Page 1 of 3 123 LastLast
Results 1 to 20 of 43

Thread: Roof Decking Recommendations

  1. #1
    New member
    Join Date
    Apr 2013
    Location
    Alabama
    Posts
    6

    Talking Roof Decking Recommendations

    Hello, I new to posting on this site, but have been viewing this forum for about two years. During the 4th's holiday I sat down and drew up some plans for a 14 x 16 main cabin w/loft, side room and porch with a 10 x 6 enclosed (artic room) for shedding out of the wet clothes and muddy boots and started a materials list for obtaining pricing. Using prices from Northland Wood's website. I have read from books, forums and the AK Extension Service about the proper way to insulate a cold climate home. Back in the 80s I installed insulation in homes for a company so that helped out a lot. I have read about how to prevent ice dams from forming on ones house. I fully understand that the roof needs good airflow between the decking and insulation and interior of the cabin be tightly sealed off from air leaks. My question is what size decking would you use under a metal roof to deal with the snow load in the Mat Su region. Rafters will be 2 x 12s on 24" centers 12/12. I saw somewhere where someone just used purlins. Sorry for everything running into one paragraph. The enter key doesn't seem to be returning to start a new paragraph. Thanks, Dan

  2. #2
    Member
    Join Date
    Apr 2006
    Posts
    2,919

    Default

    You could at the very minimum use 7/16" osb but you have to use clips midway between rafters. I recommend 5/8 OSB. I don't like purlins at all. If you ever need to walk on the roof or lean on it and miss a purlin you will bend the metal

  3. #3
    Member
    Join Date
    Apr 2006
    Posts
    2,919

    Default

    The problem with ice dams back in the day was that where the roof meets the wall the HAP was only 5 1/2" so it allowed too much heat to escape the home. New constriction and trussed now have an 11 1/2 inch which cures the ice dam problem by allowing 9 1/2" insulation at the wall vs 3 1/2"

  4. #4
    Member dkwarthog's Avatar
    Join Date
    Dec 2006
    Location
    Mat-Su
    Posts
    2,150

    Default

    They make styrofoam baffles that you install right under the roof sheathing between joists and give you 1.5" of air space under the roof deck. Then put the insulation under that and vent either at the ridge or thru an attic space to the gable walls. At 12 in 12 pitch its questionable that you will have enough snow standing on the roof to cause an ice dam anyway...

  5. #5
    Member cdubbin's Avatar
    Join Date
    Mar 2009
    Location
    KP, the dingleberry of Alaska
    Posts
    1,749

    Default

    Quote Originally Posted by Bear View Post
    You could at the very minimum use 7/16" osb but you have to use clips midway between rafters. I recommend 5/8 OSB. I don't like purlins at all. If you ever need to walk on the roof or lean on it and miss a purlin you will bend the metal
    You can walk on a 12-12 metal roof, Dave? Sounds like a trick another carpenter pulled once .....purlins are ok (2x4) on a roof that steep, not the industry standard but ok for a cabin. Use drip edge flashing and hang the edge of the roofing over 1.5" at least.
    " Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

  6. #6
    Member 4merguide's Avatar
    Join Date
    Feb 2012
    Location
    Kenai Peninsula, Alaska
    Posts
    9,748

    Default

    The thing is, that if you go 12:12 pitch with a metal roof you aren't going to have any ice building up anyway. And if by chance somehow you do, you shouldn't have any seam in your metal that water can back up under. I have a 12:12 w/ metal roof on part of my house and I never get any ice build up there.
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

  7. #7
    Member dkwarthog's Avatar
    Join Date
    Dec 2006
    Location
    Mat-Su
    Posts
    2,150

    Default

    To answer your question, I'd use 1/2" CDX plywood under the metal roof. Roof rafter joists on 16" centers. The metal h clips are a pain in the butt especially if your working alone. Ring shank nails from a framing nailer and a young guy with a strong back to lift the sheets up onto the roof...
    Good luck...

    edited to add that I think bear gave you good advice, I missed the 24" centers...

