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  • Replacing the roof deck - what material?

    What thickness and grade of plywood or OSB should be used for my roof decking? I own a bungalow that was built in 1960. My 25 year shingles have just about fried off (in 14 years) and every time I go up there to check things out the roofing plywood is so weak I think I am going to end up in the living room. The boards are not rotten, they are just too thin or too weak or both. I have decided to replace the roof, plywood, shingles and all. Is there any advantage to using plywood over OSB? Will I get better cost vs performance with OSB?
    thanks,
    Andrew

  • #2
    Re: Replacing the roof deck - what material?

    Originally posted by athuswal View Post
    What thickness and grade of plywood or OSB should be used for my roof decking? I own a bungalow that was built in 1960. My 25 year shingles have just about fried off (in 14 years) and every time I go up there to check things out the roofing plywood is so weak I think I am going to end up in the living room. The boards are not rotten, they are just too thin or too weak or both. I have decided to replace the roof, plywood, shingles and all. Is there any advantage to using plywood over OSB? Will I get better cost vs performance with OSB?
    thanks,
    Andrew
    3/4 inch plywood is the way to go. Some guys even use rough lumber planks but the danger is the dry out phase which could cause them to shrink quite a bit.

    OSB is cheaper, but watch it go to mush if it gets wet.

    Depending on how long you are planning on staying, a metal shingle roof might be a more economical route in the long run.

    Don't skimp on your sheathing. And don't go thinner than 3/4 inch....
    I'm on "The List" and I love it!!

    Comment


    • #3
      Re: Replacing the roof deck - what material?

      Forgot to mention.....check your rafter ends as well for weakness. I would assume in 1960 the deck was rough boards - should be at least 3/4 inch, maybe they were only 1/2 inch. In any case....spongy = BAD.
      I'm on "The List" and I love it!!

      Comment


      • #4
        Re: Replacing the roof deck - what material?

        I too, like to use 3/4, I hate OSB, but I'm forced to use it due to the cost factor. I have seen many companies go to 1/2"(Fools!!!), but I would never do this. Tinman says 3/4" plywood and I agree...
        Great Link for a Construction Owner/Tradesmen, and just say Garager sent you....

        http://www.contractorspub.com

        A good climbing rope will last you 3 to 5 years, a bad climbing rope will last you a life time !!!

        Comment


        • #5
          Re: Replacing the roof deck - what material?

          Originally posted by garager View Post
          I too, like to use 3/4, I hate OSB, but I'm forced to use it due to the cost factor. I have seen many companies go to 1/2"(Fools!!!), but I would never do this. Tinman says 3/4" plywood and I agree...
          Exactly....tongue and groove 3/4 inch is the ultimate, then 3/4 standard after that. I understand though, that most stuff being built today is using OSB - it is to code after all. Watch any renovation show and they're all using OSB.

          Just makes me wince every time I drive by a house being built and the rain is smashing down on the OSB on the roof and walls. It's OK if you're gonna sell at a profit in a few years.....not so much if you're gonna plan to retire there. If I was flipping a house for quick sale I'd be all over it. As far as my own place though.........not so much.

          As you noted, Garager, 1/2 inch anything is for fools even 5/8.
          I'm on "The List" and I love it!!

          Comment


          • #6
            Re: Replacing the roof deck - what material?

            Thanks for your advice Tinmack and Garager!

            Andrew

            Comment


            • #7
              Re: Replacing the roof deck - what material?

              If you're redoing a roof and it has old plywood (looks to be at best 1/2 inch) would laying another 1/2 inch on top help stiffen everything up or should the original be removed and new 3/4 inch layed down?

              Comment


              • #8
                Re: Replacing the roof deck - what material?

                Interesting suggestion. I don't think it will be equivalent to 1" of plywood but it may be as effective (and less expensive) than tearing out the existing plywood and installing 3/4". I'd be interested in hearing what others have to say about this.
                Andrew

                Comment


                • #9
                  Re: Replacing the roof deck - what material?

                  I have added more decking material on many occasions. But before anyone is to do this, you must look at your rafters/trusses to make darn sure you can do this. Remember, someone else will eventually own the home you are living in.

                  I don't know about all of the states, but for MN. you can have up to 3 layers of asphalt on your roof. Think about all this weight, grant it, it is a distributed weight, but never the less that's a lot.

                  As long as you hit/nail a rafter under the first layer of plywood, when applying the new decking. Your roof will be very strong. But if you have rot anywhere on that roof and your just covering it up, well that's not good.

                  About the only time I do add a decking over an existing one is due to gaps between boards. The old days, they used 1"x 6"-8"-10"-12"-14" and there was 1"-2" gaps between each row. Then some boards cracked to much, or lost a huge knot, etc. And usually this will also have me in the attic putting up bracing in some areas, because I added another layer of decking.
                  Great Link for a Construction Owner/Tradesmen, and just say Garager sent you....

                  http://www.contractorspub.com

                  A good climbing rope will last you 3 to 5 years, a bad climbing rope will last you a life time !!!

                  Comment


                  • #10
                    Re: Replacing the roof deck - what material?

                    Originally posted by garager View Post
                    I have added more decking material on many occasions. But before anyone is to do this, you must look at your rafters/trusses to make darn sure you can do this. Remember, someone else will eventually own the home you are living in.

