saggy roof replacement Q's

Reading Mazdeuce’s garage thread inspired me to ask a question that’s been bugging me for a long time. How much does it cost to re-roof a garage. I don’t mean a tear off and re-shingle, I did that myself 12 years ago. I mean replace the rafters.

Most roofs are built like this with the trusses as A frames

Unfortunately, my house was built in 1953, before pre-fab trusses and everything appears to have been built on site. The main house is fine, but the garage is assbackwards. The Trusses aren’t connected in an A. They are a triangle open at the bottom with what should be the bottom running at 90 degrees. Don’t’ ask me why I have absolutely no idea. All I can think is they put in the ceiling trusses and then changed the plan on direction of the peak and built it. It’s sort of like this.

Now, there are just two joists running in the correct direction, but they are on top of the main joists, I omitted them for clarity on the sketch. There is a gable on the front of the garage perpendicular to the peek.

Inevitably after 60 years the ridge has a sag in it, no surprise with nothing tying the trusses together they can splay. I do have a persistent leak in the back of the garage that I can’t find. When I re-roofed I put double ice damn plus a large copper sheet under it, plus copper flashing in the gullies, but it still comes in in extreme weather . This is a shot of the house from Google street view, you can just see the bow in the ridge, you are looking head on at the gable.

I’m wondering what I can/should do about it.

On one hand I guess I could try jacking it up with a pole from the floor to the ceiling joist, then directly above that another from the joist to the ridge. I could slowly jack it up over months then try adding some ties in the correct direction. The problem with that is I can see months, or even a year of having this great big jack right in the middle of the garage making it useless for cars.

Alternatively I could get the whole roof replaced. I don’t’ think I’d want to tackle that on my own due to how long it would take to tear off the whole roof, get the trusses into position then put a new roof on. As an evening and weekend warrior that could take months with the house a mess and the garage open to the elements. I assume a crew of pro’s could do it in a few days.

So, anyone got any guesses to what it would cost, including the gable. The garage is 20x20 internally, but I’d want to extend it out the back a bit further to give an outside covered overhand for storage behind the garage. That would either mean moving the peak further back on the house, or changing the direction of the peak 90 degrees and instead of having a gable at the font, have a fill in/gable to the main roof.

Any ideas?

This isn’t a high priority as in the 22 years my wife has been in the house it hasn’t noticeable changed, but it bugs the ever living crap out of me.

What about cables and turn buckles? Bolt the cables to the bottom of the trusses and tension them til something creaks. Let it sit and see if anything moves. if it does, crank up the tension again.

slefain wrote: What about cables and turn buckles? Bolt the cables to the bottom of the trusses and tension them til something creaks. Let it sit and see if anything moves. if it does, crank up the tension again.

Now that's a good idea. I'd thought of that after I'd jack it up, but not before/instead of.

Have you checked the walls with a level?

I would not use a jack.. but they do make adjustable poles. They are metal with a threaded sleeve. You get them adjusted properly and then turn the adjuster to extend the pole, applying tension to whatever it is under. This way you only have a 6 inch diameter pole in the middle of your garage rather than a jack

Hasbro, yes walls are fine.

Mad-machine. Those poles are what I meant by jack, but it would still be in the middle preventing car doors opening.

If you check the side walls that the roof bears on, they are more than likely out of plumb in the middle because (as you surmised) the lateral spreading force of the rafters is not being resisted by ceiling framing or collar ties. That swayback is made worse by the valleys loading it where the ridges intersect.

I assume there is a drywall ceiling in the garage, but no real attic over it? Or is it just exposed? Drywall will make the job a little more complicated, and it's probably worth removing.

Either way, you can put one of those adjustable posts under the intersection where the two ridge boards meet. Then SLOWLY jack the ridge up until it is level. You'll probably want to put a piece of steel angle or something under the ridge board so you are distributing the pressure over a few feet instead of just the nose of the jack.

The lally column / jack will help, but I would also brace the walls back to help resist the continuing lateral load. You may not want to leave the post right in the middle of the floor, either.

Turnbuckles will work but I would be worried about trying to use that to squeeze the walls in. It will work, but it's not mechanically very efficient, which means you're putting a LOT of tension in those cables to get the ridge to lift. I think you're better off lifting the ridge first and then tightening the walls back into plumb as you reduce the outward pressure. Once everything is trued up, you can install lateral members to keep it straight.

