Ridge Beam Is Cracked/Broken
I just bought a home built in 1922, and the first thing I need to do is repair a sagging roof, which is sagging due to a cracked ridge beam. I use the word "beam" tongue in cheek, as the thing is just a 1 by - not much of a beam. After reading my initial thoughts, I'd really appreciate any help I can get - advise away!
My initial thoughts are to slowly jack the ridge board up until all is level (looks to be a 3" to 4" sag). I'm thinking I should do it slowly, say a inch or so per day, so I don't cause other problems with the sheeting and rafters. After getting it jacked up and level (using a 2x6 under the ridge beam and a 4 ton hydraulic jack), I'm thinking I will permanently support this area with posts from the 2x6 to the ceiling beam beneath it. Then I think I should sandwich the cracked area with glued and nailed plywood patches between the rafters. Then I think I should probably add ties on the rafters - will 2x4 ties work? I welcome all thoughts and suggestions.
Re: Ridge Beam Is Cracked/Broken
You're not going to get an easy fix with this one. I've seen a lot of 1X ridges on the old 'mill houses' here in the south, and surprisingly most were doing pretty well 50+ years after the house was built. Sadly the ridge isn't the problem- let me explain. Let's begin with the forces which caused this. As the ridge drops, the rafters have to move outward or downward at the wall plate. If the ceiling joists are tied in properly all across and at the rafters and the walls haven't sagged, this cannot occur. So essentially, that is where your real problem is- you're just seeing the results in the ridge. Simply replacing the ridge will not fix your problem
Begin with a very good eyeball or a stringline at the top wall plate outside, spaced down and out so that the string touches only the end spacers. Measuring to the string will tell you whether the walls are good- let's say they are. Now you must have rafter tails not connected to the top plate if the ridge sags, so again measuring to the string, see if the width to the edge of the fascia is wider in the middle, especially where the sag in the ridge is worst. You may have both problems together. Go into the attic and see if you've still got 1X roof decking boards- if someone has switched to plywood/OSB deckining skip to the last paragraph.
If you can identify the problem area, that will show what to fix. If the walls are bowed there should be some separation in the ceilings perpendicular to the ridge- that will be where the movement occurred. With turnbuckles attached to either side of where the ceiling joist lap joint slipped, you can slowly pull this back in, moving maybe 1/4 inch then waiting a couple days and going for 1/4 inch more till you get the wall straight to that string. As you pull things back in, keep a very close eye on the rafter-to-wall connection If any rafters show signs of loosening there, stop and give the ridge some lift as you draw the joists in. Don't jack the ridge directly; the 1X won't take that force! Instead securely nail a 2X6 or wider to both opposing rafters with it contacting the ridge board on top. That might be a good idea anyway- I always do the pulling-jacking together at the same time. If at any point with any part something stops moving then you stop too- better to get half of it back than to lose the whole structure. And you need to be pulling and raining several joists together at the same time, not just one.
A lot of work? Heck yes! When I do these jobs (and I avoid them as much as I can) I take a close look at the shingles and roof deck. Usually they are not in the best of shape, and that is a good thing here because that gives you motivation to do the repairs the right way- by stripping everything right down to the rafters, then straightening the ridge by the method outlined above. With just the bare rafters above, you can pull things back to straight all at once as there is a whole lot lees force to contend with now. If the roof decking is sheet goods (plywood or OSB) then it will have to come off because it is tying all the rafters together crooked and holding them that way. Once you get it straight use sheet goods for decking to help hold everything laterally so this doesn't happen again. And oh, that ridge is one heck of a lot easier to replace with everything else out of the way which is why needing shingles and decking was a good thing and not a bad one like it would usually be!
A lot of work? Heck yes, but actually doing the whole thing (if it can use it) means you're good to go for the life of the shingles afterward and you can upgrade to a ridge vent, add hurricane clips to the rafters, put in additional wind collars and wind-beam bracing, plus do any other attic work a lot more easily with it all open. A lot of people don't realize just why it is so important to check a ridge for sag when contemplating buying a house- now you know what the 'little sag that probably won't hurt anything' really means- it's always a symptom of something else gone badly wrong. If nothing else ever moved and sheet decking was installed properly, a 1X ridge would probably be adequate- heck, I've seen ridgeless houses with roofs that didn't sag (but that's going way too far just to save a buck). I'd rather have the 2X ridge, properly sized to meet code, with the rest done to match code as well. The roof structure is actually the heart of the framing system as long as the walls have adequate vertical support because that's what really holds the house square and keeps the walls straight!
I know it ain't the answer you wanted, but it's the straight poop from someone who has done at least a dozen of these.
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