Author Topic: Permanent wood foundation  (Read 4430 times)

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Offline new land owner

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Permanent wood foundation
« on: April 06, 2011, 05:59:14 PM »
              After three years on my land trying to figure out what to build I have my final plan.  I am building a one story camp with a crawl space foundation.  I have been looking into a permanent wood foundation and was wondering if anyone has built their camp using this type of foundation.
   I went to Lowes in my area today and they can special order PT wood that is stamped PWF and I was surprised to find out that it was not any more than the regular stuff they carry.
   I have a guy set to set to dig the foundation if it ever stops snowing in the Adirondacks.  It does not look like setting the footings would be that bad and I could save all the labor that I would have to pay a mason for the block wall.


Offline mysimplelife

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Re: Permanent wood foundation
« Reply #1 on: April 06, 2011, 06:20:35 PM »
please elaberate. is a pwf a post and peir, or something else? ive just never heard it called that but have seen that stamp on lumber before.

Offline MountainDon

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Re: Permanent Wood Foundation
« Reply #2 on: April 06, 2011, 06:48:30 PM »
A quick and dirty answer.... PWF is basically like a stud wall built with PT  studs (lots of them... 12 " OC I believe) sheathed on the exterior with PT plywood and sitting on packed gravel filled in a trench. No concrete is involved. It is a full perimeter wall. There is a carefully written prescriptive method for building a PWF and my understanding is that it must be followed to the letter; no creative self engineering.
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline new land owner

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Re: Permanent wood foundation
« Reply #3 on: April 07, 2011, 02:28:47 AM »
There is a PDF on this page giving lots of information of this type of foundation.


http://www1.southernpine.com/applications_permanent-wood-foundations.asp

Offline John Raabe

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Re: Permanent wood foundation
« Reply #4 on: April 07, 2011, 07:02:52 AM »


A PWF basement uses good drainage and carefull bracing at the bottom and tops of the plywood walls to contain all the forces that a full basement would experience. For crawlspace walls the forces are greatly reduced and the bracing less critical. Drainage is still important. You must be able to daylight the footing drains or put in a sump pump unless you are in very well drained soil.

A properly built PWF basement is warmer, dryer and easier to finish off than the same thing done in concrete. If concrete basements were put in with the same careful attention to drainage basement leaks and dampness would virtually disappear.

Yes, Don is right - do each step properly and by the book. This isn't the place to wing-it. :-[

« Last Edit: April 07, 2011, 07:49:23 AM by John Raabe »
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Offline Squirl

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Re: Permanent wood foundation
« Reply #5 on: April 07, 2011, 09:28:14 AM »
It is very encouraging to here that.   That is one of the ideas that I was going to look into, but never had a chance.   The price puts it back in the running for me too.
I did a quick hash out of it here:
http://countryplans.com/smf/index.php?topic=10423.msg133256#msg133256
I don’t know if you got to read it.  It gives the link to the exact guidelines and specifications for the state of NY .  I am hoping to put my building in an extremely remote part of my property and weight, ease, and speed of construction might be more heavily weighted factors for me, if price is the same.  Drainage is very important for PWF’s, but an argument could be made that drainage is important for all foundations and too often ignored.  You are certainly out of the danger climate for PWF’s because the ground is frozen 6 months of the year.  Judging by the quality of many of your other projects, I have little doubt you will follow proper guidelines.  Also I remember that you had prebuilt and trailered part of your outbuildings you could probably do that for part of your foundation.  That would be a bonus in my situation too.

