Author Topic: Which foundation type?  (Read 64313 times)

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Offline ShellyShelly

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Which foundation type?
« on: January 14, 2005, 05:01:33 PM »
I am considering building the Victoria's cottage in WA along the Columbia River gorge. How do I decide which type of foundation would be most suitable? The slab is appealing for stained concrete but it seems to be less practical as far as utilities? What is the least expensive?
THANKS!

Offline John Raabe

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Re: Which foundation type?
« Reply #1 on: January 15, 2005, 11:17:11 AM »
If you have a stable flat site with well drained soil (low clay level) then the least expensive floor/foundation will usually be a slab on grade.

You are right about the utilities as they must be carefully placed by the plumber and perhaps the electrician prior to the floor pour. So this type of floor is not one for an inexperienced non-builder. You need to sub it out to experienced professionals.

The crawlspace option gets the wood floor up in the air and makes the utilities much less critical in their placement. If you plan to do your own framing then this may be the less money out of pocket solution.
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Offline jonsey/downunder

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Re: Which foundation type?
« Reply #2 on: January 15, 2005, 07:39:35 PM »
I would agree with John on the need for experienced professionals. Working with large areas of concrete requires experience and the plumbing and electrical penetrations do need to be placed with care. Having said this, not all of these need to be routed through the floor. With careful planning, you may be able to pop some of them directly through the timber framing to the outside.
If you are reasonably handy you my also be able to do your own formwork and steel placement, saving a bit on labor.
Here is a link to a slab system that is in common use here in Australia and NZ, I am sure there will be similar systems in the US.  
http://www.hunterpodsupplies.com.au/about.htm
I used a modified version of this under my laundry and carport. A great slab for highly reactive soils. (Link to my page is in the side bar) look under carport.
Jonesy
« Last Edit: January 15, 2005, 07:43:42 PM by jonseyhay »
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Offline glenn kangiser

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Re: Which foundation type?
« Reply #3 on: January 15, 2005, 09:01:50 PM »
That waffle pod system is interesting.  I haven't seen it here but I work mostly with commercial stuff.  I did see them use solid foam in a few places and have worked on a couple ICF jobs..

Another way to give yourself some room to play with an on grade slab especially for tub or shower drains is to put a box full of sand about 1/2 inch below the top of the concrete with the pipe stubbed out below it. Pour your concrete.  Do your framing -break out the thin concrete over the sand filled box, get exact measurements then cut the pipe - put in your traps etc.  When done wrap the pipes and  grout the hole in as desired.  

Aquapex crosslinked polyethelene tubing can be brought up through the slab or pulled through the studs llike Romex so is another alternative.  It is not approved in all areas but is the best- it is good for hot and cold water and is guaranteed for 25 years in a certified installation.

Glenn
« Last Edit: January 15, 2005, 09:17:46 PM by glenn-k »
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Offline Lady_Novice

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Re: Which foundation type?
« Reply #4 on: January 15, 2005, 09:55:07 PM »
FWIW, John wrote an article about the "post" (wood) or "pier" (concrete) type of foundation (see the countryplans.com home page for the link) and he includes it as one of the foundation choices in the 20x30 plan (and most likely the other plans).

For my future small home, I'll most likely be doing the pier version of this foundation. It strikes me as being the most owner-builder-friendly type of foundation and most likely the least expensive, so I'm glad to find up-to-date information about it.

At first I was going to do the "post" (wood) version, as working with wood seemed easier than working with concrete. But a friend said that he thought the resale value of my home might be less with a post foundation (as wood is not commonly used as foundation material), so I'll likely go with the "pier" (concrete) version. (My friend also thought that even pressure-treated wood would be too affected by moisture and movement underground, but I think he just wasn't familiar with wood as a foundation material. I thought his concern about resale value could possibly be valid, though, just because potential buyers might not be familiar with it.)

