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ADK_26
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# Posted: 2 Oct 2023 13:09
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Hi there,
I'm in the beginning stages of planning a cabin. Likely somewhere in the 16 x 24 size range. I'm finishing up a pole "barn" (shed) of the same size on the same property (I wrote about it https://www.small-cabin.com/forum/6_11893_0.html).
That was the largest thing I had ever built (building), by a long-shot, so I learned a lot in the process. For one, the immense cost of PT lumber. Given my experience (of 1), I was planning to use pole building construction for the cabin as well.
I've read that most building codes require PT floor joists, beams, etc if they are <= 36" from grade.
I don't NEED to build my cabin to code, but I want it to last for a generation or two. Anyone here with more actual experience have opinions on floor joists/girders/beams? Right now I'm considering sticking with pole construction as above and using rough cut lumber as floor girders and joists. I think I could set the bottom of them 36" above grade and place a vapor barrier under the structure to form a semi-proper crawlspace. I would plan to enclose this area to keep stuff out and passively vent it.
I'm also (at this time) planning to build the cabin in a fairly dense portion of forest. It's high ground, but stays pretty wet year round due to the tree cover. Takes like 3 clear days to dry out. Don't know if that would play a factor.
I want to have a good idea for my budget and if my floor system needs to be pressure treated then it may change some other design considerations due to cost.
Thank you so much for the help!
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Steve_S
Member
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# Posted: 2 Oct 2023 13:34
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The first & MOST important rule about PT Wood, is that none of it can be inside and you cannot have exposure to it. Anything exterior or underneath is fine. One thing which is common knowledge but occasionally forgotten, is to use nails/screws which are for use with PT! Straight steel etc will not last long at all. Also do not ever affix anything aluminium in direct contact with it either, it gets really ugly & fast.
Ensure that the grade below your structure is hi & dry and setup so that any water will drain away without issues. If you are insulating the floor, then there are other considerations as well.
A few tips...
1) Fiberglass is PASSE that is 1970's tech, rodents & bugs love it and it will hold moisture.
2) Rockwool like Roxul is hated by critters (gets under bugs shells & prickles mammals) and is also Hydrophobic, it resists & sheds moisture.
3) Closed Cell Foam sheets have high R value and also act as a vapour barrier but there require considerations for the different installation types.
* TIP: Retail cost is LUDICROUS ! Go check out Commercial Roofing companies (no 300% markup to retail), they "may" sell you new & fresh insulation sheets BUT they may also have good "take-off" insulation which they have to remove from commercial building when reroofing, most often they will sell the good sheets quite cheaply.
YES, Foam Insulation sheets, regardless if XPS, EPS or even PolyISO have anywhere from a 300% to 500% markup from wholesale/commercial to retail ! YES it is shocking and I consider it criminal.
Example: I use ONLY FOAM. 4'x8'x4" thick sheet of PolyISO cost me $7 a piece. 4'x4'x5.5" HD-EPS-II cost me $10 a sheet. These came from a Commercial Roofing company.
HINT: Roofing companies must dispose of used materials... it costs them $ to do so, they would rather get paid for Good Used sheets than having to pay to get it recycled. The right approach can save you Scads of Cash !
Hoep it helps, Good Luck
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ADK_26
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# Posted: 2 Oct 2023 15:32
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Wow, love the tips. Thank you!
Yes, I'm always sure to use galvanized hardware through pt lumber.
Planning to insulate. Did not know rockwool was better for critter control. I haven't though too much about it, but my friend's dad is in manufacturing and so I have access to at-cost PolyISO. However, I'm a big fan of salvaged materials when possible, so I will make some calls to some of the commercial roofing guys around.
Your reminder about PT being outside of the structure, brings up another point. As of now, I have a pole in the middle of my cabin that would be interior and not within a wall like the others. Could I use a non-PT 6x6 set up on a sonotube above grade, or since it will be contacting concrete at the bottom do I need one of those laminated posts to transition from PT at the bottom to non-PT inside the structure?
I guess my overarching question is do I really need PT wood if its ~36" above grade? And does adding vapor barrier under the structure affect the moisture levels enough to be able to get away with cheaper building materials like rough cut or non PT wood?
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Steve_S
Member
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# Posted: 2 Oct 2023 16:17
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On PolyISO... Great stuff BUT there are different types. The older stuff which was paperfaced and classed as untreated, was an Ant magnet. Treated paperfaced is quite common and ants hate it. Foil faced has always been treated. I believe that since 2015, all PolyISO has been "treated". I know this applies in Canada, the US I don't know.
When looking at the used stuff (foam sheets - all types), look at the printed date codes.
The central post idea you have for a 6x6 on sonotube is good. You may want to consider a Big Foot base - a most amazing product. Might provide additional ideas to solve some other issues. 
https://www.bigfootsystems.com/index.htm
The Vapour Barrier underneath is a "tricky" thing and it partially depends on what insulation you have in the floor. For example, a plastic sheet would really not be a good idea for a wide number of reasons. Basically if any wet gets in & under the floor it needs a way out. Often, a housewrap type of barrier works best and covered with fine mesh or perforated aluminum to keep critters out.
