Truss Modification for Car Lift

[RyanEricW]

The only difficulty is getting the trusses up next to the other ones, under the roof sheathing, and over the wall top plates. Once you get them into place, the rest of the work is easy!

Yes I might have a few words flying around getting those in place lol. Thank you for your help

 

[Falcon67]

You do realize that rafters rely on a ridge beam or ceiling joists to keep them from spreading, correct? You can't just put up a rafter without a means of supporting it.

Modifying an existing roof support structure requires engineering beyond rafter tables.

Rafters use a ridge board (not a beam) that does not carry any weight. The rafter ends merely land on it. Yes the joist works to keep the walls from bowing out, but a few missing won't have much effect. If the area is boxed like an attic stair install, the loads will transfer to the remaining joists.

 

[bczygan]

Hey Bill, yes, I have posted it here before because I am proud of the work we did and how it turned out.
A friend of mine came up with the design a few years ago. He is a structural engineer. He worked for a company in the Lansing area, I can't remember the name.
He worked it all out in about half an hour. Something about load transfer and shear strengths. Over my head, I know that. I trust him, no worries on my part.
Mark

Ahhh.....You said some magic words.

Sounds like you got a good and reliable solution.

Engineering is really just about making sure something will perform as required. Without it, you just don't know.

I'm glad you went to the effort and expense to have that assurance.

Bill

 

[bczygan]

OP,

You have a good solution with the scissor trusses.

See if the mfg. has a detail for the heel, that will make installation easier.

Bill

 

[gungatim]

there are some good ideas in this thread:
http://www.garagejournal.com/forum/showthread.php?t=251077&highlight=gungatim+truss&showall=1

my solution to the same issue starts in post #34.

I'm going on 3 years with zero issues with my setup. I worked out my design with an experienced engineer & builder relative. we discussed cable tension systems, sistering trusses, adding ridge beam/rafters, but in the end I spent less than a week working alone and only about a hundred bucks in lumber.

just pointing out that this is more common than some may have you believe, and can be done safely, properly, and cheaply IF you know what you are doing.

YMMV, use at your own risk, for entertainment purposes only, past history not indicative of future results, etc....

 

[manwithtools]

Rafters use a ridge board (not a beam) that does not carry any weight. The rafter ends merely land on it. Yes the joist works to keep the walls from bowing out, but a few missing won't have much effect. If the area is boxed like an attic stair install, the loads will transfer to the remaining joists.

I think there might be some semantics in this discussion. Rafters over an open area - think cathedral ceiling - utilize a structural ridge or ridgebeam to carry the load of the roof, not a ridgeboard. Rafters that are tied together by ceiling joist can use a ridgeboard. A ridgeboard does not carry any load from the rafters and roof, its simply a way to hold the rafters at the proper spacing during framing.

Here's a link to decent explanation:http://inspectapedia.com/structure/Cathedral_Ceiling_Roof_Framing.php

 

[ssdave]

there are some good ideas in this thread:
http://www.garagejournal.com/forum/showthread.php?t=251077&highlight=gungatim+truss&showall=1

my solution to the same issue starts in post #34.

I'm going on 3 years with zero issues with my setup. I worked out my design with an experienced engineer & builder relative. we discussed cable tension systems, sistering trusses, adding ridge beam/rafters, but in the end I spent less than a week working alone and only about a hundred bucks in lumber.

just pointing out that this is more common than some may have you believe, and can be done safely, properly, and cheaply IF you know what you are doing.

YMMV, use at your own risk, for entertainment purposes only, past history not indicative of future results, etc....

Looked at your solution, and the key difference is that your structure is a pole barn, which is moment resisting. A frame wall garage is not moment resisting, so the trusses have to have bottom chord integrity to prevent moments from being transferred to the walls. In your case, the trusses are there to hold the roof up in a convenient way, but may not be absolutely needed for structural stability in resisting lateral forces, or are only a part of the structural stability in resisting lateral forces. In a frame wall building, the trusses are essential in acting as a system member resisting lateral forces, and removing some of them may compromise that lateral stability.

