Pressure treated wood has become increasingly popular for residential construction and home improvement projects in recent years. When properly treated and installed, pressure treated lumber provides unparalleled protection against rot, fungus, termites, and other wood destroying organisms. However, there are specific code requirements regarding the use of pressure treated wood that homeowners must understand before purchasing and installing this versatile building material. This comprehensive guide will provide an overview of pressure treated wood, explain the relevant residential building code requirements, and give recommendations for best practices when using pressure treated lumber at home.

What is Pressure Treated Wood?

Pressure treated wood refers to lumber that has been infused with chemical preservatives under high pressure. This pressure treatment forces the preservative deep into the cellular structure of the wood, providing long-lasting protection against decay and insect damage. The three main types of pressure treated wood used in residential construction are:

CCA treated wood – CCA stands for chromated copper arsenate. CCA treated wood was the most commonly used type of pressure treated lumber for many decades but is no longer used residential purposes due to concerns over arsenic and chromium levels.
ACQ treated wood – ACQ stands for alkaline copper quaternary. This is currently the most common type of pressure treated wood, using copper as the main preservative. ACQ treated wood has been treated to be arsenic-free.
CA treated wood – CA stands for copper azole. This type uses copper coupled with azole compounds and is also arsenic-free. CA treated wood is growing in popularity as an alternative to ACQ.

The specific preservatives and treatment process used give pressure treated wood its characteristic greenish tint and resistance to outdoor elements. While treatment methods have evolved over time, all pressure treated lumber contains high levels of preservative chemicals that enable it to withstand exposure better than untreated wood.

Benefits of Using Pressure Treated Wood

There are several key benefits that make pressure treated lumber an ideal choice for many exterior home applications:

Rot resistance – The preservatives penetrate deeply to prevent fungal decay and rot over decades of service. This makes pressure treated wood perfect for structural applications and projects that will have direct ground contact like decking.
Insect resistance – Chemical treatments deter termites, carpenter ants, wood boring beetles, and other pests. This helps protect homes from expensive structural damage.
** Mold and mildew resistance** – The treatments make pressure treated wood inhospitable environments for mold, mildew, and other fungal growth.
Stability – Pressure treated wood retains its strength, integrity, and appearance better than untreated wood when exposed to moisture and other weathering factors.
Cost effectiveness – The longevity and resilience of pressure treated wood makes it a cost-effective choice for the long run, despite usually having a slightly higher upfront cost over untreated lumber.

Using pressure treated lumber for exterior projects, structural components, decks, landscaping, and other applications around the home provides protection and peace of mind thanks to its specialized treatment process.

Pressure Treated Wood Code Requirements

While pressure treated wood offers many advantages, there are building code requirements and standards that govern its allowable uses. Homeowners must understand the applicable codes prior to selecting and installing pressure treated lumber.

The International Residential Code (IRC) is the model residential building code adopted throughout most of the United States and it contains provisions related to pressure treated wood applications. Additionally, the International Building Code (IBC) applies to certain residential projects.

It’s important to be aware of your local jurisdiction’s specific adopted code based on the IRC or IBC. However, most municipalities adhere closely to the model code requirements. Here are some of the key pressure treated wood code rules to know:

Minimum Preservative Retention Levels

The IRC mandates that pressure treated wood must meet certain preservative retention levels based on the intended use:

Above ground, not in direct contact with the ground or foundation – 0.25 pcf
Ground contact applications like posts, deck supports, joists – 0.40 pcf
Permanent wood foundations – 0.60 pcf
Posts or columns supporting permanent structures – 0.60 pcf

These retention rates must be verified by an approved quality mark on the wood itself. Homeowners should check for stamps indicating the treatment level before purchase and installation.

Indoor Use Limitations

The IRC prohibits certain applications of pressure treated wood inside occupied spaces of homes:

Cannot be used where it may come into direct contact with drinking water except for uses like water tanks and cisterns.
Should not be installed on interior surfaces like floors, walls, or ceilings in most habitable rooms.

