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dcook
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# Posted: 10 Sep 2019 10:09am
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Quick question, as I am going to be starting my cabin build soon.
I am going to have cement sono tubes about 2 feet off the ground and then 2x6 frame for the bottom of my small bunkie (10x16)
Is it required or high recommended that my 2x6 frame on the bottom be pressure treated? Or can I use the normal framing lumber?
My thought is once the cabin is up, there will be no rain or snow able to get under there so they will never be wet, the only ones that might get some rain or snow would be on the outside edges.
Thank you
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Steve_S
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# Posted: 10 Sep 2019 10:36am
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I build my cabin on a Frost Protected Concrete Slab Foundation and even with that and being on high dry ground I used Pressure Treated Red Pine as my baseplate for my walls. Not only because of it's mould, mildew & rot resistance but also because of bug resistance. Should've Could've thing, I should have done the first course of sheathing as well as the baseplate with Bluewood / Bluwood but it was not readily available at the time. PT is not just for dealing with moisture related issues and lately, the ants & other wood borers are becoming far more aggressive & plentiful so dealing with that first & foremost is important.
Of course you do not have to and there is no need BUT for a few extra cents (ok buck or two) it's certainly worth the piece of mind... Just like I used all Galvanised Nails which only cost a couple of bucks more per box (for Nail Gun) as I hate Nail Tears dribbling down my lumber. To be fair, I also used Live Edge Cedar for siding, so nail stains are a certain no-no !
BTW: The is an old saying that applies to ALL crisis Management related jobs... It's far cheaper & simpler to prevent a crisis than to manage it when it's happening.
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SE Ohio
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# Posted: 10 Sep 2019 04:35pm
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Check your local building code. There is a spec for how high off ground your wood needs to be for non-pressure treated.
You also might check on hoist size/span. 2x6's won't meet code for even a deck where I live. Might be worth the extra expense for 2x8 just for sturdiness-
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Princelake
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# Posted: 10 Sep 2019 05:58pm
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I wouldn't worry about the floor being pressure treated. Just don't put the wood directly on the sonotube. Make sure you use metal brackets to separate them and you can get adjustable ones to help level it up.
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snobdds
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# Posted: 10 Sep 2019 06:56pm
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I hate pressure treated wood, especially for building. After it dries out, and everything shrinks and twists...it looks like crap.
If you are at least 18 inches off the ground, I would put yellow wood down (regular old SPF).
I grew up on a ranch and our head do it all guy would slaughter everything wood, exposed to moisture, in a 50/50 mix of cheap motor oil and diesel. Nothing rots. It works, I know because we still have fence post from the 50's and trailer decks never need redecked. So every year I do the same to all the foundation wood on my cabin.
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Brettny
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# Posted: 11 Sep 2019 07:19am
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Anything that touches concrete should be PT. If your putting posts on the sono tubes those should be PT also. The rest can be regular lumber. Make sure your siding comes down and covers the rim board.
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trevoracus
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# Posted: 11 Sep 2019 12:55pm
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Please spend the little extra to go to 2x8. a 2x6 span support is I think max 8 ft for SPF (spruce-pin-fir) up here in the north. For a few dollars more I would spend it on 2x8s.
As for what type, SPF would be fine if you are comfortable with no blowing snow or water touching it. If you are going to have it then I would suggest PT.
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Princelake
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# Posted: 11 Sep 2019 08:22pm
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Do not let wood including pressure treated touch concrete. It will rot just like any other wood
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ICC
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# Posted: 11 Sep 2019 09:06pm - Edited by: ICC
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Quoting: Princelake Do not let wood including pressure treated touch concrete. It will rot just like any other wood
Oh c'mon. ALL the building codes call for pressure treated wood as the bottom wall plate when building on a concrete slab. The building codes also generally call for a PT 2x as a mud sill on any concrete stem wall or perimeter concrete foundation. However, the code wording on that section can be interpreted differently in some situations. Still, virtually all contractors use PT for mudsills just the case the inspectors insists while some other one may not.
What is really more concerning is the use of short posts on top of concrete piers with the structure sitting on top of them. The use of short posts as some folks do, introduces a hinge point where the post meets the concrete and where the top end of the post meets the floor framing. Better to be very careful when setting the concrete height and then laying PT beams directly on top of the concrete.