You mention concrete flooring. For thermal mass, I want concrete or tile flooring. I'd prefer concrete (no grouting as with tile), which would go over a wood subfloor (which of course will sit atop the concrete pier foundation). So I'm searching for a simple owner-builder-friendly method of pouring a self-leveling colored concrete floor over a wood subfloor. Maybe I'm being optimistic that such a method could exist. I'll report back if I can figure this out.
Lady Novice





Offline Amanda_931

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Re: Which foundation type?
« Reply #5 on: January 16, 2005, 06:08:28 AM »
Concrete over wood?  Not for me.  

Extra work.  If your concrete floor is going to be thick--and HEAVY--enough to give you the benefits of thermal mass it will need a lot of reinforcing--Joists, beams, girders, and piers.  

A (ceramic) tile floor over subfloor sounds a lot more reasonable, give a bit of thermal storage.

A concrete (or earthen--more DIY but don't wear your outdoor shoes inside--I've heard of brick over sand as well) floor is great.   Thermal mass is good.   But maybe not a couple of feet up in the air.

Offline JRR

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Re: Which foundation type?
« Reply #6 on: January 16, 2005, 07:24:19 AM »
OK, I'm going to let a small "cat out of the bag".

I have recently finished "pouring" a 2 1/4" thick slab atop wooden joists with no sub-flooring.  This slab is 8' above the basement floor below.  I developed a method of moveable forms and poured the floor in "strips"... after the concete cured for a week, the forms were moved and another strip poured.....this process is necessary to control the slab thickness and the precise placement of steel reinforcement webs.   In my case I chose to place two layers (webs) of reinforcing mats... spaced 1 1/4" apart. There is several inches of overlap of reinforcing web at the joints between strips.  PEXwOB tubing was included... but has not been put to use yet.

I have been, up to now, very pleased with the results.   The floor is approx 16' x 20' with a stairwell included.   It is very stiff (nat freq > 20 cps) and feels very secure.  

This was a first-time experiment and I had no other person's experience to build upon.   I know of no literature that treats this specific subject.  

Since there is yet no reference literature or data.... I can only advise the non-engineer to stay away!!   Keep in mind that concrete weighs 150 lbs per cu ft.  Amanda is correct in all of the concerns she posted... and there are many more.
« Last Edit: January 18, 2005, 04:05:18 AM by JRR »

Offline Amanda_931

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Re: Which foundation type?
« Reply #7 on: January 16, 2005, 07:36:08 AM »
 ;)

Why did I think somebody would say that, JRR?

Offline Lady_Novice

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Re: Which foundation type?
« Reply #8 on: January 16, 2005, 03:00:49 PM »
Thanks to JRR for sharing the concrete flooring experience. I should have clarified that I was referring to a "thin" concrete floor that would be essentially similar to a tile floor (less than half-inch thick), but just without grouting. I would also want to end up with a polished (easily cleanable), colored surface like tile, not a rough (difficult to clean) surface like regular concrete. It may not have been a feasible or cost-effective idea (for example, if I would have to hire a concrete polisher/stainer or something).

I guess I had thought that I could get a worthwhile amount of thermal mass from a thin concrete (or tile) floor. But if the amount of thermal mass would be negligible, then I might as well just put down some pine wood planking (as planned for my loft floor above) and forget about concrete or tile.

Sorry, I hope this has not been a diversion from the original poster's question about concrete flooring/slabs. Hoping she was interested in thermal mass issues and whether you can still get a concrete floor even without a slab.
Lady Novice

shelly

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Re: Which foundation type?
« Reply #9 on: January 16, 2005, 06:42:50 PM »
Thanks to everyone for the insights, all were very helpful! I was wondering, as well, if a layer of cement could be a possibility. Not having any building experience, it appears a difficult undertaking.

