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utherjorge
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# Posted: 6 Jul 2025 10:41am - Edited by: utherjorge
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Hello to all. I've posted here before, and this place is a gold mine of information and smart people.
I ultimately decided on a 12x16 cabin shell the amish are building for me. There will be a gravel driveway to a gravel pad where this cabin will be placed, on four skids. Good local builder, so I'm very optimistic that this part will go well.
Once placed, since it's going to be green lumber, I know it needs to dry out. My plan is to allow it to dry a year before "finishing" the shell to make it what I want. This includes insulation and all that fun stuff. I can give way more details if anyone is interested.
The Big Question: As a part of making this something that will last, I will be strengthening it all over. Since the floor will be a plywood floor, the plywood shouldn't require time to dry, so I was going to add a second layer of plywood right quick. However...is this a dumb idea to help make the cabin more durable?
I appreciate any and all advice you all can provide. Thank you in advance!
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DRP
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# Posted: 6 Jul 2025 12:12pm
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A good builder dries the materials first, then culls through the warp to build a good structure. Green building is for low importance buildings. I've looked at several of these sects work. I saw problems with one group's startup enterprise and gave them span tables, grading rules and such. They were not receptive... that is not because they knew better or even what they were doing wrong. What I've seen is well executed structural ignorance.
This question is the same, explain what it is that you think another layer is going to do, what is the goal here and let's work from that angle.
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utherjorge
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# Posted: 6 Jul 2025 12:26pm
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I appreciate you jumping in. Thank you.
My understanding of this particular builder/supplier is that it's likely going to be a combination of things. The plywood floor is what it is. Skids are pressure treated. structure is dried stuff, or dried enough. It's the board and batten exterior that is going to be the rough cut stuff that will need to dry to some degree. Stated time by the builder is a couple of months to dry out, which is "fine" for me: I don't plan on camping/staying in it this year anyway.
Allow me to also say that I chose these people because of others I know who have bought their stuff, and it's help up well. I know they've made cabins for years and I spent time asking around and searching. I found no complaints. I know that doesn't mean there are no complaints. I just didn't find any.
However, since I know using something to store rakes in is not the same as occasional use as a living space. So I'd like to make the place stronger before I even attempt to live in it for any length of time. Hence...adding another layer to the floor.
Part of me asking the question here includes whether I should throw rigid foam down as a sandwich between the layer it comes with and a top layer of plywood I was planning to help with strength. Does this make sense, what I'm typing? Then, of course...am I even thinking correctly?
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gcrank1
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# Posted: 6 Jul 2025 01:14pm
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Floor insulation, where are you at? Cold floors aren't fun.
Here in WI I used 1" blue DOW under my build in '83 and last year had 2" done during the build to our prebuilt log cabin.
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Grizzlyman
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# Posted: 6 Jul 2025 01:19pm - Edited by: Grizzlyman
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My question is why do you think the plywood floor is inadequate? What is the thickness? Almost all buildings have an osb or plywood subfloor 3/4 is what you really need. 1/2 is fine for a shed, but will be too spongy for a proper living space. So if it’s 3/4 it should be fine.
If it’s 1/2, then put down another layer of 1/2. You might be able to get by adding 1/4 or 3/8 to the 1/2 that’s already there… but since the amount of work is the same and cost negligible for something that size so I’d just do another 1/2 layer.
Hope this helps
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MtnDon
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# Posted: 6 Jul 2025 03:32pm - Edited by: MtnDon
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There are plenty of reasons green wood is not a norm in construction anymore.
When considering conversion of a utility building to habitable use many people find it difficult to achieve adequate insulation and ventilation in the roof. Give it some thought too.
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DRP
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# Posted: 6 Jul 2025 03:34pm
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Gotcha, I was making a 12' lumber pallet this morning, was 2 boards short, just went down and sawed another log and those 2 boards are seasoning til the end of lunch.
Strength is a word with many possibilities 
Plywood is not where the overall load carrying strength of the floor is. If you want a floor designed for 40 pounds per square foot vs one designed for 30 psf then ordering deeper joists is the solution. Bending strength and deflection are different but related.. often when someone wants a tile floor we will need to design one that will deflect under load half as much as what is allowed by code to help prevent cracking. The solution to the problem is the same, deeper joists. However, using the tile example, the sheathing (plywood) that is spanning between joists must also be very stiff, 2 layers of plywood or stiff ply and a bedded tile backer.
