Most people planning a deck spend their energy on the part they can see. Board color, railing style, whether the stairs wrap the corner or drop straight off the back. That’s the fun part, and it matters.
But the decision that determines whether you’re still happy with your deck in twenty years happens underneath, where nobody looks. It’s the frame. And it’s the one part of a deck you cannot replace without tearing the whole thing apart first.
For years there was really only one answer to that question in Montana: pressure-treated pine. That’s changed. Owens Corning now makes a fiberglass-reinforced composite structural lumber that goes in like wood, takes the same hardware, and doesn’t rot. It costs considerably more. Whether that premium is worth it depends almost entirely on where your deck is going to sit.
Here’s an honest comparison from a crew that builds with both.
What pressure-treated lumber actually is
Pressure-treated lumber is ordinary softwood, usually southern yellow pine, that’s been infused under pressure with a preservative that makes it unappetizing to fungus and insects. It’s the default framing material for decks across the country, and it’s the default for good reason. It’s strong, it’s cheap, every lumberyard in Billings stocks it, and every framer alive knows how to work with it.
The important thing to understand is what the treatment does and doesn’t do. It slows down biological decay. It does not make wood stop being wood. Treated lumber still absorbs water, still swells and shrinks with the seasons, and still eventually breaks down when it stays wet long enough.
What Owens Corning structural lumber actually is
Owens Corning Lumber is a wood-free composite: PVC reinforced with the company’s Advantex fiberglass, with an acrylic cap. It’s manufactured in Ocala, Florida, and comes in the same nominal profiles you’d frame with anyway, 2×4 through 2×12, plus 6×6 structural posts.
There’s no organic material in it, which is the whole point. Rot and termites need something to eat. Fiberglass and PVC don’t qualify. It’s rated for ground contact and even continuous submersion, which is a claim no treated board can make.
The honest comparison
Item
Upfront material cost
Availability
Rot and insects
Dimensional movement
Ground contact
Weight
Hardware
Cutting
Warranty
Realistic frame life
Pressure-treated
Baseline
Every lumberyard in town
Resists, doesn’t prevent
Shrinks, cups, twists as it dries
Rated boards only, still finite life
Baseline
Standard hangers and fasteners
Any blade
None to speak of
10 to 20 years, site-dependent
Owens Corning composite
Roughly 4 to 6 times higher
Special order through a distributor
Nothing to feed on
Effectively none
Rated for ground contact and submersion
About 30% lighter than comparable pine
Standard hangers and fasteners
Fine-tooth blade, a bit more care
Limited lifetime residential, 25-year commercial
Designed to outlast the house
Where treated lumber still wins
We want to be clear about this, because a lot of articles comparing these two materials are really just sales pitches for the expensive one.
Pressure-treated framing is the right call for a lot of decks. If your deck is elevated with open air underneath, sits on a well-drained lot, and gets sun on it, treated lumber will give you a solid frame for a long time. Montana’s dry climate genuinely helps here. Wood that gets a chance to dry out between weather events lasts a great deal longer than wood in a humid coastal climate.
The cost difference is not trivial either. Framing is a meaningful chunk of a deck budget, and money saved on the substructure is money you can put toward better decking, a nicer railing, or built-in lighting. If the choice is composite framing under a basic deck or treated framing under a deck with the features you actually wanted, take the features.
Treated lumber also wins on flexibility. If you clip a joist wrong or need one more board on a Saturday, you drive to the lumberyard. With composite framing, you plan your order and you wait.
Where the composite earns its price
Now the other side.
Decks close to the ground. This is the big one. A deck sitting 12 to 18 inches off the dirt has almost no airflow underneath. Snow packs against it, spring melt keeps the soil damp, and the frame never fully dries out. This is where treated lumber fails first and fails hardest, often within a decade. Composite framing doesn’t care.
Freeze-thaw cycling. Billings does something genuinely hard on wood: it swings above and below freezing repeatedly through the winter, sometimes in the same day when a chinook rolls through. Water gets into the wood, freezes, expands, and works the fibers apart a little more each cycle. Composite framing has essentially no water absorption, so there’s nothing in there to freeze.
Dimensional stability. Treated lumber arrives at the job site wet from the treatment process and dries out over the first year or two. As it dries it shrinks, and it rarely shrinks evenly. That’s where cupped joists, opening gaps, popped fasteners, and squeaks come from. Owens Corning boards go in straight and stay straight, which means the deck you get in year five looks like the deck you got in year one.
Wet zones and heavy loads. Hot tubs, outdoor kitchens, anywhere the sprinklers hit, and shaded north-facing yards that never dry out. These are all cases where we’d push you toward the composite.
The frame under a lifetime decking product. If you’re spending real money on a Trex or similar decking surface carrying a 25-year-plus warranty, putting it on a substructure with a fifteen-year outlook is a mismatch. You’ll be tearing off good decking to replace bad joists, and paying labor twice.
The cost conversation, honestly
Materials are where the gap looks scariest. Owens Corning framing runs several times the per-board cost of treated lumber. That number alone talks a lot of people out of it before they’ve done the rest of the math.
But framing material is a fraction of a total deck project. Labor, footings, decking, railing, and stairs make up most of it. On our estimate calculator, a treated frame runs about $100 per square foot installed and a rot-proof frame runs about $150. That’s a real difference, but it’s a fraction of the four-to-six multiple the raw material cost implies.
The other half of the math is what happens later. A treated frame that fails at year fifteen doesn’t just cost you a frame. It costs demolition, disposal, new framing, new footings in some cases, and the labor to pull off and reinstall or replace the decking on top. That’s a five-figure conversation, and it lands at whatever the labor rate is fifteen years from now.
We’re not going to pretend that math works out the same for everyone. If you’re planning to sell in five years, it doesn’t. If this is the house you retire in, it usually does.
What doesn't change either way
A few things matter more than the framing material, and they’re worth saying plainly.
Footings below frost depth. Montana frost lines are deep. Footings that don’t reach below them will heave, and no framing material on earth fixes a heaved footing.
Ledger attachment and flashing. More deck failures trace back to a badly attached or badly flashed ledger board than to any other single cause. Composite framing doesn’t protect the house behind it. Proper flashing does.
Hardware. Joist hangers and fasteners have to be rated for exterior use and compatible with what they’re touching. Both materials take standard connectors, but the fasteners still need to be right.
Permits. Inside Billings city limits, decks require a building permit and inspection. Outside city limits, Yellowstone County doesn’t issue building permits for residential structures and Montana exempts small residential buildings from state permits, though zoning setbacks and HOA rules still apply. We handle this either way.
So which one should you build?
Walk your yard and ask three questions.
How high off the ground is the deck going to sit? Under two feet, we lean composite. Second story with open air underneath, treated framing does fine.
How wet does that spot get? Shade, sprinklers, snow drifts, and poor drainage all push toward composite.
How long is this house yours? Under ten years, treated is the better financial decision. Twenty-plus, the composite usually costs less over the life of the deck.
If you land somewhere in the middle, there’s no rule against mixing. We’ve built decks with composite framing in the low, wet section and treated lumber where the deck runs high and dry.
Let's look at your yard
Every recommendation above comes with a caveat, because the right answer depends on your specific site. A ground-level deck in a shaded backyard and a second-story deck off a walkout are different problems with different answers, and we’d rather look at yours than guess.
Run your numbers through our deck cost calculator for a ballpark, then schedule a free on-site estimate. We’ll walk the space, tell you which framing we’d use and why, and put real numbers to both options so you can decide.
Top Quality Builders builds decks throughout Billings, Laurel, Lockwood, Shepherd, and the surrounding Yellowstone County area.
