I want to install two lifts in my garage but need more height. The garage has trusses. Rafters have been around long before trusses why couldn't I just replace the trusses with rafters and rafter ties? The garage has a 4/12 pitch on one side the other is 5/12 and about 26 feet wide
Truss question. Replace with rafters?
- Thread starter ng8264723
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Jlbc212
Well-known member
Just about anything is doable with enough time and money.
Rafter ties are not always a suitable substitute for ceiling joists. You may want to look into installing a ridge girder.
Rafter ties are not always a suitable substitute for ceiling joists. You may want to look into installing a ridge girder.
WordMan
ALLIANCE MEMBER
Given your location, you're probably best off calling in an engineer.
bigdav160
Well-known member
Funny, around here cut roofs are still more popular than trusses. Cheaper too
Chuckster in NJ
Well-known member
Well you have no snow loads to worry about but wind may be a problem so I suggest consulting an engineer because when you go to sell the place this "modification" will be picked up by an inspection and either YOU or your loved ones will have to deal with it.
Do it once the right way!
Do it once the right way!
TheLawnRanger
Well-known member
Most people with trusses around here are living with a hernia.
Innovate1
Well-known member
You don't HAVE to hire an engineer (well, maybe you do to meet your local code but I am ignoring that for the moment) but is the much safer way to go. If you understand the loads on the structure and how they are transferred between the pieces then you can calculate and design the structure yourself. But there is more to it than just putting up rafters in place of the trusses. Something has to hold up the center of the roof - trusses are good at that. The older homes that used rafters almost always had interior supporting walls to hold up the center of the roof. Or a ridge beam as others have mentioned. Note that a ridge beam supports the whole ridge and so needs substantial support at the ends. Without some way to hold up the ridge the rafters will push out the side walls and the ridge will sag. It's a fairly common problem that has been discussed in other threads. Another issue is the length of the rafters and how big they need to be although yours are only about 15' long so not a huge issue - you need something significantly bigger than a 2 x 4 but nothing too crazy big for those.
matt_i
Well-known member
To size the structrual ridge beam.
The rafters are the easy part. Understanding "distributed load" and using that to size a piece of framing for the center.
Also because a ridge beam concentrates load into the ends (guessing you don't want a mid-span center post) there's now big vertical loads into the ends, and suddenly where there was a end-wall garage door with a barely-there-header, it now is pressed into extreme service.
A person with a mechanical mind and an attitude for some overkill can do a good job, the engineer will give you a rock-solid solution that's backed by a person's experience, training, and the liability of their license at stake.
ace10
Well-known member
Your first post suggested simply replacing trusses with rafters and ties alone.
That isn't how it works.
And that's why you should hire an engineer.
WordMan
ALLIANCE MEMBER
That's a theory, but no one mentioned the mods on the trusses in the garage when we bought this house.
karoc
Well-known member
I have written my thoughts on this question several times even when it was first posted. I just could not come up with an answer and I did not want to say get an engineer. But an engineer design those trusses and if that engineer figures showed that those cross braces and everything associated with that design was not needed I believe that it would not be there. I just can't figure out how to go about this using the common sense method other than taking roof off down to top plates install scissors trusses for that 26' span. There is just no short cuts on this kind project, having peace of mind is worth going at it correctly is worth it.
joe_padavano
Well-known member
Depending on how much height you need, you may be able to use scissor trusses, which will be a lot easier to swap out than rafters.
MikeF2316
Well-known member
My thoughts exactly! 26 feet is a long distance for rafters.
johnharris
Well-known member
I had 10' of concrete poured in 2 spots for the 2 post lift I'll be installing when the garage is complete. My brother in law is a civil engineer and used a program to calculate the support the 16' rafters will need. They will have a 30' ridge beam between that will be spliced in the middle. In the middle of garage will be a post under that splice. Cross ties will be 3' higher than the top boards.