  8. #8
    Member
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    3,293

    Default

    I've used 7/16 OSB for most of my roof sheathing and the last addition I used 1x4 slats. The plywood sections have been there for 22 years and other then the metal is discolored from accumulated birch sap the roof is perfect. The 1x4 slat section while younger requires me to re-torque the roofing screws every year and a few screws will be totally gone. Apparently the heating/cooling cycles work the screws out. On the slatted section the roof pops and creaks withing seconds of the sun hitting it. The plywood sections are quiet through the day. I'll never use slats again.

    By the way, my rafters are on 24" centers. No clips on 12/12 or 8/12 pitches. I didn't use raised heels for insulation. Not important on an occasional use cabin. Once the metal gets dirty ice and snow will stick to 12/12 pitches very well.

  9. #9
    Member 4merguide's Avatar
    Join Date
    Feb 2012
    Location
    Kenai Peninsula, Alaska
    Posts
    9,748

    Default

    Quote Originally Posted by Mr. Pid View Post
    Once the metal gets dirty ice and snow will stick to 12/12 pitches very well.
    Well I guess mine doesn't get dirty.....
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

  10. #10
    Member Redlander's Avatar
    Join Date
    Apr 2006
    Location
    Now in Anchorage
    Posts
    391

    Default

    I just finished a little roofing project for our small cabin up on the Yentna River; its 10' x 26' with 12:12 pitch roof. I used WIP 400 LT underlayment on the recomendation of one of the lodge owners in the area, that I got from Spenard's Building Supply (SBS), http://www.carlislewipproducts.com/Underlayments.aspx. The roof has the 7/16 OSB. Due to how sticky that stuff is and how steep the roof is, I ran it down from up and overlapped it about 1.5 inches. Then put on dark green Suntuff from Home Depot; no metal due to budget and the $0.20 per pound for freight. If I get time, I'll post some photos of the project. It was one of the scarier activities I've ever done. If you can, use scaffolds around the perimeter and for God's sake wear a harness system. You'll need some sort of ladder system to work your way around. One of our neighbors fell off a roof last year and broke a femur and his pelvis. I believe I'd rather have a bear encounter than work on that roof, but you gotta do what you gotta do.

    When we bought the cabin, it had heavy plastic and blue tarps on 16 linear feet of the cabin. Now I don't worry about a leaky roof.

    I really, really don't think you need 2x12s for the rafters, especially with a steep roof pitch. You need to check the engineering recomendations, but you measure the strength vertically through the rafter with it on angle. Mine has 2x6 and only if you are really worried would I suggest 2x8. If you get the place built and don't live there, pay a local a little bit to come by and shovel the roof if you are really worried. On a 12:12 pitch, it should take them very long.

  11. #11
    Member dkwarthog's Avatar
    Join Date
    Dec 2006
    Location
    Mat-Su
    Posts
    2,150

    Default

    Alot of the reason for a 2x12 is so you have insulation space along with an airspace when building a vaulted ceiling. But I'd agree that 2x12s are excessive structurally for a 12:12 pitch..

    Also, it may not be in your budget, but if so, I highly recommend spraying urethane foam in your roof for your insulation. That stuff is phenominal and in addition to helping keep the heat in, it does alot to keep your house cool on the few days we get that are really hot. Weve got 10" of rigid urethane in ours and I am really happy with it.

  12. #12
    New member
    Join Date
    Apr 2013
    Location
    Alabama
    Posts
    6

    Default

    I appreciate everybody's input. My intent when starting this project the first year is to get the exterior finished and the interior 75% complete. Get a outhouse and a long wood shed built. With all that to do, I don't believe I would have any time for getting enough fire wood ready for the cold months. The following year I should be able to relocate and then I will be able to finish the interior, concentrate on getting the food supply built up and firewood ready and a small power system set up. But who knows, things my flow well on the project and the burning desire to stay might take over. I feel the short rafters would work if I did use 2 x 6s but I would hate to have it come back to bite me. I'm not that concerned about the over strength of the 2 x 12s as I am more concerned about having R 30 Insulation.

  13. #13
    Member dkwarthog's Avatar
    Join Date
    Dec 2006
    Location
    Mat-Su
    Posts
    2,150

    Default

    R30 is not enough, IMO. R38 minimum for this country unless its a weekend place only. I think mine works out to about R55 or so...