 

[Falcon67]

>Rafters over an open area - think cathedral ceiling - utilize a structural ridge or ridgebeam to carry the load of the roof,

Aware of that - a ridge beam also requires supports on the ends to carry the loads down to the foundation. Rafters don't necessarily require joists - think building with concrete block walls. Rafters and joists are sized separately in the span tables, not as a combined unit.

 

[gungatim]

Looked at your solution, and the key difference is that your structure is a pole barn, which is moment resisting. A frame wall garage is not moment resisting, so the trusses have to have bottom chord integrity to prevent moments from being transferred to the walls. In your case, the trusses are there to hold the roof up in a convenient way, but may not be absolutely needed for structural stability in resisting lateral forces, or are only a part of the structural stability in resisting lateral forces. In a frame wall building, the trusses are essential in acting as a system member resisting lateral forces, and removing some of them may compromise that lateral stability.

yep. that was noted in a couple posts further down that thread...if it's a frame wall on a foundation, there would need to be some additional tying to the wall engineered to resist the lateral wall movement, but it can still be done in a couple different ways.

 

[lakeroadster]

The only difficulty is getting the trusses up next to the other ones, under the roof sheathing, and over the wall top plates. Once you get them into place, the rest of the work is easy!

Yes I might have a few words flying around getting those in place lol. Thank you for your help

They will be "relatively easy" to install IF the truss designer takes the installation into consideration (see how big that "IF" is).

The new truss will not need the extensions for the overhang, and they could easily be designed to be 1-1/2" shorter in height from the upper chord to bottom chord at the wall top plate. This 1-1/2" would allow space to maneuver the truss into position. Once located sitting on the wall top plate then a 2 x 4 doubler could be placed under the truss.

 

[ovilla]

Go to your truss builder and just ask for two scissor truss HALVES. This makes it very easy to lift into place (one half at a time) and sister next to an existing truss and then use whatever hardware or method that they recommend for connecting both halves together. Then cut out anything below the newly installed scissor truss. That's it! No big fuss!

If you are overtly worried about the trusses being able to carry your roof loads then ask them to build the halves to carry more of a load. They will typically just end up increasing the stock of the wood in use, like bumping up to 2x6's instead of 2X4's.

Remember that building codes are for the MINIMUM specifications needed. Just like when it comes to building 36" door or 36" window headers. Yes, you can do the math and figure out if you need a doubled up 2X6, 2X8, or just use 2X12 lumber and call it a day. Going above the minimum code requirements may cost more (or be deemed wasteful - I agree) but it simplifies many things. It's like using 12 gauge wire for your whole house when you're using 15amp circuits for most rooms.

 

[RyanEricW]

They will be "relatively easy" to install IF the truss designer takes the installation into consideration (see how big that "IF" is).

The new truss will not need the extensions for the overhang, and they could easily be designed to be 1-1/2" shorter in height from the upper chord to bottom chord at the wall top plate. This 1-1/2" would allow space to maneuver the truss into position. Once located sitting on the wall top plate then a 2 x 4 doubler could be placed under the truss.

The truss designer did take that into consideration (see attached)

Had a hell of a time uploading this pdf, the forum upload limits are ancient it seems. 145kb for a pdf? lol

 

[lakeroadster]

Making progress... congrat's on that.

With a 2/12 pitch you'll only be gaining about 2 ft, and that's right at the center. Have you done a layout of the lift, with the vehicles you own, and the new scissor trusses, to see if it's enough height?

 

[Radix2]

Making progress... congrat's on that.

With a 2/12 pitch you'll only be gaining about 2 ft, and that's right at the center. Have you done a layout of the lift, with the vehicles you own, and the new scissor trusses, to see if it's enough height?

I would ask the truss guy to spec out girder trusses and a ridge beam over your lift area. Then you can have the full 4/12 pitch inside and get more room as Lakeroadster points out.

It should only take buying two trusses and the rest should be regular lumber.

