Why does my roof leak?

Asphalt shingles on a house roof, if installed properly, will last many years with no roofing problems.  Today asphalt shingles are manufactured that will last 30 or more years before it is time for roof replacement.  However, a shingle roof can leak and no one likes leaks in a roof.  The following list examines some of the reasons why a shingle roof will not shed water properly but instead will permit roof leaks.

Improper Installation
The main reason there are house roof leaks with asphalt shingles is improper roof installation either on a new house or at the time of roof replacement.  This involves more than nailing down the shingles, it includes the entire process for asphalt shingle installation from day one.  The reasons include the following;

• No roof underlayment (usually called felt) or improper installation
• No water barrier - called ice and water shield
• Improper shingle placement
• Wrong roof flashing
  
• Improper nailing
• Improper size or placement of step flashing
• No step flashing at walls - caulk just will not do!!
• No metal valley under valley shingles
• Improper installation of roof vents
• Improper installation of ridge vents
• Incorrect shingle sealer - just any caulk will not do, particularly silicone caulk!!
  
• Exposed nails
• Wrong material used for sealing roof penetrations (electric mastheads, sewer vents, furnace pipes, etc.)
• The pitch of the roof is too low for asphalt shingles

House Problems
Sometimes the asphalt shingles appear to be leaking but it is not the fault of the house roof at all.  The leak(s) can be traced to other problems with the house that are allowing the entry of water.

• Cracks in wood siding
• Wood siding that needs to be repainted
• Ice dam related - see ice dam prevention for things to do to prevent ice dams
  
• Bricks or mortar on a wall or chimney that are soaking up water and then releasing it into the house
• Cracks in the brick or mortar of a chimney or wall
• Holes in a metal valley - rusted, damage from ice removal, nail holes or even hail
• Holes in roof vents - hail, animals, storm damage

Damaged shingles
Asphalt shingles are capable of withstanding considerable abuse before they are damaged enough to cause a roof  leak.  Occasionally though, something will happen to the shingles that will cause them to leak.

• Storm related damage - wind, tree branches, hail
• Ice dam related - punctures, torn shingles, torn sealer strip
• Animal damage -  holes, torn shingles
• Holes in shingles from nails pushing up
  

Older Worn Out Asphalt Shingles
 The life span of a shingle can be affected by several variable so while they may last for 30 years on one roof they will only last 15 on another roof.  The variables can include improper installation, excessive attic heat, sun exposure, frequency of ice dams and hail damage. Shingles do wear out and that is when leaks can occur.  As they near the end of their life the shingle starts to break down.  Look for some of the following to verify if in fact the shingles are worn out.  If so, it may be time for a roof replacement.

• Cracks in the shingle - vertical, horizontal and diagonal
• Loss of granules - Excessive loss will reveal the sub-base of the shingle
• Some types of shingles will begin to curl
• Buckling - The shingles will no longer lay flat but will bulge upwards in places creating a ripple affect
• Brittleness - As shingles get older they start to dry out and become very brittle and easily damaged

Proper roof installation includes providing adequate attic insulation and attic ventilation, solid sheathing, correct installation of the underlayment and water barrier (ice and water shield), installing the correct type of roof vents, the correct type of boots to seal roof penetrations and finally proper roof flashing and shingle installation.  If all these details are attended to one can expect a long leak free life for the asphalt shingle roof.