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CERTIFICATIONS for ROOFING CONTRACTORS CHOOSING A ROOFING CONTRACTOR ASBESTOS CEMENT & FIBER CEMENT ROOFING ASPHALT ROOF SHINGLES BUILT UP ROOFS CERTIFICATIONS for ROOFING CONTRACTORS CHIMNEY INSPECTION & REPAIRS CHOOSING A ROOFING CONTRACTOR CLAY TILE ROOFING CONCRETE ROOFING CORRUGATED ROOFING ENERGY SAVINGS in BUILDINGS FIRE RETARDANT PLYWOOD FLAT ROOF MOISTURE & CONDENSATION HEAT TAPES & CABLES on Roofs for Ice Dams LOW SLOPE ROOFING MATERIALS MASONITE WOODRUF FIBERBOARD ROOFING MEMBRANE & SINGLE PLY ROOFS METAL ROOFING TYPES MODIFIED BITUMEN ROOFING ROOF INSPECTION SAFETY & LIMITS ROOF VENTILATION SPECIFICATIONS ROOF VENTING ENERGY SAVING DETAILS SLATE ROOF INSPECTION & REPAIR How to Inspect & Repair Types of Roofing Slate Slate Colors, Chemistry Slate Roof Aging and Durability Ribbon Slates Slate Roof Installation Quality Other factors in Condition Slate Roof Repair history Slate Roof Leaks Slate Holding actions How to Repair Slate Roofs Copper Tab Method Slate Hook Method SLATE ROOF PHOTO LIBRARY Slate References Slate Sources, Repairs SLATE ROOF INSPECTION CLASS SOD ROOFING SIDING WOOD STAIN DIAGNOSIS on Building Exteriors STAIN DIAGNOSIS on Roofs STANDARDS for ROOFING STONE ROOFING THATCH ROOFING THERMAL EXPANSION of MATERIALS THERMAL MASS in BUILDINGS THERMAL MASS in UPSTAIRS TILE ROOFING WARRANTIES for ROOF SHINGLES WOOD SHAKE & SHINGLE ROOFING WORKMANSHIP & WIND DAMAGE More Information InspectAPedia Blog - News Updates Air Conditioning & Heat Pumps Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure Accuracy & Privacy Policies Contact Us |
This series of detailed slate roof inspection and repair articles describes procedures for evaluating the condition of slate roofing. How to inspect, identify defects, and estimate remaining life of slate roofs are addressed. The article series also references slate repair procedures, repair slate sources, and slate quarries. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website. Leaks in Slate RoofsAll slate roofs probably have at least some flashing, slate, or other damage or mechanical installation errors. Some conditions such as a side lap error, damaged slate, or even flashing error may leak only in certain weather conditions such as windy rain storms from a particular direction, water backup behind ice dams, or prolonged rains. Where slates are missing near valleys the adjoining slates may be damaged as well. Openings may cause leaks or water to pass below the valley flashing even if the flashing looks intact. Where there were previous repairs it's common for the felt underlayment to be torn as well. If there are porous slates or openings above the tears in the felt, water may leak through. Ice dams at roof eaves can be a serious leak source on slate as most other roof systems. Traditionally 30# felt was used at eaves as "insurance" against this problem. Some slate suppliers recommend this heavier felt for all underlayment, not just at the eaves. However two components conspire to reduce the effectiveness of felt as ice-dam protection: every nail at the eaves punctures the felt, and with age felts often dry and disintegrate before the slates have worn out. Ice dam protection is improved in new or re-roof applications using the newer sticky membranes such as WR Grace's Ice and Water ShieldTM. However the preferred solution to this problem is proper attic ventilation. Good venting avoids the ice-dam problem and adds reductions in winter moisture and summer heat problems. Old houses whose attics have been converted to living space, particularly with un-vented ceilings following the underside of fully-insulated roofs are likely to be serious moisture and heat traps. Slope requirements for slate roofs In conventional roofing design slates are used on roofs with a slope of at least 4" of rise in 12" of run, that is, on 4 in 12 roofs. A 3" head lap is used, often 4" when the slope is less than 8 in 12. So a 20" long slate, with a 3" head lap, would have an exposure of 8.5". For 18" slates the exposure is 7.5", and for 16" slates, 6.5". Roofs with less head lap or more exposure may be more leak-prone. Some slate companies advertised A slate roof that cannot leak, yet [was] inexpensive, easy to apply, beautiful..., durable as time," using a design which was soon found to be a disaster: 12" slates were placed with 9" exposure, leaving 3" for headlap and 6" which was backed only by a cap sheet of 32# felt interlaced with the slates. Roofs were also installed following this poor design, using 14" slates with 10"-11" exposure. Felt is not functional as a permanent roofing material: even where it is not exposed directly to sunlight, as the organics dry out the felt cracks, disintegrates, and leaks. We have reports that inspectors have been the subject of legal actions following their failure to identify this defect in slate roofs. See the illustrations above. Personal communication, Doug Sheldon, Vermont Structural Slate, December 1990. ... Technical Reviewers & References
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ROOF INSPECTION SAFETY & LIMITS Slate Roofing References
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06/30/2009 - InspectAPedia.com/roof/SlateRoofsATJ9.htm - © 2009 - 1988 Copyright Daniel Friedman All Rights Reserved - InspectAPedia® is a Registered U.S. Trademark