11/04/2013

Tips for Tackling Re-Roofing and Re-Cover Projects

Know your options for repairs and replacements

By Richard L. Fricklas

 
  • /Portals/1/images/OnlineImages/2013/1113/rr/1-recover_web.jpg

    Re-roofing and re-cover projects depend heavily on the existing roof. A solid concrete deck that will have everything removed should be primed, with added layers fully adhered.

  • /Portals/1/images/OnlineImages/2013/1113/rr/2-mop_web.jpg

    Chemical compatibility between membranes and other roof components is vital.

  • /Portals/1/images/OnlineImages/2013/1113/rr/3-mech_web.jpg

    Mechanically fastened thermal insulation or a combination of insulation and high-density cover boards provides a substrate suitable for multiple membrane systems.

About two-thirds of low slope roofing activity today has to do with reroofing or re-cover of an existing roof system. Recent emphasis on upgraded thermal insulation means that the new roof system may have to meet the latest revision of a building code.

To cope with the phenomenon of urban heat islands, in a hotter climate, a reflective roof will generally be selected (usually white). Codes also require that the roof not pond water, which may necessitate additional roof drains, tapered insulation, or both. Carbon footprints are also an issue, as global warming, and freak storms are becoming a fact of life.

Options for repair and re-cover are plentiful. While checking the roofing files on your buildings (I hope they exist), see if they include some information on age, type of membrane in place, and whether warranties are still valid.

What’s Out There?
Traditional hot-applied bituminous roofs were surfaced with aggregate embedded in hot bitumen. For a re-cover, it is possible to degravel, remove areas of wet insulation, and apply a new bituminous or MB roof system. Venting base sheets can be adhered to the degraveled surface by spot adhesion, or a re-cover board can be attached with mechanical fasteners. A new membrane can be based on asphalt, coal tar pitch, or MB systems of APP or SBS modified asphalt.

Another approach on an aggregate-surfaced bituminous roof is to degravel the membrane using a high-pressure, low-volume vacuum system. This is followed by applying sprayed-in-place polyurethane foam (SPF) followed by a surface coating.

The Current Generation
Currently, PVC and TPO dominate the single-ply marketplace. The chlorosulfonated polyethylene (CSPE) can be heat-seamed while fresh, but cross-links into a thermoset upon weather exposure. Most CSPE is applied on the West Coast.

Once an EPDM membrane is vulcanized (cross-linked), it is thermoset and is unaffected by heat or cold. To make field seams, cold adhesives or tapes are employed.

PVC and TPO are thermoplastic and can be seamed by application of heat. Polymer-modified bitumens also hold an important segment of the market. Two polymer types are used for modification: SBS can be applied using hot bitumen or cold adhesives, while atactic polypropylene (APP) has a higher melt point and is generally torch-applied.


Richard (Dick) L. Fricklas

Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems, and continues to participate in seminars for the University of Wisconsin and RCI Inc., the Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the Outstanding Educator Award from RCI, William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.


Back History and Knowledge
Prior to World War II, most commercial buildings were multiple levels, and because steel was in short supply, roof decks were timber, gypsum, or concrete. Insulation was rarely used, though when steel returned to civilian usages, a minimum layer of insulation was used to bridge the ribs (flutes) of the decking.

The roof membranes consisted of three to five layers of organic roofing felt, embedded in asphalt or coal tar pitch. Surfacings were generally aggregate embedded in a flood-coat of bitumen, although mineral-surfaced cap sheets were used for folded-plate or barrel-shaped decks.

Most of these roofs have been replaced several times over. Current versions of bituminous roofs use glass-fiber felts replacing organic or asbestos felts. The introduction of polymer-modified bitumen roofs (MB) generally are compatible with the older BUR products, and most successfully avoid aggregate surfacing, thus reducing labor.

The earlier versions of thermal insulation were three-quarters to one inch of asphalt-treated fiberboard with a thermal resistance (R-value) of 2.78 per inch. Perlite roof insulation was a fire-resistant version, as was a glass-fiber, high-density board with a Kraft paper surfacing. Today, cellular insulation such as iso-boards and expanded polystyrene are used to meet energy requirements, with specified R-values of 15-25. Iso-boards can be laid using hot asphalt, while the styrenes are generally restricted to single ply roof systems with proper thermal protection against melting. 


Pages: 1  2  View All  
 


Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

 

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

Replace core drilling with Connectrac In-Carpet and On-Floor Wireways, the proven connectivity solution in open interior spaces of all kinds. These elegant low-profile wireways are great for AV / telecom connectivity wherever it’s needed.

 


Visit our website today to learn about the design flexibility of a Morton building and the endless possibilities of partnering with our designBUILD team.


Wood construction is both cost and energy efficient. Check out Morton Buildings and our designBUILD team online today to discover all the benefits of post-frame construction.


When choosing a metal-clad building for your next construction project, consider Morton Buildings, Inc., and their designBUILD team, we’ll make your dream a reality.

We Can Help You Reduce Energy by 30%

Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
CLICK HERE to find out how.

 

Add highly responsive multi-zone comfort to any building project, in any climate. Our CITY MULTI H2i R2- and Y-Series VRF systems give you flexibility to fit the needs of any building. Enjoy 100% heating capacity at 0°F outdoor ambient, and 85% heating capacity at -13°F outdoor ambient.  For more information, log on to www.mitsubishipro.com


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.


Tennant Company is a recognized leader in designing, manufacturing and marketing solutions that help create a cleaner, safer, healthier world. With thousands of satisfied customers already using award winning ec-H2O technology, why not see what you're missing? Test ec-H2O on your soils in your facility. Get a free demo.

 

Replace core drilling with Connectrac In-Carpet and On-Floor Wireways, the proven connectivity solution in open interior spaces of all kinds. These elegant low-profile wireways are great for AV / telecom connectivity wherever it’s needed.

 


 
comments powered by Disqus

Related Products

Fire/Life Safety
Furniture
HVAC

Sponsored Links