I am a framing carpenter of all about 3 years, so my expierence is limited to being able to read a tape measure, but barely. My question is this: can I install new roof decking over exsisting shingles. My dad has several out buildings in need of repair,and I will be working for him this summer on the side. The out buildings I will be working on are 40 years old and the rafters are sagging in the middle. The rafters are 2×6 2ft o.c. about 15ft long.There is no ridge.Originally I wanted to put metal roofing on and furring up the low spots in the roof.(ps dont worry I was going to put in ceiling joists and collar ties, in which there are none at this time)The reason I dont want metal roofing,I’m not very familiar with it, building is out of plumb,level, and square.The reason I dont want to tear off old shingles, obvious. (the cost in labor,and dumpster, and mess almost cover the amount in osb,almost)So I guess I’m sold on the idea of putting in sheething over the old shingles (with the help of some furring strips) unless the experts think this is a bad idea. I really dont know. I’ve never seen it done or heard of it being done. So any information you can give me on this would be greatly appreciated. thanks guys!!
Replies
Definetly not. I`m assuming, which I hate to do, that you are speaking of wood shingles? (wood or asphalt doesnt matter, just trying to get a mental picture) Strip the roof down to its decking. Your new roof will only be as strong as your substrate. The fact that you are replacing means that the roofing is failing or at least deteriorating. This is not what you want as your base. Spend the money now or you will most certainly spend it twice later.
J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
ok, I'll bite the bullet and strip the shingles. I really do appreciate all the help. I guess sometimes an idea pops in your head and you think its cool, cause you thunk it up.(if thunk is even a word; minus 5 for grammar)so here we are I'm stripping the roof. Now how do I take the sag out of the roof? Keep in mind guys, Paul E. Wog is on a budget. My idea is to......(dare I say) to sister some 2x8 yellow pine along the side of the sagging rafters. After attaching collar ties and ceiling joists. Also I'm thinking (oh no, here he goes again) that I can get some of the sag out of the middle with the collar ties, and a sledge, and a nice piece of mason line. what are your thoughts? Thanks again man, I hope that when I am an old man with lots of experience like you guys, I can return the favor.
Edited 6/9/2002 10:12:08 PM ET by paul e wog
"I hope that when I am an old man...like you guys..."
Ya know, after a comment like that, I'm not sure you deserve any more free advice. LOL
Sistering is the way to go, but do it before the collar ties so that once its straight, you lock it in. I know you`re on a budget, but i might also recomend 3/4" ply for the decking. 2 x 8 rafters are a bit light and depending on how straight you actually get it, a thinner ply will telegraph those imperfections.
Best of luck to ya!J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
If I'm picturing your sagging rafter situation correctly, you might try nailing the sisters along the top 3 or 4 feet, flush with the top face of the rafter. (My assumption is that the tail of your sister would then be below the top face of the tail of your old rafter).
Then use a bar clamp (or or 2) to #### the old tail and new tail to alignment, kind of like walking in a fascia. Nail it as the assemble lines up. Then, when both sides are done, install your collar tie as suggested in a previous post.
Have fun.
Bite the bullet and strip it off. You are just asking for problems if you go over top of the old stuff. If you want the buildings to last another 40 years and beyond, go back to the original sheathing, repair, and put on the best shingles you can afford.
The two previous replies pretty well cover my thoughts. I don't even like to put roofing on top of the old shingles, certainly would not put sheathing on top. Think of all the extra weight that you are trying to hold up, with framing that is already sagging. Sorry, but you better strip, the roof silly.
Dan Have fun, and charge by the hour.
Paul e:
The reason your roof is sagging is that there are no collar ties to complete the structural triangle. I'll bet your bearring walls are pushed out at the top.
And yes I agree with the other folks. Strip it !
Charlie
What a noble nom-de-plume tou have! After spending a few years here, will you change it to Bullfrog-E? Welcome to Breaktime. Some of us are pretty blunt but the advice is usually good so don't take anything too personally....
The coverup idea is a bad one for sure. Would you just put a hat on when your hair is dirty and mismanaged to go to church to cover it up? When your carpet gets grubby, will you just put linoleum over it? Or when your engine oil turns black and gummy, will you just keep adding to it or change the oil and filter both?
In lots of circumstances similar to yours, the furring and metal roof is the way to go but the substandard structure needs to be adressed instead of covered up. You might still want to use metal after that. What better chance for you to learn a new skill than now when a customer is not looking over your shoulder! (Although for some of us, Dad looking on is even harder...)
I will disagree with charlie though, to some degree. Your building may need collar ties but your discription says that the rafters are sagging, not that the roof is sagging. That tells us that the rafters are undersized for the load/span they have been required to support. You might want to double up on them. Do it to make it last, this will be yours someday.
Don't do it. Period. One of the scabs around here (that is, unlicensed contractors) that I personally know did just what you're talking about two years ago on a home. That is, they fastened 1/2" OSB through cedar shingles using a boatload of air-driven 8D nails. Now, merely FOUR years later, the roof is beginning to morph, just like in a movie....it's slowly sliding and pulling...not enough to attract attention, just enough to buckle some of the new shingles and push at the eaves. Do it once, do it right, no matter how painful...or you'll be doing it again in ten years.