VENTILATION in BUILDINGS - home - CONTENTS: Building Ventilation Design, Inspection, Diagnosis, Cure - articles: How to Inspect, Diagnose, & Repair Ventilation & Fresh Air (or Stale Air) Problems in buildings
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Building ventilation diagnosis, improvement, repair, inspection, standards & specifications:
These articles explain how to inspect, diagnose and repair ventilation problems in buildings.
We suggest building ventilation methods and we describe the pros and cons of different ventilation approaches used to assure good indoor air quality, low building energy usage, and minimal building moisture problems.
Building Ventilation Design, Inspection, Diagnosis, Cure: key articles
Information is provided about visual clues of building condition as well as direct inspection for the presence or absence of proper building ventilation systems, pathways, and moisture and air barriers to stop leaks where we do not want ventilation.
Our page top sketch explaining the wind-washing effect on attic insulation is provided courtesy of Carson Dunlop Associates.
At left we show an example of severe indoor condensation at a window.
In the articles listed here we explain how to identify and correct various building leaks, moisture, and venting
problems such as ice dams, blocked attic ventilation, excessive indoor humidity, how to prevent indoor mold, and how to respond to building floods and
Our photo (above-left) shows extreme condensation at a building basement window. Moisture at this level risks severe mold growth which can be costly to clean up, and over a longer time this condition invites rot or insect attack on the building.
Below is our list of articles on the diagnosis and cure of building ventilation problems.
To find what you need quickly, if you don't want to scroll through this ventilation design, equipment, installation & troubleshooting article index you are welcome to use the page top or bottom SEARCH BOX to search InspectApedia for specific articles and information.
FLOOR TYPES & DEFECTS - inspection, diagnosis, repair, and installation tips for resilient flooring, vinyl and asphalt floor tiles, wood flooring, tile floors, carpeting in buildings
HEAT LOSS in BUILDINGS, how to determine and calculate heat loss from a building (or heat gain in a cooling climate), how to evaluate building insulation, & how to insulate buildings. What will it cost to heat the building, where are the problems
HUMIDITY LEVEL TARGET - how dry does the building interior need to be? How Low Should You Keep Indoor Humidity to Avoid a Mold Problem?
ROOF ICE DAM LEAKS - what are ice dams, what causes them, why do they cause building leaks & mold. How to inspect for evidence of leaks, identify causes, and correct bad attic ventilation, improper roof venting, and these causes of attic mold or roof structure damage
MOISTURE CONTROL in BUILDINGS - home page of our extensive list of articles on how to identify and fix sources of building water or moisture problems
MOISTURE PROBLEMS in BUILDINGS, CAUSES & CURES Understanding moisture problems can steer you free of trouble", Steve Bliss: Building it Right, Solar Age, March 1983 p. 37, 38. -- Adapted with permission, from original material to form this web page article.
SOFFIT VENTILATION - design guide for proper soffit ventilation at the building roof eaves
THERMAL TRACKING, GHOSTING STAINS how to recognize thermal tracking or thermal bridging & how to diagnose Stains on Ceilings & Walls, Building Air Leaks & Insulation Defects, as well as other indoor air quality or building concerns
VENTILATION DESIGN PROBLEMS & SOLUTIONS - describes common design issues in making a successful building ventilation system, providing solutions for various building venting and moisture problems with supply air & return air problems & solutions, Building indoor air pressure drop during ventilation, Building indoor air ventilation system noise problems & solutions, and building Ventilation airflow controls
WATER ENTRY in BUILDINGS: what the basement waterproofing companies don't tell you? Water entry prevention and repair suggestions.
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How to fix "Leaks" or condensation problem in roof at un-vented valley rafters?
I just built a new house consisting of cathedral ceilings throughout. I installed perforated soffits along the bottom of the eaves, however, I mistakenly forgot to vent the roof along the valley rafters spanning approximately 30' in length. I have discovered a leak at both valley only occurring in the spring time when the temperature finally rises above freezing.
I strip back both valleys and re shingled using snow and ice shield as well as torch down roofing, it still leaked at first snow. Is my roof sweating from improper ventilation? I also ran the ridge vent continuously along the peak, should I only have this where the soffit is vented?(not above the valley). I ran styrofoam baffles under all of the sheathing even at the valley rafter, could this be warming the roof where they are not vented to the soffit? Can somebody offer some helpful advice? - Scott
Scott, the ice and water shield approach can stop leaks around valleys - and is a good practice. The fact that you observed leaks when temperature rises above freezing suggests that a pile-up of snow or ice in the roof valleys is melting, that the water load is exceeding the present roof valley's ability to drain without leakage, and that thus water is finding its way under the shingles past the valley and into the building.
Waterproofing three feet on either side of most valleys will seem to "fix" this leak, but we really don't want to leave water trapped under the roof shingles either - that can be a source of roof damage and reduced roof life.
So in addition to the ice and water shield membrane improvement, take a look at roof valley design details including bends and sealants that prevent water from passing out of the valley and into the roof structure.
These three articles should be helpful in curing leaks at your roof valleys for all weather conditions:
Question: how do you control air flow from one room to another
how can you control air flow to the next room - George 4/19/11
Reply: Tips for Controlling airflow between rooms in a building
Assuming that your rooms have doors, a simple test can sometimes give us a clue about relative air pressure and air movement between building rooms. With the HVAC system or ventilation fans of interest running for five or ten minutes, and with all room doors shut, we open a door between rooms about one inch. Even without using instruments we might feel air movement between the rooms, and in some cases we've actually seen the door blown further open or shut depending on the direction of air movement.