I can't wait for it to stop snowing.  >:(
« Last Edit: April 07, 2011, 09:44:19 AM by Squirl »

Offline astidham

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Re: Permanent wood foundation
« Reply #6 on: April 07, 2011, 09:46:10 AM »
here is a link to a similar foundation built on this forum
http://countryplans.com/smf/index.php?topic=4640.0
"Chop your own wood and it will warm you twice"
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Offline MountainDon

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Re: Permanent wood foundation
« Reply #7 on: April 07, 2011, 10:12:33 AM »
A concrete floor slab is generally required I believe. That is to provide resistance from sideways pressure = movement at the bottom of the PWF wall. That is clearly shown in the illustration John posted.
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Squirl

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Re: Permanent wood foundation
« Reply #8 on: April 07, 2011, 10:33:01 AM »
I believe the slab is only to provide bracing for kickback, which shouldn't occur in a crawlspace with equal amounts of soil pressure on both sides.  I interpret this from the code section R404.2.4 " Backfilling.  Wood foundation walls shall not be backfilled until the basement floor and first floor have been constructed or the walls have been braced. For crawl space construction, backfill or bracing shall be installed on the interior of the walls prior to placing backfill on the exterior."  The bracing or backfill on the interior leads me to believe the slab is not needed for crawlspaces.

 The design in the project that was done by Thewire, is not exact to ICC guidelines.  Unfortunately every diagram I found was for full basement PWF's.  The insulation and finishing advantages seem to be its larger selling points for people.

Offline Alan Gage

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Re: Permanent wood foundation
« Reply #9 on: April 07, 2011, 10:33:49 AM »
I did a lot of research on PWFs when I started to plan my build was ready to go that way until I decided to ditch the idea of a basement all together and build on a slab.

There are a fair amount constructed in my area (NW Iowa) and I've heard very few reports of problems locally. I asked my local building supplier and they had no problems with them. Researching online you find lots of people who don't like them but reading between the lines it sounds like many have no actual experience with them and just dismiss them out of hand. It also sounds like most of the people who do have problems with them didn't do things by the book (poor drainage, using "plain" treated lumber, etc).  

The guys at my local builder center only knew of one person that had actually used wood for the floor as well and he reported that he liked how it went and would do it again. I was planning on pouring a concrete floor.

Good luck,

Alan

Offline new land owner

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Re: Permanent wood foundation
« Reply #10 on: April 07, 2011, 01:09:00 PM »
Thanks for all of the great feedback.  The land where I am building is good draining gravel and I will be using a concrete footings.  I figure I can do the footing myself and keep costs down.  I am calling it a crawl space but since I have to dig down to 4’ for the frost depth I will be building a 6’ tall wall.  I figure 4’ below grade and 2’ above.  I plan on using the specs for a basement when planning my foundation. 

Offline MountainDon

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Re: Permanent wood foundation
« Reply #11 on: April 07, 2011, 02:41:46 PM »
.....l and I will be using a concrete footings.


NO. Read the PWF info, look at the illustration. No concrete footing; crushed stone. Follow the PWF cookbook. The only concrete is the slab floor that is poured after the PWF is in place (if you are doing a basement or tall crawl space.

Info D/L here  http://www.southernpine.com/applications_permanent-wood-foundations.asp

it's where John got the illustration I believe
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline new land owner

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Re: Permanent wood foundation
« Reply #12 on: April 07, 2011, 04:38:25 PM »
Don

    Page 28 of the article you are referring to shows a concrete footing for a basement and page 18 shows the same option for a crawl space.  Would you not recommend this?  It seems like it would be a solid way to start the building?

Offline MountainDon

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Re: Permanent wood foundation
« Reply #13 on: April 07, 2011, 05:33:07 PM »
Well I stand corrected and red faced. I do see fig. 9 on page 18 has a concrete footing. I have to admit it's been a while since I read that document. But, everything else I recall about PWF has stressed the importance of keeping moisture away from the PT lumber. That is why everything else there used crushed stone. It is to provide drainage. So that piece of concrete surprises me.  ???

My eyes must be failing me as the only other concrete footing I see is Fig. 19 on page 25, for making a utility pass thru/under. And, it has gravel under it. So I remain puzzled on that one that shows concrete footer on earth.
Just because something has been done and has not failed, doesn’t mean it is good design.

If you didn't have the time or money to do it right in the first place, when will you get the time and money to fix it?

Offline Squirl

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Re: Permanent wood foundation
« Reply #14 on: April 08, 2011, 05:55:17 AM »
Thanks for all of the great feedback.  The land where I am building is good draining gravel and I will be using a concrete footings.  I figure I can do the footing myself and keep costs down.  I am calling it a crawl space but since I have to dig down to 4’ for the frost depth I will be building a 6’ tall wall.  I figure 4’ below grade and 2’ above.  I plan on using the specs for a basement when planning my foundation.  

