Can you safely box in a truss?

[rwhite]

Of course where I want my stove to sit splits a truss. It's a corner install so to come out farther is really not an option because of hearth clearances. I think I know the answer which is probably an elbow. Any ideas? Can you run a 2x6 across the bottom and tops of the trusses and build a cripple wall so that 2' chunk can be cut out off 1 truss? If this requires total engineering then I'll just go with an interior elbow and live with looking at it for the next 20 years.

If I go with two 45s at the ceiing am I looking at the offset charts correctly in that two 0" 45s will give me 9" of offset? I can get close enough to the front clearances to only need 8.5" of offset.

 

[rwhite]

Here's what I'm thinking, run studs down where the blue lines are drawn and cut 2' out of where the red lines are. This is a cathedral ceiling. The span from the peak to the load bearing wall on the left of the picture is about 6'.

 

[bcrtops]

Trusses are engineered -- you don't want to be cutting them.
You'll need to go between.

 

[rwhite]

Trusses are engineered -- you don't want to be cutting them.
You'll need to go between.

Kind of what I figured. I know it's been done but in every case it has been re-engineered. Which I'm not going to pay for.

 

[Hogwildz]

If it was me, I would sister a 2'x4" or 2'x6" full length on the top & bottom truss chords each side of it, then double box it. The either knee brace it or install cross webs across the trusses on each side. That will be just as strong if not stronger than those 2'x4" trusses.

 

[rwhite]

If it was me, I would sister a 2'x4" or 2'x6" full length on the top & bottom truss chords each side of it, then double box it. The either knee brace it or install cross webs across the trusses on each side. That will be just as strong if not stronger than those 2'x4" trusses.

Is this kinda what your thinking? The blue is existing trusses, black is where I would sister and box. I would do the same thing to the top and bottom truss then knee brace as indicated between the two.
My order of operations would be;
1. Sister everywhere indicated
2. Install 8 knee braces
3. Cut the pink line out then box as indicated

 

[kennyp2339]

That will work just fine

 

[webby3650]

I certainly would not cut my trusses, or anyone else's. Dura-vent DVL elbows are in the 5" offset range.

 

[rwhite]

I certainly would not cut my trusses, or anyone else's. Dura-vent DVL elbows are in the 5" offset range.

That is likely the way I will go I just want to weigh all options and learn as much as I can about a project before I dive in. The trusses are already 2x4 and 24" on center and I've got 2" of snow sitting on the roof. Not sure I'm comfortable cutting a truss.

 

[kevreh]

Can't you find an engineer for a couple hundred $ to come and make a recommendation? Maybe he will be less nervous if you give him your plan as a starting point.

If I recall, that bottom 2x4 (chord) your going to cut has tension on it thats pulling it "apart" due to the engineering of the overall truss. Boxing it in is only going to work as well as the mechanical means in which you secure the box to the bottom chord. Nails or out, screws better, but a Simpson connector plate is best, and costs a few dollars. Thats why deck code usually requires you to use joist hangers, not just toe-nailing.

BTW, you only need to cut the bottom 2x4 right? Since you can zig the exhaust pipe over a few inches in the attic. Doing this would make me a little less nervous if it was my house.

Thats my $.02.

 

[rwhite]

Can't you find an engineer for a couple hundred $ to come and make a recommendation? Maybe he will be less nervous if you give him your plan as a starting point.

If I recall, that bottom 2x4 (chord) your going to cut has tension on it thats pulling it "apart" due to the engineering of the overall truss. Boxing it in is only going to work as well as the mechanical means in which you secure the box to the bottom chord. Nails or out, screws better, but a Simpson connector plate is best, and costs a few dollars. Thats why deck code usually requires you to use joist hangers, not just toe-nailing.

BTW, you only need to cut the bottom 2x4 right? Since you can zig the exhaust pipe over a few inches in the attic. Doing this would make me a little less nervous if it was my house.

Thats my $.02.

Start adding costs of an engineer, chimney elbows, braces and other sundry items I think I might be into this 5-600. Where a few dvl elbows won't be as clean but only run $100.

 

[David.Ervin]

I wouldn't cut into my roof trusses on a dare. Any chance you can build a "decorative" box in the stove room hanging from the ceiling and hide the elbows inside that?

 

[rwhite]

I wouldn't cut into my roof trusses on a dare. Any chance you can build a "decorative" box in the stove room hanging from the ceiling and hide the elbows inside that?

Was actually thinking that although I doubt if code allows you to box in stove pipe. Maybe if it's completely noncombustible?