So, the 2nd layer of plywood will not make the floor "stronger" it may make the sheathing stronger/stiffer between joists. I do like the idea of foam between the layers, I'd use 3/4 for both layers myself, you can economize but underfoot is not the best place, nothing like walking on a wet noodle. IMO if you put one thin layer over another, they will both end up conforming to the sag of a single thin layer. These are upgrades I would have the builder do, then doors and other things at built in heights aren't a problem later.
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utherjorge
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# Posted: 6 Jul 2025 06:08pm
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Quoting: gcrank1 Here in WI I used 1" blue DOW under my build in '83 and last year had 2" done during the build to our prebuilt log cabin.
Was that sandwiched between different layers, on top, underneath? Where did you place it?
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utherjorge
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# Posted: 6 Jul 2025 06:09pm
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Quoting: Grizzlyman So if it’s 3/4 it should be fine.
It is/will be 3/4 inch plywood. I'm just thinking about preventing future shenanigans where possible.
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utherjorge
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# Posted: 6 Jul 2025 06:12pm
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Quoting: MtnDon When considering conversion of a utility building to habitable use many people find it difficult to achieve adequate insulation and ventilation in the roof. Give it some thought too.
I know this thread is about the floor, but I plan on having foam blown in between the studs and in the ceiling. I figure the floor is a place I can begin to do things with right away, not worrying about the building to dry out/shrink/crack, and so on. Depending on how things shake out, I have been planning to insulate next year, in the spring.
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utherjorge
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# Posted: 6 Jul 2025 06:15pm
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Quoting: DRP If you want a floor designed for 40 pounds per square foot vs one designed for 30 psf then ordering deeper joists is the solution.
I want to say that the floor is 2x6s. I know the four skids are 4x6, and I'll have this building set on a gravel pad that is scraped down to a good base, then built back up. I'm expecting no heaving.
I do know that another reason to do something with the floor now is so that when I swap out the janky man door or whatever it is that they're using next year for the "final" door, I'll simply build it up as needed based on whatever thickness the floor ends up being at that time.
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MtnDon
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# Posted: 6 Jul 2025 06:54pm
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Quoting: utherjorge I know this thread is about the floor, but I plan on having foam blown in between the studs and in the ceiling.
I realize this thread was about the floor. At the same time I have seen countless numbers of people who have done the shed to cabin conversion run into issues when they finally hit the roof/ceiling insulation question
Your question about strengthening the floor before you even have the structure makes me wonder how much will be spent to correct perceived and real deficiencies.
In the past, some (many?) attempts I have made to save money/time/effort, have not been beneficial.
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DRP
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# Posted: 6 Jul 2025 10:44pm
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Quoting: utherjorge I do know that another reason to do something with the floor now is so that when I swap out the janky man door or whatever it is that they're using next year for the "final" door, I'll simply build it up as needed based on whatever thickness the floor ends up being at that time.
If you build up on top of what fits a normal door size, then its going to be a custom door later. If bought that will cost more than having them do the built up floor now.
If there are 4 rows of skids with joist spans of 4' then 2x6 is fine. If the joist span is closer to 12' then it needs a 2x8 joist for a decent floor.
The stamp on plywood gives the floor and roof span in inches. For instance a common 3/4 ply stamp is 24/32, it is rated to span floor joists up to 24" on center and rafters on 32" centers (go carefully there, check snow load, the floor number is for 40 psf).
It does not sound like you are doing gravel to frost depth, why are we not concerned with heave? and, will a bit of heave matter? Will heave change the bearing structure if there are rows of skids on the wet perimeter and dry middle? All just food for thought that springs to mind. If the joists are deeper and some rows lose support the floor will not sag. The old adage is "deeper is cheaper"... in many ways.
You're also low which promotes rot, treated joists would be a good idea. You are asking a lot of wood siding that low.
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utherjorge
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# Posted: 7 Jul 2025 05:58am
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Quoting: MtnDon Your question about strengthening the floor before you even have the structure makes me wonder how much will be spent to correct perceived and real deficiencies.
I don't know what this post means, my guy. Where is the issue?
