Wood posts used in damp crawlspace construction?
Wood posts used in damp crawlspace construction?
(OP)
I'm not a structural engineer, so I figured this was a good place to get advice.
My father has a home on a lake in Northern Minnesota. The ground on which the 2 story house was built is sand/dirt mix. it is now about 10 years old. I went into the crawl space below the house to work on an air exchanger and noticed that the builder used 4x4 posts instead of what I'm use to seeing (which are metal posts). The posts are buried in this sand/dirt mixture (which is very moist) and they sit on top of concrete footings about 8 - 12 inches below the surface. The posts are space about every 6 feet. The base of the posts that are buried are damp, but there doesn't appear to be any appreciable rot that I detected in the ones I dug up.
It seems to me that this is not a very good design. The base of the posts are damp and over time, I expect these posts will rot. I have not inspected each post (there must be 40 - 50 of them).
Is this standard building practice? I would not have been concerned had I seen the posts resting on top of concrete that was above grade.
Maybe I'm worrying over nothing.
Thanks for the advice.
My father has a home on a lake in Northern Minnesota. The ground on which the 2 story house was built is sand/dirt mix. it is now about 10 years old. I went into the crawl space below the house to work on an air exchanger and noticed that the builder used 4x4 posts instead of what I'm use to seeing (which are metal posts). The posts are buried in this sand/dirt mixture (which is very moist) and they sit on top of concrete footings about 8 - 12 inches below the surface. The posts are space about every 6 feet. The base of the posts that are buried are damp, but there doesn't appear to be any appreciable rot that I detected in the ones I dug up.
It seems to me that this is not a very good design. The base of the posts are damp and over time, I expect these posts will rot. I have not inspected each post (there must be 40 - 50 of them).
Is this standard building practice? I would not have been concerned had I seen the posts resting on top of concrete that was above grade.
Maybe I'm worrying over nothing.
Thanks for the advice.






RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
1. Except in thecase of wood foundations for dry locations like a desert, wood is never to be in contact with soil.
2. There should be a vertical distance of 6" between the top of a concrete footing/stem wall and the finish grade/soil matrix below, so that there is a 6" gap between the wood post/studwall and the soil.
3. The foundation space should have adequate ventilation.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood posts used in damp crawlspace construction?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood posts used in damp crawlspace construction?
At this time, I suspect I should get a structural engineer down there for inspection before anything bad happens. Like I said, I don't see significant rot, but the wood is wet. It does not seem that there would be an "easy fix" for this. If the code says 6" between the top of the concrete footing system and the soil, is it possible to cut each post out, dig down to the footing, drill in rebar, pour on top of the existing footing and then attach a new post to this concrete above grade. I can easily dig down to these footings by hand. It's the adhesion to that concrete that would be a bit suspect. Trying to dig new footings in this seems rather impossible. Not even enough room for a hand auger.
I realize this is a job for a licensed structural engineer to recommend, but being an engineer myself, I can't help but think of fixes.
Thank you again for the perspective!
RE: Wood posts used in damp crawlspace construction?
MS has given you some good feedback. IN any crawlspace you want to have good ventilation, and most building codes have a formula for the amount of venting per the square footage of the crawlspace. In my experience, even a humid to damp crawlspace may not cause actual rot to occur. Of course, this means you need to excavate around the posts so no soil is in contact. You can then seal with a variety of materials, including bitumen (roof tar/cement may work), or wrap in building paper or sheet metal to form a moisture barrier, in case soil falls back into contact with the wood.
Also, if you can borrow or buy a moisture meter and probe the wood, you will know what you are dealing with exactly. Different species have different tolerances, many use a moisture content over 19% as getting into the danger zone.
Best of luck,
Andrew
RE: Wood posts used in damp crawlspace construction?
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Wood posts used in damp crawlspace construction?
The crawlspace has a power ventilator in it connected to a humidistat. It's far dryer down there now than when it was installed, however I have not really paid much attention to it up to this point.
I have tried to searching building codes for Wadena County MN, and I've come across a lot of information, but I've seen nothing regarding the posts supporting the structure. I have seen quite a bit on footing/pier depth. Do any of you know a good resource for something like this. Seems it would be simple to find, but I speak the wrong language obviously.
RE: Wood posts used in damp crawlspace construction?
Place the plinth block. cut off the existing 4x4 and reset. Of course you can only do a few at a time. Most lumber yards in Mn have the plinth blocks. Where up here in god's country are you?
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
per 1309.0010 "Subpart 1. Generally. The 2006 edition of the International Residential Code (IRC) as promulgated by the International Code Council (ICC), Falls Church, Virginia, is incorporated by reference and made part of the Minnesota State Building Code except as qualified by the applicable provisions in Minnesota Rules, chapter 1300, and as amended in this chapter. The IRC is not subject to frequent change and a copy of the IRC, with amendments for use in Minnesota, is available in the office of the commissioner of labor and industry. Portions of this chapter reproduce text and tables from the IRC. The IRC is copyright 2006 by the ICC. All rights reserved."
So (for the Residential Code) you need to go look at it, Or buy a copy of it. Or buy a copy of the 2006 IRC and view the Minnesota changes at the above link.