  14. #14
    New member
    Join Date
    Apr 2013
    Location
    Alabama
    Posts
    6

    Default

    DK, I would consider spraying. I saw on the TV on Building Alaska the Guide on Kodiak building his lodge and saw where a guy came out an sprayed his walls and ceiling. I will have to do some research and find out what the pricing is on that. It would definitely be a quicker and easier process. What is your setup to obtain a 55?

  15. #15
    Member
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    3,293

    Default

    You're over thinking a 14x16 cabin. Mine's better than twice as big and has been cozy for all these years with 2x8 rafters and R-19 insulation. Being too warm is a constant problem. Good luck with your dream.

  16. #16
    Member dkwarthog's Avatar
    Join Date
    Dec 2006
    Location
    Mat-Su
    Posts
    2,150

    Default

    I need to take a course in reading comprehension. I just went back and saw that it was a 14x16, I was assuming that you were building a larger bldg, as a main home. Mr Pid is correct as he usually is regarding overthinking things, and I wasnt helping... good luck

  17. #17
    Member Redlander's Avatar
    Join Date
    Apr 2006
    Location
    Now in Anchorage
    Posts
    391

    Default

    Quote Originally Posted by DanNbama View Post
    I appreciate everybody's input. My intent when starting this project the first year is to get the exterior finished and the interior 75% complete. Get a outhouse and a long wood shed built. With all that to do, I don't believe I would have any time for getting enough fire wood ready for the cold months. The following year I should be able to relocate and then I will be able to finish the interior, concentrate on getting the food supply built up and firewood ready and a small power system set up. But who knows, things my flow well on the project and the burning desire to stay might take over. I feel the short rafters would work if I did use 2 x 6s but I would hate to have it come back to bite me. I'm not that concerned about the over strength of the 2 x 12s as I am more concerned about having R 30 Insulation.
    Build the outhouse first. Seriously, pooping on a bucket in the rain while the mosquitoes try to bite you where the sun don't shine is only fun for short periods of time.

    You are going to find out your definition of hot and cold is going to change a bunch, and you are only talking 224 sq.ft. to heat. The guy that built and sold us the cabin quit on his quest to insulate the roof because..., it was too warm. He said with his little kerosene heater that he could sleep upstairs comfortably at -30 with only a decent blanket on his cot with foam padding. I'm installing windows that open and shut "upstairs" just to be able to sleep cooler spring thru fall. Since I've only been there May thru Sep timeframe, I've spent more time hot than cold.

    My wife worked the Iditarod as a vet this year and she said she was thankful she carried her shorts for the times she was able to be inside, otherwise, all her other clothes were overdone.

  18. #18
    Member
    Join Date
    Apr 2006
    Posts
    2,919

    Default

    Wow this thread turned interesting. This is the first time in my 25 years in the building trade that I ever heard anyone complain about too much insulation... Lol. Personally I would rather use less resources, oil , fuel,wood or whatever to heat vs having lack of insulation control it for me ..

  19. #19
    Member 4merguide's Avatar
    Join Date
    Feb 2012
    Location
    Kenai Peninsula, Alaska
    Posts
    9,748

    Default

    Quote Originally Posted by Bear View Post
    Wow this thread turned interesting. This is the first time in my 25 years in the building trade that I ever heard anyone complain about too much insulation... Lol. Personally I would rather use less resources, oil , fuel,wood or whatever to heat vs having lack of insulation control it for me ..
    Agreed......
    Sheep hunting...... the pain goes away, but the stupidity remains...!!!

  20. #20
    Member cdubbin's Avatar
    Join Date
    Mar 2009
    Location
    KP, the dingleberry of Alaska
    Posts
    1,749

    Default

    Quote Originally Posted by Bear View Post
    Wow this thread turned interesting. This is the first time in my 25 years in the building trade that I ever heard anyone complain about too much insulation... Lol. Personally I would rather use less resources, oil , fuel,wood or whatever to heat vs having lack of insulation control it for me ..
    The problem is with a woodstove there's so little control....when you get home and the cabin is freezing you load up the stove and it takes hours to warm the structure up...then about 2 am you wake up nearly dying because that load of wood kicked and the loft is now 100 degrees lol
    " Gas boats are bad enough, autos are an invention of the devil, and airplanes are worse." ~Allen Hasselborg

Page 1 of 3 123 LastLast

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •