Garage 'ceiling height'

[Wood Grower]

Just be careful when selecting the 'plates'. For an example, Simpson Strong Tie sells 'mending plates' that clearly state that they are not for truss applications

https://www.strongtie.com/miscellane.../mp_plate/p/mp

The last time I looked into this, the tie plates approved for truss applications were hard to come by in anything less than boxes of 500. They were made from a thicker material and had larger X-Y dimensions than anything commercially readily available. MiTech comes to mind as one supplier.

Oh ha ha, when I was thinking plates I was thinking 1/4" or thicker steel drilled with a fastener through the wood and sandwich the wood between to steel plates. I'm sure that thing you show is pretty strong, but actual steel plate must be a lot thicker and heavier duty. Even if I put a square tubing over the end of the wood I could fabricate something that would easily exceed those plates shown. Anyways I might just be pulling the trigger and bulldozing the thing, just am talking about a new garage right today. I still am unsure on sizing though and I guess I need a site survey. 40x60 with 10 or 12 foot wall would probably be ideal.

[Wood Grower]

There is a reason wood trusses are manufactured at a truss shop/factory and not onsite anymore - altho I'm sure there are rare cases where site-built or 'stick framed' roofs are still done.

Its not just about the correct geometry either, the size of the truss 'connector plates', the precise position position of the connector plates, how the truss connector plates are pressed onto the truss frame (not hammered in) and the straightness and quality of the lumber used all contribute to the strength of the truss. The quality of a typical 12' 2x4 SPF is pretty bloody poor.

I am considering that I can use white oak and it would exceed anything that was existing connected with my roof already.

[cstephens2]

The plates are available. There will be other approved methods for joints.

Sistering in an approved truss should meet standards.

Just be careful when selecting the 'plates'. For an example, Simpson Strong Tie sells 'mending plates' that clearly state that they are not for truss applications

https://www.strongtie.com/miscellane.../mp_plate/p/mp

The last time I looked into this, the tie plates approved for truss applications were hard to come by in anything less than boxes of 500. They were made from a thicker material and had larger X-Y dimensions than anything commercially readily available. MiTech comes to mind as one supplier.

[cstephens2]

I can fabricate about anything. I could probably fab an all steel truss. I would rather stay in wood. I can build a lot cheaper in wood. I could even fab some fancy steel board connections out of steel.

My concern is as stated transfer load on correct geometry to prevent wall falling over. It seems the load would be straight down and the horizontal pieces prevent roof changing from a v to a flat shape.

There is a reason wood trusses are manufactured at a truss shop/factory and not onsite anymore - altho I'm sure there are rare cases where site-built or 'stick framed' roofs are still done.

Its not just about the correct geometry either, the size of the truss 'connector plates', the precise position position of the connector plates, how the truss connector plates are pressed onto the truss frame (not hammered in) and the straightness and quality of the lumber used all contribute to the strength of the truss. The quality of a typical 12' 2x4 SPF is pretty bloody poor.

[Egon]

My concern is as stated transfer load on correct geometry to prevent wall falling over. It seems the load would be straight down and the horizontal pieces prevent roof changing from a v to a flat shape.

With a purchased scissor truss all your design criteria should be met. Just portions of the original truss will need removal. The other portions will add strength to the new additions.
https://www.youtube.com/watch?v=vM5HdHt3GmE

one type of connector that would work in sistering.

[Wood Grower]

As I said in a previous post ("There may be other issues not directly related to how it is constructed.") it has come to light that the building is illegal non-conforming. Therefore the desire to not do any work on the exterior or discuss any changes with th building official.
Fair enough. However, it doesn't mean you should make interior changes that compromise the structure. You could change the roof framing to act as some form of truss, but you would need an engineer to design the changes. Manufactered trusses are engineered and use specifically designed metal connection plates. I don't think those plates will be available to you and making up a plywood gusset isn't the same thing.
That said, its possible to make some changes that might work, but if you want it done properly...

I can fabricate about anything. I could probably fab an all steel truss. I would rather stay in wood. I can build a lot cheaper in wood. I could even fab some fancy steel board connections out of steel.