                    I don't know about all of the states, but for MN. you can have up to 3 layers of asphalt on your roof. Think about all this weight, grant it, it is a distributed weight, but never the less that's a lot.

                    As long as you hit/nail a rafter under the first layer of plywood, when applying the new decking. Your roof will be very strong. But if you have rot anywhere on that roof and your just covering it up, well that's not good.

                    About the only time I do add a decking over an existing one is due to gaps between boards. The old days, they used 1"x 6"-8"-10"-12"-14" and there was 1"-2" gaps between each row. Then some boards cracked to much, or lost a huge knot, etc. And usually this will also have me in the attic putting up bracing in some areas, because I added another layer of decking.
                    Does adding another layer of 1/2" plywood onto existing 1/2" OSB apply to factory manufactured trusses? The reason I ask is these trusses are basically 2"x 4" and whether they can handle this load?

                    Comment


                    • #11
                      Re: Replacing the roof deck - what material?

                      First off, I'm not an engineer, but manufactured trusses are more than likely able to handle this weight. Most trusses are made from 2"x 4"s, its the design of them which makes them strong. If you already have only a 1/2" decking, adding another 1/2" shouldn't affect the design load. The pitch of your roof has a big factor involved too. A 4/12 pitch can sag in your roof easier then a 8/12 pitch. But whoever designed those trusses, takes all that into consideration. Once again I wouldn't worry. What kind of attic ventilation does your home have??????
                      Great Link for a Construction Owner/Tradesmen, and just say Garager sent you....

                      http://www.contractorspub.com

                      A good climbing rope will last you 3 to 5 years, a bad climbing rope will last you a life time !!!

                      Comment


                      • #12
                        Re: Replacing the roof deck - what material?

                        Originally posted by reConx View Post
                        Does adding another layer of 1/2" plywood onto existing 1/2" OSB apply to factory manufactured trusses? The reason I ask is these trusses are basically 2"x 4" and whether they can handle this load?
                        I'm not an engineer or carpenter by any means, but I've always noted in various places the thing about wood needing to breathe. Therefore, I'm not sure stacking sheathing on top is such a good idea without taking ventilation into consideration. As well, plywood and OSB both swell/contract at different rates when moisture/heat/humidity is factored in, so I don't think stacking different sheathing may be such a good idea. Then again, if you're not in a snow region it's probably a moot point. If you've got OSB now, and you want to stack another 1/2 inch on it, I'd stick with OSB. Myself though, if the budget allowed for it, would strip off the OSB and replace with 3/4 inch plywood. That's just my opinion though, based on what little experience I have in the home renovation game.
                        I'm on "The List" and I love it!!

                        Comment


                        • #13
                          Re: Replacing the roof deck - what material?

                          Originally posted by garager View Post
                          First off, I'm not an engineer, but manufactured trusses are more than likely able to handle this weight. Most trusses are made from 2"x 4"s, its the design of them which makes them strong. If you already have only a 1/2" decking, adding another 1/2" shouldn't affect the design load. The pitch of your roof has a big factor involved too. A 4/12 pitch can sag in your roof easier then a 8/12 pitch. But whoever designed those trusses, takes all that into consideration. Once again I wouldn't worry. What kind of attic ventilation does your home have??????
                          Thanks, the resale values of these 4500+ sf homes are embarrassingly high yet the materials used during construction would make you (custom builder) cringe. 1/2" OSB roof and 1/2" fiber board for walls on 2x4 walls. Energy efficient, meets building codes but no need for kicking in the doors just use a cordless black+decker saw to break in. Got dogs + perimeter defense system + glock (kidding)
                          Any way the ventilation is ridge + Soffit vents system.
                          Last edited by reConx; 06-28-2008, 11:10 AM.

                          Comment


                          • #14
                            Re: Replacing the roof deck - what material?

                            Originally posted by reConx View Post
                            Thanks, the resale values of these 4500+ sf homes are embarrassingly high yet the materials used during construction would make you (custom builder) cringe. 1/2" OSB roof and 1/2" fiber board for walls on 2x4 walls. Energy efficient, meets building codes but no need for kicking in the doors just use a cordless black+decker saw to break in. Got dogs + perimeter defense system + glock (kidding)
                            Any way the ventilation is ridge + Soffit vents system.

                            Looks like you're as ventilated as you can get. I've seen insulation jammed into the soffit venting in the attic sometimes, though, so you might want to keep an eye on that if you're doing some renovations. Keep those soffit vents clear or you'll have moisture problems.
                            I'm on "The List" and I love it!!

                            Comment


                            • #15
                              Re: Replacing the roof deck - what material?

                              Originally posted by athuswal View Post
                              What thickness and grade of plywood or OSB should be used for my roof decking? I own a bungalow that was built in 1960. My 25 year shingles have just about fried off (in 14 years) and every time I go up there to check things out the roofing plywood is so weak I think I am going to end up in the living room. The boards are not rotten, they are just too thin or too weak or both. I have decided to replace the roof, plywood, shingles and all. Is there any advantage to using plywood over OSB? Will I get better cost vs performance with OSB?
                              thanks,
                              Andrew
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