Is Modern Lumber a Problem for New Homes?

Today, I discuss a post that regularly shows up on my social media feeds. The gist of the post is this: old growth lumber is superior to modern lumber, and therefore, houses built in the mid-20th century are more durable and longer lasting than today’s new construction.

As a home inspector in Raleigh, North Carolina, I understand the allure of old homes. I’ll admit the romantic notion of this argument is tempting. But is it true? Let’s dive into this myth and unravel the facts, starting with what makes old growth lumber different and whether that difference truly matters for new construction homes.

A Look At The Post

The Termite Resistance Argument

First, let’s tackle the claim that old growth lumber is more termite-resistant than modern lumber. There’s some truth to this: older lumber of the same species tends to be denser and contains more heartwood, which is naturally more resistant to termites and decay. However, this doesn’t mean old growth lumber is termite-proof. Termites have been around far longer than farmed trees, and they’ve always found ways to feed on wood, old growth or not. Here’s why this argument falls short:

Termites Thrive on Moisture and Warmth

Termites are less about the type of wood and more about the environment. Moisture and warmth create the perfect conditions for termite infestations. In my experience inspecting older homes in the Raleigh area, I find they are often more susceptible to these issues due to outdated or failing systems. For example:

• Older HVAC systems in crawlspaces often leak, lowering the dew point and encouraging condensation.

• Plumbing and grading issues are more common in older homes, leading to persistent moisture problems.

• Poor flashing or absent weather barriers allow water intrusion, creating damp, inviting conditions for termites.

It’s not just a matter of wood type but of the entire ecosystem within a house that determines susceptibility to termites.

New Construction Techniques Mitigate Termite Risks

New construction homes incorporate multiple layers of protection that were often missing in older construction. From treated lumber in sill plates to integrated pest barriers in foundations, today’s construction standards emphasize termite prevention. Soil treatments, including termiticide barriers, termite inspection gaps, and maintaining minimum required distances from the base of the wall to the top of the grade, all play a crucial role in minimizing termite risks. These advances render the slight natural resistance of old growth lumber largely irrelevant.

Whether a house is older or new construction, termite inspections and termite mitigation strategies are paramount.

The Rot Resistance Argument

Another common claim is that old growth lumber resists rot better because it contains more heartwood. While it’s true that heartwood is more resistant to decay, it is far from impervious to moisture. The moment water enters the equation, all bets are off. Moisture can deteriorate even the toughest materials over time—just look at the Grand Canyon.

This claim of permanence also suffers from a selection bias. We’re impressed by the durability of historic homes still standing today, but we’re overlooking the countless older homes that have deteriorated beyond repair. Survival bias gives the illusion of superiority, but the truth is that many historic homes survive because they’ve been well-maintained or benefited from favorable environmental conditions.

What really sets older homes apart is not their lumber but their design. Older homes often featured in abundance materials like plaster, skip sheathing, wood floors, brick, and stone that acted as hygric buffers—absorbing and releasing moisture. Combined with leaky building envelopes and natural ventilation, these homes dried out effectively. However, once we started retrofitting these homes with insulation, air conditioning, and enclosed crawlspaces, we created new challenges that weren’t addressed in the original design. For instance:

• Retrofitted insulation traps moisture where it once dissipated, leading to hidden mold or rot.

• Airtight renovations inadvertently trap water vapor, compromising wood elements. Many older homes quite literally had ventilation systems that drew air through and out the house. Now in the same homes, we’re trying to trap the conditioned air in.

• We began enclosing crawlspaces or adding curtain walls between existing pillars. Ducts—even well-installed ones—leak. Most ducts aren’t well-sealed, particularly older ones. When conditioned air leaks into the crawlspace, it changes the dew point. Once that drops below the exterior air’s dew point, water begins to condense, keeping wood moist and encouraging decay.

The Strength Argument

The final claim is that old growth lumber is stronger than modern lumber. Pound for pound, this is accurate. Old growth lumber can span further or bear more weight than its modern counterpart. However, this doesn’t mean new lumber is insufficient for today’s construction standards. Here’s why:

Lumber Grading and Engineering

New construction uses graded lumber, which is tested for metrics like shear capacity, bending capacity, parallel/perpendicular compression capacity, and modulus of elasticity. Engineers design structures based on these values. This is the basis of statics. It’s akin to balancing a checkbook. If the loads imposed do not exceed the capacity of the member, then what’s “left in the tank” is largely irrelevant. And keep in mind how engineers categorize failure. Failure isn’t “if the house falls down”. In the eyes of a structural designer, failure may be a floor joist deflecting (or bowing) greater than a half inch. That’s a far cry from a house falling down.

Built-In Safety Margins

Building codes require designs to withstand rare events. For instance, new construction homes in Raleigh, NC must abide by a wind speed design minimum of 115 mph. This wind gust represents a 1–2% likelihood of occurring each year. Take any code mandated distributive load that must be ascribed to a design. We’ll pick on a floor joist in a living room:

If a joist spans 15’-0” and is spaced 16” on center from adjacent joists, it must support a distributed load of 50 pounds per square foot. This means a single joist must be capable of carrying 3,333 pounds while ensuring that deflection does not exceed 1/2 inch.

That’s stringent. That’s also very unlikely to ever occur in most houses. In fact, many professionals understand that a home may never realize its factored loads. Nonetheless, every home must be designed to meet the minimum criteria set forth by the 2018 North Carolina Residential Building Code.

Residential Loads Are Small

Here’s the rub: In the world of engineering, houses don’t weigh that much. The loads that exist in a house just aren’t that great relative to the material that supports them. And where homes do require more demand, engineered wood products like laminated veneer lumber (LVL) and I-joists have become ubiquitous in new construction. These materials address many structural challenges old growth lumber could not solve, such as long-span floor joists or roof systems.

The Real Takeaway

While old growth lumber has undeniable qualities, it’s not a magic bullet for durability. What truly determines a home’s longevity is maintenance and proper design. Older homes can be charming and well-crafted, but they often come with hidden challenges such as outdated systems, moisture issues, and inadequate weatherproofing, all of which can be uncovered with a thorough home inspection. Meanwhile, new construction benefits from advancements in materials science, engineering, and building practices and must adhere to modern building codes, which are based on safety, efficiency, and past building failures.

So, should you buy a mid-century home over a new build simply because of the lumber? Absolutely not. The better choice depends on your personal preferences, budget, and willingness to address maintenance issues.

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