However, ACQ and CA treated wood that is kiln or air dried after treatment may be approved for some interior uses like framing. Verify local codes for indoor limitations.

Sealing Requirements

Cut ends, notches, bored holes, and other field cuts of pressure treated wood must be coated with a wood preservative prior to installation. This seals the exposed untreated interior and prevents moisture intrusion.

Fastener and Connector Requirements

Metal fasteners and hardware like nails, screws, joist hangers, and post/beam connectors must be hot-dipped galvanized steel, stainless steel, silicon bronze, or copper to avoid corrosion and premature failure when used with pressure treated wood.

Spacing from Soil

There must be at least 6 inches vertical separation from the soil line up to the pressure treated structural wood members. Some examples:

Deck or porch joists must have a minimum 6 inches of clearance off the ground.
Fence posts require 6 inches of space between the soil and the bottom of the post.
Sill plates on foundation walls need a gap of at least 6 inches from the ground to the plate.

Proper spacing helps airflow and reduces transfer of moisture.

Understanding these key code rules for pressure treated wood is essential to ensure safe, compliant installation and satisfactory performance. Many specifications relate to proper preservative retention and preventing untreated exposure.

Best Practices When Working With Pressure Treated Wood

In addition to following the required code guidelines, practicing certain care and maintenance habits will help pressure treated wood retain its benefits and achieve a long service life:

Allow pressure treated wood to fully dry and ventilate any initial chemical odors for several weeks after purchase before installation.
Wear gloves, long sleeves, and eye protection when handling, cutting, or drilling pressure treated lumber. Consider wearing a dust mask when sawing.
Work in well ventilated areas since sawdust and debris may contain chemical residues. Dispose of any saw dust and cutoff pieces properly per local regulations.
Use care when designing tight-fitting joinery, since pressure treated wood may shrink slightly as it dries out after installation.
Allow 1/8 inch gaps between decking or fence boards to permit adequate drainage and airflow.
Use metal fasteners and connectors specifically approved for use with pressure treated wood. Do not use standard steel.
Inspect pressure treated components annually for any cracks, excessive dryness, or other deterioration and repair as needed.
Recoat any field cut ends and new drill holes with a brush-on wood preservative on a regular basis.

Proper handling procedures, construction detailing, and inspection habits will help pressure treated wood projects provide decades of reliable performance. Check with your local building department if you have any questions about applicable code requirements.

Pressure Treated Wood for Decking

One of the most popular uses of pressure treated lumber for homeowners is decking. Here are some key recommendations when utilizing pressure treated boards for your deck construction:

Select the Appropriate Grade

Pressure treated deck boards are available in different quality grades. The most common are:

Premium Grade – Has very few knots or blemishes for a more uniform appearance. Best option for decks where you want minimal imperfections.
Standard/No. 2 Grade – Contains more knots, splits, and other marks that do not affect structural performance. More economical choice for typical deck projects.

Verify the Correct Retention Level

Decking in ground contact must be a minimum 0.40 pcf retention but 0.60 pcf is preferable in damp or wet areas. Verify the treatment certification stamp before purchasing.

Allow Time for Drying

Let pressure treated deck boards adequately dry for 2-3 weeks after installation to prevent shrinkage issues and help minimize surface checking and splitting as the wood weathers.

Plan Spacing for Drainage

Allow 1/8 inch side-to-side spacing between deck boards. This enables drainage and air circulation to keep the deck drier.

Raised Off Ground Surface

Construct the framing so there is at least 6 inches of clear space between deck boards and soil underneath according to code.

Pre-drill All Screw Holes

Predrill slightly smaller diameter pilot holes when using screws to fasten decking to prevent splitting at board ends.

Use Proper Fasteners

Use hot-dipped galvanized, stainless steel, or exterior grade screws specifically designed for pressure treated decking. Standard fasteners may corrode.

