Nov 6, 2014

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Design of Roofs – A System Perspective

What is a roof?  We have one over our heads, probably right now.  But if you had to define a roof, how would you do it?  Is it one thing?  Is it a system of things?  A roof is best defined as a system of components installed in a very specific manner, to protect the structure below from water.  In these systems are two categories:  low slope roofing systems or steep slope roofing systems.   Here is a look at both.

Low Slope
A low slope roof is mostly found in commercial buildings.  A low slope roof is a roof with a pitch of up to 14 degrees.  The installation cost is generally lower than a steep sloped roof.  Other advantages, particularly to a commercial building are:

• Heating and cooling considerations.  Heating and cooling is more efficient in low sloped roofs.  Whereas a steep sloped roof provides more interior space, the air that fills that space needs to be heated and cooled.  That’s cost that commercial properties would rather not incur.
• Maintenance considerations.  Maintenance is much easier on a low sloped or flat roof, very simply, because it’s easier to walk around on and move equipment around on.  Functionality is also a prime consideration for commercial properties, particularly if they want solar panels or heating and air conditioning equipment on the roof.

Steep Slope
Most commonly found on homes, steep sloped roofs are grouped into these categories:  asphalt shingles, tile, either clay or concrete, and metal, slate or wood shakes.  The steep sloped roof is designed and built in the following stages.

• The Decking:  The wood sheathing is attached to the rafters of the home.  This step is critical in protecting the home from wind and rain and is governed by specific installation and nailing codes.
• The Underlayment:  This is a supplemental barrier for the shingles, tiles or shakes that give added protection from rain. This underlayment has to meet specific specifications depending on the type of roof covering being installed above it.
• Eave starter shingles:  These are used to improve wind resistance for asphalt shingles.  They are integral in keeping the roof sound during severe weather.
• Flashing is a material installed where there is change in the roof’s slopes (think of a section where two slopes come together to form a valley). A special seal is needed here to prevent damage. Flashing can be either metal or a specific type of membrane recommended by the manufacturer.
• Boots are the seals around plumbing pipes and vents. These boots often fail after five years and become a source of water intrusion.
• The roof covering is what everyone on the outside sees.  It’s the asphalt shingles , metal panels or tiles.

This is a system perspective for your roof.  To find out more about the roof best for your situation, visit the website

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