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6 Bathroom Remodel Structural Considerations

New framing - 2 point loads

Old "doubled-up" floor system

Bathroom Remodel Structural Issues

With bathroom remodels people often focus on color, layout, heated floors and moving things around.

These are all important things, but if you’re not thinking about the stuff behind the walls and under the floors to make the overall design work well. If you’re not concerned about “Hidden Conditions,” You’re about to have your train derailed! Bathrooms are botched more than any other room in the house. In this article we will discuss 6 bathroom remodel structural considerations.

Hidden Structural Conditions

It is very common when doing a bath remodel to find out of level walls, deficient utilities, and floor joists that have been cut, drilled, notched or even removed to accommodate plumbing pipes and drains.

Think: uneven tile, fire hazard and bouncy floors and cracked tiles!

If you are doing a major upgrade to your bathroom consider doing a “full gut.” Removing all the plaster from the walls and ceilings, and removing the sub-floor allow years of accumulating problems to be rectified.

Old Outdated Electrical and Corroded Plumbing

Doing a bathroom renovation is a great time to deal with old outdated systems. Things like corroded cast iron or galvanized drains and water supply lines.

Even copper water supply lines can be hidden problems if there are corroding joints

No Plumbing Vent

Modern plumbing codes have changed the ways plumbers run vent lines for your sink, tub, shower or toilet. Insufficient venting can cause drains to gurgle or traps to be sucked dry, which contributes to drains stopping up.

Out of Level Floors and Walls

While not always noticeable an out of plumb wall may show itself better when covered with tile and the grout lines taper off.

If you plan on installing shower glass doors and walls like Basco Shower Doors – you want to make your walls as straight and plumb as possible. On tip I use is to install solid surface strips, like granite or Silestone for the glass to butt to.

Deficiencies in the Floor Framing

The time to address structural floor issues, like reinforcing floor joists, is at the time it was built or during a retrofit or remodel.

Contractors may cut through floor joists to accommodate plumbing or HVAC mechanical equipment as long as they properly transfer the floor load to adjoining joists by adding headers.
Understanding the different types of basic framing methods will help you to identify load paths in homes built using different framing methods.

Being able to locate key point loads will also help you know where to look for structural problems. Homes are built to transfer the structural load down through the framing to the foundation.

This is called the “load path” and it’s where most of the weight forces in a home are concentrated. Point loads are loads that are concentrated in a small area, such as where a post supporting a beam or supporting a window header.

New floor system

Heading Off and Framing Floor Openings

In a perfect world any floor joist that is cut should have a header installed, preferably two and doubled adjacent joists. All headers should be nailed to the cut joists and their ends attached to two adjacent, uninterrupted floor joists.

The purpose of the headers are to transfer the floor load to the adjacent trimmer joists. The use of joist hangers facilitates this repair.

TIP: A single header nailed to the cut joist and two uninterrupted joists will work for openings less than 4 feet. If the header spans more than 4 feet, both the header and the trimmer joists should be doubled. We often refer to doubling up of joists or other structural framing as “sistering,” or “reinforcing.”

The doubled trimmer and header joists must be nailed together properly with spaced pairs of 16d nails every 16 inches so that they are reinforcing Floor Joists like beams.

Reinforcing floor joists is best done by doubling of floor joists. Doubling of joists is recommended under walls, heavy objects like tubs and at large openings. Doubling of joists can solve a lot of problems like sagging, uneven or undersized floor joists.

Sometimes on a remodel you can’t install a full length floor joist because of plumbing, existing walls or finished floors or ceilings. In these situations it sometimes makes sense to reinforce the floor joist or even all of the floor joists.

Reinforcing Joists with Plywood

Reinforcing joists with plywood is effective technique that allows you to add strength to and fix minor problems that are affecting floor joists. I apply 3/4 inch plywood to both sides of a joist as far needed or I can reach. I fasten it the joist with construction adhesive and 12-16d nails spaced every 16-inches on center.


In areas where I know the plumber will drill through my joist I will add plywood reinforcing and keep my nails out of the pipe path.

A quality piece of plywood is typically stronger than the corresponding amount of standard wood and is an excellent choice for reinforcing weakened joists and even reducing squeaks.

Why Plywood?

Plywood is a strong laminate composed of several thin layers of heavily compressed wood glued together. Some people consider it to be inferior to standard lumber, but the opposite is almost always true!

Finish Strong!

Keep these 6 considerations in mind when planning your remodel and you will avoid derailing your “remodeling-budget-train” before it leaves the station!

6 Structural Tips Video

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