Please advise on my garage

[zadeluca]

Hello, I'm looking for some advice on my garage. I'm not a true engineer (I engineer software :)) but my degree is in math so I should be able to follow along. Please forgive me if my terminology is wrong, and also forgive the very crude Microsoft Paint drawing:

I don't have enough posts to link to images, so please go to my profile and under contact info my "homepage" is an imageshack gallery that I set up for this thread

My goals: 1) enough ceiling clearance to properly use the 7' garage door that is already installed - it sometimes gets caught on the first ceiling joist, and a garage door opener is currently out of the question (no room between the door and ceiling joists)
2) insulate and finish the garage. I'm a car enthusiast so I would like it to be a nice place to work, especially in the winter when I have nothing better to do.

My plan/idea: install a 2x6x16' rafter tie at EVERY rafter. Obviously this will not span the entire width of the garage. I did the math and in order for these rafter ties to span the roof, they would have to sit 19" above the current ceiling joists (so 19" above the top plate of the wall). This is still less than 1/3 the distance between the top plate and ridge. I did not plan on modifying/adding the collar ties.

Given that there will no longer be any ceiling joists attached to the top plate (I'll cut them out after i install all of the new rafter ties), I plan to install double plate rafter tie brackets at every rafter (they are in one of the pics).

I'm not sure of the snow load number, but I live in Central NY so we get a decent amount of snow each year.

So, am I on drugs or is this feasible? And if not, what would be? In either case, I am not confident that the garage is structurally sound in its current state. I added a few pics of it as well if they help anyone.

Thanks a ton,
Zach

[mjpliv]

Have you considered using low lift hardware for the garage door? If may save you a whole lot of time and money. This type of hardware needs a little less headroom than the standard stuff.

[zadeluca]

Thanks for the reply. Yes I have considered that, but I only have 4" between the top of the door and the bottom of the ceiling joists. Why the walls are 7' 4" is unknown to me. As it is, the previous owner already raised the first ceiling joist to get the door to even open at all.

If it were only to get a usable garage door and opener, I probably would do a combination of what you said about new hardware and repositioning of the first two ceiling joists. Heck, a friend even suggested that it may even be cheaper and/or easier to install a shorter door and reframe the front wall than to do what I am suggesting.

But I don't want to stop there. I was fortunate enough to buy a house that was gutted and pretty nicely redone by the previous owner. Unfortunately, he didnt touch the garage. I would like it to be just as nice, as I spend much of my free time out there, and would spend more if I could insulate it and heat it in the winter.

And like I said, I don't really know what the codes say, but just by walking into the garage and looking up I am not confident that it is structurally sound as-is. I mean, not only are the 2x6 ceiling joists spanning almost 24', there are only 5 of them since they are spaced every 4'. It just doesnt seem right.

mjpliv, would you be able to post the 4 images from that gallery? Or at least just the Paint drawing? It might help me get more responses, and I don't want to make 13 useless posts to get my post count above 15 :)

[mjpliv]

http://img4.imageshack.us/gal.php?g=dsc00462xgp.jpg

[mjpliv]

It should be no problem moving the 2x6's up the rafter but no more than 25% or 30% of the total rise of the rafter. The key is making sure you have a solid connection between these collar ties and the rafters. You were concerned about their span but they are not there to carry any loads. They are there to prevent the walls from being pushed out by the rafters. That being said, only relocate one at a time and don't remove the next one until the first is well nailed to the rafter. If you want to later on, you can add a "king post" or vertical piece of lumber from the collar ties up to the ridge area to help support the collar ties and if you want to throw some light weight (Note - I specified "light weight") stuff up there for storage you should be ok.

When you remove each collar tie from the rafter connection, make sure that the rafter is still well sucured to the top plate. It should be toenailed with spikes on each side. I would suggest no less than for 3-1/2" nails for each new collar tie connection with the nails clinched over where they penetrate.

[zadeluca]

It should be no problem moving the 2x6's up the rafter but no more than 25% or 30% of the total rise of the rafter.

Great!

