6 Sill Plate Replacement Tips to Consider Before Replacing

One day, while puttering around in your basement or crawl space, you may notice that your sill plate or rim joists have become rotten or damaged, and an alarm may go off inside your brain.

When this happens, know that a rim joist and sill plate replacement are imperative. For the most part, you’ll want to outsource this project to a structural engineer, but here are six tips for understanding the importance of these components, how they function, and how to maintain them.

1. Consult a Structural Engineer

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Rotted sill plate or floor joist replacement costs can get expensive—typically between $6,000 and $20,000—but the work is absolutely necessary. Both items play an integral role in the structural foundation of your home—without them, your home wouldn’t be sitting on a flat, even surface—so you should get them fixed sooner rather than later if they’re rotted or damaged. Structural rot in these areas can bleed over into other parts of the bones of your home if you don’t address the issue quickly.

With that in mind, a local structural engineer can assess the damage and guide you on whether or not you need to make the sill plate and rim joists a major project. There’s a chance the engineer will tell you the damage is minor or may not even warrant the cost of a sill plate or rim joist replacement. For example, if a small portion of the wood is rotted but can be cut out or replaced with pressure-treated lumber, you might be able to avoid structural repairs. But repairs are also often extensive and warrant a larger carpentry and demolition project.

Without a structural engineer’s guidance about code requirements and other important aspects to consider, you may wind up doing more harm than good to your home and spending thousands on additional foundation repairs later on—as well as putting your safety at risk. Structural engineers cost $100 to $200 an hour for their professional services.

2. Understand Why Sill Plates and Rim Joists Need Replacement

Sill plates and rim joists usually don’t just wear out over time. So, if yours has accumulated damage quickly (or you own a relatively new house that has rot in these areas), it’s worth further investigation to prevent any future issues, as well as to address the problem’s root cause.

Common occurrences that can lead to rotted or damaged sill plates include the following:

• Excess moisture or water pouring down near the house (due to clogged gutters, a leaky roof, or ineffective lawn grading)

• Insect infestation (particularly wood-eating or dwelling bugs like termites and beetles)

• Laying new concrete that directly touches the wood underneath the house

3. Determine If You’ll Rent a Hydraulic Jack or Build a Stud Wall

After consulting with a structural engineer, you’ll want to follow up with a skilled foundation expert or home builder to perform the necessary fixes. Foundation companies typically charge around $200 per hour for their services. This is also a project where you need to verify the pro you hire has experience with this sort of work (i.e., home building and foundation repair), and that they are licensed, bonded, and insured.

The engineer will likely advocate for one of three approaches to fix your sill plate and rim joist: 

1. Use a hydraulic jack to hoist up your home to remove and replace the rotted wood 

2. Build a stud wall to mitigate further damage and reinforce the vulnerable area

3. A combination of the previous two, which is standard for extensive damage 

All of these strategies take hours, if not days, to complete, meaning you may have to avoid the parts of your home where the rotted sill plate is located or find a temporary living situation.

4. Slow and Steady Wins the Race

A sill plate and rim joist replacement using a floor hydraulic jack takes quite a bit of time. Pros advocate that it’s done slowly—about an eighth of an inch per day or every couple hours—over several days to avoid damaging your main structure. Pros top the jack when it reaches a point where the rotted wood is safely accessible.

There are instances where, once you start, you may realize you need a second (or even third) jack to reinforce the area you’re lifting. For example, if one beam starts bowing in the upstairs portion of your home, this indicates excess pressure is being placed on another part of your foundation. A pro will adapt to changing circumstances in your specific home–another reason why hiring an experienced pro is crucial. 

Once the jack lifts your foundation, a foundation repair specialist can remove the rotted wood and replace it with a new beam. If your structural engineer recommends the addition of a supplemental stud wall, they’ll likely add it after this phase of the project, as well.

5. Repairs Inside and Out

Repairs that your professional makes to sill plates and rim joists involve gaining access from all sides of the damaged wood. This can commonly include compromised hardwood flooring, baseboards, and even the vertical studs that run to the roofline. The contractor will likely need to cut sheetrock out, replace pieces of wood, and install new drywall from the lower portions of rooms that need repairs to be sure that they’ve eliminated the issue. 

6. Ventilate the Crawl Space

Once you’ve fixed the rot and wood damage that has occurred to your property, it’s important to add additional ventilation to your foundation to prevent the problem from recurring. Except in the wintertime, when temperatures below freezing can burst your pipes, there is no such thing as too much air movement beneath a home. Consider installing extra vent holes or investing in a system to circulate the air mechanically beneath your feet to keep things dry.