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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
ENVIRONMENTAL HAZARDS
FIBERGLASS INSULATION
FIREPLACE Damage & Unsafe Hearths - Settlement
FLAT ROOF MOISTURE & CONDENSATION
FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP
FLOODS IN BUILDINGS-mold
FLOORING TYPES & DEFECTS
FOUNDATION WATERPROOFING
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 IDENTIFICATION GUIDE
INSULATION LOCATION for BASEMENTS
INSULATION LOCATION for CAPES, CRAWLSPACES
INSULATION R-Values & Properties
INSULATION & VENTILATION INSPECTION & IMPROVEMENT
  ATTIC CONDENSATION CAUSE & CURE
  Air Bypass Leaks, Thermal Tracking
  Blocked Soffit Intake Vents
  BRICK VENEER WALL INSULATION
  CATHEDRAL CEILING INSULATION
  ENERGY SAVINGS in BUILDINGS
  ENERGY SAVINGS PRIORITIES
  ENERGY SAVINGS RETROFIT CASE STUDY
  ENERGY SAVINGS RETROFIT LEAK SEALING GUIDE
  ENERGY SAVINGS RETROFIT OPTIONS
  FRAMING DETAILS for BETTER INSULATION
  FRAMING DETAILS for DOUBLE WALL HOUSES
  Inspect Attics for Moisture or Mold
  Inspect Basements for Moisture or Mold
  Inspect Building Exterior
  Inspect the Ridge Vent System from the Attic
  Inspect the Soffit Vent System from the Attic
  Insulation Air & Heat Leaks
  INSULATION R-Values & Properties
  Insulation Values of Log Home Walls
  POLYISOCYANURATE FOAM INSULATION
  POLYSTYRENE FOAM INSULATION
  RADIANT BARRIERS
  RIGID FOAM USE INDOORS
  Urea Formaldehyde Foam Insulation UFFI
  URETHANE FOAM Deterioration, Outgassing
  Vermiculite Insulation
LOG HOME GUIDE
MOBILE HOME INSPECTIONS
MOISTURE CONTROL in BUILDINGS
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
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 & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & CONDENSATION in BUILDINGS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
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: 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
  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
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Note the air path provided over the insulation and under the roof deck at the house eaves. Where to Locate Roof Vents to Prevent Attic Condensation, Leaks, Mold, & Structural Damage
InspectAPedia®  -    

  • Proper location of roof intake and outlet venting prevents Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage
  • How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems
Our site offers impartial, unbiased advice without conflicts of interest. We will block advertisements which we discover or readers inform us are associated with bad business practices, false-advertising, or junk science. Our contact info is at InspectAPedia.com/appointment.htm.

Here we explain how Proper location of roof intake and outlet venting prevents Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage. This is a section of ROOF VENTILATION SPECIFICATIONS and also ATTIC CONDENSATION CAUSE & CURE. This article describes inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems in buildings. It describes proper roof ventilation placement, amounts, and other details.

© 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.

Proper Roof Vent Location for Air Intake and Outlet

Attic ventilation sketchIntake venting needs to be at the eaves or lower roof edges. Otherwise these roof areas will not be dry and cool, and we'll find water damage, condensation damage, ice dams, and often mold in these areas.

Some people install the ridge vent (the easy part) and leave older gable end vents as "intake." This does not work very well. Simply pulling in the needed makeup air from typical gable end wall vents will not move air under the lower and center areas of roof sheathing, thus inadvertently encouraging moisture and mold to form in these areas.

In buildings where this vent design has been used we see pretty clean roof sheathing near the ridge and near the building gable walls, but at the lower roof center and looking down to the eaves, the sheathing will often be wet, moldy, damaged.

The sketch at page top is not quite right. It shows the soffit opening along the house wall where wind-blown rain may enter the soffit and wall. A better location for this opening would be at the outer edge of the soffit, just behind the fascia!

Attic knee wall insulationOutlet Venting needs to be along the length of the ridge. On some complex roof designs and on pyramid roofs there is no ridge.

The sketch at left is an example of the insulation placement and air flow pathway for homes that combine an attic knee wall space with a partial cathedral ceiling space. We recommend closing the gable-end vent on older homes that have one, installing a continuous ridge vent to assure air flow between every rafter pair.

On some hip roof designs the length of ridge is very short compared with the total roof length. In these cases there may be no option but to add multiple individual exit vent openings across the roof field. In this case they should be placed near the ridge so that the upper attic will be vented.

Putting them at mid roof or lower is ineffective. Usually such vents are placed on just one slope of the roof so that they are not visible from the front of the building. This is ok, provided the vents are near the ridge. Otherwise the un-vented roof slope simply won't be treated.

On lower single-plane shed roofs that abut an upper story building wall, venting can be provided by installing a half-ridge at the upper roof slope. Spot vents and gable end vents are a distant second choice for these designs for the reasons I outlined above.