The key is making sure you have a solid connection between these collar ties and the rafters. You were concerned about their span but they are not there to carry any loads. They are there to prevent the walls from being pushed out by the rafters. That being said, only relocate one at a time and don't remove the next one until the first is well nailed to the rafter. If you want to later on, you can add a "king post" or vertical piece of lumber from the collar ties up to the ridge area to help support the collar ties and if you want to throw some light weight (Note - I specified "light weight") stuff up there for storage you should be ok.

When you say collar ties do you mean rafter ties? Sorry im not good with the lingo yet, but i thought collar ties were within the top 1/3 of the total ridge height whereas rafter ties were within the bottom 1/3 (and if they were actually on the wall you can call them ceiling joists). Hah, I'm a newbie. The reason I ask is that there are currently collar ties on each rafter that has a ceiling joist, and they are about 1.5' below the ridge board. You can see them in one of the pics, and there is actually what you called a "king post" connecting each ceiling joist to the collar tie on the same rafter.

When you remove each collar tie from the rafter connection, make sure that the rafter is still well sucured to the top plate. It should be toenailed with spikes on each side.

Right. I was planning to use those "double plate rafter ties" that are in one of the pics to reinforce that connection. Would that be a good idea or overkill?

What about the fact that the ceiling joists only exist at every third rafter? As you explained, they are only there to prevent the walls from being pushed out, so does that mean that 1 every 4ft is sufficient? And if yes, since I will be raising the ceiling joists up to 30% of the rise of the rafter, and this will diminish the joists ability to keep the walls from spreading, would 1 joist every 3rd rafter still be sufficient at that height? Or should I do as I planed and put 1 at each rafter? (or 1 every other?).

Sorry for so many questions, but not I only am I trying to do this the right way, I'm trying to learn in the process. I have read tons about roofs and construction in general and its frustrating because the only thing I have learned for certain is that for every rule there is always an exception to that rule :)

[mjpliv]

The tie up top isn't realy doing much other than being a handy way to tie in the king post. The collar ties become ceiling joists when they have to carry ceiling loads. The place was built with collar ties at 4' OC so, if the walls haven't pushed out yet, then it is unlikely that they will if you move them to the prescribed height. You only have a 12' span on the rafter so they are not very highly loaded to begin with. If you want to add collar ties, knock yourself out. They can't hurt and will improve thier capacity to store "light" stuff on top of them.

[Don_P]

It's semantics but the terminology used in the code is "rafter tie" for a ceiling joist or lower third thrust restraining tie, a "collar tie" or ridge strap is used in the upper third to restrain the rafters in uplift, R802.3.1 in the more recent versions uses this terminology and it would be good to move in that direction for clarity, I've tried to do that here. Collar ties are required every 4'. Rafter ties at every pair.

US code limits the rafter ties to the lower third and there is a multiplication factor to reduce allowable span at the bottom of each span table in R802.5.1. There is a nail count table at the end of the rafter tables for the tie/rafter connection (it reads a little light by the theoretical math, don't skimp! They've already done that.) Yes it is a good idea to use the simpson hurricane tie to hold it down in high wind.

[zadeluca]

Collar ties are required every 4'. Rafter ties at every pair.

stupid question... the first time i read through this by "every pair" i assumed you meant at every other rafter (every 32" in my case). but should this instead be read as at every rafter(16" for me), with pair meaning one on either side of the ridge? and if so, is this still true when a ceiling will not be installed on top of the ties? not trying to cheap out or anything, im just trying to understand because you and mjpliv gave me different answers in that respect.

US code limits the rafter ties to the lower third and there is a multiplication factor to reduce allowable span at the bottom of each span table in R802.5.1. There is a nail count table at the end of the rafter tables for the tie/rafter connection (it reads a little light by the theoretical math, don't skimp! They've already done that.) Yes it is a good idea to use the simpson hurricane tie to hold it down in high wind.

hmm, well it looks like im going to need to buy a code book to do this properly. and of course they've already skimped, thats why its the minimum! i will definitely use the hurricane ties as well

[Don_P]

mjpliv gave you practical advice, I read you the law. To get design strength you need to tie every set. Its a garage, you're an adult, your call :)

No need to purchase, my state is here, its a pretty stock version, roof stuff is chapter 8
https://www2.iccsafe.org/states/Virginia/Residential/Res-Frameset.html

[mjpliv]

That shows the difference in code requirements from one area to another and one country to another. This thread made me go back and re-read our 9.23.13 code section Roof and Ceiling Framing. In this code reference ceiling joists and collar ties are dealt with in the same section and are not differentiated from each other with the exception of bracing requirements. Both can be used to used as intermediate support for rafters (by moving them up the rafter).

