Roof decks
The roof deck is the base structure on which the rest of the roofing system is built upon. 

This blog about roof decks is part of a 6 part series on roofing underlayment. To access the main page of this series and learn more go to Roofing Underlayment 101: An Overview Of Roofing Underlayment.

Most people don’t appreciate the complexities of the modern roofing system. Many layers and components play a part in keeping your house protected from the outside elements. One of the most crucial yet least discussed part of roofing is the roof deck. It is the base structure the rest of the roofing system is built upon. In this blog, we’ll give a quick overview of roof decks and its types as well as some essential guidelines. 

What is a Roof Deck? 

As already mentioned, the roof deck serves as the foundation on which all the structural components of the roof come together. In addition, it is an extra layer of protection between your roof and your home. It is important to make sure you hire a roofing contractor who understands and appreciates the value in paying close attention to the quality of the pre-existing roof deck on your home. Shingles these days will easily last for over 20 years and you want to make sure you will be set for the long term.

Types of Roof Deck 

There are many types of materials used in constructing roof decks. Below, we list the most common types here in Ontario, Canada. 

1. Plywood 

Plywood remains by far the most popular and best type of roof deck for residential applications due to its excellent moisture resistant qualities, durability and affordability. Typical plywood sheets for roofing purposes are made of spruce and are 4’x8’ long and are usually 3/8″ thick, although 1/2″ and even 5/8″ are not uncommon. 

2. Tongue & Groove

Tongue and groove applications feature a “tongue” on one edge and a “groove” on the other and are often used for cottage style homes with no ceiling. The tongue on one board slides into the groove of another, fitting together into a single flat surface. 2×6 is the most common board size.

There is also tongue and groove spruce plywood that we use in our flat roofing applications for better strength that is 4’x8′ and 5/8″ thick.

3. OSB (Oriented Strand Board)

OSB is another material commonly employed for roof sheathing. However OSB is absolutely NOT recommended for roof decks. They are manufactured by adding adhesives into wood strands then compressing layers of them in specific orientations. While you will not notice much of a difference at first, OSB is an absolute magnet for moisture over time compared to plywood. This is because the chipboard creates a lot of internal surface area for moisture to penetrate.

If you poured water on a piece of wood vs a pile of sawdust the wood will dry out much faster because there is less surface area exposure. The same principles are at ply with plywood vs OSB.

Parr Lumber agrees with our stance stating:

“My personal opinion is that OSB performs well on the wall and floor but stick to CDX Plywood on the roof. Far too often I see OSB “sag” between the trusses making your roof look wavy.”

OSB is mainly used by cheap builders who want to save a few bucks on materials. If you are looking for longevity steer clear of OSB!

4. Planks

Rare nowadays, planks are most often found on homes built prior to the 1970s. Wooden planks, while rigid and tough, tend to be more expensive nowadays and require more frequent maintenance; not to mention, carry the risk of a termite infestation. 

Most importantly, plank style roofs that we come across more often than not have expanded and contracted severely over time due to temperature fluctuations. This creates gaps between the boards which obviously isn’t ideal for shingling. You need to nail in specific areas when shingling so full coverage of the roofing field with decking is critical!

That’s why it is becoming increasingly common to re-sheet houses that feature plank style roof decking with 3/8″ spruce plywood.

Some Essential Guidelines for Roof Decks

It is important to ensure that your roof deck remains in optimal conditions at all times. Some signs of a compromised roof deck could include water seepage, sagging ceilings, and ‘spongy’ feel when walking on the roof. It is important to have any damaged areas of your roof replaced or repaired as soon as possible. Qualified roofing contractors can help you detect and remedy any compromising elements on your roof. If you are a resident of Hamilton or surrounding areas and are in need of quality roofing service, look no further than Peak Roofing. For a free estimate or any further queries, call us anything at 905-746-5792 or email us at

Published On: April 12th, 2020 / Categories: News / Tags: , /

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