If possible, ensure that the ground underneath is:
- well packed & covered with commercial grade landscape fabric. The centre should be higher and sloped out to the sides to allow for crea drainage.
- Fabric should be covered with a couple of inches of gravel.
- Ensure good natural drainage away from the structure..
Sorry I know some of this is obvious but worth mentioning, because readers later may not consider such.
Also remember that rodents + will climb up the posts to get in, Metal collars (galvanized tin) on the posts or like "lamp shades" around the posts will prevent that. The can climb ABS pipes as well... lampshade collar that too.
Another thing that pops up a lot. If you completely enclose the space you risk creating a musty & moldy set of issues. You need to ensure that there is reasonable airflow to prevent such issues.
You're in the Adirondacks and have the familiarity with living rural and the mischievous critters and what they can get up to LOL. Its best to think ahead while building than have to go back while making Blue Air This coming from a guy who lives in a Live Edge Cedar clad home within the Arboreal Forest near Algonquin Park... Dang critters, the chippies travel in herds !
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spencerin
Member
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# Posted: 2 Oct 2023 20:55
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If I were you, I'd use PT wood for the joists. You're better off paying a little extra for the rot and insect deterrence, vs. what it would potentially cost you if some reason a section of untreated wood just couldn't stay dry.....
You can mate untreated wood to concrete, but you do have to have a barrier between the two to keep the wood from wicking the moisture out of the concrete.
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gcrank1
Member
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# Posted: 2 Oct 2023 22:10
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That material between 'crete and wood can be as simple as a piece of asphalt roofing shingle.
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Brettny
Member
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# Posted: 3 Oct 2023 05:44
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Are you in the APA boundrys?
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ADK_26
Member
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# Posted: 3 Oct 2023 09:12
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Quoting: Brettny Are you in the APA boundrys?
Yes - it’s zoned as Rural Use but I have some wetlands on the property
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ADK_26
Member
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# Posted: 3 Oct 2023 09:27
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Wow, @steve. Thank you for the info! I forget vapor barrier works both ways and if anything leaked while I was away I would be making a small pond in the crawl space.
I have geotextile fabric I used for my driveway and I put some under my tent platform that I built, mostly thinking for weed control, but I guess it was a good move. Stuff is great for allowing drainage. I’ll probably go with that.
@spencer - fair point. I’ve been trying to talk myself out of using PT wood. Probably means I should just use it 
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Brettny
Member
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# Posted: 3 Oct 2023 09:41
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Quoting: ADK_26 Yes - it’s zoned as Rural Use but I have some wetlands on the property
I think your best off asking the local building inspector this question. Did you get approval from the APA to build?
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ADK_26
Member
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# Posted: 3 Oct 2023 09:57
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Planning on doing the "hunting and fishing cabin", which has some requirements like keeping it off grid that for cost reasons (I want to build far as possible from the road) would help me out anyway. However, I haven't run it by the APA yet.
Since its "Rural use" APA land, the APA only cares about the wetlands, which have a separate designation. They sent me a map of my property that highlights where the "wetlands" are via satellite. My shed is far from these and they signed off on it and therefore I only had to go through the building inspector. Sent him a $35 check and my drawings and he mailed me my permit.
I'm in the process of applying for permit to put a small ATV bridge in the wetland area... It's a very long form to fill out. I'll let you know how it goes.
I think the cabin will be the same process as my shed since its far from any wetland areas. I'm sure the town just wants to know where it is and how much to add to my tax bill haha...
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Aklogcabin
Member
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# Posted: 3 Oct 2023 10:13
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No if you are 36" off the ground you don't need p t wood. If you enclosed the foundation you may want a vapor barrier under your cabin. If it's open you should have enough draft. On our 16x24 we used laminated floor joists. BCIs. They are straight and easy to work with.
We also built a 3' overhang on the roof sides so that the drip line is away from the cabin and snow doesn't pile on the sides.
For foundation posts we used recycled utility poles. Treated cedar 4' deep. And cut a shoulder into them to hold the 6x12 joist bolted into them. Has been through a couple big earthquakes ,7.2 . And a lot of snow
Good luck n stay positive
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gcrank1
Member
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# Posted: 3 Oct 2023 11:01
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Get approval before planning too far
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Brettny
Member
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# Posted: 3 Oct 2023 15:42
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You still need to follow codes with a "hunting and fishing cabin". Please talk to the town/county first. You may even need engineered drawings.
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ADK_26
Member
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# Posted: 3 Oct 2023 16:35
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Quoting: gcrank1 Get approval before planning too far
Will do, I'll submit a jurisdictional inquiry with APA as soon as I pick a final spot, I got like 3 possible places as of now...
Quoting: Brettny You still need to follow codes with a "hunting and fishing cabin"
I didn't know that... No biggie, but glad I figured this out now! I feel like everytime I read the APA flyer I take something different away from it. The first 10 times I read it, it seemed like I don't need a town permit since I'm on rural use land (under permitting requirements)... but re-reading it now, maybe that's only in regards to building multiple.