 

[jdieter]

It'd would be helpful to hear from somebody that's added sistered scissor trusses to an existing trussed building. If the building has any age at all I would really be surprised if the existing trusses are still the same shape as there were when built. I say this because I had an addition built on my garage and the contractor wouldn't use pre-fab trusses because I would see a very definite change in the roof where the old and new meet. He built trusses on site to match the existing trusses and the transition is undetectable.

 

[Falcon67]

I'm going to deal with this and I don't even have trusses.

If I did, I'd be inclined to just build proper sized rafters in the open space. It is a bit easier when you're at 4:12 and above.

 

[RyanEricW]

Update: Still haven't gotten this done, but I've figured something else out with the truss manufacturer to get maximum ceiling height.

Basically what I need to do is get 4 x 2x6 gable trusses, nail 2 together using 10D nails, so pair them up at each end of where I need clearance. Then install "perlins" perpendicular to the truss chords, securing them to the new gable trusses using joist hangers 12" O.C.

The engineer said he accounted for installing insulation, a full ceiling, etc.

Attached are the specs, and a crude drawing I did. The trickiest part will be supporting the roof where I need to cut the top chords of the existing trusses to place the 2x6s that'll span across.

 

[lakeroadster]

Update: Still haven't gotten this done, but I've figured something else out with the truss manufacturer to get maximum ceiling height.

Basically what I need to do is get 4 x 2x6 gable trusses, nail 2 together using 10D nails, so pair them up at each end of where I need clearance. Then install "perlins" perpendicular to the truss chords, securing them to the new gable trusses using joist hangers 12" O.C.

The engineer said he accounted for installing insulation, a full ceiling, etc.

Attached are the specs, and a crude drawing I did. The trickiest part will be supporting the roof where I need to cut the top chords of the existing trusses to place the 2x6s that'll span across.

H--e--l--l--o..... I think there's an echo in here.....

Another option is a couple of heavy duty 2 ply trusses (gable end style) that utilize purlins that locate below the upper chord of the 3 trusses in question.

Once installed those 3 trusses in question could then be removed... except for the top chords.

Lots of options... all of which if done correctly require a knowledgeable truss designer who will stamp his design so you can provide it to the proper jurisdictional authorities.

Good luck in your endeavour!

Sweet, more progress. FWIW, you wont have to support the roof if you..

• Place the new 2 ply trusses that are designed such that...
• the new purlins locate under the existing top chord of the existing trusses.
• Leave the top chord of the old trusses
• Remove the webbing and lower chord of the old trusses.

 

[RyanEricW]

H--e--l--l--o..... I think there's an echo in here.....



Sweet, more progress. FWIW, you wont have to support the roof if you..

• Place the new 2 ply trusses that are designed such that...
• the new purlins locate under the existing top chord of the existing trusses.
• Leave the top chord of the old trusses
• Remove the webbing and lower chord of the old trusses.

Sorry, I meant no offense not correlating the two. I'll have to measure to see if that'll be an issue for max clearance. Placing the purlins under the top chords would definitely be wayyyy easier, but at the same time I would also lose 3 1/2" of ceiling height doing so.

If I can get someone to do this work at a reasonable price, I'll have them move forward, otherwise, I'll be tackling this project myself in one or two weekends.

From what I gather, it'll be easiest to get the trusses up if they aren't nailed together from the factory

 

[RyanEricW]

Speaking of fasteners. I'm a huge fan of screws, but they were telling me to use 10D nails.

I feel safer with something that wont get loose over time and provides clamping force.

Any reason why engineers would say to use nails over screws?

 

[lakeroadster]

Sorry, I meant no offense not correlating the two. I'll have to measure to see if that'll be an issue for max clearance. Placing the purlins under the top chords would definitely be wayyyy easier, but at the same time I would also lose 3 1/2" of ceiling height doing so.

If I can get someone to do this work at a reasonable price, I'll have them move forward, otherwise, I'll be tackling this project myself in one or two weekends.

From what I gather, it'll be easiest to get the trusses up if they aren't nailed together from the factory

Speaking of fasteners. I'm a huge fan of screws, but they were telling me to use 10D nails.

I feel safer with something that wont get loose over time and provides clamping force.