 

[Elciteeve]

Problem with a truss is that the weight of the static and live loads stress the tensile strength of the materials, not the compressive strength. Your best bet would be to add a new truss to each side of the roof. The entire triangle shape (if you will) is what holds everything together, so boxing in isn't a great idea as you would weaken *each* side of the roof which that truss is attached to. Adding an entire new truss (that spans both sides of the roof) on either side of the chimney would likely solve the problem. You'd also need to make sure your new trusses were installed with an extremely tight tolerance. That being said I'm pretty sure the code for most places is that you can't remove / alter a truss without an engineer approval.

 

[webby3650]

Was actually thinking that although I doubt if code allows you to box in stove pipe. Maybe if it's completely noncombustible?

The elbows are no big deal. I'd say 75% of the installs we do end up with elbows, there's just no way around it. Don't you think a box built around the elbows would be more of an eyesore?

 

[rwhite]

The elbows are no big deal. I'd say 75% of the installs we do end up with elbows, there's just no way around it. Don't you think a box built around the elbows would be more of an eyesore?

Could be? I'm just running through scenarios in my head. Probably gonna get the ceiling cut and pipe mounted this weekend. It may be spring before I can get a hole in the roof if this weather keeps up.

 

[rwhite]

Thanks for the tips everyone, I'm gonna go with interior elbows. I'll get more accurate measurements when I cut the hole but it looks like I'll need two 45s and a 6" piece of dvl to miss the truss.

 

[webby3650]

Could be? I'm just running through scenarios in my head. Probably gonna get the ceiling cut and pipe mounted this weekend. It may be spring before I can get a hole in the roof if this weather keeps up.

I can give you some tips to make the roof penetration take only a matter of minutes. PM me if you need some guidance.

 

[Hogwildz]

Is this kinda what your thinking? The blue is existing trusses, black is where I would sister and box. I would do the same thing to the top and bottom truss then knee brace as indicated between the two.
My order of operations would be;
1. Sister everywhere indicated
2. Install 8 knee braces
3. Cut the pink line out then box as indicated
View attachment 189798

Yep, but I's also double up the box portion also.

 

[jophysx]

"Can you safely box in a truss?"

I looked up the rules and regulations of the International Boxing Federation. There is no mention of any restriction regarding competitors wearing a truss. However, I think if you need one you are probably at a significant disadvantage. I wouldn't recommend . . . oh wait . . . maybe I misunderstood your question.

-Jim

 

[Sawset]

I had to cut trusses to get our chimney in - but - the trusses were at 12" centers, I needed 1-1/2" more, so sistering and reinforcing with heavy plywood offered 100% confidence that the result was stronger than before. Your situation - offers zero confidence. Distributing loads to the trusses on either side - no. I vote for putting the elbows in below.

 

[therdlesstravld]

I'm a carpenter so take that for what it is. I've seen so many things buikt like total crap that have stayed together. I've also dismantled enough rooves (plural of roof? I dunno) to know that homes are built to be very redundant .

Yes you would not be able to pass an inspection by cutting into a truss or an enginnered beam. That being said if it was my house I'd frame the crap out of it, tie r back to the two trusses on either side and then tie those ties back to the sill plate that the trusses sit on on either side. I'd be very confident that all the extra strapping, wood and nails would carry the weight well.

Do you happen to know the roof pitch and what average amount of snowfall you get? The higher the pitch the less you need to worry about love loads from snow.

 

[rwhite]

I'm a carpenter so take that for what it is. I've seen so many things buikt like total crap that have stayed together. I've also dismantled enough rooves (plural of roof? I dunno) to know that homes are built to be very redundant .

Yes you would not be able to pass an inspection by cutting into a truss or an enginnered beam. That being said if it was my house I'd frame the crap out of it, tie r back to the two trusses on either side and then tie those ties back to the sill plate that the trusses sit on on either side. I'd be very confident that all the extra strapping, wood and nails would carry the weight well.

Do you happen to know the roof pitch and what average amount of snowfall you get? The higher the pitch the less you need to worry about love loads from snow.

6:12 pitch and around 59" average snow fall

 

[Rearscreen]

This reminds me of the time a realtor was showing me houses in Vermont and we went up to the "attic" which was a finished bedroom. To achieve this room they cut all the trusses. That's the Vermont way.

 

[toddnic]

When I installed my chimney we had to box-in a truss. Thankfully a friend of mine was a contractor and he assisted me in the process. It really wasn't a big deal in our application. You definitely need to have someone knowledgeable take a look at it first....