Why Does My Plywood Need to Be Changed When Doing My Roof?
3/8’s Plywood Roof Deck
You have probably heard that a 3/8’s plywood roof deck will void your shingle warranty. This statement is just NOT TRUE. All shingle manufacturers allow their roofing material to be installed over a 3/8’s plywood roof deck providing the plywood is not delaminated. You have probably noticed over the past few years, more and more houses have had their plywood changed while doing their roof, while only a few were being done in the 90’s. This is mainly due to de-lamination in your plywood. De-lamination is the process where the glue applied between the layers of plywood is starting to fail. Leaving you with a brittle, falling apart piece of plywood. (3/8’s has 3 layers of plywood glued together to make one sheet of plywood, 5\8’s has 5 layers, and so on….). The process of de-lamination starts when the age of the plywood is 30 to 40 years old. Builders used 3/8’s plywood from roughly 1960 to 1980. Before 1960 was “shiplap” or it can be called “planks” after 1980 the minimum code for building new houses changed to ½ plywood. So, any house built around 1970 has a high chance that their plywood would have to be changed to keep up with warranties. If your house was built in the 80’s and has a 3/8’s plywood roof deck, it might not yet be showing signs of de-lamination. This is where you could possibly get “yes you need it, no you don’t” and both are sort of right. Technically you do not need it at this moment, but an honest roofer will explain that with today’s shingle’s supposed to last 50 years, it only makes sense to change the plywood now, as it will not last the life of your new roof. So, we will do the math, if your house was built in 1981 and it’s 2014 now, your house is already 33 years old. You got estimates for 50 year shingles; this means your original 3/8’s plywood roof deck will now be 83 years old. 43 years older than its recommended life span.
Shiplap or often called Plank roof decks
These types of roof decks will void your warranty. This is mainly due to “buckling” of the shingles, and has nothing to do with the structural capabilities of the roof deck. “Buckling” is caused from planks that have come loose on your roof deck from the winter “freeze and thaw cycle” that house’s experience when they are located in a winter season area, like Canada. As the house shifts and sinks and moves, the nails holding the planks come loose, causing them to shift around, making the shingles buckle where the two planks meet together. Another reason is because of the gaps between the shiplap. When installing shingles there is a specific nailing strip that the nails have to be nailed into, but when that nailing strip lines up with the gap in the shiplap, you are now forced to nail outside of the nailing strip. Shingle manufacturers know this, thus the reason for the warranty being voided. An acceptable method to remedy these problems is to install a new 3/8’s plywood roof deck over top of the planks. This is to ensure that the shingles have a flat, uniform surface to lay on. This will prevent “buckling” of the shingles, and also makes sure you have a solid surface to nail into so that you stay within the provided nailing strip. You don’t have to worry about structural capabilities of the 3/8’s plywood, as you would already have 1 inch of shiplap underneath it. “shiplap” roofs were most commonly built prior to 1960.
All in all, no roofer can force you to do any of this, but it is our job to inform you of it. I have written this blog to help inform the public as to what is allowed and what is not. So that you, as the homeowner, can make an informed decision when the time comes to replace your roof.