Cutting attic truss bottom chord for ceiling box?

[Aquaelvis]

So I’ve been reading about this and the overwhelming Internet wisdom is never cut a truss. Never.. unless you have to. My current install plans will require me to angle back from the stove and up to avoid a truss that’s pretty much directly over the stove’s outlet.
I really don’t want to angle the pipe. I wanted a straight run for ease of cleaning, ascetics, cost, etc.
so has anyone done it? Or should I ask if anyone will admit to doing it?
In my case I have 24“ OC trusses. The span is about 22 ft. There is a wall close to we’re id cut. (the old exterior side wall is there, then a span and the next span is what I’d cut)
my initial thought is to use 3 inch angle (I have access to a bunch free) to suspend the ends from the upper using bolts. Run long angle horizontally along the truss to add support from spreading. box the opening of course and add more lumber and angle as needed to make sure it can’t spread, can’t sag, can’t twist.
Should I use an engineer? Yes, of course but they are months out in my area. So my only option is to angle the pipe or over build these trusses and cut one.
I’ll attach a pic so you can see what I’m talking about.
The stove has to be 8 inches off the wall. (Once I get the hardie and rock up that should add around 1.5 inches to that back wall) The outlet is centered at 15-3/8” off the finished wall. Ceiling box is 14x14. That truss is about 20 inches off the unfinished wall.

 

[DAKSY]

Those trusses are ENGINEERED to do their job in whatever construction situation they are used in.
Round these parts, you need an ENGINEER to approve whatever modifications you intend to make.

 

[brenndatomu]

Use 45* elbows to put the stove pipe where it needs to be to connect to the chimney that is BETWEEN the trusses!

 

[bhutchison]

When you say cut the truss I assume you mean remove it entirely such that the truss spacing is 48” o.c. In the area of your stove pipe? or are you proposing to remove only a section of the truss in the general vicinity of the stove pipe? Its possible there are structural retrofits you could make that would allow either option to work but you definitely need a structural engineer to design this for you. You probably know this, but truss members are designed to work purely in compression or tension and each member of the truss is doing some structural work. Even small holes for wire penetrations in a single truss member can cause the truss to be compromised.

 

[Aquaelvis]

When you say cut the truss I assume you mean remove it entirely such that the truss spacing is 48” o.c. In the area of your stove pipe? or are you proposing to remove only a section of the truss in the general vicinity of the stove pipe? Its possible there are structural retrofits you could make that would allow either option to work but you definitely need a structural engineer to design this for you. You probably know this, but truss members are designed to work purely in compression or tension and each member of the truss is doing some structural work. Even small holes for wire penetrations in a single truss member can cause the truss to be compromised.

Yes, I’m talking about removing a section of the bottom chord. (Ceiling joist) This would increase the width between the lower chords from 24 to 48“ OC in that area. (Which would be boxed in) The width of the missing part would be 14 inches or so. I’m not talking about taking out anything but a section of lower 2x4- what the drywall screws to. The rest of the truss would remain in tact. I’d just box the opening (14x48) then use uprights from the cut 2x4 ends to the existing top chord of the truss. Also run supports horizontally along the truss to prevent spread. Essentially it’s transferring the load up. I’d sister all the existing 2x4’s with 2x6’s to add more rigidity. (Carry those down the top chord to the first set of uprights and tie all that in.
If I can’t make the straight run that way I’d have to 45 in the attic. (The box is 14 x 14, pipe is 6 inch so it might clear. I don’t want to mess with the upper chords.
Or I just 45 below the ceiling and go out that way.
I only have 54 inch from top of stove to ceiling.

 

[PJ41]

Strongly concur with Daksy and the others above. Truss modifications require review by a structural engineer. You do not want to mess with the loading of your roof, especially if you live in snow country!

 

[clancey]

Thinking overtime here (don't know much) but could he put another board beside the main truss to help it remain strong? Maybe on the other side so that he cut the other truss a little to fit the piping in---just thinking here and I do not know anything about engineering but curious is this possible? Mrs clancey

 

[Hoytman]

It would only be possible through an engineer or disregard for an engineer. Does that make sense?

In other words, you can get yourself into trouble if you don’t know what you don’t know, or for blatant disregard for what you do know, that being going against conventional wisdom and disregard for an engineer. LOL!

Nothing is against the law until you get caught. You can do anything you want to your home until you have it inspected.

 

[bhutchison]

Typically, the bottom chord of a truss is acting in tension (but not always.). Reinforcing other truss members to “make up” for modifications to the bottom member won’t work like you are proposing. The truss has to be analyzed to understand what individual members and their connections are doing. If this is a relatively new house with nail plate connectors you could talk to a local truss manufacturer. On jobs I work on if a sub accidentally modifies a truss it’s usually the truss manufacturer who proposes the fix. If it’s an older site-built truss with nails and gusset plates you need a structural engineer to analyze each member and connection.

 

[Bad LP]

It can be done. We did it 31 years ago for a cantilevered overhang (flat roof) that was too long and it's still as strong as ever. They were factory built with nail plates. It's had over 5feet of snow on it before.

We were required to plate both sides of the trusses with 1/2 plywood and I think they said 48 screws per plate evenly spaced. I think the nail banger added PL400 to the trusses as well.
If it was me I'd plate what I could get to and reframe as required. I'd go mental looking at a jog in the pipe for as long as I had to look at it. Yes, it would bother me that bad.

 

[begreen]

If I can’t make the straight run that way I’d have to 45 in the attic. (The box is 14 x 14, pipe is 6 inch so it might clear. I don’t want to mess with the upper chords.
Or I just 45 below the ceiling and go out that way.
I only have 54 inch from top of stove to ceiling.

