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VENTILATION in BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR LEAK SEALING PROCEDURE
AIR POLLUTANTS, COMMON INDOOR
AIR SEALING STRATEGIES
AIR TEST FOR MOLD: ACCURACY
AIR TEST SAMPLING CASSETTE STUDY
ANIMAL ODORS IN buildings
ATTIC LEAKS, CONDENSATION & MOLD
BASEMENT CEILING VAPOR BARRIER
BASEMENT HEAT LOSS
BASEMENT LEAKS, INSPECT FOR
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BRICK WALL DRAINAGE WEEP HOLES
BUCKLED FOUNDATIONS due to INSULATION?
BUILDING NOISE DIAGNOSIS & CURE
CATHEDRAL CEILING VENTILATION
CEILINGS, DROP or SUSPENDED PANEL
CHIMNEY INSPECTION DIAGNOSIS & REPAIR
COMBUSTION AIR for TIGHT buildings
COOLING LOAD REDUCTION by ROOF VENTS
CONDENSATION or SWEATING PIPES, TANKS
CONDENSATION on WINDOWS & SKYLIGHTS
DECK & PORCH CONSTRUCTION
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
FIREPLACES & HEARTHS
FLAT ROOF MOISTURE & CONDENSATION
FRAMING DETAILS for BETTER INSULATION
FRAMING DETAILS for DOUBLE WALL HOUSES
FREEZE-PROOF A BUILDING
FROST HEAVES, FOUNDATION, SLAB
GREEN BUILDING CONSTRUCTION CODES GUIDES
GREENHOUSE DESIGN for SOLAR HEATING
GREENHOUSE / SUNSPACE GLARE
HEAT LOSS in BUILDINGS
HEAT LOSS DETECTION TOOLS
HEAT LOSS INDICATORS
HEAT LOSS PREVENTION PRIORITIES
HEAT LOSS R U & K VALUE CALCULATION
HOT ROOF DESIGNS: Un-Vented Roof Solutions
HOUSEWRAP AIR & VAPOR BARRIERS
HOUSE DOCTOR, how-to be
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INDOOR AIR HAZARDS TABLE
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
Insulation Air & Heat Leaks
INSULATION INSPECTION & IMPROVEMENT
INSULATION R-Values & Properties
LOG HOME GUIDE
MOISTURE CONTROL in BUILDINGS
MOLD: A COMPLETE GUIDE TO MOLD
NOISE / SOUND DIAGNOSIS & CURE
ODORS & SMELLS DIAGNOSIS & CURE
PAINT FALURE, DIAGNOSIS, CURE, PREVENTION
ROOF VENTILATION SPECIFICATIONS
SHEATHING, FOIL FACED - VENTS
SOUND CONTROL in buildings
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAIN DIAGNOSIS on BUILDING INTERIORS
STUCCO WAll FAILURES DUE TO WEATHER
STUCCO WALL METHODS & INSTALLATION
STUCCO OVER FOAM INSULATION
STUCCO PAINT FAILURES
SWEATING (CONDENSATION) on PIPES, TANKS
THERMAL MASS in buildings
THERMAL TRACKING Indicates Heat Loss
VAPOR BARRIERS & AIR SEALING at BAND JOISTS
VAPOR BARRIERS & HOUSEWRAP
VAPOR CONDENSATION & BUILDING SHEATHING
VENTILATION in BUILDINGS
WIND WASHING INSULATION At EAVES
WINDOWS & DOORS
WINTERIZE A BUILDING
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
This article explains the effects on buildings caused by locked soffit intake vents and we explain how blocked soffit venting causes or contributes to attic condensation, moisture, and potential mold contamination problems in buildings. We also explain that attic or roof exit venting without adequate soffit intake venting increases building heating cost.
This article series 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. Also see CATHEDRAL CEILING INSULATION.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
The page top photo suggests (by the absence of visible mold) that luckily we may not find a mold problem in every poorly-vented attic or under-roof space. But after we confirmed in our lab that the mold was Penicillium sp., in our opinion the attic at left needed to be cleaned. The risk of problem mold bothering building occupants was increased when the attic was in a knee-wall area adjoining a bedroom.
