Your builder may have a preference.

Good point! I will ask him.

What's a micro pile?

A chihuahua deposit.

Sorta what I was thinking...

snow country I would be interested in whatever you find. I was just looking at ram jack helical piles. I plan to call them and get pricing this week.

Virgil Carter Fine Art It is building on skinny pillars, 6".

And what's the spacing?

The soil report doesn't seem to say. They are leaving it to the structural engineer, it seems.

Initial cost is important, to be sure, but also consider repairs (especially due to plumbing leaks).

In my limited research (we have a lot of expansive clay soil here in central Texas), I have found that slab is usually the absolute cheapest foundation to build, but it's the most expensive to fix. Leaks in/under slabs require jackhammers, which create a ton of dust -- not to mention, the whole process of identifying the whereabouts of the leak, repairing the plumbing, and patching the foundation, is fairly inconvenient to those folks living in the house. :-/

For any house that I plan/hope to live in for longer than a decade, I would seriously hesitate to build on a slab....

Just don’t build in things that leak into concrete. Plumbing supply runs never need to be in a slab. They can come down from the attic. All that needs to be in the slab are the drains.

Having a slab can be managed. The few supply lines that we need in the slab (island, master bathroom vanity) were done in 3/4" supply lines because if there is ever a leak, 1/2" lines can be inserted into the 3/4"....

And has been said - anyone with a basement already has drain lines through / in a slab.

For the OP - I think your answer will lie in how much you would have to excavate to get to suitable soils. Over excavating isn't cheap, but the micro-piles don't sound low cost either....

" In my limited research (we have a lot of expansive clay soil here in central Texas), I have found that slab is usually the absolute cheapest foundation to build, but it's the most expensive to fix. Leaks in/under slabs require jackhammers, which create a ton of dust -- not to mention, the whole process of identifying the whereabouts of the leak, repairing the plumbing, and patching the foundation, is fairly inconvenient to those folks living in the house. :-/

"

my buddy just had a broken pipe under his house. $2800 to fix but they went under the slab. they never had to break the slab.

The few supply lines that we need in the slab (island, master bathroom vanity) were done in 3/4" supply lines because if there is ever a leak, 1/2" lines can be inserted into the 3/4"....

This is pretty clever.

my buddy just had a broken pipe under his house. $2800 to fix but the went under the slab. they never had to break the slab.

Is this the norm, or more anecdotal? I haven't heard of very many of these kind of simple/inexpensive broken-pipe-under-slab situations.

I basically like to ask repair folks, "What kind of [feature named here] is the most difficult/costly to fix?" and go from there. ;-)

"Is this the norm, or more anecdotal? I haven't heard of very many of these kind of simple/inexpensive broken-pipe-under-slab situations. "

from what Ive heard, nowadays the plumbing goes under the slab and not in the slab. very little of the plumbing is actually in the slab

Hi, Snowcountry,

What did the soils report indicate as "over excavation" and what alternatives to a slab do they specify?

Charles Ross HomesThe alternative was micropile 6" thick 20' deep. It didn't say how far apart. At one point they said 3-8' deep excavation but then said 2' fill should do the job. That seems to imply 2-3' deep excavation to me.

I don't have experience with micro piles, but I have used helical piles in both new construction and retrofit/repair work. Due to their cost, they are typically a last resort.

The reason the number and spacing of piles is not indicated is because those are a function of the load they'll need to support which depends on the specific home design.

A brief meeting with your builder, architect, and engineer will determine which way is best to go. I suggest you schedule the meeting on a Friday afternoon with cold beer available immediately following the meeting. That will minimize the number of billable meeting hours.

About that beer. I will have to get over the awkwardness of a woman buying guys beer in not the most liberal state.

They say the best things in life are free...so it is with beer.

Slab $
Micropiles $$$

That would be my take as well. But it all depends...

It turned out we have to excavate deep and the cost for micropiles is somewhat less. Would deep foundation walls make a stronger foundation to justify higher cost? Spacing for micropiles will be 6'.

And what goes on top of the micropiles? A concrete slab? Girder, beams, joists and plywood?

When figuring costs you must consider the entire first floor assembly, not just one component.

Girder. And a concrete slab on top.

So...think about this...in either structural scheme a concrete slab is required.

I'm guessing, however, it may not be the same type slab, since it's likely that the one supported by piles may need special reinforcing and connections at each pile head.

Have you been told that the piles are cheaper than excavation and compacted fill?

Yes, not by much, about 10-20% cheaper.

snowcountry may I ask the price of each micropile?

thanks

When soil conditions are such that a concrete slab on grade foundation can adequately support a house, it will be the most economical foundation possible in most cases.

But...when there are problematic soils conditions...such as highly expansive soils--then other types of foundations may be required.

Said differently, foundation design is a function of the condition and composition of the existing soil.

It is not highly expansive soil. It is the terrain that is challenging at 1:2 grade and the build goes close to the edge. That in turn requires a deep excavation according to the engineer.