And like Don P says - Its a garage, you're an adult, your call :-)

[mjpliv]

Another interesting note is how the new and improved, handy dandy, recently adopted 2005 National Building Code of Canada works. They have added an "intent" feature which details the reason for the code reference. If a builder can prove that the "intent" of the code has been met without complying with the letter of the code then that solution may be found acceptable by the building officials.

Perhaps it is their way of admitting that "There is more than one way to skin a cat!"

[Don_P]

Now that would be handy. I'm in a discussion on another forum with some, ummm, young whippersnapper inspectors, who deem their interpretation of code to be its intent. I've quoted from an old code book to show how one phrase has evolved through the years thereby giving background to the intent of the current code language. I don't expect to sway them, we do have a commentary but it can fall short as well. I have generally worked around reasonable inspectors though. Are any of your code documents available online?

[mjpliv]

They may be but I have yet to run across them. There are bits and pieces but no full sets as far as I know. They make too much money selling them!

[zadeluca]

alright guys, thanks for the help. Don P, i found the codes for new york by going to the site that you linked to. i'll look into them.

i understand what you guys are saying, its obviously my call. i guess i was hoping for a more definitive answer, but from your responses it appears that its not an exact science. i think i have enough info to go on though. i'll look at the codes and try to find out or calculate the dead/live/snow loads to make sure the spans are right, if thats even possible.

one last question, if you dont mind. what is the board called that goes from the front wall up to the ridge? you can see it in the third pic. there is one at the back wall too. do i need that or can i get rid of it? or reposition it so that its above the new ties that i will install? i want to be able to finish the ceiling without it sticking out...

[mjpliv]

It is a brace that was installed to hold the roof framing square during the sheathing process or it was added to laterally brace the top of the door opening/gable against the finished roof diaphram. Either way, if you are reframing the door opening the you should be able to temporarily remove it and reposition it.

[Don_P]

It is a wind brace to keep the gable from blowing in or out. The gable is not well framed so do replace it at a minimum.

If you wish to build to code the book is pretty definitive To build to safely withstand the anticipated design loads one ties each properly sized rafter set with the required number of nails. Omitting ties yields a proportionally weaker roof that will diminish its safety margin or fail at lower loading. If you want to build it "properly" then follow the prescriptions in the codebook and feel free to ask questions. If you wish to build to a lower standard for an accessory building I'm simply trying not to argue with anyone as its probably not going to be a life safety issue.

[zadeluca]

Thanks Don, I understand. Even though it is not a life safety issue as you put it, I'd rather do it "properly" than risk the structure collapsing, etc. Spending a little more (or even a lot more, if the situation warrants it) is in my opinion almost always worth it, even if it only adds peace of mind. I think the phrase "do it right or don't do it at all" describes my point of view on this project and every other one I attempt (such as my next project, which will be getting a concrete floor poured in my 126-year old stone foundation home). Of course, "right" is often based on opinion as well, but we won't get into that...

I will study the codes and try to build as they suggest. If I get stuck I'll be sure to ask, and I'll look into the gable framing as well. Thanks again to both of you, I'll update this in a few weeks.

[mjpliv]

Don's right! Opinions are like a##holes! Everybody has one! :-)

If you asked a dozen people you would probably get a dozen diffrent nuggets of wisdom. And also. like Don says, this not a structure that houses people need not be built to the strict letter of the code.

In addition to all of that, my advice comes from experience building in my area using our codes and bylaws. Don is working under an entirely different set of rules and you could be too. It all comes down to what you want and what the local building authority wants to see. Where this is a minor renovation to the garage, it is possible that the local building authority won't even be involved.

Best of luck with the project regardless of your approach.