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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
GREEENHOUSE / SOLARIUM ROOF LEAKS
HEAT TAPES & CABLES for ROOF 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.
[Click to enlarge any image]
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?
Reader question: 4/21/2014 over at our article BEST ROOFING PRACTICES, Anonymous asked:
My roof pitch is 3/12 but the roofing company use PABMF001-34192, laminated shingles, a product of Pabco Co. Now my roof be blow back leaks occur when a shingle rain seal is breached. Are they re-roof with this kind of shingles above correct for my roof pitch less than 3/12?
Please help me to research there defects.
Use of conventional roof shingles on a low slope roof invites leaks from wind-driven rain or similar weather problems unless the roofer takes additional, special steps to prevent the problem using extra layers of felt and roofing cement.
The answer to "can we use shingles on a low slope roof?" is Yes, ... and No. Or as Mark Cramer says, "... It depends."
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.
YES: 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.
Reader Question: roof shingles installed "upside down" on low slope roof
(Oct 21, 2014) MaryS said:
My neighbor is having a new roof installed and not by an established company, more like friends of a friend. Because the pitch is a low slope roof, the installer is installing the 3-tab shingles in reverse of the normal way, leaving the black solid part of the shingle exposed, instead of the 3 tabs (which are being covered by the above shingle. This does not seem right at all. He said he is a roofer and because of the low slope roof, this is the way he installs shingles. Opinions wanted, thank you.
The roof installation you describe3 is fundamentally incorrect and will give a short life and a leaky roof.
1. The upper portion of roof shingles are not intended to be exposed to the weather. Rather they are expected to be covered by successive upper roof courses of shingles. This portion of the shingle is not finished with the same weather protection as the exposed shingle tabs.
2. The self-sealing properties of the roof shingles may not work properly when installed in this upside down orientation.
3. When installing shingles on a low slope roof, other methods are required to avoid a leaky short-lived roof.
In the article above we explain that
Continue reading at LOW SLOPE ROOF CONVERSION or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: proper location of air barrier for Hot Climate Roofs
(Sept 25, 2014) Steven said:
Location Central Florida. Inquiring about installing 1.5" foil faced closed polyiso insulation over the top of the existing 6/12 sloping OSB decking. The intention is to take the heat load off the attic space. With concerns of humidity and condensation in a vented attic space, My Question - where should the Air Barrier membrane be installed - on the bottom (original OSB deck) OR above the new decking on top of the insulboard? Any further conserns or comments to be aware of? Thanks
Steven air barriers such as house wraps are used on building exterior walls but not on roofs.
For underlayments used under roofing please see ROOFING UNDERLAYMENT BEST PRACTICES
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
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