Structural Components of the Roofing System

The structural components of the roofing system consist of many internal and external elements that often times play little or no role whatsoever as it relates to the integrity of diverting water away from the structure of a house or building.  Although each and every part of the roof is important and serves a valuable purpose, the following information is limited to the rafters, roof deck, and soffit.

Luckily, it is very rare that problems arise with the roof rafters.  However, I would strongly recommend that when the time comes that you need your roof replaced or repaired; it is sound practice to have the roofing contractor inspect all of the roof rafters to be certain that none of them are rotten or otherwise failing.  If your roof has been leaking this is obviously very important.
This shouldn’t be of any inconvenience for the roofing contractor as they should be inspecting the underside of the roof routinely when they provide you with a bid for their work.  This is necessary to determine what type of roof deck your house has, and whether or not it is required to re-deck your roof, especially if your house is older than 15-20 years.
This brings us to the next structural component of the roofing system.


Roof Deck

The roof deck is the structural platform which makes up the shell of the roofing system and supports all of the components of the roof barrier.

The roof deck is very important to maintain and preserve as it is the foundation of the roofing system.  Generally the roof deck is comprised of two primary forms: decking boards such as 1 x 6 or 1 x 8, and plywood.  Although there are various sizes of decking boards, and different types of plywood, I will limit this discussion to the relevance of roof decking as it applies to the structural value of the roofing system.

Generally when you need to replace your roof barrier (i.e. shingles, metal, tile, etc.) the roof deck should not need to be replaced unless the deck has sustained some water damage, the current roof has cedar shingles, or the roof system has not been properly ventilated.  Let’s elaborate on each of these three common problems that may be discovered during an inspection of your roofing system.

Water Damage:

Water Damage Roof DeckOften times a leaking roof may not be discovered until long after the leak started.  In some instances the leak may have been persisting for months or years, and ultimately the roof deck has become water logged and/or rotten.
Depending upon the composition of the roof deck, it may or may not be possible to simply remove the damaged portion of the decking and patch it with new material.  If the decking is made up of plywood, it may be necessary to replace the entire sheet of plywood to maintain the structural integrity of the decking.

Cedar Shingles:

If the current roof barrier is cedar shingles, chances are that the roof system is comprised of decking boards.  The best way to determine how the roof deck is built is to go into your attic and look at the underside of the roof deck.
Deck Board Gaps

If it is made up of decking boards because cedar shingles were originally installed, there are likely to be 1 to 2 inch spaces between the decking boards to allow the cedar shakes to breath.  If this is the case and the roof barrier is going to be replaced with organic or fiberglass shingles it will be necessary to re-deck over the roof boards with plywood.  The reason for this is that organic and fiberglass shingles must be fastened within a narrow strip across the shingle called a nailing flange.  When this nailing flange lines up with the 1 to 2 inch voids in the roof deck the nails are not going to fasten to the decking.  As such, re-decking with plywood is necessary to cover all the voids so the new shingles will be fastened properly.

Delaminated Plywood:

Plywood delaminating is not an uncommon problem for many homes.  However, once it happens the structural integrity of the roof decking is gone because the veneer layers separate, causing the once solid mass of plies to become individual thin layers.

Delaminated Plywoord Roof DeckEssentially there are two primary reasons why delaminating happens.  Between the years 1964 and 1975 new homes that were built saw the installation fire retardant plywood that is unlike the oriented strand board (“OSB”) commonly used today.  Unlike OSB, plywood is manufactured from thin sheets of veneer that are sandwiched and glued together.

Delaminated Plywood



From 1964 to 1975 the construction of the sandwiched veneers was accomplished using aldehyde-base glues.  Unfortunately, over time these glues have a tendency to break down causing the effect of delaminating.  One of the most common reasons that plywood delaminates is because the roofing system has inadequate ventilation which causes the attic to become very hot and humid, especially during summer months.

The combination of heat and humidity cause the glues that bind the veneer layers to deteriorate and break down, ultimately resulting in the separation of the plied layers.  Inadequate ventilation can be caused by many things and the problem can best be assessed by a local roofing contractor.



Although technically the soffit is not necessarily structural in nature, it is an integral part of the rafters and roof deck and is the conduit for the roofing system ventilation.

Without adequate soffit functionality, ventilation issues arise and ultimately result in major problems with the entire roofing system.  When a local roofing contractor inspects your roof they should also provide you with an assessment or report on the status of the soffit and whether or not there is adequate ventilation.  It is not uncommon on some homes that the soffit is merely inches in width and doesn’t have area for any intake vents to be installed.  However, there must be ventilation and there are many variations that can be implemented to provide adequate venting through any size soffit.