I have a sagging gambrel roof with the ridge 3 inches below the gable ends. It has no ridge board and only gussets at the top. No attic. It’s just rough sawn 2×4 rafter’s 16” oc. with one inch thick oak deck for the roof. I would like to get the sag out and put in some 2×4 rafter ties about every 4 feet. I am not sure how to go aboutlifting out the sag. I have set posts in the basement and living room and 2 jack posts under the worst part of the sag.
Should I lift up on 1 or 2 rafters at a time or many of them at once?
Can I push out that much sag without doing damage to the roof and then get those rafter ties in? Or should I Lift a little and put the rafter ties in and let most of the sag stay?
I want to shim out 2×4 purlins and put a metal roof on. The question is how much sag can be or should be shimmed to get the metal straight?
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sagging roof
As Dan has hinted, a lot could depend on how long this condition has existed.
My first thoughts are that you should raise as a unit. Not individule rafters. Also may need to pull the walls in that have been pushed out by the sagging at the same time you are lifting the rafters. You may not be able to do it all at one time and may never be able to totally remove all of the sag. At least without doing more harm than good.
IMHO & FWIW
Your point is well taken to push many rafters at once. I can see this as a very slow process. The house is about 70 yrs old. What method would i use to pull the lower section in? Come a long? how would i attach the cable? A temporary 1/4" eye bolt into the edge of each lower rafter?
Where, precisely, is the sag originating? Has the lower part of the gambrel spread out? What currently is cross-tying the upper rafters?
The sag is mainly the upper portion of the Gambrel. Standing outside You see the sag from the side view across the very peak of the ridge down the length of the house. I believe the sag is due to the fact that there are only gussets connecting each top end of the upper rafters. There are no rafter ties connected to the lower end of the upper rafters. That is why i think it needs to have those rafter ties. It either never had rafter ties or they were removed at one time. The spread on the lower section doesnt look that bad. I believe that those gussets and the 1 inch rough sawn oak deck boards are the only thing holding this roof up. I now have 2 jack posts and 4x4 upstairs pushing snug against the row of gussets This upstairs room is only 14 feet long to an inside supporting wall and 12 feet wide. on the other side of the wall is a room 11 feet long.
I didnt realize this situation until i considered the metal roof and saw there is 3 layers of shingles up there now.
You will need to use cables with turnbuckles or a series of comalongs where the rafter ties willgo as you jack the ridge straight, to draw the spread in while jacking the sag up.
The upper 2x4 oak rafters are 70” long with a 4 pitch. Some of those rafters are at 3-3/4 to 3-1/2 pitch some may have a bow.
What is the best way to attach this cable to the rafter in order to pull it in? Does anyone have some specifications for this? What about the max on shim thickness under the 2x4 battens? Can those 2x4 battens be attached with deck screws?
Thanks for everyone’s advice.
has the lower roof line spread.
I'm going t try to be as non technical and nonspecific as I can, because I don't want to try and Engineer this for you. Just get you to the point you're headed in the right direction.
I'm pretty sure the roofline has moved out at the curb (intersection of the upper and lower sections of the roof) line. How does the alignment there look? Has the curb line gone out in proportion to how much the ridgeline has dropped? If the roof started as 4:12 pitch, and is now a 3.5:12 pitch, the curb line should have moved out about 1-3/4-inches per every 12-feet of distance between the curb lines.
From your description there is no ridge beam, and no ceiling joists or cross ties securing the structure together at the curb. I'm hoping that the ceiling of the story below this has ceiling joists orientated so that they are under tension and holding the bottom of the roof true.
To get the sag out of the ridge, the curb will have to come back in. You need to bridge the roof, curb to curb, with something that develops enough tension to pull the curb back in at the same time the ridge line is raised. It is probably possible that sufficient tension could be developed with a cable and turnbuckle system running from curb to curb. After the structure is pulled back to true, install dimensional lumber across the curbs before detensioning the cables.
I'm not sure if the space under the roof is to be occupied, and thus needs ceiling joists. That will determine what size of lumber goes back in. 2X4s will probably work for the cross ties if all they have to do is hold the tension load. If you want to install a finished ceiling you will probably need 2X6s or 2X8s to hold the ceiling without sagging. You will need to decide how to deal with that.
I would not use deck screws in this kind of application. If I were to try this with just screws, I would check out some of the ones that McFeely's has on their site. They have some with a shorter threaded section, and longer shank, so that they will pull two boards together instead of holding them apart.
Instead of just screws, I would recommend that you read through the Simpson StrongTie catalog, (you need fittings that will develop tension), and use whatever fasteners they recommend. The counter folks at a good lumberyard may be able to help you with the selection, if you take them sketches and pictures of what you want to do. I'd look at adding some of Simpsons specialty hangers to tie things together at all the joints when you are done. I might add some of the "bend to fit" hangers at the ridge and curbs before I started pulling on things, just to make sure the roof doesn't do something unplanned. After, I had it pulled back into place, I'd add some gussets to stiffen things up.
Good luck.
Probably some sort of cable arrangement will be needed to pull things together, but it won't work to pull with just one cable. Rather, a cable about every ten feet is needed. And the cables need to be carefully anchored to the framing in such a way that they won't pull the framing apart -- hard to say exactly how without seeing the setup, but I'd maybe consider attaching strips of heavy sheet metal bent into a U to the joists several inches above and below the joint line, using through bolts, then use a yoke to pull evenly on both pieces.
The other option would be to attempt to jack the ridge line (over-jacking several inches before installing cross ties), but you'd first want to heavily strap the rafters together across the ridge to assure that jacking wouldn't split the ridge open.
Whatever you do, take your time. Old wood (did you say oak?) does not bend readily, but can be quite brittle.
For fastening the final cross-pieces, you want something very secure -- they'll be under substantial tension. Ordinary deck screws are not particularly trustworthy, especially in shear, but GRK screws or one of the other premium brands of "strucrtural" screws would work. In old oak you'll need to drill clearance holes and may need to drill pilot holes. You could instead use lag bolts or through bolts, but the structural screws would probably produce a joint less likely to split out in the future.
Hey sounds like some great advice. Id say you are right about the 1-1/2" spread on the lower section. The house is only 28 feet long so a cable every 10 feet would be 2 or 3 cables in the area of the spread. One builder told me not to use screws but a minimum of 3) 3" nails. The thru bolts sound like a good idea.
I believe that old oak is set and i will go very slow. I dont believe i can get all the sag out, but i am sure that a 2x4 tie every 16" will make it strong and resist any further sag,
One question i have left is knowing the proper way to shim the purlins when it comes time to install the metal roof. Can i nail a furring strip parallel over a rafter and then nail the 2x4 purlin thru the furring strip?
What is the thickest shim material that is still acceptable to get the metal flat?
How flat must those 3 foot panels lay?
PS I am new here but I really like this Forum
Phil