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MJW
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# Posted: 1 Feb 2013 12:38pm
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Trying to make a decision on how to insulate our cabin and was hoping to get some feedback on people that have used different methods.
We will be needing to insulate underneath the floor joists and the interior walls. No ceiling insulation needed as that will be handled in the roofing process using the 2 inch foam between the interior ceiling finish and the roof metal sheathing I have mentioned earlier.
Our ceiling rafters will be exposed.
I have found several different ways to get it done.
1. Spray foam under joists and interior walls.
2. Rigid Foam cut to fit the space with foam around the edges.
3. Standard fiberglass batts.
I really would like to get the spray foam done but have no idea on the costs and have concerns on how it will hold up under the floor joists exposed to the elements.
Any ideas or suggestions from those that have gone here before?
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mjmmessina
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# Posted: 1 Feb 2013 12:51pm
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I used Fiberglass on my walls and rigid foam in between floor joists in my cabin. Has worked very well for me. I looked into spray foam but it was not cost effective for a cabin that I use part time.
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bobbotron
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# Posted: 1 Feb 2013 01:21pm
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I'd go with roxul in the walls. It's nice stuff and better to work with.
I know you didn't ask, but in my opinion 2 inches of foam in the roof isn't much. If that's your only ceiling insulation and you're in the north, I'd opt for more, like 5 inches or more. It's roughly... r5 or 6 per inch? 2 is roughly R10, R12... 6 inches would be more like R30. Still not great for a roof, but not terrible. It'll get $$$$ but you only do it once.
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GomerPile
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# Posted: 1 Feb 2013 02:23pm
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Complicated answer:
Fiberglass is by far the easiest to work with.
Having just installed 2 huge pallets of rigid foam on the exterior of my place, I can only imagine what a pain in the rear it would be to install it into bays and them foam them up. To top it all off, two sheets of 2 inch rigid foam is only R20...same as fiberglass. If you leave any air leaks the rigid foam will not allow moisture to escape and you will get mold.
If you go with spray in foam you must apply a layer thick enough so that on the coldest day your dew point stays inside the foam. Typically that 3-4 inches depending on climate. You can fill the rest of the bay with blow in cellulose to save some $$$. This solution will probably produce the highest performing wall assembly.
If any of this is exposed to the outside as in a crawl space I would not use fiberglass....probably go with rigid and seal it up real well.
Better make sure that 2 inches of roof foam is right for your climate zone. On colder days you may find that the backside of your roof sweats. If you choose the spray in foam method you can add more "R's" on the inside if needed.
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MtnDon
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# Posted: 1 Feb 2013 03:14pm - Edited by: MtnDon
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My thoughts on what type to use...
... walls; wet blown in cellulose for walls. That should be enough in most climates. If climate is extreme (hot or cold) then I'd add rigid foam around the exterior, OR go all spray in foam in the wall cavities. The thing I like about exterior foam is it breaks the thermal conductivity of the studs.
... raised floor; spray in foam is first choice. Fibreglass next as long as it is sheathed under the joists with something like 3/8+ plywood.
... cathedral ceiling roof; If the actual roof rafters are visible from the inside exterior rigid foam, 2 or more layers, staggered seams.
How much R-value to use, and we're talking full time or major time residence, not some place that will only be visted two weeks a year. I'd use nothing less than the recommended R for the climate zone. And, even though it was not asked, I'd be certain to build with the best windows I could afford even if that meant not finishing the interior as quickly or perhaps installing lowest cost counter tops instead of the premium ones desired. My reasoning on the R-values and the windows is that once the structure is all buttoned up it is costly to add insulation or change windows. Countertops are an easy remodel. Ditto for maybe painting the plywood or OSB subfloor and installing the nice hardwood flooring or tile at a later date.
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MJW
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# Posted: 2 Feb 2013 01:23pm
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MtnDon,
I agree with you on the windows and we have chosen good ones.
I based my roof insulation on a fella a met a few weeks back and how he had done his building that was a bit smaller than we are planning. He is in the same "zone" we are with regard to weather, etc.
He said he was quite satisfied with the results from his 2 inch foam but I can see where 2 layers could be even better.
How would you propose the installation of the 2 layer system?
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MtnDon
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# Posted: 4 Feb 2013 04:19pm
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Quoting: MtnDon I'd use nothing less than the recommended R for the climate zone.
There is not a climate zone anywhere in the USA that recommends less than R30 for a ceiling/roof.
Two inches of XPS is only R10.
When we first built our cabin I installed R13 batts in the ceiling, then did the finish T&G ceiling. The plan all along was to start with that because it was quick and had the vapor retarder built in (the kraft paper facing). It took a year to get to the point of blowing in the cellulose on top of the f-glass in the attic. It made a world of difference to summer comfort and to speeding up the winter warm up. (We're at about R45 on the cabin ceiling and R50 at home.)
That's me and my preference. Being an attic it was easy to add. If there was a cathedral ceiling it's a whole different scenario; harder and more expensive to add.
Building size does not really matter, heat still moves from warm side to cold side.
Two or more layers of rigid foam means the seams between panels are offset. Foam panels are held in place with some long screws through to the rafters. Then the top sheathing is also screwed down with long screws to the rafters. That all requires some careful measuring to get the alignment to the rafters.
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redwoodgirl
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# Posted: 8 Mar 2013 05:32pm
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does anybody have any experience with self-made cellulose insulation?
i got a lot of paper dust from my uncles paper mill and am wondering if i can use it to make my own cabin insulation if i add glue and boric acid to make it fire and pest retardant.
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Birchwood
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# Posted: 1 Apr 2013 08:13am
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MJW, I have done much remodeling over the years being a carpenter in the Midwest. That doesn't make me an expert but does give me some real life experience. I have pulled my fair share of moldy, collapsed insulation out of walls. I've lived in drafty places and watched my breath turn to water on the windows. I've read the 'Hype' and watched systems fail (housewrap etc), usually blaming it on installation error. I ended up using the spray foam on my 16x16 stick-frame cabin. I do plan to live in it full time so I justified the expense. Here's what I found: It adds considerable rigidity to your structure, seems to be more sound proof, quite resistant to bugs, and waterproof. I did 5.5" in the walls, 8" in the floor and rafters. You do end up with a vault. That is good from a heating/cooling standpoint, but I have noticed I need to add some controlled fresh air intakes. Nothing is perfect, but it really exceeded my objective of no condensation and to heat it with a candle.
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