Offline glenn kangiser

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Re: Which foundation type?
« Reply #10 on: January 16, 2005, 10:36:31 PM »
Hi Shelly,

Sounds to me like you just want to try some concrete :)

Here is a link to the old forum light duty concrete floor discussion:
http://www.countryplans.com/bbs/messages/7258.html

This is a floor from Ken Kern's book that was developed in India.  It is 1" thick over 1/2 " of sand.  One top the sand is burlap or jute erosion control netting -they called for two 1/2 inch layers of concrete over the netting.  This was over about 8" of loose soil with a crowbar driven down to solid soil and the holes filled with cement before the top layers were put on. the holes made supports every 3' to solid ground.  I did it on 2' centers.  It made a great floor with no problems.  The edges will be a bit soft for the first couple weeks.

Conventional concrete slabs for houses are usually 3 1/2" to 4 " thick with at least perimeter footings.  You would need an experienced crew of probably 4 to 6 people, trowels, tamps, floats,edgers and a troweling machine to pour a house slab in one day.  I would think the best you could do is assist with the labor starting out.  Cement work has to be done fairly fast and right, because in a few hours you will have what you are going to have to live with for 40  years-- or as I had to do one time - call the demolition crew and remove it and start over - but that's no fun.

To get your feet wet, find a place you would like a small slab or sidewalk. etc.  Even do something 2'x2' if  you like.  Nail some 2 x 4s together to make a form and make a Test slab. Get  a couple bags of concrete mix, a wheelbarrow hoe and shovel for mixing and have fun.  It should be fairly thick but workable.  Too much water makes weak concrete.  Get concrete mix- bag cement does not have rock.  If you like it you can get bulk later. A straight board longer than the width of the forms is used to rod it off - or knock the top down level with the forms.  An edger makes rounded corners on your slab.  A wood float smooths the cement and opens the pores so it will dry faster and helps to work out the bumps.  Try to do everything while it is wet and re-do it as it dries.  After it is set it is too late and gets real hard to do.  

If you get a chance try to watch a concrete crew pouring a slab.  Possibly a local contractor will let you watch.  You can learn a lot just by observing.

Quickcrete publishes a book about do it yourself concrete projects.  Here is a link to it.
http://www.quikrete.com/diy/howto.asp

Also check the links section of this board or go through their site for tons of free info.
« Last Edit: January 16, 2005, 10:41:30 PM by glenn-k »
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Offline jonsey/downunder

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Re: Which foundation type?
« Reply #11 on: January 17, 2005, 12:01:37 AM »
Here is another possible solution, still not cheap, but if time is not a problem you could do this as you can afford it.
You have probably done some research on staining concrete so you will no doubt be familiar with concrete counter tops. You Build a form from 3/4-in.-thick melamine-coated particleboard about 2' sq and make up your own pavers. I would suggest they be about 1" thick. If you vibrate the concrete well there should be no need to polish . Of course you will still have to beef up the supporting structure, but you will save on having specialists for the concrete work.  You could make a couple and see if it will work out for you. By taking this approach you get to perfect the art of working with concrete without it costing you a fortune. It will still be costly but it may be a way for you to have what you want. Get friendly with some of your local concrete workers they will often have small amounts of concrete left over on their jobs. If you have some moulds ready they may fill them for you.
You bed these slabs the same as you would tiles, I would suggest you use something like Hardibacker 500 instead of timber underneath.
jonesy
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Offline JRR

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Re: Which foundation type?
« Reply #12 on: January 17, 2005, 04:19:52 AM »
Lady_Novice
Now that I understand your idea, don't let me discourage you.  In fact, I've had the same thoughts....on top of standard subflooring, with all the usual preparation for installing a traditional wire reinforced mortar bed and tile....install the metal lath and mortar....just don't install the tile ....and add a bit more mortar thickness.   Don't know why that wouldn't work.   The challenge would seem to be controlling the surface to be flat and level.  But with today's laser level gadgets, it may be doable.