My walls will be 12' so I did call lumber yards to get estimates on scissor trusses. If lumber prices do drop I will purchase scissor trusses instead of making my own rafters.
My walls will be 12' so I did call lumber yards to get estimates on scissor trusses. If lumber prices do drop I will purchase scissor trusses instead of making my own rafters.
rsanter
Well-known member
Are you putting 2 post or 4 post lifts in.
I was looking ata house that had an extra garage that if I bought I would have wanted to add a lift. Like you the ceiling height was not enough.
My though was to install 2 posts, one on either side of the 2 post lift posts and in the same concrete footing that would have to be done for the lift.
Span a steel I beam across the posts and then I would have support for the roof when removing the ties a small well as a point for a chain hoist for lifting stuff
Bob
I was looking ata house that had an extra garage that if I bought I would have wanted to add a lift. Like you the ceiling height was not enough.
My though was to install 2 posts, one on either side of the 2 post lift posts and in the same concrete footing that would have to be done for the lift.
Span a steel I beam across the posts and then I would have support for the roof when removing the ties a small well as a point for a chain hoist for lifting stuff
Bob
Natty Bumppo
Well-known member
How much height are looking to gain? If you're going through the trouble and expense of removing the trusses to increase the height for your lift, can you simply increase the wall height once the trusses are off and then put them right back on?
I am not an engineer, but I do think 2x12' rafters spaced 12'" OC are going to be just within the load limit for a 26' span...I think. But that's for a 12/12 pitch roof. If you then put metal on the roof you will have almost no snow load.
I am not an engineer, but I do think 2x12' rafters spaced 12'" OC are going to be just within the load limit for a 26' span...I think. But that's for a 12/12 pitch roof. If you then put metal on the roof you will have almost no snow load.
CraigStu
Well-known member
I think we need some pics or drawings of what you have and what you are thinking of doing. Too many different trusses as well as different rafter designs.
firebirdparts
Well-known member
It's traditional in this forum to treat people with disdain who ask framing questions. I don't know why that is, but I can say that this exact question has been asked here in this forum many hundreds of times, and that makes a difference in the answers of course. A question you might ask yourself is what do you personally understand about forces? Do you understand where the weight is going?
In a 26 foot wide building, modest size rafters are graciously adequate. It should be obvious to anybody with an ounce of sense that the weight of the roof would like to push the rafters down, and the best way for the rafters to fall is to push the walls apart, or break loose from the roof and slide. So the rafters would like to push the walls apart. There are two ways to deal with this; you can either tie the walls together or you can hold the center of the roof up. The former is much easier, by a mile. The latter takes a lot of stress off the rest of the roof.
Since you want to raise the effective ceiling height, by definition you don't want to do the former.
So this raises a question that is something like this:
If I tie the rafters together above wall height, increasing the bending forces on the rafters, then how big would the rafters need to be? That's an engineering question.
Or, if you want to hold up the peak of the building, you need structure spanning the entire buliding holding up half the weight of the entire roof. No joke.
I am only going to change the interior height above the lifts. If the garage was framed traditionally I would just need to raise the rafter ties. I think this is in becoming unessarily complicated....
I plan on having rafter ties just above the lift. In my case I would be raising the ceiling about 2 feet. I would if I could just order some scissor trusses. I would just replace the trusses over the lift with the scissor units
I plan on having rafter ties just above the lift. In my case I would be raising the ceiling about 2 feet. I would if I could just order some scissor trusses. I would just replace the trusses over the lift with the scissor units
Dustball
Well-known member
Do you plan on re-roofing when you do the framing changes?
Firebrick43
Well-known member
If you use the appropriate size rafter for your area(anyone with some intelligence can read a rafter table!) you will be fine. A ridge beam is entirely unnecessary IF using rafter ties. What many think of a beam is just there to help install rafters in place and not necessary in your case. I would screw (with structural rated screws, many are not) the rafters to the sides of the existing truss and then once in place(and properly fastened to the top plate) cut the bottom of the truss away. This will allow the roof deck attachment to be done without reroofing.