I should probably call the code officer and just ask...
Thank you all for the help, feedback!
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ADK_26
Member
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# Posted: 3 Oct 2023 16:46
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Aklogcabin
Love that design! I've been trying to get my hands on some recycled utility poles to use, maybe incorporate them into my cabin design somehow.
Your cabin/site looks awesome (having checked out your journal). Thanks for the info!
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ICC
Member
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# Posted: 3 Oct 2023 17:44
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PT wood should be used for girders and beams when the lower edge of the beam is 12" or less above grade. Floor joists should be PT wood when the lower edge of the joist is 18" or less above grade.
FWIW, poyiso is great stuff but polyiso insulation loses some R-value when the exterior temperatures fall below 50 F. Not a big factor but it is there all the same. Polyiso costs more than XPS and has a higher R-value. But if the weather gets very cold, much of that extra r-value per inch of extra thickness disappears.
So I ask myself what is more desirable? Better hot weather performance or better cold weather performance.
Quoting: ADK_26 I should probably call the code officer and just ask...
Yes.
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ADK_26
Member
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# Posted: 12 Jan 2024 12:16
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Just to follow up....
I finally got a hold of the codes guy who obviously deals with APA hunting cabins a lot. Will not need engineered drawings due to my planned size, but will need inspection. He mentioned specifically the grey water pit and wood stove.
Thanks for all the help!
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Brettny
Member
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# Posted: 12 Jan 2024 18:52
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What did he say about the gray water pit and stove?
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ADK_26
Member
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# Posted: 10 Feb 2024 05:53
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Said APA will have to sign off on grey water pit when I send my jurisdictional inquiry form to them (JIF), but they provide a guide on their website to base your design parameters on, so as long as you follow it, it's typically approved without an APA site visit and then the town deals with the rest. If you build near wetland, it is more stringent and requiries APA inspection. I've narrowed my build site down to two potential ones at this point, one of which is within 150' of wetland as designated by APA (they will send you a map of your property with an overlay of where wetland is) so I may need a site visit if I build there. Not planning on starting site prep until 2025, so I'm still debating. I've been camping at the different potential spots in various seasons to see what they're like at different times of year before I commit to one.
He said the woodstove requires a town inspection, but again as long as I follow the code it shouldn't be an issue. He mentioned the woodstove as an example, it sounded like the foundation, etc would be reviewed on my submitted drawings and then he would let me know if additional inspections are required based on the plans.
Nice guy, he's just so darn hard to get a hold of...
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Brettny
Member
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# Posted: 10 Feb 2024 07:58
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Calling the correct people at the town/county can really give you alot of information really quick.
If you want to build in 2025 I would do site work/land clearing in 2024. Its alot nicer to build on dirt that isnt all tracked up and has time to settle and grow something like grass.
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gcrank1
Member
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# Posted: 10 Feb 2024 10:34
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Yeah That!
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Brettny
Member
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# Posted: 11 Feb 2024 06:57
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Can you post the lint to the grey water design they show? I'm not finding it, only full septic design. I would like something to base my system off of that the agency has alreaty approved.
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ADK_26
Member
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# Posted: 25 Jul 2024 19:38
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Oof. Little late on this, but here is what I was referring to Brettny
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Brettny
Member
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# Posted: 25 Jul 2024 23:16
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Thank you. Didnt know that file existed. I was in the understanding that a outhouse or gray water discharge wasn't legal in NY. This proves other wise...and it was released in 2016 so not that long ago.
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socceronly
Member
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# Posted: 12 Sep 2024 16:12 - Edited by: socceronly
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Two questions in one I guess.
Let's say you are building on skids, and put in cross members to stiffen the underlying skid structure.
2x10 laminated skids with 2x6 cross members.
This would make it easier to put down a PT plywood bottom for your joists. (outside with PT)
1. Should you do that or leave them open and insulate above. (3 season cottage with AC)
2. If you build the plywood base use regular lumber for the joists.
Thanks
JM
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ICC
Member
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# Posted: 12 Sep 2024 20:30
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Your question is unclear to me.
If you have wood (solid timber or built-up lamination) skids that are in contact with the ground and place any wood materials horizontally between the skids, those materials should be PT, same as the skids should be PT.
Normally, then floor joists would be placed on top of the skids. Those floor joists should also be PT wood (or galvanized steel) if they are less than 18 inches from the ground. That is what the IRC states. The IRC also references that beams (skids) should be PT if less than 12 inches above grade. They measure both distances from the lowest edge.
Any sheet goods attached to the joists should also be PT if the required distances from grade are not met.
Does any of that help sort it out?
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socceronly
Member
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# Posted: 12 Sep 2024 22:14
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Sorry if that was unclear, the cross members are not the joists. They are PT between the skids that do not touch the ground.
They are there to stiffen the underlying structure. Perhaps not necessary. I was mostly thinking it would be easier to put down a layer of PT plywood than trying to flip over the joists with the PT attached to the bottom by myself.
I'll just use PT either way.
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