i’ve moved the rafter ties,now what?
alwaysoverbudget
| Posted in General Discussion on
i’ve got a 24×24 garage 8′ walls ,4/12 pitch with site built rafters 2’center and rafter ties. couldn’t take the low ceiling so move the rafter ties up a foot to at least give me 9′ ceil.
so i’ve used 2×6 that are spaning 16′ on 2′ centers,they are pl glued and screwed tight then nailed on the connections at the ends.
what would you guys suggest to do for braceing up to the rafters? one in the center,copy how a truss is made,strongback down the center or what. i will hang 5/8 rock on these with insulation and nothing else as i feel i’m pushing the limits of 2×6 anyway.larry
if a man speaks in the forest,and there’s not a woman to hear him,is he still wrong?
Replies
ASSUMING your rafters are properly sized, and since you didn't move the rafter tie up very far you *probably* haven't overstressed the rafters, then all the 2x6 is doing is keeping the walls from spreading. A post/strut/sag rod/whatever hanging down from the ridge will keep the rafter tie from sagging. Angled struts like you see on a truss would help keep the rafters from sagging if they were undersized.
i stayed in the lower 3rd of the rafter ,thats the rule i have read. the rafters are 2x6 approx. 13' from top plate to ridge. if it matters the ridge is a 2x8 thanks larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
You're right, the rule of thumb is to keep the rafter tie in the bottom third of the span, but there are caveats. You can still overstress the rafters which will cause deflection, if the rafters aren't big enough. I don't know what your live loads are in Texas but my guess, like Jim's (hard not to say Blue!), is that you are pushing it. Probably won't fail, probably will sag a bit.
Oh, standard disclaimer, any engineering information you receive here is worth exactly what you paid for it, blah blah blah. ;-)
Any reason why you didn't ask the right way to do it first?
Joe Carola
well to tell you the truth,i have and i have read a lot of threads here on this. they all say stay in the bottom third no sweat.somewhere here even pulled up a diagram of this exact thing.heres the one with pics
44081.70
now i sit here with 5 replys and it sounds like it's going to fall down.lol i still have the old ties in place,maybe i shouldn't cut them out huh?
so whats your take on this? need anymore info?
whats the worst that can happen,the walls fal outward as the ridge comes down.....you guys are ruining my day. larry
if a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
Edited 11/17/2007 10:39 pm by alwaysoverbudget
You might get a big dip in your roof, or a little one. You might just move one or two up and leave the rest down.Or, if you really want them up there, add some beef to the roof in some way. Either add struts or something. Get creative.
FKA Blue (eyeddevil)
jim,just sitting here trying to figure if i really screwed up or what .if i understand what your saying is the weight of the tie plus the weight of the ceiling will have a downward force on the tie/ceiling joist cause it to bow downward in the center, as this happens it will be pulling on the 2x6 rafter about a foot above the top plate,this will create a downward bow in the rafter?
so if that is the problem,if i nail a 2x4 straight down from the ridge to the rafter tie/ceiling joist,is that enough? or do i then need to go from the tie back up to the rafter at a 45 degree angle and tie to it?
if i were to lay a 2x4 by lets say 8' along side of rafter from the top plate toward the ridge to double up the wood where the rafter tie connects? just trying to get a little clearer picture of whats next. larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
I plan on doing the same thing in my garage. So moving the ties up a bit is ok?
I'll demo the drywall frist and then take pictures of the framing.
well i don't know i thought i had a green light with what i was doing and made this post to see if i could strengthen it up a little more before i insulated. but i' getting kinda concerned. so stay tuned and don't run out and do yours tommorrow!
you can do a search on rafter ties and get lots of info. larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
When I do mine I will figure it out with some help ;^) To me there two kinds of DIY builders or builders in general. One is driven by necessity, time, and cost. So they make decisions based on those drivers.
The other is driven by a desire to make their surrounding more efficient, longer lasting, beautiful, etc, etc. The cost, time, and work required is secondary. They will find a way to pay for it.
Sometimes a person has good intentions and thinks they have done it "right" but they really didn't see what was happening. I think that is the excerption though. If they are muddling through things on a regular basis they might be fooling themselves into thinking they fall in the later group.
I find that people drought my integrity all the time in small ways. So I've learned to disregard those people who do it without really knowing me or my work. People can be small minded. What I try to do is build it so that when I'm gone someone who looks at it will say, "he did a good job". I let my work do the talking. If people around me don't get it, so be it. I'm not doing it to please them.
You runnin' for an office?Remodeling Contractor just on the other side of the Glass City
I knew I'd get flak for my post but that's where I'm at. If people don't like it I'm ok with it.
The houses in this neighborhood were built quickly and inexpensively. It was fine for the time they were built. But I think the roof was under built. Last year they had four feet of snow that stayed around. The inspector said they got a call from the owners of this house because the ceiling was sagging. Someone had braced from mid rafter span to the ceiling. The garage has a valley that has cracked and sunk about an inch where it is nailed to the ridge.
My point is, if I change the ceiling in the garage I might as well improve the roof structure. Why let the house stay the same or run down hill? It's a nice house. It just needs some work.
