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Why Don’t You Use Pressure-treated Wood to Repair Sagging Floors?

crawl space filled with debris

On the surface, pressure-treated lumber seems like the ideal material for home construction.  It’s resistant to both insects and rot, making it more durable and less prone to damage.  So why don’t foundation repair companies use it? 

Acculevel is a family-owned and operated company that specializes in waterproofing and foundation repair.  Since our start in 1996, we’ve helped over 35,000 homeowners restore their homes to optimal health and stability.  We understand the importance of your home’s safety and value, and our goal is to provide a whole-home solution that preserves your home for years to come. 

In this article, we’re going to explore what pressure-treated lumber is, what its ideal purpose is, and why it is not something that should be used to repair sagging floors. 


What is Pressure-treated Lumber? 

Pressure-treated lumber, sometimes referred to as pretreated lumber, is wood that has been soaked through with chemical preservatives.  These additives are forced into and through the wood with high pressure.  

This chemical infusion is done to make the lumber resistant to rot and insects.  Because of the complete saturation, there is a prolonged drying time after the treatment.  In fact, pressure-treated lumber is often still damp when it arrives at lumber yards.  


Your Safety is Essential 

Obviously, any home improvement should be done with safety of foremost importance. But if you are working with pressure-treated lumber, there are additional safety concerns you need to consider.   Because there is a high concentration of chemicals in this lumber, you need specific PPE (protective personal equipment).  At a minimum, you need an N95 mask to protect your respiratory system & goggles for eye protection.  

The pretreated wood is tougher to cut and shape than standard un-treated lumber.  You also need to keep any scraps or sawdust from this process separate from any “standard” lumber debris.  Pressure-treated lumber should not be burned; dispose of any scraps or debris in a landfill.  If you burn this wood, it will release toxic fumes and harm every human and animal that breathes them in.


What is Pressure-treated Lumber Used to Build? 

Pressure-treated lumber is designed to be used for outdoor projects.  These include items like decks, swing sets, or fences.  All of these structures are open to the elements, so the added protection from both rot and insects is invaluable.  

While it is possible for the lumber to give off some small amounts of vapor as it dries, the great outdoors provides all of the ventilation needed.


Why Don’t Builders Use Pressure-treated Lumber for Homes? 

Construction companies don’t use pressure-treated wood inside homes because it’s unsafe.  The preservatives that are added to the lumber are highly flammable.  If you have a house fire, treated lumber would accelerate the burn rate and give off highly toxic fumes.  (Remember- this is why scrap wood and sawdust have to be discarded in a landfill!)  

Additionally, if and when these pressure-treated components begin to break down, they would release harmful vapors.  If a structure is entirely outdoors, there’s plenty of ventilation to clear out any vapors; the same cannot be said for your home. Houses are designed to keep out the cold, so they’re going to trap those fumes inside. 


Why Isn’t Pressure-treated Wood Used to Repair Sagging Floors? 

If your home only has a crawl space, you might think this would be a safe option.  Your crawl space can have vents in it, so why wouldn’t you use rot-resistant lumber in a dark, frequently damp area?

There are two major reasons why Acculevel (and other repair contractors) will not use pressure-treated lumber in crawl spaces.  


Air from Your Crawl Space Travels Into Your House

Your home is not not sealed and separated from the crawl space.  Even the best-built homes are not perfectly air tight, and wood is a porous material.  (If it wasn’t, how could we saturate the lumber with preservatives?)  

Air can seep up through your wooden flooring structure.  Furthermore, your HVAC ductwork and ventilation system also connect the different levels of your home.  

The exact measurements will vary depending on your individual home, but in general? Between 30% – 50% of the air in your home originates in the crawl space.  


Have more questions about your home’s air quality, and how it’s affected by the conditions in your crawl space?  We explore the problems and solutions to air quality issues in this article.


Forcing Preservatives into Lumber Makes it Expand

Even if your home is somehow built in a way that keeps all of the crawl space air out of circulation, pressure-treated wood is still not a good option.  When additives are forced into the wood, they fill in tiny gaps that used to contain air.  This means the boards swell up, making them slightly larger.  The difference isn’t large, but it’s significant.  

The old expression, “measure twice, cut once,” is a reminder that even the slightest variation in measurements will have an impact.  If you take out an old, damaged sill plate and replace it with a slightly larger sill plate?  You’ll be lifting your house up higher than it was originally.  

Illustration of structural wood framing
This is a diagram of your home’s flooring structure.  The sill plate is the board directly on top of the foundation, and the floor joists rest on top of it. 


Even A Slight Increase is a Significant Increase

This adjustment will be slight- but it will have a dramatic effect on your home.  Every single joint and connection in your home will now shift just a teeny little bit.  So what happens when every single thing in your home moves a teeny little bit?  

  • Every floor joist is now a bit higher, forcing the subfloor up.  This can cause the subfloor to detach.  If you have any tiled floors installed, these will crack. 
  • Your drywall will crack, both on the walls and the ceiling.  
  • Framework will shift or twist, making it harder to open/close windows and doors. 
  • The main beam could be damaged, because only the ends of the main beam rest on the sill plate.  So the ends will shift up, but the bulk of the beam won’t. This can cause tiny cracks in the beam.

Overall, it is much better for you and your home if the damaged sill plate is replaced with the untreated wood that is the exact same size. 


Want More Information about Sagging Floor Repairs?

If you have noticed any sloping, sagging, or low spots in your home’s flooring, we can help!  Our free guide to crawl space repairs answers all of the most commonly asked questions about damaged flooring structures and how to repair them.  Some components, like the sill plate, need to be replaced.  Others, like floor joists, should be “sistered,” a form of shoring or reinforcement.  

Crawl Space Guide link

Our guide describes the warning signs that indicate your crawl space needs repairs, explores the causes of damage, best repair methods, and costs of each.  Even if you do not live in our service area (our coverage map is here), this guide is a valuable resource available to every homeowner, for free. The best consumer is a well-informed consumer.  The more you know about your home and what it needs, the more confident you will be when hiring the necessary contractor to make repairs. 


Ready to Schedule an In-home Assessment? 

Call Acculevel at 866-669-3349, or complete our online form.  We’ll schedule an appointment for you with one of our project advisors.   Our PAs are friendly, knowledgeable, and experienced experts who will listen to your concerns, and discuss what you have noticed about your home.  They will thoroughly evaluate your home and foundation, document any signs or symptoms, and then review this information and their diagnosis with you.  Together, you will determine what the best whole-home solution is for you.  

Acculevel’s goal is to provide 5 star customer service from start to finish.  It begins the moment you contact us, continues through your home’s assessment and repairs, and extends all the way through our best-in-the-industry warranty program. We want you to help you preserve and protect your home for years to come. 


Kelly Kater

Over her twenty year career, Kelly has worked in a wide variety of fields: secondary education, nursing, biology, elder care, the postal service, multicultural development, and academia. She has developed a skill for translating industry-specific jargon into everyday language. Her goal is to share the knowledge and experience of the Acculevel team with homeowners, in a way that is both engaging and informative.

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