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utherjorge
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# Posted: 7 Jul 2025 06:12am
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Quoting: DRP If you build up on top of what fits a normal door size, then its going to be a custom door later. If bought that will cost more than having them do the built up floor now. If there are 4 rows of skids with joist spans of 4' then 2x6 is fine. If the joist span is closer to 12' then it needs a 2x8 joist for a decent floor. The stamp on plywood gives the floor and roof span in inches. For instance a common 3/4 ply stamp is 24/32, it is rated to span floor joists up to 24" on center and rafters on 32" centers (go carefully there, check snow load, the floor number is for 40 psf). It does not sound like you are doing gravel to frost depth, why are we not concerned with heave? ... The old adage is "deeper is cheaper"... in many ways. You're also low which promotes rot, treated joists would be a good idea. You are asking a lot of wood siding that low.
As this was a floor post, I didn't go into other details, but I'm happy to. After the shed dries out, I plan to side the outside with something like Hardie board siding. As such, since it's just a shell, I'll be cutting out the windows and door at that time. It's coming with a generic "man door" but I'll be putting a door of my choice in when I do windows. I know that this will require an adjusted opening. I'm making no plans for doors or windows at this time (size-wise) because I want it in place first.
Roger on the plywood stamp.
The geology of the site is such that I can't tell you how deep the gravel will be at this time. Allow me to explain! The site is on a hillside that overlooks a river. I could clear cut the lower portion of the property and have a good river view...from the top to the bottom, there's a 150 foot drop over some 400 feet of length. Maybe 20 or so feet past the edge of property is a steep drop off. However....I don't really want to turn the forest into a field. The entire hill is slate, as per the area survey. I have some flat spots on the hill side, most notably at the top, and then another terrace maybe 100 feet down. I thought these were chewed into the hill when the entire hill was logged in the 1920s; my property border is an old forest service logging road. These aren't man made terraces: in some spots, the slate has broken free of the topsoil. so, the contractor will be getting down to that bedrock and then placing some base stone, with clean gravel on top.
They are treated skids, and as the skids do not go all the way to the edge, by my math, there should be just under 4 feet between the skids. I don't have number of joists but I remember the nail patterns on their other work and it can't be more than 4 feet. Of course, my memory is imperfect.
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gcrank1
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# Posted: 7 Jul 2025 10:10am - Edited by: gcrank1
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My 3 structures with under-skids since 1983 have all been sitting on solid cement 'silo blocks/staves' on a prepped and crushed limestone graveled base After #1 I decided to Always use more blocks than the min spec (NO Downside). Not that I had trouble with #1, I just know more 'foundation' is better. I do not like the idea of even pressure treated skids sitting right on the ground/gravel. I laser leveled each block to +/- 1/8".
Note that your build starts right at the base, if anything do overkill there rather than regret it later.
Well, pretty much all the build comes down to that...do it all 'right ++' as you go.
As to my floor insulation, on #1 I nailed 1x2 furring strips 1" down in each 16"oc joist bay then cut the DOW to fit/sit there under my 3/4" plywood deck. I did not use any critter/insect guard before the insulation went down, also never saw any problem because of it in the 30+years BUT, Id do it now 'cause I know more about being proactive and preemptive.
I did also use that same insulation on the outside on top of the sheathing and under the repurposed barn board & batten siding.
Doing again Id use 2" for both.
And Id design from the beginning for a 'hot roof'.
On our #2 new last year prebuilt milled log cabin I ordered 2" under the floor and roof, really dont know just how they did it as I did not micro-manage the build (oh, how I sooo wanted to). I suspect it is sandwiched under the floor. I also had pine wood flooring installed over the decking ($ but worth it for us, ready to move into) and the floor feels just fine.
Admittedly #1 & 2 are bigger structures than yours, #1 was 12x24 and #2 is 12x28. Our #3 10x16 prebuilt 'tool shed' is comparable to yours. I bought it because I needed a building QUICK. We have 3 pre-built shed companies here, all pretty much building off the same playbook. At best I can say mine is 'adequate'; I can see I could have used one as my starter cabin if I was just starting cabineering on the cheap but there is hardly anything about it that I wouldnt have done better if I had stick built it (Im NO 'pro' but do tend to overkill and my stuff has lasted).
So, if you want what you build to last, start out strong and build strong from there up. It doesnt take that much more to do it well than to just do 'good enough'.
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utherjorge
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# Posted: 7 Jul 2025 11:14am
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gcrank...Thanks for your insight.
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