Nobody should be using motor oil and diesel mixtures as wood preservatives. Nobody. You may as well go pour some down your well.
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Princelake
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# Posted: 11 Sep 2019 09:12pm - Edited by: Princelake
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You should be using a sill gasket between any type of wood and concrete or like in a basement plastic between
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ICC
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# Posted: 11 Sep 2019 10:07pm
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You simply stated that PT on concrete will rot. That is not true.
However, sill gaskets are a very good idea, but the main purpose is for air sealing. They can help with keeping moisture from wicking up though. PT wood will not necessarily rot when placed against concrete. My point was simply to correct the mis-statement about PT wood.
I have an old shop built in the 80's with PT wall bottom plates bolted to the concrete slab. No gaskets used. No rot.
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ICC
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# Posted: 11 Sep 2019 11:15pm
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Girders (beams) should be PT if the lower edge is less than 12" above grade. Floor joists should be PT if the lower edge of the joist is less than 18" above grade.
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ICC
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# Posted: 12 Sep 2019 12:29am - Edited by: ICC
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2x6's for floor joists may be undersized. Depends on the load per sq ft. A normal living space floor uses a load factor of 40 lbs. per sq. ft. That limits the 2x6 span to 9 ft 4 inches. At 30 PSF the span is 10 ft 3 inches. Depends on what the contents will be. A workshop with power tools might need a higher rating; a sleep only hunt cabin is fine at 30 PSF unless you intend to have a heavy fridge, freezer or gunsafe. Also depends on whether or not the beams that support the joists are under the long walls or if there is some cantilever.
There is a great span calculator at AWC
The Android and iPhone apps are super handy to have.
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Princelake
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# Posted: 12 Sep 2019 06:46am
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I've seen first hand of pt rotting to nothing. I've pulled out a 10 year old front deck on a house. They put the joists right on top of the old concrete stairs. There was an over hang on the roof helping protect it to. Another job I went to look at was a 2 story deck. Built with sono tubes and 4x4 posts and it was all stained. The 4x4s were mush at the sonotubes. Beginning a second floor deck the weather easily gets at those posts.
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Princelake
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# Posted: 12 Sep 2019 06:46am
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I've seen first hand of pt rotting to nothing. I've pulled out a 10 year old front deck on a house. They put the joists right on top of the old concrete stairs. There was an over hang on the roof helping protect it to. Another job I went to look at was a 2 story deck. Built with sono tubes and 4x4 posts and it was all stained. The 4x4s were mush at the sonotubes. Beginning a second floor deck the weather easily gets at those posts.
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snobdds
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# Posted: 12 Sep 2019 11:21am - Edited by: snobdds
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Quoting: ICC Nobody should be using motor oil and diesel mixtures as wood preservatives. Nobody. You may as well go pour some down your well.
Don't knock it until you try it. It's the best organic wood preservative there is...plus the water just beads off. Love the stuff.
Here, every rim board and post beam get an annual treatment. That little cabin in the background, the siding is going on 75 years. Yep, diesel and cheap new motor oil.
Plus I thought it was known fact that if you want grass to grow next to a highway, put some oil based bitumen down 
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snobdds
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# Posted: 12 Sep 2019 11:41am
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Direct contact between concrete and pressure treated lumber does not cause accelerated rot.
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sparky30_06
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# Posted: 12 Sep 2019 02:15pm
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snobdds
We have use old motor oil on the wooden floor of hay wagons and shit spreaders for years. One farm I worked on kept wooden posts in a 55 gallon cut barrel with used motor oil. Those posts never rotted out
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ICC
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# Posted: 12 Sep 2019 02:27pm
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Keep in mind that some PT wood are labeled for above ground use while others are labeled for ground contact and have a higher concentration of preservative. There is also a likelihood of deterioration when the piece is frequently sitting in water, especially end grain in water, no matter what, unless the PT is the even higher grade that is spec'd for foundation use. So yeah, PT can rot when used in a manner it was not designed for. However, to flatly state that PT will rot if used in contact with concrete is not a completely true statement.
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beachman
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# Posted: 13 Sep 2019 10:37am
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Old-growth hemlock may be a good alternative to PT and other treatments if there are environmental worries. I say old-growth because I understand that it has more natural resin in it. It will rot like most woods but takes more weather abuse. Princelake speaks volumes about the use of sill gaskets. Not sure about code violations with this.