This has been informative. I have a similar sitution to do. remove a bearing wall from under a 24 foot span or 2x6's 16" o.c. that overlap on the bearing wall. From the charts the ceiling joists (attic floor joists) are sized ok but the 13' rafter span of 16" o.c 2x6 rafters supporting the 4/12 pitch roof are slightly undersized. So what this discussion has taught me is that rafter ties cause even correctly sized rafters to sag.
I should mention that the bearing wall spans 20' and 7". So the solutions are 1) flush beam: Made of three 1.75" x 14" glue lams, or 2) structural ridge or three 1.75" x 16" glue lams (both of these options would be metal connected to and supported by 4x6 douglas firs that go down to the foundation) or 3) engineer stamped plans to retrofit in sizzor trusses, site built, that use existing rafter as top chord, or 4) pull roof and ceiling, replace with sizzor trusses and reroof. Seems to me that the flush beam option (after building 2 shoring walls) is the least expensive and eastiest and less wasteful of existing insulation. Does it make sense that the flush beam is smaller than the structural ridge? that's how the lumber yard designer sized it. Do the three 14" glue lams seem undersized for 20' 7" span? I don't want this baby to sag. Thanks for imput. Hope this was an ok place to put this queary.
I don't think this is the right thread to make this post, but I'm not the thread police either. You should have posted that post in your original thread. It makes no sense to have parallel conversations ongoing at the same time about the same subject. I'd suggest copying and pasting your post into that other thread. FKA Blue (eyeddevil)
I'll do just that..... post it new.... kind of related though.
It's related but it's also annoying for those that are already advising you in the other thread. From experience, I know that sometimes the debate will start referencing answers that might have been posted in this thread. I'm not telling you that you can't carry on here with it....I just don't think it's that great of an idea, and that doesn't even take into consideration that Larry's trying to figure something out in this thread. It's still an active discussion, meaning, that it hasn't reached the silly stage yet when just about anything might pop up as a post. That's coming soon...
FKA Blue (eyeddevil)
>> The other is driven by a desire to make their surrounding more efficient, longer lasting, beautiful, etc, etc. The cost, time, and work required is secondary. They will find a way to pay for it. <<
Right... but even artisans need to put food on the table. If one is not building professionally, or really doesn't need to work, this doesn't apply. The pro's who are really successful make the craft and the money both work.
I guess everyone wants to find a superb craftsman who's work is his art and doesn't mind making $8 an hr and loves to work 80 yrs a week. I've got some other fantasies too. The other day a real estate agent I know was talking about a neighborhood that had a 2500 sq ft minimum and a $750k minimum price. Where do I sign up???? :-)
BTW take a look at my profile. Also BTW - You aught to fill out your profile too.
Edited 11/18/2007 2:53 pm ET by Matt
The thing about keepoing the ties in the lower third has to do with whether it will funcion as a rafter tie to keep the walls from spreading with no styructural ridge. What these guys are hitting on is that it can trnsfer aa point load to the rafter at the cconnection point so the rafter needs to be large enough to handle that. Soimetimes is, sometimes ain't
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Years ago, in my dumber youth days, I also attached my garage ceiling ties to the rafters. I had an 8' rear wall and a higher front wall, so the wall tie sat on the front wall and was attached to the rear rafters.
It caused the rear rafters to sag.
I suspect you will experience the same fate unless you beef up the rafters that are supporting the ceiling tie with some form of a strut that truly trusses the installation.
FKA Blue (eyeddevil)
When he said he moved the tie a foot up, I was thinking along the length of the rafters. I'd be surprised if that would cause deflection.
Then I re-read and saw he has a 4/12 and raised the ties a foot, or a quarter of the span. That's not good.
I'm not an engineer.
I've come across this in the past.
If you don't put your braces in the right places to actully "truss" it, all you are doing is adding to the dead load weight hanging off of the rafters, and making it worse.
At this point I would probably get in my time machine. Go back to the day before I did this and plan it out through to the end.
One of the first things I would have considered, is just putting up a ridge beam and cutting them all out.
Remodeling Contractor just on the other side of the Glass City
You are dealing with 2 things here: Rafter sizing and ceiling joist sizing.
Ceiling joist sizing: Take a look at page 8.4 of this Florida building code .pdf document: http://buildingofficial.com/2005code/2004_Florida_Revisions_Residential_building.pdf Disclaimer: I'll guess you don't live in Florida, but the values will still be a good general reference alos noting that these values are for zero snow load. If you can't open that doc (hope you aren't on dialup) Google for "CEILING JOIST SPANS FOR COMMON LUMBER SPECIES" or similar.
Rafter sizing: Take a look at page 8.10 of that same document. Same disclaimer applies. If you can't open that doc Google for "RAFTER SPANS FOR COMMON LUMBER SPECIES"
Here is my point though: when looking at that rafter table 802.5.1(2) look at the notes at the very bottom of the table where it says "The tabulated rafter spans assume that ceiling joists are located at the bottom of the attic space or that some other method of resisting the outward push of the rafters on the bearing walls, such as rafter ties, is provided at that location. When ceiling joists or rafter ties are located higher in the attic space, the rafter spans shall be multiplied by the factors given below:" Which basically says that the rafter spans are reduced by a specified amount as the ceiling joists are moved up higher. The higher the ceiling above the wall top places, the larger the rafter required.
