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Thread: Foundation Gravel and Insulating the floor Question

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    Default Foundation Gravel and Insulating the floor Question

    Hello, I am in the beginning stages of planning to build a 16 X 20 cabin on our remote property. We bought some property out in the Lake Louise area. I know the ground is discontinuous permafrost. I am planning on building my foundation above ground by pouring gravel over the organics and then first building a pad with railroad ties or some type of treated lumber, and then laying pier blocks on top of that. Then I am going to be using adjustable brackets in the pier blocks to attach to the beams that will support my floor joists and floor package. My question is about the gravel that I will be using underneath the railroad ties or treated lumber. Does anyone have any recommendations on what type of gravel to use for this application, and how much of it I should use. Also, should the gravel just be placed underneath the lumber, or should it be continuously spread over the whole entire area underneath the floor?

    Also, another question I have has to do with the insulation in the floor. Does anyone have any good suggestions on how to insulate the floor? I was thinking about using some type of metal strapping or bracing (or chicken wire etc.) to hold or support the insulation between the floor joists. I would think it would be unnecessary and actually detrimental to sheet underneath the floor, because you would want any water that leaks through the floor when the cabin is being built to drain away and dry out. If you sheeted the floor, I would think any rain water would accumulate in the floor and mold and rot.

  2. #2
    Member Dirtofak's Avatar
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    There are many different soils under the tundra in that area. Some lots have sand, some rock, some really tough to build on actual permafrost. What gravel is available nearby? You shouldn't need to do the entire area under the cabin. I will say that most people use the area under their cabin for storage and that stumps can be a pain. Cut them short.

    I really like that you have a small cabin footprint. Construction should be fast, heating should be reasonable. Look at RVs to setup the kitchen and the layout.

    I would go with 12" JCI for the floor. R38 or better. The floor makes a huge difference. If you don't want to sheet the bottom use a 1/4 steel mesh. Use sheetrock screws and fender washers to hold it up.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
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    Moderator bkmail's Avatar
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    We stuffed regular insulation beteen our floor joists (2x10's on 16" center) and then held it in place with the plastic snow fencing vs. chickenwire. I used a stapler to tack up the plastic fencing. Works great and went quickly as it was all done from underneath on my back.

    Sorry, can't help with the foundation question, we dug holes and inserted posts.
    BK

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    Member cdubbin's Avatar
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    Don't know what you have for gravel up there, but I'd go with a couple feet of D-1....you could also place a layer of green spruce limbs underneath the gravel, "poor man's typar" we call it .....I built my cabin four feet off the ground....made for instant storage, and was easy to sheet under the floor with CDX.....I don't recommend wire.
    " Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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    Moderator bkmail's Avatar
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    Can anyone educate me as to why you would not want chicken wire to hold the insulation in place?
    My neighbors did the same as you Cdubbin.
    My other cabin has the chicken wire holding up the insulation since '84 and it works great.

    BK

  6. #6

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    The bad thing about Chicken wire is that it is possible for Squirrels and other rodent's to get into the insulation.Once they stake their homestead they are hard to change their mind.Not saying that they will it is just possible.

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    Member cdubbin's Avatar
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    Yeah I've replaced a few chicken wire scenarios....usually they're pretty well nibbled at least....in some cases, full of rodent poo, or even carcasses! Squirrels are good at B&E lol....also lots of dampness from the ground....a well-nailed and caulked sheathing is the best way to go in the absence of skirting IMO.
    " Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

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    Member dkwarthog's Avatar
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    Be careful if you cover the underside of your floor joists with plywood. If you seal in the space it won't breathe well and when it frosts, you can have moisture in there that cant escape and can rot the joists after awhile. A friend of mine did that and had to pull it all off and replaced it with chicken wire.

    May not be the same in all conditions, maybe worse in the colder parts of the state where -40 s are more common and frosting happens more.

    i think skirting is the best when possible.

    the best solution for squirrels is a 22lr....shoot on sight, when the wife's not around

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    Member Dirtofak's Avatar
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    Quote Originally Posted by dkwarthog View Post
    Be careful if you cover the underside of your floor joists with plywood. If you seal in the space it won't breathe well and when it frosts, you can have moisture in there that cant escape and can rot the joists after awhile. A friend of mine did that and had to pull it all off and replaced it with chicken wire.