When removing problem mold from an attic we must also correct the moisture problem by both removing the moisture source and by correcting any attic venting defects. See Correcting Roof Ventilation for more details about correcting under-roof ventilation. See the Mold Information Center for guides to inspecting, testing, and removing mold in buildings.
Why is Blocked Soffit Intake Venting a Factor in Attic Condensation Problems?
Here are some examples of blocked intake venting in an attic:
Why Does Blocked Soffit Intake Venting Increase Building Heating Cost?
It's simple. If we make the mistake of providing exit venting from a roof cavity or attic, such as a nice open ridge vent or gable end vents, we also need about twice as much (by square inches) of intake venting at the building eaves. Otherwise here is what happens:
Heat and warm air flows into and is lost from the building roof cavity or attic - warm air rising creates upwards convection currents in the building.
The rate of movement or "strength" of the up-flowing warm air current from the building occupied space increases as it enters the attic and finds a ready exit vent at the ridge or gable ends. (We prefer continuous ridge vent to assure even ventilation across the roof deck underside).
As air flows readily out of the exit venting high on the roof (ridge vent or gable end vents) it creates a negative pressure with respect to the air pressure in the building occupied space.
But if there is not adequate intake venting of outside air, that same negative pressure tends to draw still more conditioned air (or heated air) out of the building space. Essentially we are increasing the heat loss from the building.
Conversely, if there are open soffit vents to allow free flow of air into the attic (or cathedral ceiling roof space), the negative pressure or "vacuum" created by the exiting attic air is more easily satisfied by inflowing (cooler, more dry) outdoor air than it is by leaking air from the occupied space. That slows building heat loss during the heating season.
Why aren't gable end vents the best idea for attic venting?
Gable end vents alone do not uniformly cool and dry the whole roof underside.
Gable end vents combined with a ridge vent tend to become intake vents feeding air flow currents created by air exiting at the ridge, thus failing to draw air up along the roof underside, failing to cool and dry that area, even if soffit intake venting is present.
How do I Unblock Obstructed Roof Eaves by Installing Roof Vent or Soffit Baffles in the Attic
The best place for locating or placing attic insulation, from the view of avoiding attic condensation and ice dams, is in the attic floor or up the sides of attic knee walls. This leaves a cold, drafty attic, but it means longer shingle life and no attic condensation problems. Avoid placing insulation between the rafters unless special venting measures are also taken.
Question: Faux Soffit Vents - Can I Vent My Soffits by Working From Inside the Attic?
Hello- I just finished reading your piece on attic ventilation and unfortunately believe that work done on my house was incorrect. I am a 71 year old female who hired a gutter man to put new gutters on my house. The soffits needed painting (there had never been any vents) and I gave him the job of replacing the soffits.
I now believe that he just covered the old soffit with vinyl soffits that had perforations every few feet without cutting any holes. This past winter, I had a problem with icicles forming along the edge of the new gutters. I called him about the problem, but he claims that it was a bad winter.
He has agreed to return next week, as the gutters are leaking in a few places. I don't think that the attic is venting at all except for the gable vents. My question is this : Can holes be cut from inside the attic and what would be the best way to attempt this? Would I be better off calling an insulation company to check out the attic?
Technically, there are 2 soffits - one the original plywood and the vinyl one on top. The first order of business is to get into the attic and see if he cut any openings. If not, it sounds as though the entire job needs to be removed. If a continuous channel is cut, would I not be able to reuse the vinyl soffit? I'll attempt to send a photo that I took during the winter that shows icicles along the gutter and you can also note the type of vinyl soffit that was used. Again, thanks for your input. - P.
Reply: Usually access from in the attic is too limited. Check for venting, and add from outside if it's absent.
You can't cut holes into the soffit from inside most attics - it's just too difficult to crawl down into the roof edge and almost impossible to reach into the soffit with a saw.
Besides, drilling a few holes just won't provide adequate air inflow.
The work to provide air intake venting at a building's eaves or soffits is almost always performed from outside.
From outside, if the soffit undersides are safely and readily accessible (don't work from a ladder if you're not fit and experienced, don't work alone, don't put a ladder on an icy surface, etc) then often we can push upwards on those vinyl soffit panels. If they are over solid wood they'll feel solid - nothing moves. If the soffit vent panels were installed only after the original solid soffit wood or plywood was removed, the vinyl panels will flex upwards easily for 1/2 inch or even more.
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