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paulz
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# Posted: 12 Jun 2014 12:15
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I'd like to keep my floor as low as possible for wheelchair access. Would two 6x6 beams and 2x6 joists on 12" centers, walls cantilevered 6" suffice for a one story with loft?
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JJHess
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# Posted: 12 Jun 2014 17:41 - Edited by: JJHess
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What is the size of the cabin? Span of the joists and span of the beams? The 2x6 joists could span about 11'-4" on 12" centers if they are only carrying the 1st floor and the loft loads are transferred directly to the beams and posts to footings. Beams shouldn't span more than about 8' if you are using 6x6.
EDIT: Sorry, just so the size in the subject line.
For 6x6 beams, put your posts for the beams at 8' centers. Then your joists on top, cantilever 6" like you said. You'll be maxed out with your spans but should still be fine. For a little extra floor strength, add a continuous row of 2x6 blocking mid-span in your joists. If you are going to have a couple posts to support your loft that will be sitting on the floor, make sure to install an extra footing/post under that location so the floor joists do not carry the loft above.
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MtnDon
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# Posted: 12 Jun 2014 19:30
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The snow load is needed to make an accurate assessment of girder / beam size and spacing of piers....
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Don_P
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# Posted: 12 Jun 2014 22:43
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I agree with MD, you can't determine span without quantifying loads. Low means all treated materials.
Slab on grade?
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paulz
Member
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# Posted: 12 Jun 2014 23:55 - Edited by: paulz
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Thanks guys. No snow. I already have 1,200 BF of non treated 2x6 fir, can I treat it with something?
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MtnDon
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# Posted: 13 Jun 2014 22:20
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Nothing that will be as good as or as permanent as using factory made PT lumber. Soaking immersed in a borate solution helps (Solubor) , especially if you can keep the wood from getting wet afterwards; the borate can leach out.
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paulz
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# Posted: 14 Jun 2014 10:21
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So the motor oil/diesel fuel mix treatment isn't worth much then?
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MtnDon
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# Posted: 14 Jun 2014 11:31 - Edited by: MtnDon
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That is a pollutant! I know most of the wood would be off the ground but the use of oil for a wood preservative bothers me. I've seen it done going way back, but it bothered me then and still does today.
Also there's nothing like coating wood with a fuel... I use a mix of old motor oil or diesel to aid with starting slash / trash wood fires in winter, with a small amount of gasoline to get it going.
PT chemicals do tend to stay in the wood and borate is a human friendly substance.
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Don_P
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# Posted: 14 Jun 2014 20:37
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You'll probably get 5-10 years out of non treated lumber or site treated lumber in ground or close to ground contact. a false economy IMO. Use the untreated or self treated wood higher up.
Fir doesn't treat well even comercially, that is why it is typically incised to get more of the chemical in. They are using incising, temperature, vaccum and pressure in the attempt.
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MtnDon
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# Posted: 14 Jun 2014 21:31
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Quoting: Don_P Fir doesn't treat well even commercially, that is why it is typically incised to get more of the chemical in.
That went over my head or thru it  it's very true. I've cut PT treated for and even incised you can see where the PT chemicals didn't make it. Especially bad when there is heart wood present; that does not penetrate.
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Nirky
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# Posted: 15 Jun 2014 02:58
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Quoting: paulz So the motor oil/diesel fuel mix treatment isn't worth much then?
Quoting: MtnDon That is a pollutant!
How does coating wood with oil cause pollution? What gets polluted?
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paulz
Member
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# Posted: 15 Jun 2014 10:36
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How about paint? Seems to work on boat bottoms. I know, buy PT, just curious.
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Don_P
Member
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# Posted: 15 Jun 2014 19:59 - Edited by: Don_P
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It's your call but I've found they are all false economies in my world, for a low floor it's hard to beat a slab. I just sent drawings and job script for shoring and hand excavating under an old farmhouse, rebuilding the foundation and replacing a number of rotten joists, it isn't going to be cheap. I'm wrapping up one and have 2 of those jobs ahead... it pays to get the low work right. We do have to remove and rebuild the roof on one (broken and sagging overspanned rafters), but that'll be a piece of cake compared to working under it.
