Venting a toilet
I am installing new fixtures in an old house that had no venting.
The toilet is more than 6ft from the main stack so it requires a vent. The toilet drains towards the front of the bowl across the room and continues for 5ft before a 90 degree turn. Is it possible to vent the toilet behind the tank? Also the 3inch drain needs to cross through a joist to get to the main stack, but I read that you cannot notch more than 1/6th of the joist.
Any guidance would be greatly appreciated.
Venting a toilet
There are several different ways it could be done. Keep in mind that some codes call for all vent fittings below the flood rim of the fixture to be installed in drainage pattern. So unless the fittings that you plan on using to go up into rear wall, (behind the toilet) are installed in this manner, it could be against code.
This meets UPS code (if you have other vents) and is how I generally vent for the situation you have described when space is a real problem. I come off the closet bend at least 6" (a foot or 2 if I have room) and install a 3 x 3 x 2 wye (if you have room in the wall, use a 3" wye and install a test tee [cleanout] on the vent). A 2" 45 is put into the 2" hub of the wye so that the outlet is pointing in the same direction as the 2 3" outlets (rather than inserting the 45 so that the outlet is at a 90 degree angle to the 3" outlets, turn it around). When this is installed, the 2" must be rolled so that the take off is above the center line of the 3" pipe. This is your vent. You can run the line to the wall behind the toilet and longsweep 90 (drainage pattern fittings) up the wall and out the roof. Code says that you should have a clean out, but in real life, toilets are pulled and toilet lines are usually snaked from the toilet location. I always like to check out the toilet as best I can since a main line backup can also cause a trap clog, too.
Can't advise on drilling the joist, other than to say that you generally cannot cut through the top or the bottom, should try to keep the hole as centered as possible, should drill the smallest possible hole. The kind of joist, the size of the joist, the spacing of the joists, and what it is supporting contribute to how much of it you can take away. It is not uncommon for joists to need to be drilled to accomodate 3" drainage lines--there are joists that you can do this with. We just cannot tell you if yours is one.