As Reroof America is a full service contractor... I have been spending quite a bit of time in attics this week looking for roof leaks and otherwise diagnosing roofing problems. A thought occurred to me that when most people think about roofing they think about what they see… usually shingles or some other type of roofing like wood shingles, slate, metal roofing or a composite roofing material (for residential homes). While the roof covering is important, equally important is what is underneath the waterproofing materials (shingles and underlayment).
First I thought I would describe why the roof deck is so important then the different kinds of residential roof decks that we see and why they work or don’t work.
Purpose of The Roof Deck
This is relatively simple, the deck must be strong enough to:
- Bear the weight of the waterproofing system above
- Hold the fasteners in place
These are two very important factors in roof system design. The strength of the deck must be considered in conjunction with the joist spacing. This will determine the type of roofing system, in terms of weight, that your home can have. In terms of the holding capability of the deck… the most common wood and OSB systems meet most manufacturer’s requirements. As for the fasteners… they should be long enough to penetrate through all layers of roofing materials and extend through the underside of the roof deck or penetrate at least ¾ inch into wood plank or board decks. The only time we get in to potential trouble with deck fastener holding problems, is when the use of insulation board or some other type of decking is used (or attempted to).
Common Types of Residential Roof Decks in North America:
1. OSB or Plywood:
The most common materials used for roof decks are plywood or oriented strand board (OSB). For plywood a minimum 15/32 thick or ½ inch nominal plywood for 16-inch rafter spacings and 5/8 inch nominal thickness for 24-inch rafter spacings. For OSB, a minimum 15/32 inch thick or ½ inch OSB for 16-inch rafter spacings.
Potential problems with OSB - stability because of the effects of moisture
Potential problems with pressure Treated or otherwise chemically treat wood decks – premature deterioration due to chemical reactions.
2. Solid Board Decking & Spaced Decking:
In older homes (before circa 1990) many homes used 1x6 or more commonly 1x8 decking like the ones pictured below:
Potential problems can occur on these when the decking is separated by more than 3/8 of an inch. Many local codes will require spaced decking with more than this space between boards, to be re-decked.
Really old homes, built before 1950 probably have a tongue and groove pine decking and would have to be replaced with such.
The decking under old wood roofs is typically a spaced decking. Many homes in the Southwest and Midwest, that have composition over wood roofs, will have plywood or OSB installed directly over the spaced decking upon reroofing.
In some cases (as I have personally seen here in Oklahoma…) wood roofs have been roofed over with a new wood roof. That’s right… two layers of wood roofs. This is obviously not code.
As you can see… the type of decking you have plays a critical role in the aesthetics and performance of your roof… and your home. This is one of the reasons when ever we come out to inspect a roof we complete our inspection from the inside out. If you hire a roofer who does not enter your attic to look at your decking before they provide you with an estimate… beware. How can he know what to expect when they tear off the roof??? Avoid hidden and unforeseen costs with your roofing project by hiring a local reliable roofer like Reroof America.
