R.Townley Roofing

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What Life span to expect from your roof

Composition Shingles

 

Average Lifespan

The average lifespan of a composition shingle is usually a minimum of about 20 years.   But keep in mind this is based on the type of shingles.

 

Type 0f Shingle

In determining the life expectancy of a composition roof, the first type of composition used.  About fifteen years ago, shingle manufacturers began converting the dies in their plants to manufacture a “metric” shingle which covered more area per shingle and therefore reduced the amount of labor involved per square.  Consequently, all ”3-tab” roof either have 12” or 13”  tabs.  The metric shingles (installed 18 years ago or earlier) have 12” tabs.  This is important because a 12” tab is a sign that the roof is at least 18 to 20 years old, making the possibility of certification for 2 more years remote. 

Metric 3—tab shingles however, have a minimum 20 year warranty, with some up to 30 years.   The Architectural shingles all have a minimum 30 year warranty, making certification much more likely.

 

Recovers

When a composition shingle has been installed over an older roof, it will usually reduce the lifespan of the roof by 3-5 years.  Consequently, recovers are usually done with heavier shingles which will compensate for lack of performance.  (A 30 year shingle might be expected to last 25 years).  Also, a common problem with older recovers includes nails backing up out of the shingles, poking through the top layer.  This is usually due to improper nail length, although it is sometimes evident when a roof deck consists of shiplap or boards and nails has not gripped correctly.  If an 0lder 3-tab roof is reroofed with a 3-tab metric shingle, the shingle courses will not match and will result in a somewhat “lumpy” look.  To avoid this, recovers should be installed by either matching the course (“sweet nailing”) or using a heavy Architectural shingle instead.

 

Ventilation

Proper ventilation on a composition roof is very important and inadequate vents can result in a much shorter lifespan.  Poor ventilation results in excessive movement of the roof deck (due to abrupt changes in temperature resulting in contraction and expansion) which can loosen fasteners over time, and often result in shingles curling and hairline cracks.  In extreme cases the plywood roof deck will delaminate and will need to be replaced.

 

Flashings

The most common problem areas on composition roofs involve the metal flashings around chimneys, skylights, roof-to-wall junctions, plumbing pipes, and vents.  These can all be corrected rather easily if the roofing material is in good enough shape to warrant certification.

 

Homeowner Installations

It is not uncommon to be asked to certify a composition roof which has been installed by the homeowner.  Just because the job wasn’t done by a licensed professional roofer, it does not mean the roof is inadequate.  While there are sometimes changes which must be made to flashings, ect, generally speaking in terms of certification it is irrelevant who installed the roof.  Many homeowners are MORE meticulous than some roofers!