rafter ties how 2 make connections
i have a 24′ wide garage,4/12 pitch with comp shingles. the rafters are currently 2×4’s 2′ oc with no collar ties.there are rafter ties every 4′ made with 2×6’s that are currently free spaning the 24′ width and sagging. this garage is only 5 years old,why someone didn’t use trusses i’ll never know but they didn’t…. anyway i want to raise the ceiling height a foot,that keeps me in the bottom 1/3 of rafter so i think i’m ok there. so when i raise these i’m planning on 2×6’s again,the span on them will be about 16′ placing on 2′ centers.how’s this sound so far? what i can’t decide is how to make my connections between the rafter and the tie. the tie will come in on the side so i’ve thought about pl glue and a couple lags at each end plus there would be some nails/screws to temp hold it till the lags screw in.is this enough to hold the strain these will recieve from the outward push of rafters? what would work better? thanks larry
hand me the chainsaw, i need to trim the casing just a hair.
Replies
Sounds like your first impression , "why didn't they use trusses", needs to be addressed. Your description of how you plan to attach the collar ties is ok, Why don't you follow up with some webbing, maybe call an engineer buddy and come up with a schedule.
Your first problem is that your existing rafters (2x4 @24" O.C.) are quite a bit undersized depending on your area and snowload factors.
Maybe take a good look up there first and see if you can see the rafters themselves sagging allready. You also should call your building department and ask them what the required rafter size is for that situation. For me in my location it would be 2x10 rafters so you might have an expensive job ahead of you.
You must get a load of snow for 2x10 over 12-13 feet spans or so. I think 2x8 are ok... maybe even 2x6... iirc the cut-off point from 2x6 to 2x8 is right around there.
Anyhow, I agree that if he posted correctly, 2x4.. especially 2' oc, are huge problems even without snow. Maybe some yokel figured if trusses use 2x4's he could too.... of course he forgot to add all the webbing that makes it work.
24' rafter ties? those are pretty long too. If the rafters were adequate, the ties could be supported by tying them inot the rafters above. The ties do not have to have strength for load but serve to keep the building from spreading.
http://www.petedraganic.com/
First, I think that I would forget about touching the garage. I would look into suing the person that built it.
Second, if I was to do anything structural, I would
Sounds like the dude that built the roof structure was a bad self taught wanna-be truss maker. Check with the building department and let them know of the existing conditions, and/or check with an structural engineer. The original rafters are undersized.
well here''s my chance to spread the word about the builder,i don't know if they are else where in the country but it was built by bullock garages.this is a company that fabracates all the walls,siding everything.pulls up and in one day puts you up a garage.[as cheaply as possible]previous owner had just had this thing built when we bought the place and was really proud it "only cost him 11 grand!] i thought to myself you overpaid.so thats what i'm workking with and if i get to where i needto rip the roof off ,it's time to start over. thanks larryhand me the chainsaw, i need to trim the casing just a hair.
As others have said, the 2X4 rafters are grossly undersized. Hanging a ceiling on them would make the situation much worse.
ok here we go,one thing leads to another.i did look tonight i have a 2x8 ridge board. looks like i could sister a 2x6 on the 2x4's.when i raise the rafter ties i would thrown in some webbing [not as good as fact.truss's but] would that fix this pretty well.i could go in and use 2x8 or 2x10 for the ties but i don't see this helping much since they are not resting on top plate.this isn't my house it's just a cheaply built gararge holding a couple toy cars in it that are worth more than the garage. so i'm not going to be storing anything in attic,it just has to hold itself up and 5/8 rock.thanks larryhand me the chainsaw, i need to trim the casing just a hair.
What you are calling 'ties' are ceiling joists, especially when you are going to hang ceiling board from them. That is a big load in itself. So the 2x6s are way over spanned. There is little savings in not having one at the bottom of every rafter position.
As far as tieing the rafter ends together, you would be wise to leave them down on the plates and check the code for nailing reqs. Lottsa nails into the plate and into the rafter bottoms. this is especially important on such a low slope roof where the roof load is pushing out as much as it is transferred down.
