Most deck builders learned from their boss and never questioned how stairs should be built.
Stairs are the first thing to rot on any new deck–Lets do a deep dive into how we build stairs to last!
Perhaps this is why your average set of steps on a deck lasts roughly 10 years before becoming dangerous. Building deck stairs is important. When stairs fail, it’s no joke. People can get injured badly. A fractured hip could be a mild outcome. That’s why we take it so seriously. It isn’t just how to build solid stairs, its about avoiding premature rot. Why does wood rot happen? How can you prevent rot?
What Causes Wood To Rot?
In order to understand why deck stairs need to be built differently (and no, CODE does not have answers), we need to understand why does wood rot happen?
Fungi and associated microbes feed on wood.
They only require 3 things to do this: food, Moisture, and Oxygen.
Climate, Location, and Species-Specific Factors
We don’t all build decks in one place, and not all species have the same amount of bioavailability (what rot feeds on) in the wood. Every area has varying yearly rainfall, and every deck is different for ventilation. That means in areas where rot is more prone like Seattle and Ontario and Florida how you build long lasting deck stairs will involve flashing tape and building heavy!
As wood gets wet ,it absorbs moisture primarily into the end grains and swells. When wood gets wet and freezes, it swells even more. It’s not just the wood soaking up the moisture and enlarging, the water swells as it freezes. This moisture freezing shatters the grain, allowing more moisture and oxygen within the lumber ends.
In the Toronto area, we have up to 250 freeze-thaw cycles per year. Moisture comes off the lakes as well and keeps the humidity high. Every time the sun comes out on a -3 day, it can melt the deck and then freeze again as the sun wanes.
Wisconsin may see 50 freeze-thaw cycles a year since it mostly gets cold and stays that way–, BC, possibly 10 since it is moderated by the ocean.
Texas is so dry in some areas that you don’t have to seal the ends. Minimal rainfall and freeze-thaw cycles mean that things just last longer when it comes to framing. You will also find that the exterior stain will get torn up by the UV. Strong direct sun is hard on wood, composite… everything. .
Florida can see 300 rain showers a year, depending on the area, with no frost normally, but, in the Southern States, termites are a factor as well. We won’t get into that aspect. Maybe we will get into that during an article on steel framing.
Why does Wood Rot Happen more in some Species?
WOOD SPECIES vary in their rot resistance.
In different areas of North America, we use everything from Spruce, Pine, Douglas Fir, Hemlock, and Southern Yellow Pine for pressure treatment. These vary in density and strength as well as natural rot resistance. In the Rust Belt (Great Lakes Area) as well as in BC, Spruce lumber, even if pressure treated, will only last 5-10 years without employing our tricks of the trade to make them last longer.
In BC, naturally occurring species like Red Cedar and Redwood have developed ways of coping with the rainforest-like climate by utilizing tannins to last longer. In Ontario, Hemlock was traditionally used as cladding for barns and in some cases can last more than 100 years as cladding. We’ve used rough-cut hemlock for rustic-style decks, and they are still solid after 15 years.
PRO INSIGHT:
About 15 years ago, the EPA banned arsenic-based Pressure Treatment in favor of ACQ-treating for Pressure-treated Treated Lumber. We often have people call to have their decking replaced on an older deck. Often, decks that are facing south and more than 20 years old (Arsenic PT) can be re-decked, whereas a 10-year-old structure facing west may be a total write-off.
Our Method for Building Deck Stairs:
Building long lasting deck stairs just takes some forethought. Deck stairs are the weak point on most decks. For this reason, we put more time and materials into our staircases to help them age more gracefully. Sealing end cuts with high VOC stain or paint helps, but tape is also helpful on top of the joists, beams, and blocking. Stair stringers when cut are untreated ends that are prone to rot. The open end grain sucks water in like a straw. Plugging those grains with an oil based, high VOC paint will give far more protection when coupled with flashing tape than any end cut preservative.
Notice how the exterior stringers encase the lower and upper rim joists. That helps lock it together structurally.
A foundation and solid mount up top are also critical. Movement means weakness long term. The double joists are also less than 1′ from the main beam. For larger staircases, we often increase the size of the beam to carry the additional load of the staircase.
You will notice that the top of the joists and stringers are black. That is joist tape by G-Tape. It’s our top choice for protecting beams and joists and deck stairs from rot.
Our PVC decks always have a double rim joist for durability. Stair stringers are roughly 8″ on center and rail mounting blocks within the deck stairs is made of 6×6. We isolate the deck stairs from the concrete support using a piece of PVC.
Build it once- Build it right.
Did you know that there are species of lumber that you can buy from a local mill that will likely outlast PT lumber? Check out our article on Sustainable Decks!
Lawrence
