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Mobile View INTERIORS of BUILDINGS ACOUSTICAL SEALANTS AGE of a BUILDING - how to determine AIR BYPASS LEAKS AIR LEAK DETECTION TOOLS AIR LEAK MINIMIZATION AIR SEALING STRATEGIES ANIMAL ALLERGENS ASBESTOS IDENTIFICATION IN BUILDINGS ATTIC LEAKS, CONDENSATION & ATTIC MOLD ATTIC VENTILATION BASEMENT HEAT LOSS BASEMENT LEAKS Moisture or Mold BASEMENT WATERPROOFING BATHROOM VENTILATION BLOWER DOORS & AIR INFILTRATION BRICK LINED WALLS BUCKLED FOUNDATIONS due to INSULATION? CATHEDRAL CEILING INSULATION CHIMNEY INSPECTION DIAGNOSIS & REPAIR COMBUSTION AIR for TIGHT BUILDINGS CRAWL SPACES DEW POINT CALCULATION for WALLS DEW POINT TABLE - CONDENSATION POINT GUIDE ELECTRICAL INSPECTION, DIAGNOSIS, REPAIR ENERGY SAVINGS in BUILDINGS ENERGY SAVINGS PRIORITIES ENERGY SAVINGS RETROFIT CASE STUDY ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE ENERGY SAVINGS RETROFIT OPTIONS ENVIRONMENTAL HAZARDS FIBERGLASS INSULATION FIBERGLASS HAZARDS FIBERGLASS MOLD FIREPLACE Damage & Unsafe Hearths - Settlement FLAT ROOF MOISTURE & CONDENSATION FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP FLOODS IN BUILDINGS-mold FLOORING TYPES & DEFECTS FOUNDATION WATERPROOFING FRAMING DETAILS for BETTER INSULATION FRAMING DETAILS for DOUBLE WALL HOUSES FREEZE-PROOF A BUILDING HEAT LOSS in BUILDINGS HEAT LOSS DETECTION TOOLS HEAT LOSS INDICATORS HEAT LOSS R U & K VALUE CALCULATION Heat Tapes: Use on Roofs for Ice HEATING COST SAVINGS METHODS HOUSEWRAP AIR & VAPOR BARRIERS HUMIDITY LEVEL TARGET ICE DAM PREVENTION Ice Dams: Comparing Two Houses INSULATION CHOICES INSULATION FACT SHEET- DOE INSULATION IDENTIFICATION GUIDE INSULATION LOCATION for BASEMENTS INSULATION LOCATION for CAPES, CRAWLSPACES INSULATION for GREENHOUSE or SOLARIUM INSULATION MATERIAL IDENTIFICATION GUIDE INSULATION MOLD INSULATION R-Values & Properties INSULATION & VENTILATION INSPECTION & IMPROVEMENT LOG HOME GUIDE MOBILE HOME INSPECTIONS MOISTURE CONTROL in BUILDINGS Mold Growth Resistance of Foam Insulation MOLD INFORMATION CENTER ODORS & SMELLS DIAGNOSIS & CURE PAINT FALURE, DIAGNOSIS, CURE, PREVENTION PLASTER & BEAVERBOARD & DRYWALL RADIANT BARRIERS RADIANT HEAT RADIANT HEAT Floor Mistakes to Avoid RADIANT SLAB FLOORING CHOICES RADIANT SLAB TUBING & FLUID CHOICES ROOF VENTILATION SPECIFICATIONS Inspect the Ridge Vent System from the Attic Inspect the Soffit Vent System from the Attic Insulation Air & Heat Leaks Roof Venting: Intake - Outlet Area Ratios Roof Venting: Proper Locations Roof Venting: Both Ridge & Eaves Venting Needed Roof Venting: Eaves Intake if no Overhang Roof Venting: Soffit Intake Vent-Continuous Roof Venting: Un-Vented Roof Solutions ROOF VENTING ENERGY SAVING DETAILS ROOF VENTING NEEDED? Soffit Ventilation ROT, FUNGUS, TERMITES TERMITE SHIELDS vs TERMITICIDE ROT, TIMBER FRAME SAFETY HAZARDS & INSPECTIONS SEARS KIT HOUSES SOLAR ENERGY SYSTEMS PASSIVE SOLAR DESIGN METHOD PASSIVE SOLAR HEAT PERFORMANCE PHOTOVOLTAIC POWER SYSTEMS SLAB INSULATION, PASSIVE SOLAR SOLAR COLLECTOR AIR or GAS COLLECTION SOLAR COLLECTOR FILMS SOLAR COLLECTOR WOOD HOUSINGS SOLAR HEATING SYSTEMS SOLAR HOT WATER HEATERS SOLAR HOUSE EVALUATION SWIMMING POOL SOLAR HEAT, INDOOR SOUND CONTROL in BUILDINGS STAIN DIAGNOSIS STAIRS, RAILINGS, LANDINGS, RAMPS STUCCO OVER FOAM INSULATION STRUCTURAL INSPECTIONS & DEFECTS SUMP PUMPS GUIDE THERMAL EXPANSION of MATERIALS THERMAL MASS in BUILDINGS THERMAL MASS in UPSTAIRS THERMAL TRACKING Indicates Heat Loss VAPOR BARRIERS VENTILATION in BUILDINGS Air Bypass Leaks, Thermal Tracking ATTIC CONDENSATION CAUSE & CURE BATHROOM VENTILATION Blocked Soffit Intake Vents BLOWER DOORS & AIR INFILTRATION BRICK VENEER WALL INSULATION CATHEDRAL CEILING INSULATION CRAWL SPACE VENTING & Dryout Procedures HEAT LOSS: How to Calculate Heat Loss in a Building HOUSEWRAP AIR & VAPOR BARRIERS HUMIDITY LEVEL TARGET ICE DAM PREVENTION Inspect Attics for Moisture or Mold Inspect Basements for Moisture or Mold Inspect Building Exterior for Moisture Problems Inspect the Ridge Vent System from the Attic Inspect the Soffit Vent System from the Attic Insulation Air & Heat Leaks MOISTURE CONTROL in BUILDINGS MOISTURE CALCULATIONS MOISTURE PROBLEMS: CAUSE & CURE ROOF VENTILATION SPECIFICATIONS ROOF VENTING ENERGY SAVING DETAILS ROOF VENTING NEEDED? Soffit Ventilation VENTILATION DESIGN PROBLEMS & SOLUTIONS WHOLE HOUSE VENTILATION Strategies WATER ENTRY in BUILDINGS WIND TURBINES WINDOWS & DOORS SKYLIGHT LEAK DIAGNOSIS & REPAIR SITE BUILT DOUBLE GLAZED WINDOWS SLOPED GLAZING DETAILS VERTICAL GLAZING DETAILS WINDOW / DOOR ENERGY EFFICIENT, DOE WINDOW LEAKS INTO BASEMENT WINTERIZE A BUILDING WOOD Burning Heaters Fireplaces Stoves 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 article discusses the options for venting versus un-vented roof. Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Readers should not fail to review the more extensive information about the need for and methods of roof ventilation found at ROOF VENTILATION SPECIFICATIONS. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. Article on the Need for Roof Ventilation and Options for Un-Vented Roofs
