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caducus
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# Posted: 4 Jul 2018 02:13pm
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Anyone have a cabin with r21 or so insulation between 2x6 rafters? What's your climate and how does it perform?
I'm in a very temperate climate. Temps are generally 50-80 deg. Occasionally it can get down to 35 for a night or up to 95 in the day, but it's rare. The site is mostly shaded for all but a few hours of the day in the summer. The few structures we have right now (shed, toilet) have no insulation and are fully shaded and generally are pretty good temps. I DO plan to insulate the cabin but am wondering just how much I need. I'd rather not go up to larger rafters if I don't need to, hence why I'm asking.
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ICC
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# Posted: 4 Jul 2018 02:20pm
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Does the roof need venting between those rafters?
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caducus
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# Posted: 4 Jul 2018 02:46pm
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Nope.
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toyota_mdt_tech
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# Posted: 4 Jul 2018 05:40pm - Edited by: toyota_mdt_tech
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Interesting you mention that. Its required in the walls where my cabin is. I was unable to find it in my home region, we have R19, while, over there, its available in the stores. My home is on the warmer side of the cascade range, cabin is on cold side. We get very long and cold winters at my cabin.
My cabin climate is very cold, R21 should be plenty. Its the roof and floors what will need lots more. I think the roof/ceiling will be a R38 or greater?
It sounds like you may be in a warm region, 35 at night, the R21 would be more than required i bet.
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caducus
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# Posted: 4 Jul 2018 06:22pm
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Pretty warm, yeah. It never hits freezing. I'm less concerned with the cold and more concerned with the heat. I'd hate for the cabin to be way too warm on a hot day.
I'm not sure what my walls will get. But the best I can find for the rafters is r21.
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ICC
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# Posted: 4 Jul 2018 07:18pm - Edited by: ICC
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Deeper rafters = space for more insulation. Sometimes it pays to make the rafters deeper than required for structural reasons and have the space for more insulation. Unless you switch to a foam insulation you have pretty much hit the max R-value for a 2x6
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cspot
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# Posted: 4 Jul 2018 07:48pm - Edited by: cspot
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Personally for the ceiling I would go with R30 for a recreational use cabin and R38 if it is full time or will be in the future. I think it would pay for itself over time and would make it more comfortable. Here is a good resource to see if you do compress insulation and what the corresponding R value is. The 2nd page has a nice chart so you don't have to do the math on the 1st page. 
https://insulationinstitute.org/wp-content/uploads/2016/08/Compressed_R_values.pdf
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caducus
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# Posted: 4 Jul 2018 08:31pm
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Interesting to see those numbers about compressed insulation.
"It will pay for itself." I'm not sure about that. Our woodstove is largely for ambiance and doesn't need to be hyper efficient (and our wood is free) and there's no electrical heating or cooling costs.
Fair point about comfort though.
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cspot
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# Posted: 4 Jul 2018 09:46pm
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In that case then you may be ahead just to go with R-19. You didn't give us all the information. LOL. Only thing to consider is if your situation may change in 10 years and you decide to put in a cooling system. Do you stay there full time or is recreational use? I assume that you haven't built the cabin yet. What type of roof/ceiling are you planning on using? What are you doing about venting?
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caducus
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# Posted: 4 Jul 2018 10:42pm - Edited by: caducus
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Ha. Sorry, I should have been more clear. This being a small cabin forum I assumed it was a given that the cabin was likely small, for occasional use, and lacking in central heating or cooling.
This is a weekend cabin in a very temperate climate. Off the grid. It'll have solar eventually, but that won't power any sort of heating or AC or likely even any fans.
We've got a wood stove which will obviously be in use often for ambiance and keeping the temps comfortable, but it doesn't need to do a ton of work given our temperatures.
I'm still interested in degree of insulation though as sleeping in hot loft is a real pain and I'd rather the place not get cold the second the fire goes out. We don't need much, but we do need some insulation.
Cabin is somewhat built. Walls are framed and sheathed. The roof was going to be SIPs but that deal fell through so I'm currently redesigning the roof. It's a single pitch shed roof.
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cspot
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# Posted: 5 Jul 2018 06:13pm
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This forum has a wide range of people. Some have their main and only residence as a cabin and all the way up to those that have a small shelter that gets used a time or 2 per year.
Maybe someone else can chime in, but I think if you are insulating even a shed roof that you would need something for ventilation between the insulation and the roof. I have never had insulation in a building with a shed roof, so I am not sure how you do that.
I guess the only other question or comment I have is to make sure that 2x6's are large enough for your span and loads where you are building. Maybe if redesigning you may want to consider a prebuilt truss so you would have more roof slope. Just a thought. What is your span length?
As far as the degree of insulation that is kinda difficult. In my experience a loft is always hot. Even in well insulated buildings. The only way it isn't is if you have a ceiling fan running constantly to keep the air circulated. I decided to go against a loft and went with a single floor for that reason in my cabin.
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caducus
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# Posted: 8 Jul 2018 05:43pm
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The spans and rafter sizes are fine. I can size them up for accommodating more insulation, but I don't have to. It's really just a question of how adequate r19-21 is for a cabin seeing that type of use in that type of climate.
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fiftyfifty
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# Posted: 9 Jul 2018 08:03am
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"It's really just a question of how adequate r19-21 is for a cabin seeing that type of use in that type of climate"
Totally adequate. I lived 3 months in a totally uninsulated, unheated cabin in a temperate climate like you describe. It was chilly some mornings, but otherwise fine. If you have a woodstove, you are set. If it gets a little warm occasionally you can open a window.
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