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Nick32
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# Posted: 30 Jul 2012 10:22am
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Curious as to how many people insulated their cabin floors. I am in MO, it gets cold, but a woodstove puts out a lot of heat. Grew up in a small long cabin in the woods, and in winter we often had t-shirt and shorts on with a window open due to how warm the cabin stayed. Cost and time are no issue with adding insulaiton to floors, but seems like it won't be needed in a wood heated cabin. Any feedback would be appreciated. Starting my cabin soon.
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MtnDon
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# Posted: 30 Jul 2012 10:34am
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We have R25 in our cabin floor. It makes the floor warmer in the cold weather. Walking about without shoes or slippers after the cabin warms is nice. We heat with wood too for the most part, but having a well insulated building in oit's entirety means we have fewer and smaller fires. That means less work cutting wood, less chain saw wear and gasoline and less chimney cleaning.
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Nick32
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# Posted: 30 Jul 2012 10:49am
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Thanks MtnDon. I will go ahead and add insulation, probably would make things easier down the road. Another question. I am building my cabin on 6x6 posts sunk 4' down on a footer with backfill of just dirt. Question is should I add a metal plate, or shingle between the post and beam connection? Thinking of just connecting my beam to post with metal tie plates, or a 1x6. Would this work, or should I use some type of 6x6 post base? Worried if I don't add a metal plate between the post and beam, that over time the beam could bend, or damaged from a wood on wood contact.
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MtnDon
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# Posted: 30 Jul 2012 02:46pm
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I assume the piers are PT wood. foundation grade if you can. If the beams are more than 12 inches above ground level they can be non treated wood. I used a piece of flexible window flashing on top of the post just to assure myself that moisture was not going to travel up the post to the beam. That was probably really not needed. Give termites a thought though. We don't have them up at 8800 feet in northern NM. But if you do then metal flashing can be former to make a cap to help make it difficult for termites to build their mud tubes up to wood they can eat.
Heavy metal plates on the inside and outside of the pier/beam connection can help to make that solid and guard against beam rollover or tipover from lateral forces. Bolted through is better than nails or lag screws. 2x6 PT lumber with no or few/small knots can also reinforce that connection. A vertical length that overlaps the beam and down the pier 12 inches, inside and outside, and through bolted with large washers like those used for J-bolt connections through wall bottom plates can also reinforce that pier to beam connection.
Placing the floor joists between the beams with hangers also can build in rollover resistance, although there is also a lot to be said for placing joists on top of the beams. Probably a toss up.
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vtbros
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# Posted: 30 Jul 2012 06:01pm
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I would insulate the floor. We used the blow in type, but just shoveled it in. It is supposed to be much more rodent resistant than the normal fiberglass type
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Nick32
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# Posted: 30 Jul 2012 06:34pm
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Yes, MtnDon I am going with foundation grade 6x6. I have been tossing around just doing concrete sono tube piers, but to me a small cabin in the woods, just looks more natural and rustic without concrete, even thought the piers will eventually be hidden. I am in a termite area , I figured I would just spary for them for a few times a year. Been reading and seems to me people suggest gravel, or dirt as a better back fill then concrete. But, if concrete would be better, i will drop some in the hole to increase strength. Also, assuming I don't need to connect the post to the footer, will be 4' deep...weight of house should hold post in place?? The Post will rise 12" about soil line, so knowing I don't need PT wood for my beam, joist and subfloor, will save money.
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MtnDon
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# Posted: 30 Jul 2012 07:04pm
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Note that true fopundation grade PT 6x6 will not have any heart wood. That's because heart wood does not absorb the chemical treatment. I mention that in case someone tries to pass off ground contact grade as foundation grade. See if you can find the termite pre building treatment that is used by builders.
Do NOT use concrete around wood posts/piers. DO use a poured concrete footer with rebar in the middle. Do NOT use gravel undder the pier. Refill the holes with the dug out dirt. Pack in in a few inches at a time. A digging bar with a mushroom head works well for this.
If the pier is 12 to 13 inches above grade with the beam on top there is not much room for bracing. Four feet deep for sure; deeper is better from the standpoint of lateral resistance/ 3/4 inch plywood "plates" nailed over the pier to beam connection with lots of nails make a good reinforcement and will help with potential pier tilting.
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Nick32
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# Posted: 30 Jul 2012 07:25pm
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Thanks a lot MtnDon, your feedback & time is appreciated sounds like you are very educated with construction. This is my first cabin, so I still have concerns and have not made up my mind 100% on the plans. I am torn with wood vs concrete piers. I like the idea of wood, but seems that maybe I should go with concrete, then I won't have to worry about foundation grade, termites, or bracing. If I do go with concrete I will place them at 8' oc, going with a 16x24, seems to be a popular size.
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MtnDon
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# Posted: 30 Jul 2012 08:19pm
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Concrete has the advantage of being termite proof! That's good. But even concrete piers, as done by most folks with a couple of feet and more above grade, they need bracing. Bracing is not needed because wood might be weaker than concrete. Bracing is needed as the earth can not be counted on to provide lateral stability. Right now with the drought conditions many posts have the dry earth shrinking away from the post... there goes the stability.
Bracing can be made easier by casting j bolts in the sides and bolting wooden bracing. Or steel. However if they are short above ground and deep below ground you can probably get away with casting some HD Simpson (maybe CB66) brackets into the concrete tops. 8 inch dia would be better than anything smaller.
If that 16x24 is a single story and you have a main beam down each long side, with8 ft OC, doubled 2x12 will take the load. Or tripled 2x8's
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Nick32
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# Posted: 30 Jul 2012 11:16pm
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Well MtnDon after much consideration, I think I have made my mind up to go with concrete piers. Just seems like less worry with concrete & more strenght. Thinking of doing 12 total piers, 3 rows, 4 piers per row at 8' OC. I will do a 16x16x8 footer with 8x8 sono tubes, I will attach the CB66 bracket. I will use 3-2x8x8 as the beam. Should I splice the beam in 3s, or should I use 16' & 8' foot boards for the beam? I am going with 3 rows, so I can use 2x8s & 2x6s as beams and joists. Since I will only have my girlfriend as daily help, I would like to deal with smaller boards. I will bring the piers up above 12", so I can save on the cost of pressure treated wood. Probably will use PT lumber for beams as insurance, and save on the floor. Do you think this is a sound foundation? Overkill? Could I use 9 piers, or should I bump to 15? I will also add the bolts, so I can add bracing. What is the typical lumber dimension for bracing?
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MtnDon
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# Posted: 31 Jul 2012 01:20am
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The best concrete piers are done with the Bigfoot Footing System. Big poly forms that accept the Sonotube cardboard tubes. They do need a large hole (pit) dug to bury them. They are their own footing and an excellent base for the tubes. Google them.
Beam splices should be over a pier. You could do 8 + 8 + 8 but 16 + 8 and then 8 + 16 so not all the splices are over the same pier would be better. The third could be whatever. Many people will laminate two strips of 1/2" plywood between the 2x's for the full length. That's a waste; you only need short pieces of ply at each bracket. Nail the 2x's together about an inch to 1 1/4 in from the edge. With the splices over the piers you only need nails every 32 inches according to code but a nail every 16" is better. Use the plywood as patches between the nailed together 2x's and the metal of the brackets. The plywood does not really add any strength to the laminate. Build the 2x beams on the piers so you don't have to try and lift the completed beam.
I made an error in the beam recommendations; Sorry about that. I got a hinky feeling about the sizes I listed when I re-read that. For a single story with 8 feet between piers supporting a beam down each long side and no center beam you would need three 2x10 to be safe, for a 16 foot wide building. Triple 2x8's would likely be okay if you kept the loading light, no big heavy appliances, no big gun safes, no waterbeds. Very sorry about the error.
You could do this with two rows (8 bigfoot piers) under the outside long walls with triple 2x8 or 2x10 beams. Then use 2x12 x 16" for floor joists on 16" centers. OR go with three rows (12 piers). Then use 2x6 floor joists, 8 foot, 16" centers. For three beams triple 2x8 on the outside beams and a double 2x8 center beam should work. More digging, more concrete vs more wood. The bigfoot system has very impressive lateral resistance numbers in tests I've seen from them. They can probably work well with no bracing materials if you keep them to 18" out of ground.
The rule for PT wood is; beams need to be PT when closer to ground than 12 inches. Floor joists PT when closer than 18 inches to the ground. So if you want to hang the joists between beams go with taller concrete piers and save the cost of the PT wood.
FYI, when looking at the beams, if we look at the beam deflection between piers, a 16 foot 2x across three piers at 8' spacing, will deflect less between two piers than a same size 8 foot 2x between the same two piers. That's why it is better to try and use a couple of 16 footers to make the 24 foot beam. Does that seem clear?
Will you be wanting to skirt the foundation with anything? Or leave the sides open?
(You could start your own thread on this too)
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OwenChristensen
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# Posted: 2 Aug 2012 10:07am - Edited by: OwenChristensen
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I insulate floors in about one tenth of the cabins I build. Floor insulation has little effect in summer compared to cieling insulation. There's not much difference in winter either, unless the space bellow is circulating cold air a lot. I bank up my cabin with snow if there is any. I can insulate floor real well for people and they still wonder why their floor is cool.
Heat rises and the cool air fall to the floor no matter what. On a weekend cabin it's the worst, because it's been cold all week, then everything but the floor warms up first. In northern climates slabs for cabins work terrible as the slab takes two weeks of warmth to get up to a tolerable temps.
Skirting a floor is tough too as the ground freezes it swells up and will buckle it. I did one time make a slip joint skirting for one cabin.
Owen
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GowandaNY
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# Posted: 5 Aug 2012 12:44am
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I used 2" R-10 Foamboard insulation under the floor. Just cut the board to the width of the floor joists and screwed it into the 3/4" plywood with large washers to keep it in place. I think foamboard is the way to go for insulating a floor. You can and probably should put it on top of the ply wood, but then you lose 2" of head room.
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