The ANSI / AF&PA PWF-2007 should be referenced in it. But as I only have the 2003 IRC I can not state for sure.
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Wood posts used in damp crawlspace construction?
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
When I go up next, I plan to do the following:
1) dig around the posts to determine what they are sitting on
2) Determine if there is a pin in the center or if they are just sitting on the concrete
3) Determine the moisture in the wood and condition of the wood in a larger sampling
4) Check against code (may even get an engineer in there).
Once that is done, I'll have a better idea of possible remedies. You guys are a great help!
RE: Wood posts used in damp crawlspace construction?
The post has a faint black mark on the right hand face. Is this a grade stamp? Do you know whether or not the posts were PWF material?
PWF foundations entail wood against granular material but it should be well drained. Treated wood piles have been used to support buildings for many years in wet soils. If there appears to be no evidence of rot so far, maybe annual inspections would be an option.
BA
RE: Wood posts used in damp crawlspace construction?
I strongly believe the wood is treated but I didn't notice the mark on the wood until you pointed it out. Sorry for the blurry photo, my eyes aren't so good anymore and I was swaying I'm sure. The vapor barrier is covered with pea gravel about 2 inches thick. It would be great if this were PWF but as you pointed out, it should be against well drained granual material (and as you can see if you squint at the picture, wicking is present so there is moisture). The wood did not seem soft except at the very surface. I plan on reading the pwf information provided by woodman88 and can get a better idea of whether it's used or not. If it is, maybe this is a red herring of sorts and following the recommendation by a2mfk is enough to ease my concerns. If it's just untreated lumber, or if the moisture content is high (regardless of treated/non-treated), I may be looking at what sewerrat suggested. Wish I was still up there now, could easily figure some of this out.
Thanks!
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
"The crawlspace has a power ventilator in it connected to a humidistat."
You have a vapor barrier and this, you are way ahead of the game.
I would invest in a moisture meter and probe the posts, if you are less than @ 19% or so then you are probably OK. Keep checking on them on an annual basis.
All of the other suggestions seem on point if you have actual wood rot.
RE: Wood posts used in damp crawlspace construction?
I'm just trying to get ahead of any rot... I would like to think that there isn't any but I believe a meter test and getting the soil away from those posts is the simplest most prudent things to do. If there is no rot, I will coat them or use borate rods to preserve them better. All of this is a minor amount of work in comparison to if they rot.
Thank you for all the excellent advice. This is an excellent forum.
RE: Wood posts used in damp crawlspace construction?
Borate rods sound like a good idea although I have never used them and cannot comment on how effective they are. This would be something you might want to read up on.
I tend to agree with the philosophy "If it ain't broke, don't fix it" and give it periodic inspections to confirm that rot has not become a problem.
BA
RE: Wood posts used in damp crawlspace construction?
Perhaps a product that inhibits microbial growth but does not form a moisture barrier would be the better prescription, and do your best to keep the humidity down in the crawlspace which is being done. All of this effort is far more than I have ever seen in any other crawlspace, which is commendable!
RE: Wood posts used in damp crawlspace construction?
Yeah, it's a lot of work to go through for a crawlspace, but we want this home to last well into our retirements (when we won't be able to afford any big sructural repair bills). Regardless, I plan on fishing for walleye with my spare time, not crawling around in that crawlspace trying to fix something I coulda/shoulda prevented years ago
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Wood posts used in damp crawlspace construction?
I have not been able to tell if you have properly preservative treated posts... there is nothing wrong with embedded wood posts in soil provided they are properly preservatve treated. I specialize in Post Frame Engineering (see www.postframeadvantage.com for more information about Post Frame) where at least 75% of the commercial building projects I work on in Wisconsin - Minnesota - Iowa utilize embedded wood posts... completely code compliant. If your columns are not properly treated, it may be possible to shore up the building temporarily, replace the embedded portion of the existing posts with properly treated posts and make a structural connection to the existing 4x4 posts above grade.
I applaud you for taking this observation so seriously, but I wouldn't presume the posts are bad just because you're not familiar with the practice. We tend to distrust things we're not familiar with, right? If the 4x4 posts are not properly preservative treated, or if you're not sure, you may be able to hire a qualified post frame contractor to come in and give you a better opinion for less cost than hiring a structural engineer to come in. I think a qualified post frame builder would probably give you better results than a structural engineer not familiar with this type of construction. Consider checking out the Find a Designer or Find a Builder feature at the postframeadvantage website.
Note that the American Society of Agricultural & Biological Engineers (ASABE) has an engineering practice #EP486 called Shallow Post Foundation Design and this is referenced in the International Building Code 2006, adopted by the Minnesota Building Code. Although this is a dwelling, structural considerations are allowed to be analyzed under the IBC provisions to meet the requirements of the IRC.
RE: Wood posts used in damp crawlspace construction?
RE: Wood posts used in damp crawlspace construction?
My first reaction to what I saw was "WTH?!" as I am not familiar with wood posts supporting a home like that. However it appears, based on the feedback, that this can be done to code and there are several options I can choose from if problems actually occur. I am headed back up in Oct and will get a much better view of what's going on there. I will take the advice from ajengineer and if I need a pro down there, will look up someone on postframeadvantage.
Clean motor oil eh? So simple.