Rout Edges for Cleaner Appearance

Routing the edges of deck boards creates a rounded over edge that helps prevent splinters and gives a more refined look.

Seal All Cuts or Holes

Brush on end-grain wood preservative to protect any field cut ends, miters, drilling, notching, or other holes that expose untreated interior wood.

Inspect and Clean Regularly

Inspect decking several times per year. Use a pressure washer and brightener to periodically clean and maintain the wood’s color.

Following these best practices for selecting, installing, and caring for pressure treated deck lumber will help the deck remain splinter-free, structurally sound, and look its best for years to come.

Pressure Treated Wood for Fences

Another very common application of pressure treated lumber around homes is wood fencing. Here are some important recommendations when building a wood fence using pressure treated posts, rails, and pickets:

Select Appropriate Lumber Grade

Use Premium posts paired with Standard/No. 2 boards for pickets and rails to balance cost and performance.

Verify Treatment Levels

Make sure posts and components in ground contact are rated for 0.60 pcf retention since they will be structural. 0.40 pcf is acceptable for above-ground members.

Choose Suitable Post Dimensions

Use 4×4 or 6×6 posts for spans of 8 feet or less. For longer spans or taller fences, use larger dimension posts up to 8×8 or consider reinforcing posts with rebar.

Space Posts According to Height

Follow these maximum post spacing recommendations based on fence height:

Up to 4 ft height – space posts 8 ft on-center
4-6 ft height – space posts 6-8 ft on-center
Over 6 ft height – space posts 6 ft or closer on-center

Pre-drill Posts for Hardware

Drill pilot holes in posts when using fasteners and hardware to prevent splitting. Avoid screwing bolts directly into posts.

Install Caps on All Posts

Use metal post caps designed for pressure treated wood to limit moisture exposure at the end grain.

Allow 1-2 Inch Pickets Gaps

Leave 1-2 inches between pickets to permit air circulation and drainage. This can help minimize warping.

Use Exterior Rated Fasteners

Connect pickets and rails with hot-dipped galvanized, high-quality exterior screws that won’t corrode.

Inspect and Repair as Needed

Check fence periodically for any loosening, decay, or vegetation contacting the wood and perform maintenance promptly.

Properly installing pressure treated wood fences with these best practices makes them very low maintenance while still looking great.

Pressure Treated Wood for Retaining Walls

Retaining walls are commonly constructed from pressure treated lumber. Here are some key guidelines when building retaining walls with pressure treated wood:

Use lumber with 0.60 pcf preservative retention since the wall is structural and permanent. Some brands indicate the retention right on the wood.
Select posts and framing lumber rated for “in-ground use” or “ground contact.”
Allow at least 6 inches of gravel drainage behind the wall to direct moisture away.
Construct retaining walls shorter than 4 feet tall by sandwiching gravel or drainage fill between two parallel rows of pressure treated boards.
For retaining walls above 4 feet, utilize post and beam construction with substantial footings instead of just using boards.
Use galvanized steel rebar pins, epoxy coated nails, or stainless steel screws to assemble the wall – do not use regular fasteners.
Do not backfill behind the wall for at least 2 days after construction to allow adequate curing of any adhesives or anchors.
Inspect the completed retaining wall after heavy rains to check for washouts, leaks, soil movement or other damage and repair promptly.

With the right design, high quality preservative treated lumber is an attractive and economical choice for building sturdy retaining walls up to 6 feet high. Careful construction practices are essential.

Sourcing High Quality Pressure Treated Wood

Installing pressure treated wood that meets all building code requirements and standards comes down to sourcing from reputable suppliers. Here are some tips for sourcing high quality pressure treated lumber:

Check that the wood bears stamps from verifying agencies like the ALSC (American Lumber Standards Committee) indicating the preservative retention level and other attributes that show it is compliant and safe for residential use.
Purchase pressure treated wood bundles with intact end tags stating the treatment retention certification and manufacturing details. Removing tags eliminates the ability to verify the lumber’s legitimacy and process.
Acquire pressure treated wood from established, professional lumberyards that stand behind the products they sell and have a relationship with their treatment suppliers.
Be wary of lumber that seems excessively dried out and cracked or otherwise does not appear to have been produced by a quality-controlled pressure treatment process.
Ask lots of questions to any vendor about the specifics of the pressure treated lumber they sell so you fully understand what you are purchasing.
Compare prices across retailers while being wary of lumber that seems too cheap and does not have proper stamps and documentation. Higher costs generally reflect better treatment processes.