This article provides a review of roof ventilation theory, explaining the importance of preventing attic moisture (and mold), ice dam leaks, and at the same time, energy loss in buildings. Mr. Bliss explains how moisture and the resulting condensation gets into roof cavities and building walls following moisture laden air that leaks through gaps in building drywall, around exposed beams, intersecting walls and ceilings, at light fixtures, electrical outlets, and other openings by riding air convection currents that move air in and out of building cavities as building interior conditions change. Arguments for and about Un-Vented RoofsMr. Bliss points out that often the air/vapor barrier installation is imperfect or has been compromised, permitting leaks into building cavities. He also points out that improperly installed ventilation (such as installing a ridge vent at the top of a roof without installing air intake openings at the soffits or eaves) can make building air movement, moisture, and condensation problems worse. Bliss cites researchers at Lawrence Berkeley Labs who found that in a mild climate (3000 degree days), most attic moisture comes from the ventilation air itself, not from air inside the house. In general attics are wetter in winter than summer (due to cooler temperatures causing condensation in that space), but in both daily and seasonal cycles, the water entering from outside vent air is stored (and later released) safely from the attic lumber and sheathing. The "no-vent" or "hot roof" design is discussed, and the author points out that construction, including the vapor barrier, must be just about perfect for this approach to work. While the article omits later field experience of experts like Henri DeMarne, we caution readers that the hot roof design is extra vulnerable to severe rot and mold damage from hidden, un-discovered leaks that cause more rapid, more extreme damage in enclosed un-vented building cavities than in well-ventilated ones such as a vented roof space. Ice dams (see the sketch at page top), form when snow sits on a roof for three or four sub-freezing days. Light dry snow makes good insulation on top of the roof, permitting warmth from or inside the attic space below to warm and melt the underside of the snow. This water runs down the roof surface until it meets the cold roof edge or eaves where it freezes to form a dam of ice along the roof edge. When sufficient water backs up above the ice dam, over the warmer sections of the lower roof edges, water leaks up under the shingles, into the attic, or into the building wall cavities. Mr. Bliss points out that super-insulated modern homes may be at less risk of ice dams than older homes with poorly-insulated attics or roof cavities. In theory, enough insulation can prevent ice dam formation on roofs, except probably on low-slope roofs that hold so much snow as to compete with the R-values provided by the roof insulation. The article also cites a few complaints of rain or snow blowing in at ridge vents, though in nearly 40 years of building inspections we have almost never found building damage nor mold from this cause. Conditions Under Which Un-Vented Roofs Might WorkBased on research in Sweden, an un-vented roof can work if:
Roof Vent Debate Conclusions
Readers should not fail to review the more extensive information about the need for and methods of roof ventilation found at ROOF VENTILATION SPECIFICATIONS. Also see ICE DAM PREVENTION and Ice Dams: Comparing Two Houses. Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. ... Technical Reviewers & References
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. ICE DAM PREVENTION ROOF VENTILATION SPECIFICATIONS
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10/10/2009 - 02/01/1985 - InspectAPedia.com/Energy/Roof_Venting_Need.htm - © 2009 - 1988 Copyright Daniel Friedman All Rights Reserved - InspectAPedia® is a Registered U.S. Trademark