A kingpost truss, or google Howe truss or Fink truss for pictures of truss designs. Through bolts with plates (those big cast washers), you could make a nice truss. Definitely sister the rafters with 2x6s and collars ties 2/3s of the way up, if you don't built trusses in place.
How about this.....Put a structural beam under the ridge. How long would this have to be? A couple of 15" LVLs can carry a big load.Posts int he walls down to the foundation, with 45 degree braces. That takes a bunch of pressure off the ceiling joists, gives you the chance to move them up as quasi-collar ties.
i've thought about doing a couple lvls.the garage is 24' long with the biggest problem being that one end falls over the 16' overhead door,so then it would need modified to transfer the load to the foundation.that gets to be a lot of wood! thanks larryhand me the chainsaw, i need to trim the casing just a hair.
If you're determined to leave the outside alone, and you really want to make this right, I think you need to re-build this roof from the inside.
If i were to do it ,my instinct would be to get an engineered LVL for both a structural ridge, and a header to carry it over the garage door. Then sister the 2x4 joke rafters with 2x8 or 2x10 and make enough attatchment to carry above.
Biggest pain would probably be the attachment at the ridge, and the fact that the bottom of the rafter would be dropped below the top plate, making it necessary to anchor some kind of ledger to the wall ( other wise your heel cut on the new 2x would be so deep that it would turn it into a 2x4 which defeats the purpose.
On the other hand, doing it this way would eliminate the need for any collar ties or other horizontal members across at wall height, giving you a couple more feet of ceiling height if ya need it.
Where are the building inspectors when these guys throw this crap up? I wouldn't span 13 ft. with a 2x4 for a tree house.
Good luck,
Bing
I would build trusses in place. If you dont have a snow load to worry about you could easily build trusses that would be fine. The one thing that I would worryabout is if you want to raise the cieling height you will be puting a huge amount of stress on the 2x4 at the end between the collar tie and where it comes down on the wall. That would be the weak link. You would need to at least make that a 2x6 and a 2x8 would be better.
I have worked on old houses here in the Seattle area that had 2x 4 rafters spanning 14 ft with 4 layers of roofing that were still standing. Sagging alot, but still holding the roof. If you have a local building department you may be able to get an inspector to come out and tell you what he would like to see done. That wont cost anything but may also open a can of worms if the rest of the garage is sub standard also.
building insectors were here,when i bought the place the permit signed off was still hanging on the wall. you know i never thought about this,but wonder if it was really a inspector that signed????? larryhand me the chainsaw, i need to trim the casing just a hair.
You're asking for advice on how to properly fix the garage, but you don't want to meet minimum building codes to do it?
Beer was created so carpenters wouldn't rule the world.
From your initial description I assumed this project was built by someone's BIL or maybe an uninsured hack contractor.
Normally I avoid builder bashing, but in this case I'll take a swing. In my state a 10 year structural warranty is required by law and builders are liable for this. What about yours? Also what about licensing and a state licensing board? What about building codes? No US code would allow 12' 2x4 rafter spans 24" OC in any situation.
What state do you live in? If your state doesn't have licensing, codes and your locality doesn't have inspections I bet you now see the value of them. If it does, I'd go after the builder and his license before I touched the structure.
Sorry, but to modify this roof would just be trying to shine a turd - It will still stink, only worse; if you raise the ceiling joists like you are talking about you will further weaken the roof system by putting more strain on the undersized rafters. I wonder if the thing actually has any kind of footers or is it just a 4" slab on grade? Anchor bolts? or were nails "good enough"? I'd put a string line or an eyeball on the top of the ridge to check for further problems.
if my bil built this deal it would be better than this,might be crooked but it would be built better!lol as far as any liabilty staying with the builder "bullock garages" there bankrupt and gone,that says it all doesn't it. larryhand me the chainsaw, i need to trim the casing just a hair.
you know it's sat. nite and everybody needs a good laugh. yes i know it has footings and rbar because i actually picked this thing up and moved it 50' and set it on a new slab,so at least i know the foundation is there. back when i was moving the garage i ask for advice here and describe it as a poorly built,light construction,i put it on a car trailer and moved it.lol larryhand me the chainsaw, i need to trim the casing just a hair.
Use your chainsaw to take the old roof off. Get some trusses built to give you the height you want, then rebuild the roof.