Only if you want a true cathedral ceiling does one need a roof ridge beam.
Remember you can NOT put the rafter ties more than 1/3 of the roof height up from the bottom. Also if you plan on insulating/installing a ceiling they shouldn’t be rafter tires but ceiling joist which are much deeper to span that length. Ceiling joist can function as rafter ties but rafter ties can not function as ceiling joist.
Also it’s wise to add collar ties to help prevent uplift.
Most of the time Trusses are used because they are cheaper than conventional framing but they eat up your headroom and attic storage space.
When you replace them make sure you size the new rafters properly, rafter span and load for your location. As said above this is where an engineer or architect may be of help. Also as said above make sure you have proper collar and rafter ties.
When you replace them make sure you size the new rafters properly, rafter span and load for your location. As said above this is where an engineer or architect may be of help. Also as said above make sure you have proper collar and rafter ties.
tstaude
Well-known member
I have trusses that span 25' and here is what I did to gain clearance:
first I sistered 2x10's to the existing top 2x6's, I was really picky about them fitting perfectly at the top.
Then I added a 6' long 2x10 collar tie at the top.
Finished off by through bolting everything with 1/2-13 hardware.
then was the moment of truth....cutting the bottom chord
I cut and it didn't move at all!
this method worked great in my pole barn, let me know if you want any pictures.
first I sistered 2x10's to the existing top 2x6's, I was really picky about them fitting perfectly at the top.
Then I added a 6' long 2x10 collar tie at the top.
Finished off by through bolting everything with 1/2-13 hardware.
then was the moment of truth....cutting the bottom chord
I cut and it didn't move at all!
this method worked great in my pole barn, let me know if you want any pictures.
Falcon67
Well-known member
Should not be a problem - see the tail end of my build thread for similar. I raised an area way more than 2'. As "rafter ties" move up from the plate, they will increase the roof loading on the rafters, so be sure you take that into account. IMHO and experience, "collar ties" are virtually worthless, good for maybe wind areas to help prevent rafter uplift off the ridge board and a nice place to hang ceiling material.
firebirdparts
Well-known member
Well, feel free to let us know what you want to do. The less you do, the cheaper it is, and the less it'll weigh.
Also, like I said, this exact question has been asked hundreds of times. Literal hundreds. Not saying you need to read any of that, but it might save you trying to explain what you want to do.
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Michigan Mike
Well-known member
Get some scissor trusses made that match the pitch of the existing trusses. Cut out all the bracing in the area that you want to raise. Slide the scissor truss next to the existing truss. Nail screw or otherwise fasten the old truss to the new truss. Cut out anything on the old truss that hangs below the new scissor truss. Redo the bracing . This is probably the least disruptive method no removing the roof no collar ties no reroof.
karoc
Well-known member
That's a good ideal,good plan Mike
theoldwizard1
Well-known member
Properly sized you can. Don't even THINK about using the top chord of your existing rafter.
The second problem is fitting a ridge board in FIRST while the trusses are still there.
A ridge board is used to join rafters at the top of a roof structure. It is not a structural member acting in compression or tension or carry any load, it simply receives and holds together the rafters. A ridge board is most commonly 1″ thick or less.
Simple solution to the OP situation that has been documented in the GJ and other forums:
buy the lift,
install the lift,
use the lift** to raise the complete roof assembly *24”,
install 24” wall around the complete garage.
*24” could be 36” or what ever dimension required.
**4 corner cribbing with jacks are the alternative to the lift to raise the roof.
Sureshot
ALLIANCE MEMBER
I've sat and looked at mine quite a bit wondering how to raise it as well. My thought was to sister to the side of the existing trusses with glue, screws, plywood etc then run "joists" on hangers in between under the strapping. My current trusses don't all sit on posts so I would add a post under those trusses. My shop is a pole building with metal roof and I have no snow load.
imjustdave
Well-known member
This seems the best idea so far, especially if your just doing a small section of the lift area I suspect you looking at 4-6 trusses.