Do the offset in the stove pipe. It is not an impediment to cleaning. We have one and a sooteater goes through it easily. 45's are not permitted in chimney pipe in the attic, just 30º offsets.

 

[clancey]

https://webmail.centurylink.net/service/home/~/?id=28562&part=2&auth=co&disp=i

Yea I understand and maybe a structural engineer would be the very best solution but just an idea here..for my brain is working overtime with wood stove looking but had to ask anyway just for my own curiosity..Thanks for the space..Hope the above link goes through for it will make your day...clancey

 

[Hoytman]

It can be done. We did it 31 years ago for a cantilevered overhang (flat roof) that was too long and it's still as strong as ever. They were factory built with nail plates. It's had over 5feet of snow on it before.

We were required to plate both sides of the trusses with 1/2 plywood and I think they said 48 screws per plate evenly spaced. I think the nail banger added PL400 to the trusses as well.
If it was me I'd plate what I could get to and reframe as required. I'd go mental looking at a jog in the pipe for as long as I had to look at it. Yes, it would bother me that bad.

You “...we’re require...” which infers someone in the know was involved, which was precisely my point. I never said it couldn’t be done...and I realize you never inferred that. I’m simply making another point.

 

[bholler]

It would only be possible through an engineer or disregard for an engineer. Does that make sense?

In other words, you can get yourself into trouble if you don’t know what you don’t know, or for blatant disregard for what you do know, that being going against conventional wisdom and disregard for an engineer. LOL!

Nothing is against the law until you get caught. You can do anything you want to your home until you have it inspected.

Yes you can absolutely do anything you want in your home. But doing the wrong thing can end in undesirable results

 

[Bad LP]

You “...we’re require...” which infers someone in the know was involved, which was precisely my point. I never said it couldn’t be done...and I realize you never inferred that. I’m simply making another point.

Seeing the “fix” on a group of reworked trusses would not stop me from going it alone if there were no framing inspections involved. It’s only one truss, not the entire roof.
Looking at an offset would drive me crazy knowing what was in the way.
My level of taking a risk is higher than most. I’m the guy who razed a 12k sqft building that was still being fed with a live 600 amp service because the electric company dragged their butt on dropping the feed. It happened on the same day a brand new building inspector started his new job. He came by. Introduced himself and asked what is that hunk of roof rubber doing? He said I was crazy and walked away shaking his head. We’re still good friends.

 

[bholler]

Seeing the “fix” on a group of reworked trusses would not stop me from going it alone if there were no framing inspections involved. It’s only one truss, not the entire roof.
Looking at an offset would drive me crazy knowing what was in the way.
My level of taking a risk is higher than most. I’m the guy who razed a 12k sqft building that was still being fed with a live 600 amp service because the electric company dragged their butt on dropping the feed. It happened on the same day a brand new building inspector started his new job. He came by. Introduced himself and asked what is that hunk of roof rubber doing? He said I was crazy and walked away shaking his head. We’re still good friends.

Yes but with trusses on 24" centers loosing structural integrity on one is a big deal.

 

[Bad LP]

Yes but with trusses on 24" centers loosing structural integrity on one is a big deal.

My garage in Maine is built with 24” centers. It ain’t going anywhere. In fact I’ve been thinking of dormers.
I wouldn’t give cutting out one or two a second thought if able to side plate them but that’s me.

 

[bholler]

My garage in Maine is built with 24” centers. It ain’t going anywhere. In fact I’ve been thinking of dormers.
I wouldn’t give cutting out one or two a second thought if able to side plate them but that’s me.

Yes 24" centers is perfectly fine. 48" after you cut the bottom web out which holds everything together is not fine. Restructuring after cutting out a part that is under compression is much easier that the bottom which is under tension.

 

[Bad LP]

Yes 24" centers is perfectly fine. 48" after you cut the bottom web out which holds everything together is not fine. Restructuring after cutting out a part that is under compression is much easier that the bottom which is under tension.

Plate it, cut it out and reframe.
I had a so called engineer spec a huge cantilevered footing for a spec house. What a joke that was. It was absolutely not the way that house was built after I demanded it be changed. I’ve never seen such overly designed garbage. A spread footing is one thing in loose material. An offset 6 x 1 foot footing is another.

 

[Rearscreen]

I remember a realtor showing us a house years ago in Vermont (of course) and we went upstairs where the attic was and in the space were a bunch of trusses that were cut to make a lovely bedroom. I still remember that frightening vision and I guarantee no engineer was consulted.

 

[gthomas785]

If you are lined up with a joist in the ceiling then doesn't that mean you're also going to hit a rafter when you reach the roof? Easier to just offset the pipe imo

 

[Bad LP]

As for the pipe after the initial penetration and out of sight in the crawl space I deal with more the finished aspects. That’s what we look at.

 

[Rearscreen]

Thank you. Please make check out to "Cracker Jack Box Engineering LLC."

 

[Hoytman]

Yes you can absolutely do anything you want in your home. But doing the wrong thing can end in undesirable results

I’m pretty certain that was my point.

 

[Hoytman]

Seeing the “fix” on a group of reworked trusses would not stop me from going it alone if there were no framing inspections involved. It’s only one truss, not the entire roof.
Looking at an offset would drive me crazy knowing what was in the way.
My level of taking a risk is higher than most. I’m the guy who razed a 12k sqft building that was still being fed with a live 600 amp service because the electric company dragged their butt on dropping the feed. It happened on the same day a brand new building inspector started his new job. He came by. Introduced himself and asked what is that hunk of roof rubber doing? He said I was crazy and walked away shaking his head. We’re still good friends.

I’m right there with you. I haven’t said I would take the risk. It’s just that some people have no business taking the risk.