    May not be the same in all conditions, maybe worse in the colder parts of the state where -40 s are more common and frosting happens more.

    i think skirting is the best when possible.

    the best solution for squirrels is a 22lr....shoot on sight, when the wife's not around
    Rat traps baited with peanut butter.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
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    Member dkwarthog's Avatar
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    Quote Originally Posted by Dirtofak View Post
    Rat traps baited with peanut butter.

    That won't cut it, I got a kid that likes to stick his fingers where they don't belong and is allergic to PB.... LoL

    but newspaper tubes with 120 conibears and dog food will clear out 20 acres of red squirrels in no time...takes a couple years before you start having problems again.....

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    Member Dirtofak's Avatar
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    Quote Originally Posted by dkwarthog View Post
    That won't cut it, I got a kid that likes to stick his fingers where they don't belong and is allergic to PB.... LoL

    but newspaper tubes with 120 conibears and dog food will clear out 20 acres of red squirrels in no time...takes a couple years before you start having problems again.....
    I was using 3 in the ceiling but not getting hits, only getting cleaned out of bait. Got the big rat traps from AIH..... they are 5 for 5......maybe 6 for 6 we will see.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
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  12. #12

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    Quote Originally Posted by Dirtofak View Post
    There are many different soils under the tundra in that area. Some lots have sand, some rock, some really tough to build on actual permafrost. What gravel is available nearby? You shouldn't need to do the entire area under the cabin. I will say that most people use the area under their cabin for storage and that stumps can be a pain. Cut them short.

    I really like that you have a small cabin footprint. Construction should be fast, heating should be reasonable. Look at RVs to setup the kitchen and the layout.

    I would go with 12" JCI for the floor. R38 or better. The floor makes a huge difference. If you don't want to sheet the bottom use a 1/4 steel mesh. Use sheetrock screws and fender washers to hold it up.
    Hey Dirtofak, I tried to respond to your pm, but your inbox is full.

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    Member Music Man's Avatar
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    1/4" screen [hardware cloth]. Critters cant get in and it breathes.
    When seconds count, the cops are just minutes away.
    '08 24' HCM Granite HD "River Dog"

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    Member Dirtofak's Avatar
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    Quote Originally Posted by Bushwhack Jack View Post
    Hey Dirtofak, I tried to respond to your pm, but your inbox is full.
    Should be good now.
    I don't mean to sound bitter, cold, or cruel, but I am, so that's how it comes out.
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    My cabin is in the LL area and I did my foundation almost exactly like you mentioned. I doug down past the tundra and roots (about a foot) and was lucky enough to have gravel under that. I then compacted and leveled the gravel and put 2 layers of 36"x36" long 2x12 treated, one layer criss crosses the other. I then cribbed up with RR ties to my main beams. My place is 24x24, 8" log and setttled a bit after the first year but has stayed put since. Diffently use plywood to cover under the joist's! You WILL have squirrels, porcupines, ermine and voles trying to get up in there. The area is extremly dry both in the summer and winter so you shouldn't see moisture issues. Goos luck!

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    Not the best pic but you can kinda see what I did in pic #1.



  17. #17

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    I"ve done a bit of thinking about this foundation idea. First...keep a few things in mind. Your factored load for a cabin including slow, dead, and live loads is ~140 pounds per square ft. Your 16x20 cabin is therefore about 44,000 lbs with a full load and a giant snow load on top with nothing sliding off. Ok...sounds like a lot. The bearing capacity of good gravel is about 3000 psf...and no so good ground about 1,000 psf. Using the 1000 psf number you need 44 sq ft of bearing area. across four corners that's 11 sq ft per corner. An 11 sq ft foundation is 3.3ft by 3.3 ft. Not very much. I'm building a 12 by 16 on days off. I'm doing it in winter so no concrete for now. IN the time being I'm going pioneer style on a tree stump or two and log cribs. If you like you can fill the cribs with gravel and river rock. I suspect the log cribs will last decades, but I'll replace it with concrete. And before you ask, it will settle. That's a good thing. Soil gains bearing capacity by making it denser. To make it denser you have to compact it. ONe of the best ways to compact soil is to to put weight on it. If you are on permafrost put some styrofoam insulation between teh crib and the ground. Once it freezes up life is good.

