InspectAPedia ^®

This is chapter 7, "How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in Buildings", part of our discussion of "Attic Condensation". 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.

These recommendations are based on 30 years of building inspections, on the observation of the locations of moisture, mold, ice dams, condensation stains, and other clues in buildings, and on the correlation of these clues with the roof venting conditions at those properties.

I have also measured changes in airflow, temperature, and moisture before and after installing roof venting. More in-depth, un-biased, expert information on these topics and on building defect inspection, diagnosis, & repair can be found at " More Information below. © 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.

How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in Buildings

Home inspectors and building owners should be especially concerned about insulation placed directly under the roof sheathing such as between the rafters. This can trap heat and moisture and damage sub-roofing as well as roofing shingles.

Also, cathedral ceilings without vents in the soffit and up at the ridge or without adequate air path between the roof insulation and the underside of the roof sheathing can lead to major condensation problems, rot, insect damage, and severe structural damage in just a few years.

Do look for those dark rafter lines and don't underestimate the damage that can exist.

The best "fix" for cathedral ceilings and un vented roof cavities is to assure that there is an air path into the attic up the under side of the roof along the building eaves.

If insulation blocks this opening, it is corrected simply by installing soffit vent baffles at the house eaves between every rafter pair (cardboard or Styrofoam pieces made for that purpose and sold at most lumber yards) and adding vents if not in place.

An alternative un-vented "hot roof" design is touted by some building experts who argue that under-roof venting is not needed whatsoever. Roof surface temperature affects the life of the roof covering. Studies in Florida confirmed that asphalt roof shingle surface temperature varies more as a function of shingle color than as a function of whether or not the under-roof cavity is ventilated. Mark Cramer informs us that an insulated roof is only 7 deg. F. hotter than an un-insulated roof. By this view roof life may not be reduced significantly by an un-vented design. Here are some concerns that the "hot roof" design leaves incompletely addressed:

• Hidden leak damage: If insulation is placed between the roof rafters, especially using some water resistant foam insulation products, leaks into the roof cavity from outside are likely to cause significant and costly structural damage (and possibly mold infection) before the leak is discovered.
• Higher heating/cooling costs: A sloped, insulated roof has a larger radiating surface area than an insulated attic floor, increasing building cooling or heating costs. The conversion of the attic space to a "conditioned" space (by placing insulation between roof rafters) is a bonus in some buildings if the space is to be used, but a cost in buildings where it is not to be occupied.
• Lack of moisture damage resistance: A building with an interior moisture problem that results in moisture movement up through the building to the roof underside is more likely to suffer mold and rot problems if that moisture is trapped in an un-vented attic or roof cavity. Good building management includes identification and correction of leaks or other sources of un-wanted moisture. But good building design takes into account "real world" conditions that actually occur in the field, not just optimal conditions that describe what people should do.

Leaks and moisture problems are common on buildings in most climates and these conditions are likely to occur over the life of a building. Good building design resists water damage. Readers who have hot roof designs or hard-to-vent roof cavities should also see Un-Vented Roof Solutions.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
• 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.
• Additional technical contributors & reference sources for this article are listed below.
• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.

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
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
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
  VENTILATION DESIGN PROBLEMS & SOLUTIONS
  WHOLE HOUSE VENTILATION Strategies
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
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

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• ...

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:

• What Mold and Allergens Look Like: mold identification photos to help identify mold - choosing what to sample in buildings
• How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
• Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens.
• How to Find and Test For Mold in Buildings A "how to" photo and text primer on finding and choosing the right spots to test for mold in buildings
• Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
• Simple Adhesive Tape Sampling of Moldy Surfaces - how to send a mold sample to our lab
• Mold Sampling Methods in the Indoor Environment - In-depth article: detailed critique of popular mold testing methods - Is your mold test kit worth the bother?
• Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
• Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.

InspectAPedia® 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.

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

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting