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NateVT
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# Posted: 29 Oct 2015 12:11pm - Edited by: NateVT
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Hello everyone - great site! I've spent lots of enjoyable time reading the posts on this site and really appreciate everyone sharing their knowledge (and pictures!).
I'm going to be building a 16x20 cabin next spring/summer and I've been doing lots of research on keeping it warm. My plan is to use light insulation in the walls (1" polyiso foam) with 2" of the same in the roof and floor. Cabin size of course will be 320 square feet, roof pitch is 8/12 so gable height is around 14'. I have a wood stove I'll be using - a Jotul Nordic. The stove is rated to heat 1000 square feet. From everything I've read in books and online - this should be plenty to keep the cabin warm.
I guess I'm frankly confused about the use of heavy insulation (R30 etc) in a small cabin *if* people are using a wood stove. Do people only insulate this much if they're using propane or a similar heat source?
I have a 12x12 wall tent that I heat with a small steel stove and it gets plenty hot in there when temps outside around freezing - often too hot. I've also stayed in a 400 square foot cabin that was not insulated, with outside temps in the low to mid 20's - the stove kept the cabin hot enough that we were opening windows for relief.
I must be missing something here! So those of you who "super insulate" your small cabin - could you illuminate me as to why? Given that wood stove don't like to be choked down (creosote) are you using a different heating source?
Thanks for reading! I'll look forward to your replies.
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thes10kid
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# Posted: 29 Oct 2015 02:30pm
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Nate,
I am in Southern VT and have been wondering the same. I spent last weekend in an uninsulated cabin on a mountaintop and it was snowing. This was not a true log cabin, just a simple post-and-beam cabin with board and batten siding. I stayed very warm with that woodstove, and even had to open the door on a few occasions to let heat out (about 300sq cabin). This allowed me to form two cabin concepts. Either an insulated building with a "mini" woodstove like the Cub, or a full-size wood stove and an uninsulated (or minimally insulated) cabin. Now this is not exactly what you were asking, but it seems like I stayed in a cabin similar to what you plan to build, and stayed quite warm...
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Steve_S
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# Posted: 29 Oct 2015 02:56pm - Edited by: Steve_S
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Welcome Nate !
The more insulation you have the less will be required to get the heat up and to keep it in.... Also in the summer, it means less heat transfer into the cabin for those Hot & Sweltering days and if you have Air Conditioning in your cabin, it will reduce how much that runs.
I love PolyISO, easy to work with (cutting & fitting), light, great insulation R value and critters dislike it ! Mice & Chippies love batten insulation... Flying Ants & borers will chew up Type-2 EPS and make homes in it... Shocked me when I first say that as I thought they would hate the Blue Foam but I now have a couple of pieces that when split open looks like one of those glass ant farms, filled with eggs to boot.
Buying ISO from "retailers" is expensive and limited in thickness. Call around to Commercial Roofing Companies for "Take Off PolyIso" as they often replace the ISO when upgrading the roofs or if they can supply new product (many do).
The advantage of going through a commercial roofer, is you can get 3", 3-1/2", 4" Sheets in either 4'x4' or 4'x8'. Some will also be able to provide Foil Faced ISO but that's harder to come by.
Super Insulating:
I'm just putting my cabin up now but my Pump/Powerhouse (6x14) is super insulated. I can quite literally warm it with a candle but that takes time... If I use my buddy heater on Low, I can gain 15C / 37F in 15 minutes, shut it off and it stays that way for 12 hrs plus, and that is with the unheated concrete floor.
Ask yourself if you want to be wasting Propane / Wood to heat the cabin & the outside... how many times do you want to chuck wood in the woodstove to stay warm (overnight too !) and in the summer do you want to be cooler & have a cool spot to relax in ?
In my Location in the summer it's nothing to hit 30C/86F with 80% Humidity as an average and in winter -30C/-22F is a typical cold day (that time of yr 0C/32F is a Heat Wave) and besides the Arthritis prefers warm in winter & cooler in summer... (That's my excuse & I'm sticking to it, forget the age part too)
My cabin is setup for Radiant Heating in the slab BUT I am also installing my Jotul 3TD Woodstove which is the smaller Iron unit but my "shack" is only 20x24 with cathedral ceiling and a 12x10 loft over 1/2 the floor space.
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creeky
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# Posted: 29 Oct 2015 03:06pm
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Really depends on your climate. For my studio with r25 walls and r 40 ceiling ... at -35 sure my wood stove keeps the place warm, but how much wood do you want to burn?
Burning wood = cutting down trees, chainsaw in sections, chopping wood into splits, drying, stacking, carrying
And, how much do you enjoy getting up at three in the a.m. every night to restoke the woodstove.
Very practical reasons to superinsulate.
Now, if yer a weekender it might be all romantic to get out of a nice warm bed to go feed the stove at 3.
For me the romance wore off after the first winter. 
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beachman
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# Posted: 29 Oct 2015 03:51pm
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One problem that I am aware of is that if you do not insulate, the roof (and walls) get warm and then you leave and everything turns to ice. You may develop leaks and other moisture problems with no insulation and vapor barrier. VT gets pretty cold at times and for even a small place - it will probably be worth the effort
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bldginsp
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# Posted: 29 Oct 2015 04:57pm
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I don't think the best solution is to use less insulation, the better thing to do is insulate well (and ventilate the attic well) and then adjust your heat source to the need. Better quality wood stoves can be dampered down a lot to reduce heat output. Any wood stove in a 300 sq ft building is too much unless you get an ultra small marine stove. Creosote buildup in the flu is certainly a consequence but you can buy a sweep brush and clean it yourself.
A good combination is a small wood stove and a wall mounted direct vent propane heater. Your small woodstove will not take enough wood for an overnight burn, but the wall heater will kick in at 3 am by thermostat to keep you warm til morning. And the wall heater will provide just a little heat in early fall and spring when a woodstove is too much.
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MtnDon
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# Posted: 29 Oct 2015 05:11pm - Edited by: MtnDon
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Insulate! It's good in summer and good in winter. I wouldn't call our cabin super insulated with R19 walls and floor and R50 ceiling. Well maybe the ceiling is super. I like it very much.
However I feel our cabin has superior air control. I took extra care during construction. Preventing infiltration of cold air is possibly even more important than super-insulation. We are 16 x 30 and heat with wood in a VC Aspen and use propane when the weather is not bone chilling. The VC Aspen is rated to 600 sq ft; still largish for a 320 sq ft cabin.
If you don't insulate and use the aforementioned Jotul there is a good chance you will have areas that are too hot while having areas where you can feel the cold falling off the walls and windows. Plus you will have to cut much more wood which takes time, effort and gas/oil. If you do insulate and use the Jotul there is a good chance you will over heat almost all the time, when the weather is moderate. IMO.
Small cabins that are well insulated are easy to overheat, when using large wood burning stoves. Finding a good suitably sized wood burner is the biggest dilemma faced by those with a smallish cabin. There are not too many made, at least ones that are well constructed.
Is the Nordic a newer stove with lots of firebrick? If it is what I find is they take a while to get everything warmed up and then, if the weather is moderate, the mass continues to radiate heat for hours after the fire has died down. Can be good and can be bad as you can imagine.
To my mind it makes most sense to insulate according to the current energy conservation standards for your area and use a combination of a more suitably sized wood burner and a direct vent wall heater running on propane. Best of all worlds, IMO. Not to mention that when arriving at a cold cabin in winter having the 2 heaters going at the same time warms the building more rapidly.
Also the comments about frost on the interior if you don't insulate are quite valid. The roof could be cold enough at times to cause condensation from your breathing and cooking to form and drip down inside.
Of course my opinion about insulation is predicated upon using the cabin fall through spring.
I'll close with noting that the first winter we used our cabin we only had R13 in the ceiling. It took "forever" to warm up the interior. We added the blown in cellulose and found an amzing difference the second heating season.
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Nate R
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# Posted: 8 Nov 2015 04:04pm
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The problem I'm seeing is that even the small wood stoves apparently can NOT be dampered down too much, or they start to make too much soot and then not meet EPA regs. Most stoves via EPA test seem to make 9K-12K BTUs dampered down. Even the tiny NSW Little Cod makes 10K BTUs on low! This will cook someone out of a well insulated 16x20 in mild weather, and you end up with a fire that just dies faster.
I'm also planning on building a 16x20 in a couple years, and am struggling with the same questions.
The Cubic Mini or the Gray stove (not EPA certified) might be a way to be able to at least reduce the heat output further, but at some point you're not making enough heat to keep the chimney hot enough, I assume.
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NateVT
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# Posted: 9 Nov 2015 01:01pm
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My thinking is - for right or wrong - that a small lightly insulated structure will work much better than a heavily insulated structure when using a wood stove. I'm sure it won't be perfect but I figure if I get too hot, I can open a window or two. If the temps are 40ish, I can run a small propane heater and/or just put on more layers. I'm going to be building a post and beam cabin so my plan is to use rigid foam *over* the sheathing, then another layer of sheathing over that. So the inside will still appear "bare". I've heard this type of insulation called a "poor man's SIP" (structural insulated panel). I'm also going to use the foam over the roofing sheathing with roofing over that - again keeping the rafters bare. I'm figuring to go with light insulation and if for some bizarre reason, I end up too cold - I can get a bigger stove or add insulation to the inside.
Like I mentioned above - I've run a small wood stove in a 12x12 tent and have been plenty warm when it was about 30 degrees outside. Just MHO but I feel a lightly insulated cabin with a small wood stove makes the most sense. Excess heat can be gotten rid of by opening a window as needed.
Nate - where are you building?
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Nate R
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# Posted: 9 Nov 2015 01:25pm
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Nate,
I'm building in northeast Wisconsin.
I'm coming to agree with your thinking on the small structures and woodstoves, especially after I pored over the EPA data, looking at the LOW BTU rating on woodstoves. I can choke it down to a point, but if, for example, 10K BTU is STILL too much, then what? I think the options then are this:
Open a window (if it's only a little too much heat, OK, then this works)
Build bigger
Build less insulated
Buy a used or Non-EPA woodstove that could be choked down more. (The Cubic Mini woodstoves or Graystove)
My own thought: I'll complete the cabin design first (Doors, windows, foundation, etc), and THEN design heating for it with wood, using the best options available to fit the BTU calcs for the design.
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