  18. #18

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    Quote Originally Posted by trailblazersteve View Post
    My cabin is in the LL area and I did my foundation almost exactly like you mentioned. I doug down past the tundra and roots (about a foot) and was lucky enough to have gravel under that. I then compacted and leveled the gravel and put 2 layers of 36"x36" long 2x12 treated, one layer criss crosses the other. I then cribbed up with RR ties to my main beams. My place is 24x24, 8" log and setttled a bit after the first year but has stayed put since. Diffently use plywood to cover under the joist's! You WILL have squirrels, porcupines, ermine and voles trying to get up in there. The area is extremly dry both in the summer and winter so you shouldn't see moisture issues. Goos luck!
    Quote Originally Posted by trailblazersteve View Post
    Not the best pic but you can kinda see what I did in pic #1.


    Quote Originally Posted by Ak Steve View Post
    I"ve done a bit of thinking about this foundation idea. First...keep a few things in mind. Your factored load for a cabin including slow, dead, and live loads is ~140 pounds per square ft. Your 16x20 cabin is therefore about 44,000 lbs with a full load and a giant snow load on top with nothing sliding off. Ok...sounds like a lot. The bearing capacity of good gravel is about 3000 psf...and no so good ground about 1,000 psf. Using the 1000 psf number you need 44 sq ft of bearing area. across four corners that's 11 sq ft per corner. An 11 sq ft foundation is 3.3ft by 3.3 ft. Not very much. I'm building a 12 by 16 on days off. I'm doing it in winter so no concrete for now. IN the time being I'm going pioneer style on a tree stump or two and log cribs. If you like you can fill the cribs with gravel and river rock. I suspect the log cribs will last decades, but I'll replace it with concrete. And before you ask, it will settle. That's a good thing. Soil gains bearing capacity by making it denser. To make it denser you have to compact it. ONe of the best ways to compact soil is to to put weight on it. If you are on permafrost put some styrofoam insulation between teh crib and the ground. Once it freezes up life is good.
    Thanks for the input Trailblazer Steve and AK Steve. Trailblazer Steve, nice looking cabin. I was wondering a few things about it. I noticed that you have a few log posts underneath your cabin and your deck. Are those just cosmetic, since you supported your cabin with cribbing? Or are they also there to support your cabin? Also, when you sheeted underneath the cabin, did you do anything to allow it to breath, like drill holes in it? If it is not breathable, how did you prevent water from getting trapped in the floor while you were building the cabin?

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    To be honest when I built the cabin I thought I did enough research but found I put the outside beams to far inside from the outside of the building and noticed the cabin starting to "bow" slightly. I think I went in 4 feet from the sides. I quickly doug down to gravel and placed 12" dia logs on all four corners and since I had left overs I placed them along the sides also. The cabin hasn't moved since. I like the way it looks and hope to skirt between them one day with something nice. I put the insolation in the floor after the roof was on. It was kinda a pain rolling around under the cabin but since I built off of a hill it wasn't that bad. The bottem of the floor is covered everywhere except inside the cribs so there is breathable room. But like I said, it's so dry year round and with the critters constantly trying to get in, I'll be closing it up solid when I get the time. I put posts under the deck to help with support as I like to have 2 cords of wood (mostly birch) stacked on it which lasts me just under 3 years of weekend use. Last time we added it up, with the property, material, tools, generator, everything sitting on the property, we have around $130,000 into it. Hope to move there real soon...