My concern is as stated transfer load on correct geometry to prevent wall falling over. It seems the load would be straight down and the horizontal pieces prevent roof changing from a v to a flat shape.

[Egon]

The plates are available. There will be other approved methods for joints.

Sistering in an approved truss should meet standards.

[Inspector Ron]

As I said in a previous post ("There may be other issues not directly related to how it is constructed.") it has come to light that the building is illegal non-conforming. Therefore the desire to not do any work on the exterior or discuss any changes with th building official.
Fair enough. However, it doesn't mean you should make interior changes that compromise the structure. You could change the roof framing to act as some form of truss, but you would need an engineer to design the changes. Manufactered trusses are engineered and use specifically designed metal connection plates. I don't think those plates will be available to you and making up a plywood gusset isn't the same thing.
That said, its possible to make some changes that might work, but if you want it done properly...

[cstephens2]

Isn't something like this able to do the same job as a horizontal board? This is what I am thinking of doing building in place the remove the old system out after something like this is built. It seems with the right geometry something like this is fully capable of doing the same job as the horizontal board.

Yes, an engineered truss like that changes the location of the 'in compression' and 'in tension' truss members.

When you purchase a vaulted truss like that from a truss manufacturer it comes with an engineering drawing thats been signed off by a structural engineer. I highly doubt you can site build something like that and have it a) be approved by a structural engineer and b) pass any sort of inspection.

There is a reason we have engineers and inspections. But you do you boo.

[Wood Grower]

Go to a truss supplier with all your details. They should be able to spec the truss you require. Buy one for design details that you copy and use in prefabricating replacement parts for your truss.

You might be able to sister a new truss to the existing one and then remove parts of the old truss???

Do you estimate it isn’t bad for a single truss? I have a friend out of area who is a journeyman carpenter I just might consult with.

The twin then remove method is more or less exactly what I am thinking.

I think 6 to 10 feet roughly would do. I could even double or triple the horizontal Work at the start/ finish area....Probably right at rear wall and right by bay door track ending.....

[Egon]

I have a concrete block wall garage with a wooden roof and everything to hold it up. Inside the wood goes straight across from wall to wall. Is it possible to cut off that long piece and change the ceiling height into a vaulted ceiling to give more working height inside the garage? And if this is possible, how do you go about getting it done?

Thank you.

Go to a truss supplier with all your details. They should be able to spec the truss you require. Buy one for design details that you copy and use in prefabricating replacement parts for your truss.

You might be able to sister a new truss to the existing one and then remove parts of the old truss???

[Matt Matt]

What you are thinking about doing applies a lot of load spreading your outside walls from snow load and a collapse of the whole building. If you don't really care, just rip the whole trust system off and redo the roof. If you want to modify it you can do this with a few sheets of plywood, but if it is bigger than 100 ft.² you will have to have an engineer sign off on it.

[Kayak Jim]

An engineer would need to work out the sizes and fastening schedule as even an experienced carpenter would not likely know how.

This. So you just need to hire an engineer to design a truss system for you.

[iamtooler]

Isn't something like this able to do the same job as a horizontal board? This is what I am thinking of doing building in place the remove the old system out after something like this is built. It seems with the right geometry something like this is fully capable of doing the same job as the horizontal board.

That is what I had in mind and not too difficult when you do not care about the cost of a few extra 2x6s, unlike when original supplier built them. You will be doing one at a time so not a big deal, especially as you don't cut the ceiling joist till it's replacement framing is bolted in.
Rob

[Wood Grower]

My shop is framed with scissor trusses like that but it was designed that way and brought in as part of the truss package. You would be the first person I have ever heard of that wanted to convert to them in situ. An engineer would need to work out the sizes and fastening schedule as even an experienced carpenter would not likely know how. It would be a lot of work but you could do it without being noticed unlike raising the roof I suggested earlier. ;)

Pete

Yes that's the idea, I have a legal non-conforming building, so anything external is a big no no. If it's work being done inside and nobody saw it, that seems to be exactly the way I bought it and always remember it....