Plumbing Bathroom in Bonus Room Trusses

[ptt49er]

G'morning!

Almost to the point of building the bathroom in the bonus room over my shop.

I am going to need to cross a 3 trusses with a drain for the shower and sink.

I've attached the drawing of the trusses used in my build.

I cannot find any information online regarding running the plumbing drains through the bottom chord of the trusses.

Can I drill holes large enough for the 2" PVC pipe or do I have to run them on the bottom of the truss (the ceiling in the shop)?

TIA!
Phillip

 

[FredP]

I would not. Others may disagree but you will be drilling a 3" hole in what looks to be a 2x6 bottom cord. That doesn't leave much. 2.5" may fit but will be tight and lead to squeaking issues as the wood moves. Trusses are designed to be structural members.

 

[ptt49er]

The bottom chord is a 2x10. But I think I'm going to build a bulkhead among the outside wall.

 

[Bigdog72]

I can speak as an expert on this subject because I helped design and managed the construction of several thousand homes over a 47 year career. Most of them had some form of bonus room truss. One thing I know is you must have an engineer sign off on this type of truss alteration. Assuming you will get a permit, the building inspector will demand an engineer‘s letter before passing your inspection. In the future, when you go to sell the house, you may be asked for the same paperwork. my experience with the trusses is that you can’t cut the bottom chord. Also assuming you will have a toilet in your bath you will need to run a 4” drain for it and a 2” drain thru the roof for a vent. The shower and sink can run into the 4” drain. Your best bet is to drop below the truss into a soffit for the drain line.

 

[mkepke]

I think Geoff has a better answer, but mine is: cutting into a manufactured truss in any way is a no-no unless it is allowed by the manufacturer. There is nothing on the drawings you provided to indicate it is allowed.

(Contrast it to something like manufactured I-beams, which will tell you allowable hole size and placement).

-Mark

 

[junquecol]

You could, but as others have said, you will need a PE to sign off on it. It would involve scabbing plywood (glued and screwed) or steel plate ( thru bolted) on both sides of the trusses where holes are bored. Most likely, your inspector would require the original builder of trusses to also sign off also. Because these are floor supporting trusses, they are not just in tension, but compression also, which changes the rules. Why not run lines parallel to trusses and then down the wall?

 

[jlwest]

Never cut a truss without a PE written approval.

 

[Oka]

Easy answer - Call the truss company and talk to the engineering dept.
Ask the question this way. "I have to cut 3 cords @ this location in the building, how do I reinforce the trusses that will be cut? What reinforcing modification do I need to do?"
If both sides of the remaining cord have been tied into other walls, make sure you detail that as well.

 

[JimD]

Is it possible to raise the floor of the bathroom so you can run the plumbing over the truss?

 

[Alan in Little Washington]

Where are you going to run the 4" soil drain? Is your shop heated? What is the thickness (framing) of the exterior shop walls, 2X4 or 2X6? Generally you can't run water lines nor soil drain in an exterior wall, or ceiling or wall that adjoins an unheated space if you can do it any other way. Even if you do have the needed wall cavity depth, you may need to box the lines (a shop bump out) so you can insulate the vertical run properly

As to modifying the truss check with the truss company and/or a structural engineer. You'll need a sign-off.

Is the bonus room, already an actual room designed, intended for, and with floor rated for living loads, or is it a storage space with attic trusses that you converted to a bonus room w/o a permit? If so, I wouldn't even think about applying for a permit without seeing a structural engineer and possible upgrading the framing.

 

[Gotcha6]

While I can't refute any of the answers above regarding consulting the engineer, you may be able to mitigate the cuts by using a 3" waste drain. IIRC, the number of fixture units you have would not require a 4" drain. Nonetheless, consult with the truss manufacturer. Let them CYA. They MAY suggest reinforcing with 3/4" CD plywood on both sides of the cut. YMMV

 

[ptt49er]

The bath will be situated such that the waste drain will go down the end wall of the shop.

For some reason I hadn't though to run the shower/vanity drains parallel to the trusses and down the side wall.

I had already planned to build a chase down the end wall for the waste drain and will now add one down the side wall, to maintain consistency and provide the space required to get the drains all tied together.

I appreciate the advice!