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    Quote Originally Posted by Bushwhack Jack View Post
    Hello, I am in the beginning stages of planning to build a 16 X 20 cabin on our remote property. We bought some property out in the Lake Louise area. I know the ground is discontinuous permafrost. I am planning on building my foundation above ground by pouring gravel over the organics and then first building a pad with railroad ties or some type of treated lumber, and then laying pier blocks on top of that. Then I am going to be using adjustable brackets in the pier blocks to attach to the beams that will support my floor joists and floor package. My question is about the gravel that I will be using underneath the railroad ties or treated lumber. Does anyone have any recommendations on what type of gravel to use for this application, and how much of it I should use. Also, should the gravel just be placed underneath the lumber, or should it be continuously spread over the whole entire area underneath the floor? Also, another question I have has to do with the insulation in the floor. Does anyone have any good suggestions on how to insulate the floor? I was thinking about using some type of metal strapping or bracing (or chicken wire etc.) to hold or support the insulation between the floor joists. I would think it would be unnecessary and actually detrimental to sheet underneath the floor, because you would want any water that leaks through the floor when the cabin is being built to drain away and dry out. If you sheeted the floor, I would think any rain water would accumulate in the floor and mold and rot.
    I have built a lot of cabins over the years on bad soils. The foundation and the roof are the two most important things to make a cabin last. Try to dig down to non organic soil for your pads as that will limit settling. If you have gravel or rock in the area use it to build back up to above the ground or moss area and compact it with water. Keeping the wood above any possible water will make it last forever. Tacking a tin water shield on the outer blocking where the roof run off splashes is also a good idea. A couple of 2"x2"s nailed to a foot or two of 6"x6" or stump makes a great hand compacter. You should have at least 2'x2' gravel pads and cribbing. Try to keep your cribbing and gravel pads back under your eves to keep them dry. Just crib up your beams and skip the pier blocks and adjusters. You can always jack it up and level after it settles with shims. Those adjusters are not made for a cabin or house even though some people have used them. They are weak and can fail causing major damage. They are fine for a deck or small shed. Keep at least two feet of clearance under your floor for access and three or four feet would be much better. Also lets the wind take away the heat so it stays frozen under there. Do not remove or cover with gravel any of the moss under the cabin. Moss is what helps keep the ground frozen. If you have permafrost under there you do not want it to start thawing and oozing water and muck or even get a sink hole. Do not skirt it in if you think there may be permafrost as the heat loss from the floor will speed the thawing. Everyone stores stuff under the cabins but keep in mind that it compresses the moss cutting down on its ability to insulate. I would go no more than 8' between pads. More pads means more support. You might cheat on the center beam at ten feet. A log cabin is heavy if that is what you are building with so have plenty of support. Do not set your beams in. Place them on the outer edges so they are in line with the walls. As one of the other commenters noted that he started to get some sag because of his placement. If you used the proper sized JCI's you could skip the center beam. I kind of like regular dimensional lumber for building and built a small bandsaw mill that works great if you have the trees handy. If you are going to use larger logs to build with you should either build your floor inside the logs instead of under it or add an extra floor joist on each end to help support the log weight so it will not start to roll in and down. I usually move mine in the width of the log flat support and then insulate with my scraps in that smaller space. Old timers alway built the walls and got the roof over it and then built the floor on the inside of the first and or second log. That way none of the weight of the wall was sitting on a skinny little 2x and it got the place closed in from the weather quickly so you could do the floor and insulation out of the rain. I would use the 1/4" hardware cloth metal mesh under your insulation. Keeps out the animals and breathes well plus it is easy to haul in. Most water gets held up in the plastic vapor barrier when building in the rain. It can be a problem as it just sits in the valley between the floor joists under the plywood. After you get the roof on and before you insulate the floor (from below) crawl under with your sharp knife point and poke little holes in the visqueen (plastic sheeting) so the water drains if any. The little left will evaporate eventually. Use 6 mil plastic sheeting and buy a roll of the proper tape to fix the holes that you will end up putting in and by accident elsewhere. Stuffing friction fit insulation overhead is a pain and sometimes it does not want to stay. A friend showed me a neat trick for holding it temporarily up until the mesh goes on or the visqueen if working on the roof from inside. Use a very light string and staple gun. Just criss cross where it is needed and staple the string up. Works well if in a windy area also. I try to put my foundation in in the fall as the ground where I may have to dig is thawed under the moss by then or as much as it ever will be. You can do all your cribbing and floor joists but leave the visqueen and plywood off. Come back in March or April before the rains start and do the rest. No bugs and it is quick getting materials in if using a snowmachine. Lots of daylight to work in. Talk your friends (victims) into coming out for a couple of weekends to help get the roof over it. Scott

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