I recommend against cables. I'd rather see you use 3/8" steel rod with threaded ends and turnbuckles. Take little chunks of 3/8" steel angle, maybe 3" x 3" x 6" long, and lag bolt them down to the top plate of the bearing walls every 48" or so. You can probably skip the last bay at each end, because the end walls should be tying that together pretty well. Set the angles so the leg sticking up is parallel with the bearing wall. Then run your rods from angle to angle across the garage in the same direction as the roof framing, with turnbuckles, or just using the threaded ends to bring tension into each rod as the walls come back to vertical.

Hhmm, I'll plum out the top of the walls this weekend nad see what I find. Good points. I doubt I'll do anything about it until next spring, but we will see.

The internal culing is wet plaster over very thin drywall type material like the rest of the house. They hadn't started using straight drywall 60 years ago for finishing. There are cracks all over it plus a hole at the back beneath where the water comes through the ceiling, but not the roof, it runs down from elsewhere.

slefain wrote: What about cables and turn buckles? Bolt the cables to the bottom of the trusses and tension them til something creaks. Let it sit and see if anything moves. if it does, crank up the tension again.

This. It's fairly common, around here, with all the old houses we have in downtown.

They call them earthquake bolts. A lot of them were installed after the shelling during the Civil War to pull the houses back into shape.

Yeah, a lot of times you'll see cast iron stars bolted on the outside of old masonry-wall buildings. Same thing - it's effectively a big fender washer on the end of a through-bolt.

Works on a 200 year old house, would look a bit odd on a mid century ranch!

Just hide the bolts up under the eves. You could even use a bracket that hooks the top plate in the attic.

If the walls are really plumb, then the roof has not sagged from it's original construction.

In order for the ridge to sag, the walls MUST bow out.

Put a string along the top plate (outside, under the rear soffit, and a 2nd one over the garage door). Space the 2 ends of the string from the wall with small spacer blocks. Measure to the string. If your spacer blocks are 1", the string should be a consistent 1" off the wall the entire length.

I'm betting it's not. The walls will be bowed. Gambling man here say's you will find a 1 1/2+" bow in the back wall, less in the front ( because the triangulation in the gable would help resist the spread).

There is not actually anything wrong with the ceiling joists running the opposite way from the rafters, but there would need to be a structural ridge or collar ties to counteract the spread.

The things you called "2 joists (runnng the correct way)" are known as collar ties. You might need more of them, or their connection may have failed.

You need to first determine if it is actually sagging (which my string suggestion will tell you), or if it was built E36 M3ty in the first place.

If it is sagging, jacking the ridge will be much cheaper than replacing the framing. You can do it over a few days- months will not be necessary. I've done it on several occasions in a day.

If it was built crooked, you can't straighten it. Raising the ridge will bow the walls in. Re-frame it, or live with it.

SVreX wrote: If the walls are really plumb, then the roof has not sagged from it's original construction. In order for the ridge to sag, the walls MUST bow out. Put a string along the top plate (outside, under the rear soffit, and a 2nd one over the garage door). Space the 2 ends of the string from the wall with small spacer blocks. Measure to the string. If your spacer blocks are 1", the string should be a consistent 1" off the wall the entire length. I'm betting it's not. The walls will be bowed. Gambling man here say's you will find a 1 1/2+" bow in the back wall, less in the front ( because the triangulation in the gable would help resist the spread). There is not actually anything wrong with the ceiling joists running the opposite way from the rafters, but there would need to be a structural ridge or collar ties to counteract the spread. The things you called "2 joists (runnng the correct way)" are known as collar ties. You might need more of them, or their connection may have failed. You need to first determine if it is actually sagging (which my string suggestion will tell you), or if it was built E36 M3ty in the first place. If it is sagging, jacking the ridge will be much cheaper than replacing the framing. You can do it over a few days- months will not be necessary. I've done it on several occasions in a day. If it was built crooked, you can't straighten it. Raising the ridge will bow the walls in. Re-frame it, or live with it.

This is why I asked if the walls are level. That would be the first thing to check.