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Just picking your brains here,
I’m putting a room addition on a 1965 split level, turning the new ridge 90 degrees to the existing straight gable- small saddle framed over the old roof to tie the two together.
Here is the question- the existing rafters are 20′ plus in length spaced 24″ o.c. 2×6 spf collar tied every other one for about a third of the ridge length- then nothing. In some places on both sides of this roof the rafters have sagged as much as three inches. I am placing a stiffback under my new saddle and posting down to bearing walls below. The owners would like me to take the sags out of the roof plane- not a problem on the back side- there are bearing walls there.
The front of the house is another story. Nothing to post to- the bearing walls are all 4′ rear of center of the house. The ceiling joists are also 2×6- I don’t want to transfer any roof load to them for fear of creating cracks in the drywall below. So I am planning to attach a 2×10 stiffback to the front at midspan and draw everthing tight with lag bolts- collar tie every rafter-
Anyone have a better way?
fergot- the ridge is straight and true- posted back to the bearing behind it.
thanks
hub
Replies
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Sounds like there's a lot of ways to make sure this thing doesn't sag but now that it has...quite a bit of force needed to straighten it up.
If I get it right, you need to straighten bowed rafters on only on face of the roof. Ridge hasn't bowed and eaves aren't pushed out. Seems like you've got to push against something and that something will move as much as the rafters do if you don't separate the ridge or collar ties or eaves first.
Sorry I wasn't any help...just some doom and gloom to ponder.
*Joe-Exactly like that. The saddle ties into the rear of the house- just as you've drawn.I want to straighten both sides of the roof- they look like hell and my name is going on it so that ain't accecptable.Pitch is 4 in twelve, length is 40' and width is about 32'. No attic use.Ryan-you are correct in you're understanding. I should have added- the collar tied rafters have not sagged.I need to pull the sagging rafters into plane with the others and don't feel there is anything to push against. Once I have them there I'd like to keep them there...no doom and gloom- I'll fix it.I am not worried about the roof failing, just want to make it look better...thanks
*Doug, I'd put a "snow" brace on and tie a brace back to the bearing wall. I'd nail it soidly to the ceitling joist directly above the wall. We do it all the time around here. It tends to become a modified truss.blue
*Blue-please explain- I am not familiar with a snow brace.thanks,hub
*A snow brace is a built up beam that is pushed up tite at midspan. For instance, your rafters are about 16' -6" long. I'd put a 2x10 on edge at the halfway mark and add 2x4 supports that ran back to the bearing wall. I might double the 2x10 if I couldn't put supports at about 6' oc.blue
*okay fellasBlue it was a guess- I counted five rows of sheathing plus a bit and guessed at a total span. You are right- 32' span works out to about a 16-6 rafter.anyway the rafters are in fact in excess of twenty feet long. the snow brace and my stiffback seem to be one in the same.the angle of bracing back to bearing seems to be extreme- I question its' usefulnessJoe-we get snow infrequently- but heavy at times. Again I am not worried about failure- this roof has been intact since 1964- it's not going to fall in tomorrow. It needs straightened- the gluelamm would be ideal- not feasible.I am talking about the stiff back used as the purlin-again bracing back strikes me as inefective as the angle will be too oblique...
*I fergot- thanks guys
*Doug,Do you think that by the time you got that stiff-back jacked in there across all the swaybacked rafters and maybe posted at the end(s) on tbe bearing wall you will have lifted the ends of the offending rafters away from the ridge and off the plate? And, if you can get a 2x stiffback into the area, why can't you get a LVL in there?
*Ralph,I was thinking the same thing. With 3" of sag and 35 years of "set", I don't think he will be able to jack them straight. Might get some of the sag out but not all of it. Here's a crazy idea: jack each rafter individually (maybe even without damage to the ceiling below), then sister a 12' 2x8 or 10. I know it's labor intensive... like I said, crazy idea.Jerry
*use shoring to get some bearing under the ceiling at the points you need to jack at.this may mean going down to the garage/wreck room etc.. post to ceiling, then upstairs, post to ceiling...now you can lay a 2x10 down on the ceiling joists, and bottle jack against the bottom of rafters, then collar tieplan on jacking multiple pairs of rafters at the same time. multiple layers of comp? don't need me to tell you its heavy, and can require lots of force to correct. The shoring, hubcap. Use the shoring.
*okay- more good points. maybe I can wrestle a gluelam in place. Hadn't considered pushing the rafters off the ridge or plate. Have to watch that.Might be a good time to get some engineering done-thanks everybody
*This is what I'd do (I think) I'm thinking you've only got 2x6 rafters on a too-long reach. They could probably use a sandwich (maybe 2x8) anyway, so I'd find the center where the greatest sag is, cut a 3" slot out of the back of the offending rafter (one at a time) which would weaken it considerably at that point. Push up on it until it was straight and attach the 2x8 alongside. The 2x8 bearing would be the new rafter when you were finished. Pushing a bowed board without creating a weak spot you had some control over, could cause problems. I've done the knotch thing on bowed studs and it worked quite well.