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Steve_S
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# Posted: 13 Sep 2019 12:49pm
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Sill gaskets are the best option between concrete and ANY wood and in Ontario, the code is very clear about using Gaskets between surfaces. Alternately (the 0ld way) is to put a shingle between concrete & wood.
150% agree with ICC Never Ever use Oil, Gas or other crap as suggested... That is proof WHY you must always think through the bafflegab that is pushed on the web. Some opinions have value while others....
Also it is correct that there are different classes of PT and the green stuff (which is what was used 20+ years ago) was nowhere near as good as the current Brown PT. The best on the market but hard to get is Bluwood which incorporates a few different things and is 100% non-toxic to humans. PT also uses different types of wood, even poplar in some cases ! This is yet another factor to consider is what species of wood is used... Of course if it's Spruce or White / Red Pine then of course your getting a better graded lumber to start with.
Bottom line, ask questions (never be afraid to do so) but be prepared to engage common sense, critical thinking and accept the Opinions & Advice filtering it with a grain of proverbial salt and decipher what makes most logical & rational sense to you. It's your build & you want It to be the best you can build & to last as long as it can, so you have to think that through.
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Princelake
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# Posted: 13 Sep 2019 05:54pm
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The best wood is preserved wood. It's tough to come by. It's designed to go below grade for 100 years plus. It's designed for wood basements. I'm not sure why it's not more main stream as an option for decks and what not. It looks exactly like pressure treated
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KinAlberta
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# Posted: 13 Sep 2019 10:41pm
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There’s lots to know before using treated wood.
A start here:
What's the Difference: Pressure-Treated Lumber - Fine Homebuilding
2015
https://www.finehomebuilding.com/2015/01/07/whats-the-difference-pressure-treated-lum ber
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paulz
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# Posted: 14 Sep 2019 01:28pm
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Question: I have a bunch of good PT lumber, age unknown. Some green color, some brown. Does the green stuff have the old chemicals and the brown the new?
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Princelake
Member
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# Posted: 14 Sep 2019 05:39pm
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Paul's read kinalberta link he posted. It explains it there.
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paulz
Member
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# Posted: 15 Sep 2019 01:29pm
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Quoting: Princelake Paul's read kinalberta link he posted. It explains it there.
I must be missing it.
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ICC
Member
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# Posted: 15 Sep 2019 04:10pm
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paulz, I did not see any references to color and type as to old/new in the linked document either. Is the green stuff you are wondering about a more green-green or a more olive-green. Both the old CCA and some of the newer treatments use copper and that is where the green color comes from. The newer types don't have the arsenic or other heavy metals. The newer tend to be less green, more olive toned.
I believe the tans and browns are all going to be one of the newer types.
Both old and new come in different retention rates; above ground through foundation and salt water grades. And that is the big decider as to where it can be properly used.
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paulz
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# Posted: 16 Sep 2019 05:54pm
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ICC, here's a pic, a faded light green, was a fence.
And a back story: A friend in the area thought his property extended past the fence line, so he had a surveyor come out. Low and behold, turned out the fence was on the neighbor's property, like ten feet! And those surveys get filed in the public records. Not only did he have to tear down the fence, he had a stone stairway next to it leading to his house he had to demolish. Shoulda let sleepng dogs lie..
Anyway, I hauled off about two dozen of these 2x6s about 14' long after cutting at the posts. No idea age of the fence, my guess is the old pt.
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ICC
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# Posted: 17 Sep 2019 02:29pm
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paulz, that does appear to be old CCA PT. I haven't seen very many 2x6 with incising though. The incising I have seen is usually on timbers, 4x4 or 6x6 when they use something like DougFir which does not take the PT chemicals very well.
I have some old CCA treated pine used as equipment shed posts that look like what you pictured. The oldest are now about 30 years old. Still in good shape.
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NorthRick
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# Posted: 17 Sep 2019 05:49pm
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Nearly all the PT wood sold up here (Alaska) is incised. About the only boards that are not are 2x6's meant for decking. They are not rated for ground contact.
The species of wood used for general lumber in the northwest does not absorb the chemicals well and anything rated for ground contact or burial will be incised.
My guess on paulz's boards is that they are rated for ground contact regardless of the actual chemical in them.
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