Roof truss

I need to cut a roof truss in the garage to run a stove pipe up. I could put the pipe between trusses but it would be too far out into the room. What is the correct way to brace the cut truss between the ones on either side? Cut will be right in the center of the truss.

Don't cut the truss; find another way to run the stove pipe. You might as well take that truss out completely as cut it.

Yup. What Dick2 said. DO NOT cut a truss. They are made the way they are and spaced the way they are for a reason. Way better to put in a couple elbows and reroute the pipe.

I agree with Dick L.
do not cut the truss, Your piping needs to be away from any combustible surfaces anyway. Relocate the stove or possibly go to a thru wall thimble. But I would not cut the truss. jmho gobble

You can cut a truss, but to do it safely you need to carry the load elsewhere. The "easy" way in your case is to add a new truss next to each of the adjacent trusses and run purlins all the way from each new truss under the one you will cut. That way you can use two new trusses to replace the old truss and support the roof all along the old truss.

While you may not like the solution, you won't like a sagging roof during a heavy snowfall.

I had to cut a truss in my post-frame shop in order to install an attic ladder. The larger ladders are too big to fit between 24" OC trusses, so you have to cut a truss in order to install them. Here's what I did; I won't say it's right, but the roof didn't collapse when I cut the truss and the roof is still fine five years later. There's really two considerations: How do you properly brace the truss temporarily to make the cut? And how will it be braced permanently?

In order to temporarily brace the truss, I propped it up on either side of the cutout with 2x6s wedged between the bottom of the truss and the floor. I also clamped boards across the bottom of the truss to be cut and the adjacent trusses. (Which you can't do because the ceiling will be in the way.)

I cut a section of the truss out where the ladder would go. The section removed was 3 inches longer than the final opening, to allow for 2x4 framing.

I installed two 2x4 crossmembers between the adjacent trusses and across the cut ends of the cut truss. Attach the crossmember to the cut truss ends with long screws. Don't use nails, because the bottom of the truss is normally in tension and will want to pull away from the crossmembers; nails won't hold in end grain.

I then added two more 2x4s parallel to the trusses to finish the framed opening. In my case they were spaced to fit the ladder; in yours they just need to be wide enough to clear the chimney.

Once everything was framed up I removed the temporary bracing. I do not believe it compromised the integrity of the trusses at all, since the loads are now distributed between the adjacent trusses and the new framing. By the way, the winter before last broke all records for snowfall in SE Michigan, and my roof held up fine.

Talk to the supplier of the truss. There may be a simple way to build around your stove pipe. If not, try to do what they say so your building will remain safe.

Do NOT cut the truss! You will totally ruin it's strength and there is no way to brace it that will make it as strong as it was before being cut.

They do make elbows for stove pipe.

You obviously don't have enough problems if you are SO determined to make a problem!

Bad idea

It seems an overwhelming majority think you shouldn't cut your truss. Cutting a truss to pass a chimney through the roof would not be my preferred solution, but sometimes you don't have a choice but to cut a structural member. As long as it's properly supported before cutting, and the integrity of the structure is restored when the job is finished, you CAN safely cut a truss. To say it's impossible to make the truss as strong as it was originally is a bit silly, since all but the shortest trusses are ALREADY CUT: Most trusses have splices in them; if you can build framing that's as strong as a splice, then you've restored the truss to its original strength.

I earlier assumed you were just cutting the ceiling joists of your truss. Obviously if you cut the top chord as well it gets more complicated, particularly since you would be cutting through internal bracing. But I think it is still doable; new bracing would need to be added.

try this
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I think I would try to double up on the trusses on each side to strengthen them and then box to the truss on each side. Then, and maybe most importantly, I would run diagonal bracing from the cut truss to the trusses on either side. Triangles are extremely strong (that is what trusses are), so triangulating to the adjacent trusses should help tremendously. I am NOT an engineer or architect, just thinking about what should make it strong.

If you cut the bottom chord, the truss is definitely rendered useless. I have seen webs cut and alternate webs and or bracing installed in some instances to carry the load.

You can field modify in some instances, but in reality, the proposed field modification needs to be submitted to the truss manufacturer's engineer, for review and alternate design approval. That's how it was done at the truss shop I worked in. Though it could be likely that there may not be any way to find the manufacturer, they're out of business or similar etc.

Professionally speaking, a modification to a structural component should always be reviewed and analyzed by a licensed professional engineer, to recommend otherwise can create an unsafe or hazardous situation. That just has to be said.

Wood framed structures don't always get the benefit of the above, and field modifications of same are commonly done by contractors and others, based on experience or knowledge of wood framing, but it should always be known to anyone considering structural modification, a professional designer, qualified in the area of expertise should always be consulted before modifications are made.

>Professionally speaking, a modification to a structural component should always be reviewed and analyzed by a licensed professional engineer, to recommend otherwise can create an unsafe or hazardous situation.

Agreed.

wrong idea! thats what they have elbows and pipes for . the stove pipe can be run to where ever needed just by using elbows. the stove pipe does not have to go straight up from the stove or heater.

Thanks for all the info. I know about the elbows, but the wife and I thought it would look better to have a straight pipe going up through the ceiling and put the elbows in the open space above. I guess I'll have to think about this.

Always have any vent pipe that is run horizontal run up hill a little.
Any vent pipe that is run close to the ceiling and above in a cold area needs to be class A if it's for a wood stove.
So putting the elbows below will be much cheeper.

Do Not Cut The Truss. It is considered a defect should you have a home inspection.

That is entirely true, I did these for awhile and the report would have to state to seek a qualified licensed professional engineer to determine what is needed to repair it.

So, move the stove maybe a foot to clear the truss.