Truss/Rafter changes - several questions

[Code54]

Our 30' deep, 40' wide shop building needs a few changes. It is all in excellent shape but I am adding a new auto lift and need a little more than the current 10' ceiling height in one bay.

My thoughts is to clean up the current ceiling - remove air lines, take put the garage door opener, and rewire anything that is needed to be moved. I would like to change 2 of the trusses from the current arrangement to a scissor style truss. Currently the bldg. has 11 trusses running from left to right if looking at the photo above. 1 on each end, 9 down the middle. This means that 2 of the middle ones are in the way if I install the new lift on the left door (doors are 12'). Below is the current view of what I have.

I figure if I can change 2 of these out I will have plenty of room to lift the car. Currently they are made from 2x4's except for the part that attaches to the roof, that is a 2x6 (the Amish builder said they normally used 2x4 but since I had 2x6 handy he would just use them).

Is there a certain style/type that is better than my current plan. It seems I could sister the new truss to the 2x6 along the top and gain some extra strength. (We have VERY little snow load here if you are wondering). My over all goal is no loss of strength, just some gain in height. The building is on concrete (5"), the side walls are metal on the outside,a layer to OSB, 2x4"s placed horizontally, then the posts (4x6"), then a framed wall with a layer of OSB 8' up around the entire perimeter.

Thoughts?

 

[gstrom99]

Your door tracks might be in the way too. I'd just sister the 2x4's of the chosen layout, to the ones you want/need to replace, to give you the 12' 6" height.

Here's what my new shop w/lift looks like.

 

[Code54]

Thanks.

I can currently run the lift up between the door tracks (doors are 12' so got lucky there) but I am thinking that once the ceiling gets all changed out I will get the tracks that follow the ceiling and allow the door to be higher.

 

[Code54]

Here is the style I am thinking about:

 

[Midniteoyl]

There is also a 'Cambered' Truss which would probably suit you better. Gives more clearance along the length:



I agree with sistering it into place. Cut off any tails so they sit even and flush on top of the girders, lag bolt them to the 2x6, and then remove the guts of the old trusses.

 

[Code54]

Thanks - they look like they would be easy to build and would give some clearance. When I read about trusses it seems fairly easy to modify two of the 11 without too much risk/difficulty. I certainly will overbuild them and hope to get people with more experience to weigh in.

Last night I picked up a Jackdrive (side drive) garage door opener and will install that today. Figure one step at a time.... Lol

 

[EddieWalker]

I would be very hesitant to take apart an existing truss and rebuild it into a scissor truss. My biggest concern would be getting it wrong. While it's not rocket science, and all you are doing is copying the design of a scissor truss while building it in place, there are limitations to how far it can span based on the design. If you get the design wrong, you will have issues. The other concern is how much height you will gain by doing this, and if it will be usable height?

If it was me, my first option would be to add onto the end of the building. Pour a new concrete pad, frame it up with taller walls, and not make any changes to your existing roof.

Second option would be to install a ridge beam that spans the width of the area you want more height. The beam would need continuous support under it at each end, so a post would have to be installed in the middle of your shop. The rafters would run from the wall to the beam. Then you would not need any ceiling joists, and you would have open space from the floor to the roof.

Ridge Beam Detail - Home Design Ideas

Wood framed roof structures using ridge beam images browse 153 stock is a ridge board beam required for a

image.regimage.org

 

[Code54]

Thank you!

That is an interesting idea. I would not be against the idea of a center post. The hard part of this is I only want to do 2 trusses out of the 11 that are currently there. Just raise one small area so we have more height for a lift, maybe 18"-24" would be huge.

I was thinking about finding an engineer and seeing if they could come up with a design that would work for that area. I would add to the building but it would be a BIG project at this point and probably cost prohibited.

The two I would like to change are the ones indicated with the arrows