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Roof Decking – The Foundation for Your Roof

Decking of a Roof

Roof decking is like the “foundation” for your roofing system. These are the boards that must go down first so that all the other roofing layers can be built on them. Roofs may use Solid Sheet Decking, OSB, Plywood or 1×6 Slat Decking. Before roofing, the roof decking should be free of old nails to create a flat surface. It should have no rot or delamination in order to hold roofing nails properly.

There are several important points to consider with decking.

  1. Decking Delamination.
  2. Proper nailing techniques.
  3. H Clips.
  4. Thickness and spacing of deck boards. 

Decking Delamination:

Delaminated Decking

Delaminated Decking

Roof Rot

Roof Rot

Delamination of the decking is usually caused by extremes in the weather. Heat of summer can affect the glue and winter weather can bring about condensation. The contrast of the two overtime can be very trying on decking boards. Over time local codes have been developed to assure that attics have enough ventilation to prevent these issues from occurring. The ventilation assists in eliminating issues like condensation build up on the boards. During summer months proper ventilation helps to keep attics cool so as to prevent too much heat from melting the deck board glue. Your roof decking is the foundation for your entire roof. So when the board becomes spongy or saggy it can lead to leaks and even the possibility of the roof itself caving in. In short, the health of your decking is critical to the overall health of your entire roof.


Proper Nailing Techniques:

Nail ShanksLitespeed Construction recommends ring shank nails be used instead of smooth shank nails when putting down deck boards. The reason behind this is because ring shanked nails have a better shape to grip with, thus holding onto the wood. This is particularly helpful in wood that is soft enough to not splinter. It’s important to note that ring shanked nails are very helpful for wood types that often expand and contract due to weather. Nail SpacingAs this change in the wood can cause smooth shank nails to work their way back out of the board. As mentioned above, decking is prone to weather causing warping over time, so it is critical to put in that extra effort to keep the boards in place with nails that will stay fastened in place.

The spacing of the nails is equally important. Two nails should be fastened in where each board crosses a rafter, every 8 inches. See the video below for a full tutorial of how to tear a deck off and put it back on correctly:


Decking and H Clips:

H-clips are not required with roof decking, but can be a critical for keeping deck boards secure. H-clips go around the edges of the boards to help provide them support. It can help prevent saggy edges on the board from bowing. These also are known as panel edge clips or plywood clips and are made of metal for durability.Insurance Companies Paying for Starter Shingles:

Roof Decking 1

Thickness and Spacing of Deck Boards:

Typical roof plywood or OSB thickness runs about ½”. This is according to the APA-Engineered Wood Association. Wood planking on the other hand would normally be 1” thick. It is more common for roof decking to be completed using OSB or Plywood over wood planking. Plank deck board is considered an older method that can splinter under continued heat exposure. It is noteworthy that OSB takes longer to get wet but also longer to dry out, so it can be more prone to rot than plywood. However, in the case of the newer products it is necessary to be sure and use the proper thickness, as to thin of boards can result in sagging, which of course will make your whole roof sag. Note: The IRC (International Residential Code) has increased the thickness of all roof decks to min ⅝” as of 2015.

It is worth mentioning that in the case of a metal roof that pearlins are often used in place of traditional decking boards. These are metal or wood strips that would run run across the rafters.

Roof Decking 2

Board spacing is also critical to making sure the roof holds up the way it is supposed to and avoid issues such as sagging. Boards should be installed with a minimum of ⅛” space between them to allow for expansion and a maximum of ¼” between them. This assures there is not so much space between as to allow for issues such as sagging and lack of support to the shingles above. Keep in mind as mentioned above H-clips often times will go around deck boards which also accounts for some of the necessary space between boards. Keep in mind that there is a certain pattern that is supposed to be maintained when putting these boards down on the rafters. Refer to the illustration above for the proper jigsaw pattern.

Roof Decking 3

Roof decks are rarely ever perfect. Most shingle manufacturer companies will only warranty a roof if the roof decking meets their criteria for spacing and nailing. However, many homes can have roof decking that is close but not exactly meeting the manufacturer’s requirements. While warranties are an important thing, it can become a very costly situation to have to replace all of your decking boards if they are in otherwise good condition, just to meet a spec guideline. In reality many people will chose not to do this, and we understand this.

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