In a habitable structure oil is a pollutant to you as much as anything, used is worse but either is not good for you 24/7. When it is in ground contact or eventually becomes ground contact it is a water pollutant. That said, just like every country boy, I've done it and it does work to some degree. It is a better powderpost beetle repellant than non toxic borate... but then one might ask what they know that we don't seem to be able to wrap our pea around 
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MtnDon
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# Posted: 15 Jun 2014 21:18
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Quoting: paulz How about paint? Seems to work on boat bottoms.
"A boat is a hole in the water into which you pour money". Constant maintenance. Much worse than a house.
Ditto what Don_P said about oil; plus ... just because it has been done in the past does not mean it is correct or good. People used to smoke tobacco a lot, people used to wash their greasy hands in gasoline, we never used to wear hearing protection, carpenters and cabinetmakers never used to be concerned about wood dust being breathed ..... all which join a list of hazardous things or actions that can be avoided and help one to live a better healthier life.
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MtnDon
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# Posted: 15 Jun 2014 21:40
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Please do not take what I posted above to mean that I'm bashing everything old and promoting everything new.... the food grown back when I was a kid was better for us than most of what most people eat today. Pre-Monsanto food was better than most food grown and sold today, for example.
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KinAlberta
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# Posted: 5 Jul 2014 21:14
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Just some quick thoughts on reducing the risk of rot if using non pressure treated wood. Not sure if any of it would be allowed by code.
Put a layer of a solid composite decking on the bottom where any moisture or runoff might wick upwards and rot the plate or beam. (If I ever put a garage on a concrete pad I'll be doing this.)
Put GRACE or asphalt shingles or galvanized cladding on the top and sides of the beam if water can somehow get on to it. (Overlapping shingle or siding style to shed water and not trap or collect it)
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paulz
Member
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# Posted: 10 Jul 2014 10:24
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I am finally just about ready to put the first nails in my cabin (floor). My joists will sit 18" about the dirt. Ground is flat and level underneath and I think I have drainage away from the cabin sorted so the ground should stay free of standing water. I'm on the west coast, a week or two of 32F nights in the winter, no snow, a few months of rain, 70-90F in summer with low humidity. Wood stove for heat, no A/C. Planning some skirting around foundation with venting.
Is it a good idea to put plastic above the floor joists before I lay the plywood? What about insulation?
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Don_P
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# Posted: 11 Jul 2014 21:29
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I wouldn't put a vapor barrier there. I'd lean towards foil faced foam on the underside of the joists with the seams taped, unfaced fiberglass on top of that, plastic on the ground and let the wood dry to the inside, or sprayfoam.
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces
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Nirky
Member
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# Posted: 27 Aug 2014 15:41 - Edited by: Nirky
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A little perspective in using recycled engine oil as a preservative
https://www.youtube.com/watch?v=DLe1h9xL2sQ
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crchaumont52
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# Posted: 26 Jan 2015 20:28
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Quoting: MtnDon Especially bad when there is heart wood present; that does not penetrate.
That's a bad thing? sounds good to me.
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Don_P
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# Posted: 27 Jan 2015 12:10
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If you are trying to get treated wood then untreated heartwood can be undesireable. For instance foundation grade treated lumber is not allowed to contain heartwood.
For the other side of that, which is where I think you are going, there in no natural decay resistance in the sapwood of any species where the heartwood of "naturally durable" species is decay resistant to varying degrees. I imagine most folks have seen an old cedar fencepost that the white sapwood has rotted off of but the red heart is still as good as new. In something like treated pine however the heartwood is only moderately decay resistant so for a long term structural member one would want the preservative to get all the way to the core.
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