Are you excavating the full area under the house?  Using specs for an unsupported basement wall vs. a crawl space wall may be a higher unnecessary expense. The code charts can be found here:
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec004_par039.htm
The height of in the chart is only used "When the height of fill is more than 12 inches (305 mm) above the interior grade of a crawl space or floor of a basement."  Unless you plan on having more than 3ft of crawl space under your floor, the chart is not needed.  Building to the largest basement specification would be for outside wall pressure that just isn't there.

According to the code charts as long as it is no more than 24 inches of unequal fill on the outside vs. inside of the crawl space you can go with 3/8 in. plywood with 16” O/C studs, vs. 19/32 plywood or 12” O/C studs. (Note B) The extra height above grade shouldn’t affect the stability or longevity of the foundation.  Here you can see the difference between the two and a cut away of the code approved designs.
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec003.htm
You can also see the slab for full basements and no slab for crawlspaces.  Be mindful that the pictures provided in the code only show gravel for a footing, but I cannot find anything explicit that gravel must be used instead of concrete for a footing.  Don’t be surprised if a building department requires it.  It shouldn’t be a big deal, gravel is cheaper anyway.
http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_4_sec003_par019.htm

Offline Squirl

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Re: Permanent wood foundation
« Reply #15 on: April 08, 2011, 06:42:49 AM »
I read through parts of the pamphlet provided by southerpine.  There are many discrepancies between what they call "possible" designs and the actual requirements by the codes of the state of NY, where you are located, or the ICC.

Offline John Raabe

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Re: Permanent wood foundation
« Reply #16 on: April 08, 2011, 08:50:10 AM »
I think the use of the concrete footer still requires the full footing drains so gross water is carried away. This footer is a good idea in soils of varying quality and bearing capacity. It provides a concrete reinforced grade beam that can span these softer sections of soil. In uniform solid bearing soil the gravel footing is usually used. You would want to anchor the sill to the foundation with bolts or straps. These may need to of a higher grade material or at non-standard spacing.
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Offline new land owner

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Re: Permanent wood foundation
« Reply #17 on: April 08, 2011, 01:56:39 PM »
I read through parts of the pamphlet provided by southerpine.  There are many discrepancies between what they call "possible" designs and the actual requirements by the codes of the state of NY, where you are located, or the ICC.

Do you have a link to NYS code for this type of foundation.  I believe you said it was on your other post but I could not find it.

Offline new land owner

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Re: Permanent wood foundation
« Reply #18 on: April 08, 2011, 04:14:49 PM »
NO. Read the PWF info, look at the illustration. No concrete footing; crushed stone. Follow the PWF cookbook. The only concrete is the slab floor that is poured after the PWF is in place (if you are doing a basement or tall crawl space.

Info D/L here  http://www.southernpine.com/applications_permanent-wood-foundations.asp

it's where John got the illustration I believe


Don

    I found a copy of the NYS code for a wood foundation and no where does it show a concrete footing so you may be right afterall!

Offline Don_P

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Re: Permanent wood foundation
« Reply #19 on: April 08, 2011, 06:16:11 PM »
from AF&PA;
Quote
Technical Report (TR) No. 7 and Wood Construction Data (WCD) No. 6 do not clearly identify a concrete footing as an option to gravel beneath a basement wall. Figure 19 on page 32 of Southern Forest Products Association (SFPA)'s PWF Design and Construction Guide, however, does include a concrete footing under an exterior basement wall as an option. You will notice that if a concrete footing is used, gravel, crushed rock or coarse sand is required along the sides of the concrete and beneath it or alternately, drains through the footing are required. It would also be ok to combine both methods.

The above methods allow water to move to the designated drainage area. The preferred method of drainage is by gravity to day light. Other options include use of a sump or drainage to a sewer.

The code referenced standard can be ordered here, really for design use;
http://www.awc.org/standards/pwf.html
For typical construction details the AF&PA points to the Southernpine document