For cathedral ceilings that have minimal vent space see our suggestions at CATHEDRAL CEILING INSULATION

For roofs that have no soffit or eaves overhang to provide an intake opening, see Roof Venting: Eaves Intake if no Overhang.

For roofs that cannot be vented, roofs whose structure, shape, or choice of insulation (such as sprayed foam insulation under the roof deck, or the "hot roof" design, see Roof Venting: Un-Vented Roof Solutions.

For irregular or hard-to-vent roof shapes, condensation (winter) or summer heat build-up can be relieved by a thermostatically operated attic fan - with a cutout switch to turn off the fan in case of a building fire. (Otherwise the fan spreads and speeds the fire.) But such fans do not run in cold winter weather, so you're only solving the heat problem not the winter condensation and ice dam problem.

Optimum roof ventilation design: provides continuous ridge venting, continuous soffit venting, and then, close off those old gable-end vents to force the intake air to come where you want it to flow. Otherwise the exiting air at the ridge will usually pull its makeup air from the closer gable end vents and not from the soffit or eaves vents.

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Technical Reviewers & References

  • Daniel Friedman - principal author/editor of the InspectAPedia® Website
  • Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
  • Alan Carson Carson Dunlop Associates, Toronto, Ontario. Mr. Carson is a home inspection professional, educator, researcher, writer, and a principal of Carson Dunlop Associates, a Toronto home inspection and education firm. Mr. Carson is a past president of ASHI, the American Society of Home Inspectors Some great illustrations of the proper under-roof ventilation pathways are offered by Carson Dunlop.
  • Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06 & 12/08
  • John Annunziata, P.E. - NY Metro ASHI during informal chapter discussions about roof and attic ventilation options (1986-1996).
  • Technical reviewers are invited to comment or ask questions - contact us

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.

INTERIORS of BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR SEALING STRATEGIES
BATHROOM VENTILATION
FREEZE-PROOF A BUILDING
ATTIC CONDENSATION CAUSE & CURE
Air Bypass Leaks,Blocked Soffit Intake Vents
CATHEDRAL CEILING INSULATION
Comparing Two Houses
omparing Two Houses
Heat Tapes: Use on Roofs for Ice
HEAT LOSS: How to Calculate Heat Loss in a Building
HOUSEWRAP AIR & VAPOR BARRIERS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INSULATION INSPECTION & IMPROVEMENT
Inspect Attics for Moisture or Mold
Inspect Basements for Moisture or Mold
Inspect Building Exterior
Inspect the Ridge Vent System from the Attic
Inspect the Soffit Vent System from the Attic
ROOF VENTILATION SPECIFICATIONS
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
HEAT LOSS: How to Calculate Heat Loss in a Building
HOUSEWRAP AIR & VAPOR BARRIERS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INSULATION INSPECTION & IMPROVEMENT
THERMAL TRACKING & HEAT LOSS

INTERIORS of BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR SEALING STRATEGIES
BATHROOM VENTILATION
BASEMENT WATERPROOFING
BLOWER DOORS & AIR INFILTRATION
BRICK LINED WALLS
BUCKLED FOUNDATIONS due to INSULATION?
CATHEDRAL CEILING INSULATION
CRAWL SPACE VENTING & Dryout Procedures
MOISTURE, MOLD, ICE DAM LEAKS in ATTICS & ROOFS
ATTIC CONDENSATION CAUSE & CURE
HEAT LOSS: How to Calculate Heat Loss in a Building
HOUSEWRAP AIR & VAPOR BARRIERS
HUMIDITY LEVEL TARGET
HOUSEWRAP AIR & VAPOR BARRIERS
ICE DAM PREVENTION
INSULATION INSPECTION & IMPROVEMENT

More Information

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More Information on Building Diagnostic Inspections and Repairs

More Reading about Dealing with Attic Mold, Identifying, Removing, and Preventing Mold in Attics

Be sure to review HOW TO FIND MOLD: How to Inspect Homes and Other Buildings for Mold - the Basics of How to Find Problem Mold Indoors in our Mold Action Guide. Here are other articles that will be helpful in evaluating attic mold presence, causes, and cures:

InspectAPedia.comInspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.
GO TO the MOLD and INDOOR ENVIRONMENT INFORMATION CENTER for in-depth advice on avoiding testing for or cleaning up mold and other indoor environmental hazards, odors, gases, contaminants
The Mold Information Center:
What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
GO TO MOLD TEST KITS: This expert-recommended mold test kit is cheap and yet top performing *IF* you use a competent analysis laboratory!
Use this simple, economical mold test kit
by following our instructions on how to collect and mail mold samples to our lab
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02/09/2009 - 06/02/1990 - InspectAPedia.com/interiors/atticcond9htm - © 2009 - 1988 Copyright Daniel Friedman All Rights Reserved - InspectAPedia® is a Registered U.S. Trademark