used in the manufacture of Portland Cement.

[Bill Houghton]

Hello. I am new to the forum, but have been reading over some of the material and thought I would post a question that has been bothering me. I live in Central Texas and plan on building a small lake house (24*32 w/ loft), on a somewhat sloped lot (5-6' drop over 32'). From everything I am reading I should drill down half-way to china, place columns half a mile wide, and make sure everything is reinforced with titanium. Like I say, I am in Central Texas, so snow loads and frost heaving just do not exist. I have seen everything from a 2-story house with 16"x16" pads with a couple of cinder blocks sitting right on the ground standing since the 1930's, to a "box house" with 3/4" thick walls that sat on dry stack rocks since the 1890's. Is this need to publish facts and figures way beyond what is needed just a legal out in the event something goes wrong, or are the 50% of the homes in the U.S. ready to fall in at any second? My plan was a simple a 2'-3' hole, 6" gravel, 6"x24"x24" reinforced pad, 12" form tube to make up the remainder allowing the tube 6" above grade to accept a 6"x6" treated post via galv. base, and 3- 2"x10" to make a girder, and overkill my joist to 2"x8" - 16o.c.

Are you originally from Michigan?  I love your sarcasm.  Best laugh I have had in a long time.