Taking the time to properly source quality pressure treated wood from trustworthy dealers will give homeowners confidence that their lumber meets all residential building code requirements for safe, durable, and effective performance. Installation is also much smoother when the lumber is stamped and can be verified during building inspections. With a knowledgeable supplier and adherence to the standards outlined here, pressure treated wood can deliver lasting beauty, protection, and value to outdoor home projects.

Pressure Treated Wood – Frequently Asked Questions

Q: What are the different types of pressure treated wood?

A: The main types of pressure treated lumber used residentially are CCA, ACQ, and CA. CCA treated wood is no longer approved for most residential uses. ACQ and CA treated are the most common – both use copper-based preservatives and contain no arsenic.

Q: Can I use pressure treated wood indoors?

A: Limitations exist on interior uses of pressure treated lumber. It should not touch drinking water or be used on floors, walls, and ceilings in living areas unless approved dried lumber is used. Always verify local building codes for indoor applications.

Q: How long does pressure treated wood last?

A: When properly treated and installed in above ground applications, pressure treated wood can last from 15-40 years or more before replacement. Preservative retention levels, wood species, and exposure conditions impact lifespan.

Q: Does pressure treated wood need to be sealed or stained?

A: Sealants and stains are not required but can provide added protection. Use water-based semi-transparent stains formulated for pressure treated wood only after letting it dry out thoroughly first.

Q: Is pressure treated wood safe around pets and children?

A: Pressure treatment chemicals pose little risk once the wood has dried. Avoid contact with sawdust and wash hands after working with the wood. Normal precautions apply when using lumber.

Q: What can I use to seal the cut ends of pressure treated wood?

A: Brush-on end cut wood preservatives specially formulated for pressure treated lumber should be used to coat any exposed cut ends, holes, or abrasions according to the manufacturer’s directions.

Q: How long should pressure treated wood dry before sealing or painting?

A: Allow approximately 6 weeks of dry time before applying any sealants or paints to pressure treated wood. This permits thorough drying to prevent issues with finishes adhering or penetrating properly.

Q: Can I burn pressure treated wood?

A: Pressure treated wood should never be burned in open fires, stoves, fireplaces, or residential waste burning containers because of the chemicals it contains and the toxic smoke and ash residue released. Always dispose of pressure treated wood properly rather than attempting to burn it.

Q: Is it safe to use pressure treated wood in raised garden beds?

A: Only certain pressure treated wood labeled safe for garden bed use should be utilized. ACQ and CA treated lumber that has dried adequately poses minimal risk, but CCA treated wood should not be used where direct soil contact may occur. Verify which type of pressure treatment was used if reusing wood for beds.

Q: Can I dispose of pressure treated wood in my regular household trash?

A: Typically not. Many municipalities prohibit or restrict disposal of pressure treated wood waste in normal garbage collection because of the preservative chemicals. Always check local regulations on proper disposal methods in your area. Proper disposal is important for safety and the environment.

Conclusion

When used thoughtfully, pressure treated wood is an ideal choice for decks, fences, landscaping projects, and structural outdoor construction around the home. Utilizing high quality pressure treated lumber and adhering to residential building code requirements provides performance, protection, and value over the long run. Always check with local permitting agencies regarding specific regulations and applications in your jurisdiction. With proper installation and care, pressure treated wood can provide decades of reliable service while resisting rot, pests, and weathering. Follow the expert recommendations and code rules discussed here to leverage the benefits of pressure treated lumber safely.

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