Roof truss advise needed

These are the trusses I used to provide a 12 foot ceiling when my city limited me to 15 foot max elevation.

In reply to dimarra:

You are assuming a trussed roof in an area with no snow is designed equally strong as one in an area that has snow. It's not.

Trusses are engineered to the required specs and no more. A 24' truss designed for use in Maine is engineered with a higher live load than one designed for use in GA.

You do equal damage to either when you cut them.

Plus, snow is NOT the biggest load on a roof. Wind lift is.

Trusses cannot be modified without an engineer. Period.

KyAllroad wrote:

Woody wrote: Roof trusses are bad. Modified roof trusses are really bad. Please don't do that.

For those who aren't paying attention here, that is the viewpoint of every firefighter I've ever spoken with. Due to how fire burns the connection plates of a truss compared with how it burns a stick built (through nailed) roof system. Truss roofs collapse catastrophically and stick roofs sag more gradually. This is important to the guys who run into burning structures while the rest of us run out.

Thank you.

In summary: Roof trusses kill firefighters.

Google ^those exact words and you will find plenty to read about.

I'm kind of surprised at all the nay sayers in here.

I mean yes I get that this is something to take seriously, but it's also not THAT complex of a science. I would think where there's a (smart) will, there's a way, that doesn't involve tearing the entire roof off and installing new trusses/roofing.

If you need say a 3' raise to make a bubble over a 4x4' section of roof, you're not modifying ALL the trusses, and as noted, there's likely ways to get an approved overkill modification done one at a time from underneath, GRM style, to avoid reshingling and all the other costs.

I personally know of at least 2 who have done this, succesfully, in Michigan, with many years of snow use and no issues. I won't name names or what not for potential liabilities, but there's ways to do this correctly AND be GRM'ish.

P.S. Also looking to do this in my 3rd stall bay.

A trussed roof will fail within the first ten minutes of a fire. Firefighters will not walk on the roof to cut a ventilation hole (stopping the horizontal spread of fire), nor will they go inside the building, for it will collapse on top of them.

If you have a small fire inside of your trussed roof building, you will lose the building and all of its contents.

In reply to xflowgolf:

Duke is an architect. I am a builder. I apologize if it sounded like either of us was a naysayer.

If you read what we said carefully, neither of us said anything about tearing off the entire roof nor installing new trusses.

The job is simple. I've done it many, many times. It does not involve new trusses. It involves engineering, and it's not expensive.

But very few people are qualified to actually do the math on the various loads involved, and the law requires a licensed engineer.

And it doesn't matter how many trusses you are modifying. 1 broken member in a single truss requires engineering.

I'm real happy for your friends in MI, but if they did not hire an engineer, it was illegal.

After reading all of this I think the solution to your problem is quite clear - burn it down and build another.

From the sound of things it won't take but 15-30 for the fire to take care of the old building, but the insurance company will take longer.

Then build what you want on the property and you'll be golden.

gearheadmb wrote: Here is a question. If I wanted to make the wall's two feet taller do I need to completely reframe the garage, or could I make a two foot tall wall to set on top of the existing wall?

I would guess that it would be simpler and stronger to lift the entire garage and a build a block wall under it.

I'm happy to see so much disscussion that this has brought about. Will try to fill in a few blanks here.

I will need to change/modify 5 or 6 trusses. They are 24" on center and yes, snow is a thing here in Michigan. Garage was built in the late 90's and is in very good shape. Current ceiling height is 9'6". The trusses are 'storage' style with a floor. Garage is 36' feet long, just doing bay 3. Doors are not on the gable end.

Plan A is to add extra peices to existing truss and cut out unwanted section.

Plan B is to build an 'mini truss' in the middle of the current truss

Plan C is to place a scissor truss next to the current one if it could be done in 2 peices (assemble in place)

Would be more than happy to pay an engineer for his time, but haven't found one interested in talking to me.

BrokenYugo wrote:

gearheadmb wrote: Here is a question. If I wanted to make the wall's two feet taller do I need to completely reframe the garage, or could I make a two foot tall wall to set on top of the existing wall?

I would guess that it would be simpler and stronger to lift the entire garage and a build a block wall under it.

yes, this

Woody wrote: A trussed roof will fail within the first ten minutes of a fire. Firefighters will not walk on the roof to cut a ventilation hole (stopping the horizontal spread of fire), nor will they go inside the building, for it will collapse on top of them. If you have a small fire inside of your trussed roof building, you will lose the building and all of its contents.

How do you determine the roof construction when arriving on scene? I've also heard that engineered floor beams (OSB on edge with a 2x4 cap) is a nightmare too.

In reply to Gearheadotaku:

Food for thought...

Note the triangles.

A free body diagram with known loading and known/needed dimensions make this pretty simple.

It's the E, Fb, Fc, Ft ”wood calc factors” that makes it complicated. Measure it up and call a structural engineer. S/he will solve this riddle in about an hour with 40 minutes to spare.

With a stamped design, some 2x lumber, some screws, glue and some plywood gusset plates this is a two weekend project. One if you're Amish (or named Mazdeuce). Those guys build wood trusses like this all the time.

Modify one truss at a time and it can pretty much be done solo.

(Don't forget to unload that attic floor first)

Laatly, watch out for nails in the underside of your roof. Wear a plastic hardhat if you can't remember to duck.

I finally have a designer working with me. We are disscussing a "mini truss" that will attach to the exsisting one and will allow this modification.

In reply to Gearheadotaku:

I'm hoping that your "designer" is an engineer. When the design is done you must have a structural engineers stamp on it, or you will not be able to get a permit.

Yes, he is engineer, I used the wrong term.

In reply to Gearheadotaku:

Cool. Look forward to seeing the results.

Gearheadotaku wrote: I finally have a designer working with me. We are disscussing a "mini truss" that will attach to the exsisting one and will allow this modification.

Awesome! please keep us posted.

Ok, I've got the design form the engineer. Just a "simple" matter of attaching this to the exsisting truss then cutting away the unwanted section.

I'm sure there are more details to cover, but progress is being made.

Are those existing chords in the diagram or a new truss to place beside the old ones?

In reply to Gearheadotaku:

THAT'S the drawing you needed.

Are you having the truss made, or building it with plywood gussets?

SVreX wrote: In reply to Gearheadotaku: THAT'S the drawing you needed. Are you having the truss made, or building it with plywood gussets?

From the notations on the drawing it looks like it will use the metal plates. Can't remember the exact name, been 30 years since I worked in the truss factory for a couple summers.

In reply to Hal:

I understand the drawing.

But he can't use gang nails (the metal plates) if he is building the truss himself.

My question was if he had an alternative design for the attachments which would enable him to build the trusses, or if he would be buying complete trusses and sistering them in.

I will be buying complete trusses and nailing them on.

Post photos. This type of project looks fun.