Remodeling: Reinforcing Joists for New Drain Lines

How we reinforced existing 2x10 floor joists to accommodate a new 3 1/2" drain

An issue that often arises when designing a remodeling project is the problem of adding or relocating the main toilet drainpipe for an upstairs bathroom. The problem is that when the house was built using 2x10 floor joists for the second level, a plumber cannot drill directly through the floor joists to route the drain - he must drop the pipe below the level of the ceiling. This creates all kinds of problems with needing soffits to hide the drainpipe, or reconfiguring the bathroom to allow for a more direct route.

Why can't we drill through the joists you ask? Well the building code (I'm referencing the Michigan 2015 Residential Code, based off the IRC) stipulates that the size of the hole can be no larger than 1/3 the size of the "Actual" joist depth - and since a 2x10 is Actually 9 1/4" deep, the largest hole we can drill is just a hair over 3" diameter. 

In the past, we've paid a structural engineer to do some calculations and draft a letter allowing us to 'sister' 3/4" plywood to each side of the joist where the hole is located, thereby allowing us to drill the 4" hole we needed to run the drain line.

The problem with this is that most structural engineers are already busy solving interesting and complex structural problems, and have a hard time taking the time to address small questions like this, not to mention taking on the risk for a fairly large structural risk that might pay them $150, plus require a drive to the site... etc. 

So you can imagine that not only is it a bit costly to bother an engineer with this situation, but it ends up taking some time for the approval. But until now, I thought it was the only way.

While searching around for a solution, I came upon a company called Metwood which produces a line of floor joist hole "Reinforcer™ Technologies", which attach directly to the side of the floor joist and are pre-engineered to distribute the joist load around the larger (up to 4") hole.

As the inspector will require engineering confirmation on a product like this, I called to verify that this type of official verification would be provided. The very helpful people at the company assured that this certification is delivered with each shipment - and would meet the requirements of the inspector. When the shipment arrives I'll be sure to upload this verification report to include with the blog post, along with installation photos.

You can check out Metwood on their website here - which include not only joist hole reinforcement, but notch reinforcement, I-Joist Web Reinforcement, and even I-Joist Flange Reinforcement.

Good Luck on the project!