Understand, I've never laid a piece of tile in my life... but its in my plans.  
« Last Edit: January 17, 2005, 04:28:46 AM by JRR »

Offline John Raabe

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Re: Which foundation type?
« Reply #13 on: January 17, 2005, 03:48:43 PM »
I don't know how common it is everywhere, but we often pour concrete on wood floors for radiant heating systems. For most houses the builder just adds an additional plate for the 1 1/2" thickness of the slab. The slab can be Gypcrete (lighter weight and self leveling) or standard concrete (adds thermal mass and can be stained, dyed, scored or whatever to be a finished floor).

This house http://www.countryplans.com/bjork/ has concrete floors on both the main and upper floors. This is a traditional house as you can see so the floors are wood, carpet and tile over the slabs.
« Last Edit: January 18, 2005, 01:34:16 PM by jraabe »
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Re: Which foundation type?
« Reply #14 on: January 18, 2005, 08:04:26 AM »
Quote
I don't know common it is everywhere, but we often pour concrete on wood floors for radiant heating systems. For most houses the builder just adds an additional plate for the 1 1/2" thickness of the slab. The slab can be Gypcrete (lighter weight and self leveling) or standard concrete (adds thermal mass and can be stained, dyed, scored or whatever to be a finished floor).

This house http://www.countryplans.com/bjork/ has concrete floors on both the main and upper floors. This is a traditional house as you can see so the floors are wood, carpet and tile over the slabs.


Is there a plan available for that garage?

Offline John Raabe

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Re: Which foundation type?
« Reply #15 on: January 18, 2005, 01:35:31 PM »
No there isn't but it is not a bad idea!

Thanks, John
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Offline ShellyShelly

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Re: Which foundation type?
« Reply #16 on: January 18, 2005, 07:06:38 PM »
Thanks all! Great ideas!  ;D

The NZ pod method looks interesting and somehow "easier". I did not find an American company that deals with this in my search. Does anyone know if it has and can be used in the states? Jonesy did a creative substitution! Great to recycle those tires and use less concrete!!

Do the country house plans have details on radiant floor heating? Which is better for radiant floor heat, the slab or a concrete layer over the wood.....for cost and efficacy?

Well, I am off to play with some concrete! Shelly

Bart_Cubbins

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Re: Which foundation type?
« Reply #17 on: January 18, 2005, 08:12:24 PM »
Fine Homebuilding's More Small Houses has a couple of houses with concrete floors. With one floor, boards were used to divide the floor into squares of managable size. The boards, which were left in place, also served as leveling screeds and to control cracking. The result was a very attractive floor, though it might not meet the easily-cleanable criteria.

Bart


Offline John Raabe

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Re: Which foundation type?
« Reply #18 on: January 19, 2005, 06:07:05 AM »
Shelly:

My plans do not spec out specific heating systems. However, any house plan can be set up for radiant floors by adding a plate to the walls and checking the joists for the type of concrete used.

The cost trade-off and other issues have to be addressed locally by finding a good installer with local experience. Your climate, fuel costs, etc. come into play here. In most cases, if you can build slab on grade and treat the slab for a finished floor, that will be the most cost effective.

Radiant floor heat is more expensive than most other options. I tell my custom home clients (who are not building their own houses, for the most part) that the entry fee is $5,000 to 10,000.

What you get for that money is spoiled! The warmth and comfort is very even, quiet and invisible. Nobody ever builds their next house with a furnace.
« Last Edit: January 19, 2005, 06:09:55 AM by jraabe »
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Offline glenn kangiser

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Re: Which foundation type?
« Reply #19 on: January 19, 2005, 09:46:36 PM »
About the floor over wood- I did the floor in the underground bedroom over wood with soil cement 3 inches thick.  The mix was clay only as dug from the ground (my clay is hard with claystone and rocks- fairly non-expansive) -no added sand - 10 % cement -this also greatly decreases my shrinkage in the clay (from about 5% to about 2% and makes the clay water resistant).  It won't wash away and makes the clay set up in about 1 hour instead of 2 weeks to dry.  It is still a little soft without the added sand, but is easily repaired.  I added 5 handfuls of straw for reinforcement to each 10 shovels of clay.  Near the door I set local slate into the floor.  I have 3/4 inch sawn lumber over joists on 2' centers.  I find that the  soil cement floors have a nice warm ancient look even if they are fairly new.  We use concrete cure and seal to harden the surface and give it a shine.  Pledge polish will give it a quick new shine although there are better things to use I'm sure- it's what we had at the time.
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Offline Lady_Novice

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Re: Which foundation type?
« Reply #20 on: January 19, 2005, 10:38:20 PM »
Thanks to everyone for adding to my knowledge about concrete and concrete flooring possibilities.