If we find that a room is pressurized by the HVAC system when the door is shut, in particular when the room is heated or cooled only by supply ducts (without a local return air duct), we know that providing a method for air to flow out of the room (and presumably on towards the central air returns) will increase the inflow of conditioned air into the room - better heating or cooling performance will be the result.
Airflow between rooms as well as control over that air flow is made possible by:
doors remaining open or shut
doors that are undercut (or overcut) to provide 3/4" to 1" of open space for air movement
a through wall opening, usually near wall top, in a partition between the rooms, covered with louvered grille
a through wall opening, usually near wall top, in a partition between the rooms, covered with louvered grille and equipped with a circulating fan that blows air in the desired direction.
If your rooms have no doors to close between them you may still have some impact on air flow from "room A" into "room B" by studying how air leaves "B". If room "B" has a window, vent, or door that is providing an exit path for airflow, closing that can slow air entry into that room from "A".
Question: Perforated soffits, no ridge vent, cathedral ceilings: condensation or roof leaks?
I just built a new house consisting of cathedral ceilings throughout. I installed perforated soffits along the bottom of the eaves, however, I mistakenly forgot to vent the roof along the valley rafters spanning approximately 30' in length. I have discovered a leak at both valley only occuring in the spring time when the temperature finally rises above freezing. I strip back both valleys and re shingled using snow and ice shield as well as torch down roofing, it still leaked at first snow. Is my roof sweating from improper ventilation? I also ran the ridge vent continuously along the peak, should I only have this where the soffit is vented?(not above the valley). I ran styrofoam baffles under all of the sheathing even at the valley rafter, could this be warming the roof where they are not vented to the soffit? Can somebody offer some helpful advice? - Scott 11/11/11
Seems to me that if the problem were really a roof leak it would not occur only in spring. So yes, I would start looking for an indoor moisture source and condensation trap. Your valley rafter roof section has no intake venting so that could be related. Look for ceiling penetrations sending moisture into the roof cavity. I would consider making an inspection cit into the ceiling under the "leak" area to inspect the roof cavity avd insulation for trapped moisture, stains that may help diagnose water passage or sources, and for a hidden mold or rot problem. Let us know what you find, and send photos of the roof problem areas outside and inside and we may be able to offer more useful comments.
Check for ice dam leakage as well.
Question: driving rain leaks into dormers?
I have old fashioned dormers. The driving rain and snow accumulation seems to get into dormers and cause leaks down below. Can I construct a shield in front of dormer that will permit air flow but shield against the driving rain and especialy built up snow that melts into the dormer? - Ed Harrison 8/13/12
Ed, first we need to identify where driving rain or snow are leaking into your dormers. Posting your question here suggests you think it's entering through a roof or ridge vent? If so, check that the vents have not lost the usual baffles or flashing that is designed specifically for this protection.
Thank you for your sharing, it was really helpful to solve the ant problem in my house.
By the way do you think is it good idea? Because actually I already tried it before.
But I will try again according your article saying. Thanks! Have good one! Shafiqur
(May 29, 2014) Pete said:
Does the cold air return duct placed in the marriage wall of my modular home need to be moved and the marriage wall resealed?
I can't really say, Pete. You probably have a reason for asking but a duct problem was not stated.
(June 22, 2014) Victor said:
No ridge vent. Two louvers in gable ends. Should I use perforated soffit under the front and back overhangs?
Victor in North America and some other countries gable-end-only venting was a traditional practice into the 1960's. It is not effective at cooling the attic except under a few wind conditions combined with large opening and exit vents, and it won't cool and dry lower roof edges.
If you add soffit intake venting that will help by allowing air to enter at those lower roof edges, moving by convection upwards as the attic air is heated by sunlight; that opening will also reduce the tendency of exit-only attic vents to suck heat and conditioned air out of the building (increasing energy costs).
But optimum would be to install soffit and ridge vents and then close off the gable end vents.
(Aug 22, 2014) Anonymous said:
We have a static vent on the roof of our mobile home (a #301 MAXIMUM vent - since July). We have soffits (10'') - (this also since July) as well as gable vents. We are having ventilation problems. The hot air from the attic is entering our living space. We temporarily closed the gable vents (as best we could) and this seems to have solved the problem. However when we open the windows there is a smell as if the air from the attic is coming down the soffits and entering the house. Is this possible. Our mobile home is 66' x 14' and we are in Canada. We are wondering if the MAXIMUM vent on the roof is doing its job considering that the house is 66' long. D.S.
If the roof intake venting is insufficient then it's quite possible that the negative pressure created by your roof exit vent is increasing air leakage into the attic space.
(Mar 30, 2015) Laurie said:
Who is responsible for installing a gas dryer with no exterior ventilation? My home warrenty did this and I was told it was illegal and very dangerous
The danger depends on more than no exterior venting: is this a gas dryer or electric?
In any case, the appliance installer would be expected to either connect the dryer to an exterior vent or to tell you that you need one.
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ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
2005 ASHRAE Handbook : Fundamentals: Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover)
by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479
"2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 ,
"The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
Energy Savers: Whole House Systems Approach to Energy Efficient Home Design [copy on file as /interiors/Whole_House_Energy_Efficiency_DOE.pdf ] - U.S. Department of Energy
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and correct bad attic ventilation, improper roof venting, and these causes of attic mold or roof structure damage
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