Any reason why engineers would say to use nails over screws?

You would have to use structural screws... your best bet, get a pneumatic nailer. Screws also tend to split the wood, unless you pre-drill every hole.

In regard to the retrofit: The roof sheathing is nailed to the top chord of your trusses. If you need that extra 3-1/2" of space, and want the top chord removed, the sheathing and roofing will have to be removed and replaced.

 

[RyanEricW]

You would have to use structural screws... your best bet, get a pneumatic nailer. Screws also tend to split the wood, unless you pre-drill every hole.

In regard to the retrofit: The roof sheathing is nailed to the top chord of your trusses. If you need that extra 3-1/2" of space, and want the top chord removed, the sheathing and roofing will have to be removed and replaced.

If I put the purlins in without removing the top chord, how do I fasten the existing top chord to them? There must be a special hanger somewhere someone makes

 

[RyanEricW]

H--e--l--l--o..... I think there's an echo in here.....



Sweet, more progress. FWIW, you wont have to support the roof if you..

• Place the new 2 ply trusses that are designed such that...
• the new purlins locate under the existing top chord of the existing trusses.
• Leave the top chord of the old trusses
• Remove the webbing and lower chord of the old trusses.

Manufacturer said this:
"No, the top chords would have to be removed if we did this. If we ran a beam at the ridge then you could do rafters that went next to the existing trusses and you could leave them there."

 

[Falcon67]

Speaking of fasteners. I'm a huge fan of screws, but they were telling me to use 10D nails.

I feel safer with something that wont get loose over time and provides clamping force.

Any reason why engineers would say to use nails over screws?

Nail flex, screws break. If you use some screws, use construction grade screws. By and large, 10d is the way to go. A decent full head framing nailer makes it easy work.

 

[RyanEricW]

You would have to use structural screws... your best bet, get a pneumatic nailer. Screws also tend to split the wood, unless you pre-drill every hole.

In regard to the retrofit: The roof sheathing is nailed to the top chord of your trusses. If you need that extra 3-1/2" of space, and want the top chord removed, the sheathing and roofing will have to be removed and replaced.

I brought up what you stated at the end of this as it's a very good point. I'm waiting for his response. This whole project might be moot because of that. Unless I can like.....notch the top chords where the purlins will run and somehow secure them together...

 

[lakeroadster]

I brought up what you stated at the end of this as it's a very good point. I'm waiting for his response. This whole project might be moot because of that. Unless I can like.....notch the top chords where the purlins will run and somehow secure them together...

Simpson Hurricane Tie: http://www.homedepot.com/p/Simpson-...lvanized-18-Gauge-Hurricane-Tie-H1Z/100374935

Attaches to the purlin and to the top chord.

No reason that the purlin and top chord idea won't work... it's just different from what the cookie cutter truss guys are used to. They'll come around if they are worth their salt.

 

[RyanEricW]

I just thought of something. Was just checking all of my measurements before placing an order.


So if the top chord of the new truss is 2x6 (1.5" x 5.5"), and I am placing the purlins under the existing 2x4 (1.5 x 3.5") top chords, that means the purlins will only be grabbing 2" of the new top chords at the joist hangers with 3.5" of the 2x6 hanging below it.


Maybe that's why he said it wouldn't work. I literally need 3.5" of more width to make the connection solid. I guess I could goto a 2x10 top chord truss if they make those?

9.5 - 3.5 = 4.5", it'll be 1" too wide, but better larger than smaller right?

 

[lakeroadster]

The truss designer needs to design the new trusses based on your existing trusses...

 

[Radix2]

I just thought of something. Was just checking all of my measurements before placing an order.


So if the top chord of the new truss is 2x6 (1.5" x 5.5"), and I am placing the purlins under the existing 2x4 (1.5 x 3.5") top chords, that means the purlins will only be grabbing 2" of the new top chords at the joist hangers with 3.5" of the 2x6 hanging below it.


Maybe that's why he said it wouldn't work. I literally need 3.5" of more width to make the connection solid. I guess I could goto a 2x10 top chord truss if they make those?

