What kind of plywood is used for roofing?

WAIT, WHAT IS PLYWOOD?

Plywood is a manmade type of wood, made up of thin layers of veneer (also known as ‘plies’) that are glued together. The wood’s grain is rotated 90 degrees with each additional layer, making it super strong and very resistant to bending – so using plywood for roofing is a good idea. 

All plywood is made from the bonding of resin and wood fiber sheets, and the direction of the grain in each layer is rotated in a process called cross-graining – which has several important benefits: 

• Plywood doesn’t split as easily when it meets with nails
• There is not as much expansion and shrinkage compared to solid wood – super beneficial for roofs
• The strength of the wood is consistent in every direction
• The stability of plywood is very high 
• It doesn’t warp, so again this is very useful for a long-lasting roof. 

GENERAL PLYWOOD

General plywood, the kind you might have come across in DIY, is not strong enough to use in construction or roofing services – it mainly gets used in interior projects like windows, tables, and doors. 

EXTERIOR PLYWOOD 

It might be a relief to hear that there is a kind of plywood called ‘exterior plywood’ and this is a favorite among the roofing community. It remains strong even when exposed to moisture over long periods of time, comes in at a lower cost than other roofing materials – plus, installing it is straightforward.

There are several types of exterior plywood we use in our work, and there is a lot of discussion about the best plywood for roofing. 

The most commonly used are:

• Construction structural plywood
• CDX plywood
• Zip wood 
• FRT plywood 

CONSTRUCTION STRUCTURAL PLYWOOD 

This kind of plywood is strong, with great performance and durability – it is a multipurpose material, so it is often considered the best plywood for roofing. Structural plywood can have two different types called A and B-Bond. A is stronger than B-bond, but B  is still perfectly great used in exterior structures. 

CDX GRADE PLYWOOD

CDX is a super popular option for roofers. The C and D initials refer to the grade of the front and back of the plywood sheets, and the X is the type of moisture-resistent glue to stick the wood together. CDX plywood is an affordable material, because it is made from the two lowest – but still great performing – grades of ply, C and D. 

ZIP WOOD

Zip wood isn’t just a cool name – it is a kind of engineered wood that is strong, durable, and has a special water-resistant barrier that still allows the wood to breath. The moisture proof layer means you don’t need to use roofing felt with zip wood. It is made up of five layers and all of these great characteristics make it weather proof in the Texas climate and popular with commercial and residential roofers. 

FRT PLYWOOD

FRT stands for fire retardant treated – this is a great choice for residential roofs, because on any street, fire can be so easily spread from home to home. Building codes quite often instruct roofers to use FRT plywood for roof sheathing – if there ever is a fire when this wood has been used, a chemical process involving acid hydrolysis is activated, which actually increases fire resistance when it is needed.

OSB 

Oriented strand board, or OSB, is created by gluing small bits of wood together and compressing them very tightly – OSB panels can be as large as 16 feet long, sometimes bigger. You can identify OSB pretty easily, as you can see all the pieces of wood that have been used to make it and, although it is not a plywood, it can be used for roofing as well as other projects. 

OSB VS PLYWOOD FOR ROOFING

There is debate among construction workers about whether OSB is better than exterior plywood. 

In the end, OSB is a little less expensive and more environmentally friendly than plywood, but it can swell when wet, doesn’t look that pretty and contains formaldehyde, which is flammable. Plywood is the best out of the two, because of its variety of sizes and finishes, its resistance to water and its lack of formaldehyde, as well as how super strong and good looking it is!

TALK TO US

So there we have it, there are different kinds of plywood for roofing, including different grades and costs. There are also different sizes, thickness, and weights, all of which your roofer will decide on when doing their job. 

In the end, it is best to talk to your roofer about the materials used – and make sure that everything is clearly itemized on your estimate so you know exactly what you will get!