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ROOFING INSPECTION & REPAIR
AMERICAN CEMWOOD ROOFING
BEST ROOFING PRACTICES
BUILT UP ROOFS
CATHEDRAL CEILING VENTILATION
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY FLASHING Mistakes & Leaks
COLD WEATHER ROOF TROUBLE
DECKS, ROOFTOP CONSTRUCTION
EPDM, RUBBER, PVC ROOFING
EXTRACTIVE BLEEDING on SHINGLES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLAT ROOF MOISTURE & CONDENSATION
Green House or Solarium Roof Leaks
HEAT TAPES & CABLES on Roofs for Ice Dams
ROOF ICE DAM LEAKS
MASONITE WOODRUF FIBERBOARD ROOFING
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF INSPECTION SAFETY & LIMITS
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
SADDLE CONSTRUCTION at CHIMNEYS
SNOW GUARDS & SNOW BRAKES
STANDARDS for ROOFING
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
TREES & SHRUBS, TRIM OFF BUILDING
TRUSSES, Floor & Roof
UNDERLAYMENT REQUIREMENTS on ROOFS
VENTILATION in BUILDINGS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WORKMANSHIP & ROOF DAMAGE
Low slope roofs, inspection, installation, troubleshooting: this article defines low-slope roofing and describes low-slope roofing materials, choices, installations, inspection, defects, roofing repairs, and product sources.
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Low Slope Roofing Materials, Choices, Costs, Life Expectancy, Characteristics, Installation Guidelines
A "low slope roof" is one that slopes 2" in 12" to 4" in 12" of run.
Because low slope roofs also drain water more slowly than moderate or steep sloped roofs, systems such as slate or asphalt shingles that rely on mechanical drainage for successful performance, are not used.
Instead we use sealed or membrane type roofing systems similar to those used on "flat" roofs.
According to ARMA, the Asphalt Roofing Manufacturers Association, "The two broad categories of asphalt roofing systems for commercial, industrial and institutional buildings are Built-Up Roofing (BUR) and Modified Bitumen Systems (MBS). "
But a wider range of materials has been used on low-slope roofs, as we describe in the articles below.
Summary of Definitions of Roof Slope Types: Flat, Low Slope, Steep Slope Roofs
The illustration at left, courtesy of Carson Dunlop & Associates, summarizes the ranges of roof pitch or slope for flat, low-slope or conventional or "steep slope" roofing.
What is the Difference in Slope Between Low Slope & Flat Slope Roofs?
Actually most flat roofs are not dead flat and in good design also include slope towards their drains.
Flat roofs (0" to 2" in slope) are flatter than low sloped roofs and pitch just enough to drain water. In our photo (left) the roof slopes less than 1" per foot - notice that dark ponding area at the center of the photo.
Details about how roof slope is measured or calculated are at ROOF SLOPE DEFINITIONS.
Table of Low-Slope Roofing Options: Pros & COns of Roll Roofing, BUR, Modified Bitumen, & EPDM Roof Systems
Why Low-Sloped & Flat Roofs Become Leaky
Even if a low slope roof was properly constructed when new, a combination of age, sunlight exposure (UV-radiation), temperature variations, a history of leaks, and gradual sagging of the supporting wood structure increases rooftop ponding, drainage defects and thus the frequency of leaks.
Flat and low slope roofs and the roof drainage system should be inspected annually and any leaks or drain clogs repaired.
That's my Saab at the right, parked on the flat roof of a private residence located on the West bank of the Hudson River immediately south of the Tappan Zee bridge. Like the TappanZee, this older roof may be due for replacement soon. Certainly unless a building was designed to carry the extra weight, the added loading of vehicles parked on the roof would be expected to contribute to ponding and sagging.
For a roof-recover that is keeping the low slope structure, a roofer may add tapered insulation and then a new roof covering of EPDM or other roofing material.
But in some climates such as areas of deep snow cover, the property owner may prefer to convert to a more steeply-sloped roof structure - a procedure we describe at LOW SLOPE ROOF CONVERSION.
Minimum Slope for Low-Slope Roof Systems
-- Adapted with permission from Best Practices Guide to Residential Construction.
Can We Apply Asphalt Shingles on Low Slope Roofs?
Yes, and no.
We do not apply asphalt shingles nor other shingle types on low slope or flat roofs using ordinary shingle installation methods because lacking adequate mechanical drainage, such a roof installation will be leaky and short-lived.
But Carson Dunlop's sketch (left) illustrates a low-slope asphalt shingle application method permitted by some roofing manufacturers. You will note that this approach will be labor intensive.
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