Once you look through these span tables (or similar) and apply your specific scenario, let us know what you have found.
ok,so i read the florida charts and no good news.if i read it right it's barely to code before i touched it,now going by the charts it's not even close.remember this is a garage and just wanting to make it function and perferably the roof stays in place. to say the least there won't be any attic storage.
so here's what i'm thinking now that i'm into this thing. i'm going to go in and double up the 2x6 rafter from the top plate up about 7'. this will put the connection with the rafter tie about midway in that 7 foot and looks like to me it would stiffen that connection and rafter up where it is the weakest.
any thoughts or does this make it worse? thanks for everyones input.larry if a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
I agree that the 7' 2x6s scabs would stiffen up the rafters in the area where they would have been likely to bend/sag. I'd say put a lot of 3" nails in them, like at least 6" OC staggered. Whenever I have a truss repair or similar that requires a scab, the eng always specifies lots of nails - like maybe even 3" OC staggered, which I think is kinda crazy... I assume you will be using the old ceiling joists that you are gonna cut out so there won't be much if any material expense.
BTW - what is the actual length of the new 2x6 ceiling joists? 16'? 18' 20'?
you hit that nail on the head,i 'm going to use the old ties to reinforce the old one's. span on the new clg. joist are right at 16.5,so they are not really big enough either,could kick myself for not stepping to 2x8 but rationalize the old ones were 2x6 spanning 24' so thought it would be ok. may hang 1/2 high strength rock instead of 5/8 to help a little. thanks larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
That sounds like a good practical solution. The nails at the ends of the 7' board do the most work, so throw any extras there. Also a little PL Premium never hurts. That stuff's like magic. If they made rafters out of PL Premium you could just use those.
i love pl, at the end of the day if i don't have glue all over me ,it just hasn't been a good day! then for about the next 3 days looks like i have some sort of skin dying disease.. guess i'll get the chainsaw out and cut down the old ties and see if the walls creak outwards. thanks larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
LOL I know what you mean about the PL.
When you cut out the old ties the walls probably won't move much, maybe a tiny fraction of an inch. The deflection will occur over time. Probably. Maybe.
Good luck though. I love a good excuse to break out the chainsaw.
Is this a gable roof? If so, how about turning the ridge board into a ridge beam?
it is a gable roof and i thought about a ridge beam,but it would land in the middle of a 18' oh door. so then i get to dealing with the load across the header.i thought that would create more problems so went this way. larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
So you want the ceiling higher... here is another idea: Raise the whole building except for the foundation up a foot or so. Jack it up and add a block and brick stemwall or add to the existing stemwall. You get the higher ceiling, and keep the same roof structure.
OTOH, if you do go through with the initial method for raising the ceiling, at least put some hurricane ties at the rafter to top plate connection - H2.5s or similar.
roflmao....let me tell you why. bought a house did a addition,didn't like the looks of the existing 2 car garage,so run a slab 50'away,thought about a stem wall ,but then i have to relocate doors,reside,etc.so went with the slab.picked the thing up and moved it and now trying to finish it out to a little workshop.
today i'm thinking instead of all this effort i screwed up,should've knocked it down and built something bigger with 10' ceiling and been ahead of the game,my rational was it was only 2 years old when i bought the place.
ah hindsite ever notice how perfect it is....... larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
Larry, I don't think you have to be too worried. I just finished a job on our very anal structural engineers house, finishing off the upstairs of his garage. He has a very similar situation to yours. Rough 2x8 rafters 16" o.c., rafter ties somewhere near the 1/3 point of the span. It's only a few years old but there was a noticable bow in the kneewall the rafters landed on. Probably 3/4" out in the center of a 30' long wall. He said he wasn't worried about it. We shimmed the strapping on the rafters (I know you guys don't use strapping down there but this is why we do) and let it go at that. And we have snow load. Worst case you'll have some bowing in the rafters and the wall.
I think Matt is right. Raise it up about 3 1/2 feet with block. Put a brick veneer on the bottom and redo the doors...no big deal. Add a little interesting details over the doors instead of residing everything. Do you need us to come over there to have a shop raising? FKA Blue (eyeddevil)
lets see if we could figure the cost for raising.i've already moved this thing once so i know it's around 7k lbs. now if each guy lifts 100lbs=70 guys x 4 beers before lift +another 4 after =560 x1.50 =900.00 70 staeks for after the liftx 10=700.thats 1600.00 just for labor.
read my sign on name,i think i'd be better off just getting the bobcat out and make a pile of sticks.
what was that about something getting silly? :] larryif a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
If you have a bobcat, lifting that will be a piece of cake. Just lift it one block at a time on each corner. You'll be done before your first pot of coffee, working alone! These things can get complicated in a hurry eh? FKA Blue (eyeddevil)