Always looking for the "E-Z" solution, I was intrigued by John's mention of "gypcrete" due to the magic words "self-leveling." It sounds to me like some sort of underlayment product, but could I color it and use it as actual flooring (and then polish it to get a cleanable surface)? Or is it too soft to be flooring? Would it be just about as durable as tile? Would it provide less thermal mass than tile? Does it look decent?
Lady Novice

Offline John Raabe

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Re: Which foundation type?
« Reply #21 on: January 20, 2005, 10:31:01 AM »
I am only familiar with the light duty Gypcrete that is used as an underlayment and needs to be covered. It adds a little thermal mass.

However, while searching for a link I found there are more options than I knew about.

http://www.durexcoverings.com/gypcrete.htm

Some of the higher density mixes could well be colored or stained and might do fine as a finish floor.

PS - About thermal mass. If you have sun to store or just want a thermal flywheel effect in the house, the best thermal mass is a thinner layer spread more evenly as opposed to a big pile sitting somewhere. Thus the first 2" of a concrete slab do much more work moderating the temperature than do the next 2" or the 2" below that.
« Last Edit: January 20, 2005, 10:36:00 AM by jraabe »
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Offline Lady_Novice

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Re: Which foundation type?
« Reply #22 on: January 30, 2005, 03:28:21 PM »
Thanks to John for the durexcoverings.com link. It was interesting and it will give me another avenue for researching this. My eventual goal will be to find a self-leveling substance that could be a DIY finish (top) floor (plus easily colored and polished). Wishful thinking, perhaps.
Lady Novice

Don Fletcher

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Re: Which foundation type?
« Reply #23 on: October 22, 2005, 12:27:21 PM »
I would think that seismic considerations would be part of the decision process, as would any potential subsidance. (Might you have to re-level the structure for less than perfectly stable ground).

Wood allows for re-leveling, and will tolerate more seismic activity.  If it is covered with stucco inside and out, wood can remain draft free and at the same time have a bit of thermal mass.

However, in our region we can not put wood structures within one foot of the ground because of carpenter ants.  

As a consequence we have a slab on grade, but with a tamped gravel base, and concrete walls insulated on the outside with SM blue insulation, backfilled to one foot below the floor with granular fill.

We solved the problem of putting the pipes under the slab on grade by not doing it for anything but the main DWV to the toilets.  We put a single greywater entrance into the main (10 cm).

We ran cold water pipes along the floor to the sinks, shower, washing machine, and a 2 gallon electric heater at each of those destination points.

As our house is passive solar, and earth embanked, pipes on the surface have no freezing problem even with no auxiliary heating.  We have recorded our temperature for 26 years, amd with wind and outside temps of -25C our inside temp has never dropped below +9C.

We have no seismic activity greater than Richter 3.6.

Ours was an experiment in poverty driven design. We maxed out our debt at $15,000, but that did not include our farm land.      

Offline glenn kangiser

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Re: Which foundation type?
« Reply #24 on: October 22, 2005, 05:28:48 PM »
Sounds like it was an interesting project, Don.  Now we have Aquapex so through the wall plumbing or under the slab is easier.

What area are you in, Don?

Much of the construction around central California is on grade slabs with all house plumbing under the slab.  Waste lines going through the slab have to be wrapped with insulation or cardboard  etc. to keep the concrete from grabbing the pipes and stressing or breaking them.
« Last Edit: October 22, 2005, 05:29:03 PM by glenn-k »
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