We had some big decisions to make when starting Maine Porch & Pergola Company. The selection of materials for our wood screened porch kits was one of the most important. We wanted to research this thoroughly. Our biggest concerns were rot (fungal decay) resistance and insect resistance. Woodworking stability, appearance and costs were also concerns, as was structural strength is also a concern.
We hunted for information and recommendations from forestry professors, wood scientists, lumber companies, trade groups and professional builders. We did this by talking with them, studying research papers, reading web articles, and scouring blogs and forums.
Rot and Insect Resistance
Here is what we found on materials for wood screened porch kits:
- Hardwoods: Teak, old growth Cypress White Oak, Black Walnut and American Mahogany are the most rot and insect resistant hardwoods. These are followed by imported Mahogany, Cherry, young growth Teak and young growth Cypress in the moderate-resistance group. Other than White Oak, pretty much all of the commonly available lumber-yard hardwoods are in the low-resistance group (e.g., Maple, Ash, Beech, Birch, Poplar).
- Softwoods: Old growth Redwood and old growth Cedars (white, yellow and red) are the most rot and insect resistant softwoods. These are followed by young growth Redwood and young growth Cedars, Tamarack, Douglas Fir, and old growth Pines, which provide moderate-resistance to both rot and insects. All other untreated softwoods that are commonly available at the lumber-yard are in the low-resistance group (e.g., Pine, Fir, Spruce).
These findings are based on research cited in the USDA Forest Service 2010 Engineering Handbook, as well as anecdotal experience that dates back decades. But according to Professor Gene Wengert of University of Wisconsin, the problem is that as old growth forests are logged out, the quality of young growth lumber for even the highest rated species can be all over the place. This is because the proportion of sapwood (new outer rings of a tree) vs. heartwood (older inner rings of a tree) has been increasing in commercially available lumber. And it’s the heartwood that provides the best rot and insect resistance.
Conventional Wisdom on Cedar and Redwood is NOT Reliable
These concerns about cedar and redwood became most evident when reading blogs and forums where professional builders were comparing notes on fence posts. These are perhaps the most rigorous testing-ground for rot and insect resistance. According to these hands-on experts, years ago you could trust Cedar and Redwood to last several decades or more. Today this is no longer the case. Longevity may be as low as 10 years or even less.
This calls into question whether today’s Cedar and Redwood really are worth their high cost (see below). Many retail lumber providers will not be able to answer questions about old vs. young growth or sapwood vs. heartwood. This makes it very hard to know exactly what you are buying for a wood screened porch kits.
It’s not clear to what extent these quality concerns apply to hardwoods, but hardwood forests in developing countries are very susceptible to over-harvesting. This bring up environmental and sustainability concerns.
Cost is Important
Cost in a business like ours is very important. We are always seeking the best trade-offs between rot resistance, insect resistance, strength, appearance, wood working stability, sustainability and cost when selecting materials for wood screened porch kits. Here are some cost comparison ratios to consider.
Suppose you were going to buy $100 worth of commonly available Spruce-Pine-Fir 2×4 dimensional lumber. The same amount of similar grade lumber in other selected species would cost approximately:
- Regular Pine-Spruce-Fir – $100
- Atlantic White Cedar – $210
- Alaskan Yellow Cedar – $332
- Redwood – $468
- Western Red Cedar – $595
- Imported Mahogany – $880
Pressure Treated Lumber
Then there is pressure treated (PT) lumber. Treating lumber dates back to ancient Greece, where bridge wood was soaked in olive oil.
PT lumber is specially treated to resist rot and insects. It is generally trusted to be rot resistant for 20-30 years or more. This is well beyond even the best hardwoods, Cedar or Redwood. This “20-30 years or more” is anecdotal, however. Wood treaters resist providing specific duration warranties due to site variability, installation and maintenance factors.
PT lumber is also relatively cheap. Extending the cost comparison above:
- PT Pine-Spruce-Fir – $113
One important attribute of treated lumber is that the treatment process is done under uniform quality control. This ensures that every piece is treated to the manufacturers specifications. So there is no variation and uncertainty in rot and insect resistance which you find in today’s Cedar and Redwood.
But PT lumber has its drawbacks. Regular PT lumber can be very wet when you purchase it at the lumber yard. Raised grain, splitting, checking, twisting, warping, and shrinkage can occur as it dries out. This makes using it a dicey proposition when appearance is important as is the case with our wood screened porch kits.
Our solution is to use “kiln-dried-after-pressure-treatment-Pine (KDAT Pine). The most important attribute of KDAT lumber when compared to regular PT products is that it is dry. Because it is dry, KDAT lumber can be sealed/primed and painted right away to protect it from natural weathering such as raised grain, splitting, checking, twisting, warping and shrinkage.
Extending the cost comparison:
- KDAT Pine – $148
See our article on wood selection for pergolas for more information on the attributes of PT and KDAT lumber.
Our Strategy For Wood Screened Porch Kits
Because of all the factors discussed above, we use a combination of materials to get an optimal balance of rot and insect resistance, strength, aesthetics and cost:
- We use KDAT materials for the components that are in contact with the ground or concrete. We try to use a minimum of these for aesthetic reasons, but always enough to adequately protect against prolonged exposure with wet surfaces.
- Wall panels are made primarily of Alaskan Yellow Cedar or Western Red Cedar. Wall panels are where appearance is most important.
- Doors, which take a beating over many years and are also susceptible to moisture are almost always made of Mahogany. And if a customer wants and can afford Mahogany for wall panels, we will gladly oblige.
- Rafters, ledgers, closures, and roof sheathing which are protected from the elements are generally made with economy Spruce-Pine-Fir to minimize costs. If appearance is critical in the case of exposed rafters we will use clear (knot free) Douglas Fir.
- We also use small but strategic amounts of PVC (polyvinyl chloride) in key locations as moisture barriers in our wood screened porch kits. These are generally ½ inch thick PVC layers to protect components that would otherwise be in direct contact with a deck or concrete slab. We also use PVC barriers where the screen/glass inserts nest into the wooden wall panel. These areas collect rain and dew and are particularly prone to rot.
Enjoy Outdoor Living!
Materials for Wood Pergola Kits