9.5 - 3.5 = 4.5", it'll be 1" too wide, but better larger than smaller right?

Why all this talk of purlins?

Normal construction would be to add girder trusses (doubled up trusses) at each end of the opening to support a ridge beam. Rafters support roof in raised area.
In your case the rafters would be added along side old truss top cords if they are not sufficient for your span. Ridge beam could be positioned under old top chords for easy install. No notching or odd joinery required. You would have a small flat area at the peak if you wanted to drywall under the ridge beam.

 

[lakeroadster]

I guess I could go to a 2x10 top chord truss if they make those?

The trusses in my barn are 2 ply and have 2x10 top chords, 2x8 bottom chords. Purlins are2x8's.

Why all this talk of purlins?

Normal construction would be to add girder trusses...

Girder trusses? You mean Kingpost Trusses?

 

[LX-Markham]

A little late to the discussion here, but I thought I would add what I did with my garage and the same problem.

Added structural steel (2 horizontal beams and 2 end ties) around the base of the existing trusses, then sistered new rafters to the existing truss top chords. The steel frame prevents the rafter from spreading out. Then the truss bottom chords and diagonals were cut out. The whole thing was done in place without removing the roof.

 

[lakeroadster]

A little late to the discussion here, but I thought I would add what I did with my garage and the same problem.

Added structural steel (2 horizontal beams and 2 end ties) around the base of the existing trusses, then sistered new rafters to the existing truss top chords. The steel frame prevents the rafter from spreading out. Then the truss bottom chords and diagonals were cut out. The whole thing was done in place without removing the roof.

Interesting.

Looks like C-channel, laying on it's web, with the flanges up? And some sort of steel brackets were used to attach the C-channel to the wall / rafters? Any chance of getting some close up photo's of that attachment / bracketry? And lastly do you know what size and weight channel was used?

I'd like to run some FEA on that just to get a feel for the strength of the assembly.

 

[GLTHFJ60]

Lots of good ideas in here. I really like astroracer's design.

 

[Falcon67]

I've been thinking about using some steel here too.

 

[LX-Markham]

Looks like C-channel, laying on it's web, with the flanges up? And some sort of steel brackets were used to attach the C-channel to the wall / rafters? Any chance of getting some close up photo's of that attachment / bracketry? And lastly do you know what size and weight channel was used?

C250x23 (C10x15.3) fastened to the wall top plate.
2"x8" rafters bearing on the wall top plate and notched into c-channel.

The roof sheathing is still attached to the truss top chord. The new rafters pick up and support the truss panel points.

 

[Radix2]

Girder trusses? You mean Kingpost Trusses?

AFAIK "girder truss" is more of a functional description than a structural one. It refers to a truss designed to support and work with other roof elements or to support loads beyond those normally assigned.

What you often see is that the "girder truss" is just the same as the other trusses but with multiple laminated together to carry the spanned area. The truss drawings will call out the laminated trusses on their own sheet with the loads calculated for the assembly. (you have to look closely to see which is the normal one and which is the girder since the drawing is identical)

In this case, yes they would likely be some type of kingpost configuration - either to form a beam pocket or to provide a place to attach hangers to carry the beam.

 

[lakeroadster]

C250x23 (C10x15.3) fastened to the wall top plate.
2"x8" rafters bearing on the wall top plate and notched into c-channel.

The roof sheathing is still attached to the truss top chord. The new rafters pick up and support the truss panel points.

Thanks for the photo's, that helps.

How does the steel channel attach to the wooden wall? lag screws, through bolts, or ??

If I understand correctly, you are attaching the flange of the channel to the wall top plate, via the 1-1/2" thickness of the wall top plate?

 

[LX-Markham]

The channel is designed much like a wind girt: unsupported in the strong direction, and suspended from the rafters at every 4th one to prevent it from sagging.

 

[lakeroadster]

The channel is designed much like a wind girt: unsupported in the strong direction, and suspended from the rafters at every 4th one to prevent it from sagging.

Could you perhaps post a photo of how it is attached to the rafters?

Thanks...

 

[kbs2244]

This guy has done it more than once