*Doug my fishing buddy, I've read all the posts and I have a little trouble with the ridge being straight and true with a major sag on the roof face.Normally, when you lift the ridge the ends at the corniche lift or draw back.I think you can still do an effective load transfer, but it's a lot of work.Sistering the top chord with a midspan cross member to stiffen the assembly my be your easiest and most effective way of dealing with this.Anyway you can post a shot of the inside view of the attic?Gabe
*Jerry - I don't think you're idea is crazy at all. But you're correct in saying that it's labor intensive and a real pain. My neighbor did sonething like that last year. The 16' long 2X4 rafters had a lot of sag in them. He cut them in half one at a time with a sawzall and nailed a 2X10 alongside them. Cutting them makes it a lot easier to pull things back into alignment.
*To clarify or perhaps muddy the waters- time will tell...Gabe-good to hear from you--get that deer?the ridge and walls are straight and true. The ceiling joists are well attached to the rafters and the ridge is posted and static. The sag seems to be confined to the individual members- they deflect as I walk across them. This leads me to believe I can push them to some extent back towards plane with the collar tied rafters.what to push against? the ceiling joists if not overspanned don't miss it by much and surely cannot accept any more load. so my tiny little pea brain has been picking at this I feel I can get some micros in place and push against them- post up and secure things- collar tie everything.I'll secure the rafters with 3/4" plywood gussets at the ridge and expose the heels from above and tie them down. Walk in the park... one two three HA!I laugh at me. It'll be a job, but if it was easy they'd let women and kids do it.thanks everyone!you got me out of the box and problem solving.I'll let you knowRon you're on to something - any of these guys that won't move I can cut and sister in a piece to carry the load
*Doug,
View Image © 1999-2000"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe-ya lost me...hub
*Doug, i don't mean to intrude, but Joe's post could be in response to your question, "Anyone have a better way?" He took his pix with him, but they are still under the search function.
*ah-yes I see. Thank you splinter.Did you go sing?
*I've spent the last two hours searching the archives trying to figure out why my formerly well-behaved boiler is singing to ME. Looks like a go-to-town-for-parts-day tomorrow instead!Hey, give a shout when you're coming through the Big Sky next year--i'll spring for Moose Drool for the tall contractors and sarsaparilla for the short ones.
*Doug, don't let that oblique angle fool you. It'll probably be somewhat similar to the 4/1 pitch....perfect!Don't put the weight on the ceiling joist now. If you had started that way originally, it might have stretched itself out before the board was hung. Now, you will add a new stress and you will certainly have repairs to do.I'd opt for an oblique re-inforcement, especially since it hasn't caved in. Keep in mind that you needn't put that snow brace (beam) at the midpoint. If you cheat it toward the ridge, you will reduce that obiqueness.blue
*Thanks everybody.Here's what I didgot micro's spect for the long spans, built up 2x12s for the short ones- installed them on top of the cj's- everthing calculated to carry the roof loads over the cj's to bearing- cut the rafters above the new beams and posted up to plane- tied everything together with 3/4" plywood gussets (18" equalateral triangles) both sides of each rafter- what a pain. We are going to reroof with dimensionals to hide the remaining discrepancies...
*Doug, I just remembered the book term for snow braces....Purlins!Glad to hear you got it straightened out.blue
*thanks blue...
*hey!I think by maybe this time next week I will have a web site and some pictures posted.We took shots last sunday.My daughter looked at the last house I built and said"DAD?! You built that? It is so awsome..."she almost walked home...
*
Just picking your brains here,
I'm putting a room addition on a 1965 split level, turning the new ridge 90 degrees to the existing straight gable- small saddle framed over the old roof to tie the two together.
Here is the question- the existing rafters are 20' plus in length spaced 24" o.c. 2x6 spf collar tied every other one for about a third of the ridge length- then nothing. In some places on both sides of this roof the rafters have sagged as much as three inches. I am placing a stiffback under my new saddle and posting down to bearing walls below. The owners would like me to take the sags out of the roof plane- not a problem on the back side- there are bearing walls there.
The front of the house is another story. Nothing to post to- the bearing walls are all 4' rear of center of the house. The ceiling joists are also 2x6- I don't want to transfer any roof load to them for fear of creating cracks in the drywall below. So I am planning to attach a 2x10 stiffback to the front at midspan and draw everthing tight with lag bolts- collar tie every rafter-
Anyone have a better way?
fergot- the ridge is straight and true- posted back to the bearing behind it.
thanks
hub