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Dustin79
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# Posted: 17 Feb 2013 03:03pm
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I have just found this site, I find myself addicted. I have some land, and have been planning a small 16x20cabin. I have to admit I don't have much consturction experience, so I have been reading up. I would like to run my roof by everyone. Some feedback would be nice for whoever has time to help. Going to be a gable roof, 5/12 pitch, 30lb snow load, no loft, just attic space maybe with a few boxes stored up there. I am not going to insulate my rafters, but insulate my celing joists & I can always add more insulation to keep the cold out. I figure since this is my first roof/cabin, might be a good idea to leave the roof open, to watch/repair any mistakes. Using 2x6 rafters spaced 24"on center with 2x8 ceiling joists & a 2x8 ridge board. Using metal roofing. Would this work? Want to make sure my family is safe.
Dustin
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Borrego
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# Posted: 17 Feb 2013 07:59pm
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Welcome - Where are you located? What is the wind like? 8 ft walls or 10 ft?
And what do you mean by leaving the roof open?
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MtnDon
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# Posted: 17 Feb 2013 11:05pm - Edited by: MtnDon
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Quoting: Borrego leaving the roof open?
Me too on that head scratcher...
Your roof design will work with 2x6 rafters on 24" centers with pretty much any of the commonly available grade 2 dimensional lumber species.
2x8 ceiling joists might be another matter depending on what species and grades you have available and also dependent on what the attic load will be and what material is used for the ceiling panels itself. 16" centers make it better for some species/loads. Give that a think and check on what species are available to you. Grade #2 is the common grade. Species vary around the country.
You can use the AWC Calc for both rafters and ceiling joists, as well as floor joists. Note
: for an uninhabited attic with NO storage LL (live load) is usually considered to be 10 PSF. Uninhabited attic with limited storage is usually rated for 20 PSF LL. DL (dean load, the joists, ceiling, etc) is usually taken to be 10 PSF.
A 5/12 pitch roof puts more force on the heel joint, the connection of rafter to ceiling joists, than a steeper pitch. For the span and snow load you have 6 or 7 - 16D Common nails should be used as a minimum on each of those connections. Try to space them evenly and keep then an inch from any rafter or joist edges.
Blown in cellulose makes an excellent insulation for a ceiling like that. That's what we have; about R45 total. There is not much headroom in a 5/12 attic 16 ft wide. I laid a strip of 2 ft wide osb down the center from end to end. Used that to crawl on while blowing in the cellulose. Blew it under the osb and then piled it on top.
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Dustin79
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# Posted: 18 Feb 2013 12:06pm
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Can you tell I am still learing? My terminology is terrible. Pay no attention to the "open roof" comment...I am exhausted, can you tell? Open roof to me is not insulating inbetween the rafters, and just blowing in on top of the ceiling joists. So, sorry about the confusion, bear with me.  Going with 8' walls. I am in Illinois, in the range of 15-30 SPF snow load. I am more central, so I assume the 30 is for up north...but to be safe, just going off of 30 psf. I think I will just go with 2x6s rafters on 16" on center, and use 2x8s on 16" on center for the ceiling joists. Looked at the AWC, 2x8s are plenty strong, just as long as I am on 16"oc.
Talking things out is great, your help is greatly appreciated!!
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MtnDon
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# Posted: 18 Feb 2013 12:17pm
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G/L with the project!
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