In terms of design "Engineering" I suspect any reputable truss company has a computer that can whip out the design in 5-10 min for you. and get you stamped design if needed. I called a local place to get some idea on costs for a shop and ended up with 4 different truss designs and pricing in about an hr from the sales guy. And they already know the snow, wind loading ETC...
I feel your biggest issue is how are you going to install a truss without opening up the roof some. Most trusses extend past the wall, IF you removed a few trusses you might be able to angle the new one in, otherwise I suspect your going to have to get some sort of 80% pre built truss so you can slide both sides in then do some sort of finish connection work. I suspect they have something just never done it.
You didn't mention how your roof "age" or how big the shop is, but you might really like doing the entire thing, and put some 6/12 7/12 in it's place I know it might sound extreme but your talking a few more rafters and sheathing especially if the roof is near replacement time. might even be able to pull up sheeting that is ok to reuse depending on age and how easy the pop up.
You don't seem to be liking your answers; lets streamline the process: Height can be had in either of two ways, raise the roof or lower the slab. Since the slab will be a future discussion, just put in the new slab at the proper elevation.
What makes you think there are no snow loads? In central MA, better be planning for a couple of feet.
LX-Markham
Well-known member
As a structural engineer, I tackled this exact problem.
I had a 19x19 garage that I was going to put in a 4-post double lift. I just needed to get rid of all the trusses. Structural steel framing around the top of the walls to handle the “kick”, and new rafters installed sistered to the top chords of the trusses. All work was done in place, and much to the contractor’s surprise quite easily.
Full details in my sig link
I had a 19x19 garage that I was going to put in a 4-post double lift. I just needed to get rid of all the trusses. Structural steel framing around the top of the walls to handle the “kick”, and new rafters installed sistered to the top chords of the trusses. All work was done in place, and much to the contractor’s surprise quite easily.
Full details in my sig link
firebirdparts
Well-known member
Thank you for posting this! That is awesome. I have a stiffened wall design in my garage also, and I didn't even mention it in this thread because it's so unusual. I don't know if somebody approving plans would even approve it.
That's a nice plan. Joinery is key to keeping the rafters on, and that's the only difficult part with a stiff wall retrofit.
stingry
Well-known member
As a structural engineer, I tackled this exact problem.
I had a 19x19 garage that I was going to put in a 4-post double lift. I just needed to get rid of all the trusses. Structural steel framing around the top of the walls to handle the “kick”, and new rafters installed sistered to the top chords of the trusses. All work was done in place, and much to the contractor’s surprise quite easily.
Full details in my sig link
In your educated opinion, as an engineer, would rafter ties placed 1/3 of the way up the rafters have performed as well as the steel top plate reinforcement?
LX-Markham
Well-known member
No. As mentioned somewhere else in this thread, rafter ties are (almost) useless. They are not completely useless, but the higher up you put them, the higher the stress on them and the rafters. Not easy to make them work, especially here where we have a lot of snow.
I have “collar ties” placed on mine, but only because I wanted a flat portion to the cathedral.
I have “collar ties” placed on mine, but only because I wanted a flat portion to the cathedral.
No. As mentioned somewhere else in this thread, rafter ties are (almost) useless. They are not completely useless, but the higher up you put them, the higher the stress on them and the rafters. Not easy to make them work, especially here where we have a lot of snow.
I have “collar ties” placed on mine, but only because I wanted a flat portion to the cathedral.
I'll call you on this statement. Either you have 'perma snow' piles on both sides of your garage or you're really someplace that doesn't have snow, not Ontario. What would top plate steel do to hold the walls together?
LX-Markham
Well-known member
Across the the two gable ends, there are heavy steel angles to tie the steel channels together. So it forms a square frame, with the channels acting as beams on the sides, and the angles acting as ties to hold everything together.
