Getting the Wood Out: How PHNX Solved the Combustibility Problem

At the Resilient City Expo in Houston this month, PHNX founder and CEO Laurie C. Fisher was invited to speak; here are highlights from her presentation “Getting the Wood Out”.

After the 2017 Tubbs Fire, Laurie helped families in Santa Rosa rebuild the homes they lost. That process was long and painful, and it compounded the trauma of loss they were already carrying. She became determined to do something about it; near the end of the process she asked them what could have made it a little better, and what they wanted for the future. Every single one of them, 100%, said the same thing: we do not want to have to go through this again.

But look at what the industry is doing. Those homes are being built back with the same materials that burned the first time. It has been more than 20 years since these wildfires changed and started getting more severe, yet builders are still searching for solutions - because no one is asking the right questions.

We should start by asking what materials actually make the most sense for a fire resilient home. Instead, the industry has been spending valuable time solely focused on one material, and how to make it not burn: wood. Wood is fuel for fire, and as it decays it becomes even more vulnerable. We cannot bend the laws of physics; yet we’ve spent decades trying to convince ourselves that it’s possible.

So PHNX asked the question that nobody else was asking: why don’t we build with materials that don’t burn in the first place?

We asked, and what we came up with was concrete and steel, two materials every experienced contractor already knows how to work with. If you are building in concrete and steel, you have to think about it differently. These materials have significant advantages over wood; if you’re simply replacing wood with concrete and steel in your design, without taking those advantages into account, then yes - your building will cost more.

PHNX did look at those advantages. Concrete has enormous compressive strength, and has been the workhorse of construction since the Romans. Steel has high tensile strength and spans great distances. Maximizing that potential is how we found the efficiencies and savings; optimization of concrete and steel is how a PHNX home achieves cost parity with a wood-framed one.

The only load bearing walls in a PHNX home are the exterior walls. They are Fox Blocks insulated concrete forms (ICF), filled with concrete and rebar, and the foam stays in place and insulates the wall to R-30. Everything else inside is light gauge steel, and none of it is structural. If a wall does not need to be load bearing, PHNX does not make it a concrete wall.

The hard part was the roof. Structural framing needs sheathing, whether that framing is wood or steel, and there is no feasible noncombustible alternative to plywood or OSB. Getting the sheathing out of the roof is the most important innovation PHNX has brought to the table, the patent-pending PHNX Longspan™ Structural System. The joists run perpendicular to the roof slope and span up to 32 feet at 8 feet on center. Insulated steel panels lay in across them, and that is what gives the roof its rigidity. The rigidity gives the lateral resistance, and that is what eliminates the plywood sheathing.

That is four structural parts in all: the ICF walls, Longspan™, a composite steel and concrete floor deck, and the insulated roof panels. Four types of fasteners hold them together, there is no welding on site, and a roof or a floor frames in a day.

The Yosemite Lake House sits just outside Yosemite National Park in a very high fire hazard severity zone, on a difficult site in an isolated mountain town. 2,500 square feet, finished in under a year, on budget, at the same cost as a comparable wood structure. 80% less construction waste. All electric, net zero, with an R-30 plus fully insulated and sealed envelope. It took First Runner Up and People's Choice in small residential at the 2026 ICF Builder Awards and made the cover of ICF Builder in September.

Fire is not the only reason to get the wood out. Wood is an organic material and organic material breaks down. Rot, pests and decay are inevitable, and water accelerates all of it, whether from a leak, a flood or a moisture barrier that fails. Something that gets overlooked about hardening a wood structure is that as the wood degrades it becomes more vulnerable to fire. A newly hardened house may be relatively safe for its first few years. That vulnerability comes back as the wood ages.

Laurie doesn’t hate wood; on the contrary, she loves and respects it. Wood is a beautiful, noble material, and she just thinks it deserves better than sitting hidden behind a closed up wall, decaying and rotting and being eaten by insects. Wood deserves to be seen and touched. And our buildings should last longer than the time it takes for wood to rot.

Back to those families in Santa Rosa. Every one of them asked for the same thing, and at the time nobody could honestly deliver. Now we can. None of this needs a new material, a new trade or a new code. It needs a question we stopped asking. What should this building be made of, and what are those materials capable of doing?

Different isn't always better, but better is always different.

We are building the same way right now in San Diego, Altadena and other jurisdictions in California. PHNX also plans to expand to other states. More on how fireproof and noncombustible construction differ is on our fireproof home and noncombustible facts pages. If you are rebuilding after a fire and want to talk through your options, schedule a consultation.

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