In previous blog topics, I identified what a sheathing or roof deck is, and identified that it is commonly plywood or oriented strand board (OSB). I have further expanded this discussion to identify how plywood is manufactured, how OSB is manufactured, and why both are superior to wood planks that may have been used in distance past. However one of the questions I regularly field is OSB vs. plywood, which is superior?
From a roofing contractor perspective, for new house construction the sheathing or roof deck is installed by the carpenters. For replacement roofs, for jobs the roofing contractor tears off the old roof, we have an opportunity to inspect the sheathing or roof deck and replace is necessary. Where we see damages to sheathing or roof deck, it is usually the result of a roof leak.
Some factors that enter into the homeowners or roofing contractor’s decision to use OSB vs. plywood for repairing damaged sheathing or roof deck include typically limited to cost. As both are wood commodities the price of plywood and OSB are variable and change almost daily. Sometimes plywood is cheaper, sometimes OSB is cheaper. When the contractor built your house, you can bet this was the deciding factor.
While some roofing companies will sell you on performance differences, the Engineered Wood Association identifies that plywood and OSB are structurally equivalent. Among the general public, there is a perception that plywood is higher quality; probably based entirely on appearance as plywood is still recognizable as wood and has an appearance they are familiar with. For this reason alone, the homeowners decision would drive plywood vs. OSB decision.
I will tell you that there are distinct differences in performance with prolonged exposure to water. With prolonged exposure to water plywood is definitely the superior product. When plywood gets wet, it swells consistently and will return to its original dimensions as it dries; not so with OSB. When OSB gets wet, it can remain swollen as it dries out, resulting in sheathing or roof deck that is no longer smooth and this will telegraph through to the finished roof when using asphalt shingles (we previously identified that smooth sheathing or roof deck is critical).
As a roofing contractor that has been in business over 25 years, I didn’t stay in business this long because my roofs leak. Since my roofs don’t leak, the decision to install plywood vs. OSB is job specific and includes input from the homeowner on what they prefer and the finished cost.
After the last snow event in Lees Summit, I went out into the neighborhood and snapped some pictures. This picture shows a different solution to ice dams than I discussed previously, albeit not a solution your roofing contractor would probably recommend.
Recall earlier that I explained that ice dams form when snow melts over the heated area of your house, and re-freezes over the eaves (the edge of the roof that overhangs the wall)? This house provides a perfect illustration of this phenomenon as the roof is completely free of snow until you get to the eaves. And yet there is no ice dam or icicles forming, why is that and perhaps this is a solution that would work for me as well?
Obviously the snow melted on the roof, but the snow melted rapid enough and that provided sufficient water flow to prevent re-freezing when the melted snow hit the cold roof over the eaves. That is a lot of heat that is being lost into the framing space under their roof to melt the snow that fast. The water from the snowmelt was flowing like a relative torrent coming off that roof, and there was no chance that it would re-freeze even though the area of the roof that overhangs the wall was cold. Had the snowmelt and resulting water flow been slower, there was significant potential for ice dam to form.
While this homeowner doesn’t suffer from ice dam problems, the thought of the cost of their utility bill makes me shudder. If you have this sort of pattern of snow melt, your roofing contractor will probably want to anticipate that the heat loss problem might be solved during the life of the roof and recommend other solutions to prevent or minimize ice dams.
Have you noticed any evidence of roof leaks in your house? These are usually telltale signs of ceiling stains on your sheetrock. Here in Lees Summit, our typical heaviest rain season would be April through September, with each month exceeding four inches of rain. Within this, June is our heaviest rain month with typical rainfall exceeding six inches.
The problem with roof leaks is diagnosing the source of the leak. To do this, you would normally look immediately above the stain that provided the evidence of the roof leak. But the roof leak could be a good distance from the stain as water has surface tension that can be stronger than gravity. Have you ever noticed beads of water on a leaf after a rainstorm? What prevents gravity from pulling that water down to the ground? You are observing the effects of surface tension.
What this means in a small roof leak (all leaks start small) is that the small amounts of water are leaking through the roof and adhering to structural members such as roof joists, roof sheathing material, or plumbing or HVAC vents. Those water droplets will adhere to these materials the same way water droplets adhere to leaves. As these members slope downward, gravity acting on the water droplets coupled with surface tension will cause the water droplets to follow this material as it flows downward. It is only when these droplets get sufficiently large or a dissimilar material “breaks” the surface tension that the force of gravity exceeds the surface tension forces, and this is where your ceiling gets stained.
If you notice a small stain on your ceiling, this may be evidence of a roof leak. It’s always wise to have any ceiling stains or leaks diagnosed early as it is usually much less expensive to fix a small leak. If you can’t find the source of the roof leak, call an experienced local roofing contractor based in Lee’s Summit to find and diagnose the leak for you.
When you look at roofs in your neighborhood, have you ever noticed some that have black roof stains? Have you ever noticed a pattern on those stains? Have you ever wondered why those stains appear or what causes them?
The cause of these black stains is algae. Here in Lees Summit, we have a moisture rich environment that contributes to the growth of this algae. The patterns you see on individual roofs relate to moisture (such as dew) and areas with less sunlight, including north-facing portions of the roof or areas with heavy tree coverage. This algae also travels through the air, so if you notice a neighbor’s roof appears to have this discoloration, it can travel through the air to adjacent houses, and it just might come your way. This algae is mostly an aesthetic nuisance, and should not affect the life of your roof. It can be cleaned with a mixture of tri-sodium phosphate (TSP, available at local hardware stores), bleach, and water. This should be considered annual maintenance as this algae growth will be a recurring problem.
You may also notice a pattern where there are no black stains below skylights, plumbing vents, or other areas that have flashed roof penetrations. This is because zinc in the metal flashing is a natural algae deterrent. As rainwater flows over the flashing, it dissolves minute amounts of zinc from the metal and provides a small portion of your roof that doesn’t support algae growth. When you install a new roof, your roofing contractor can provide methods to prevent this algae growth from ever developing. A roofing contractor familiar with the Lee’s Summit, Missouri area will be the most knowledgeable about how much algae growth is usual for roofs in this area, as well as what some other climate impacts on your roof will be.
We are an experienced Lees Summit roofing company with over 15 years experience in repair, service and installation.