Roof Installation - Installing The Underlayment

As we a saw in "Why does my roof leak"? the #1 reason of roofing problems is improper installation.  Since proper roof installation is so important we are going to begin to examine the asphalt shingle roof installation process in this post.  We are going to assume that the roof sheathing is solid, bare, clean, in good condition and ready for the roofing process to begin.

The first step is applying the underlayment.  There are 2 roofing materials used as an underlayment.  As the word suggests these roofing materials lay under the roof shingles and provide additional protection in deterring water penetration.

Ice and Water Shield or Water Barrier
Ice and Water Shield is important for helping to combat ice dams and is very necessary in the "snow belt" regions.  Shingle roofs are designed to allow water to flow from the highest part of the roof to the lower sections where it will exit the roof.  The shingle roof is not designed to hold water or prevent water from being forced up and behind the shingles.  If the ice and water shield is installed properly any water that may back up and under the shingles because of wind or an ice dam will not soak into the roof sheathing and leak into the house.

The waterproof water barrier is placed directly on the sheathing of the roof.  It is self-adhesive and comes in 3 foot rolls.  In most cases one course of the water barrier applied at the bottom edge of the roof is not sufficient protection.  It is best to apply a second course by slightly overlapping the first course so the protection is extended further up the roof.  If there are any walls adjoining the roof such as upper level walls, dormer walls or chimney walls a course of the water barrier should be applied along the wall and roof junction and should extend up the wall a minimum of 4 inches.

It is vital that the first course extends down over the edge of the roof and behind the gutter (if there is no gutter extend it down to the point that the edge metal will cover it).  This will seal the junction of the roof sheathing and the fascia board.  Please note that any edge metal such as the drip edge or gutter edge is then secured over top of the ice and water shield.  If it is placed under the water barrier it will be possible for an ice dam to force water behind the fascia board and into the soffit or up and under the edge metal where it can soak into the roof sheathing and cause leaks.

If there are valleys on the roof one course of the water barrier is applied the entire length of the valley before the metal valley is installed.  If the slope of the roof is low an additional course on each side of the valley that overlaps the middle course will extend the protection.

Roofing Felt or "Tar Paper"
After the water barrier is applied to the roof the rest of the roof is covered with roofing felt that is also applied in courses from the bottom of the roof to the top.  Each course will overlap the previous one and is installed over any metal valley.

The combination of the ice and water shield and the roofing felt plays an important role in deterring water penetration on asphalt shingle roofs.  If installed properly the shingle roof will have added protection and successfully divert water off the roof and on to the ground even during periods of wind, snow and ice dams.

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.