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Photograph of evidence of ice dam leaks from outside the homeRoof Venting Defects seen from Outside
How to inspect the building exterior to find roof & attic ventilation defects & damage caused by poor venting

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Roof ventilation defects & mistakes:

What are the common mistakes found in roof ventilation systems? What are the effects of inadequate roof venting? What happens if there is too much roof venting? What happens if ridge vent outlet area is greater than roof intake vent areas at a building eaves? What happens when we leave open gable end vents on a building with ridge and soffit venting?

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.

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Inspection Tips for Roof Venting & Ice Dam Problems

Missing snow on this cape shows where there is missing or poor insulation and/or no under-roof venting.

The first signs of a probable attic condensation problem may there for observation before even entering a building.

Look at the roof. If you're in a cold climate during winter months you may see areas of snow-melt showing where there is an insulation defect.

Or you may see actual severe ice dams at the roof eaves. If the shingles are exposed look for signs of attic moisture in their condition: if there is a high level of attic moisture, unless the roof is quite young, you might see puckered shingles in the classic "fishmouth" pattern.

This shingle curling is quite obvious. If you inspect the exterior roof surface first, on an old roof you'll note shingles which are brittle and which may crack or break. (Don't walk on such surfaces.) If the roof sheathing is plywood, you may sense surface deflection which could simply be thin 3/8" plywood (no longer permitted in most jurisdictions) or it could be damaged from heat or moisture. (Beware of falling through).

  1. Look at the ridge. If there is no ridge vent there is no good outlet for an under-roof attic venting system and this roof will be difficult to ventilate.

    When you make your inside inspection you will also inspect the roof below any "apparent" ridge vents seen outside, as sometimes we find that a faux ridge vent was installed with no openings cut into the roof cavity.

    See RIDGE VENT, ATTIC INSTALL & INSPECT
  2. Look at the eaves or soffits. If there are no continuous intake vents at the soffits, this roof will be difficult to ventilate. And when you make your inside inspection you will look for light or other indications that the eave or soffit vents you found are real, not faux.

    See Inspect Attics for Moisture or Mold.
  3. Look at the roof lines. If the building has no roof overhang, flat roofs, low-slope roofs, roofs abutting Building walls, or complex roof lines, these roofs will be difficult to ventilate.

    See ROOF VENTILATION INTAKE if NO OVERHANG

    and HOT ROOF DESIGN PROBLEMS

Also see CATHEDRAL CEILING INSULATION

and ROOF VENTILATION INTAKE if NO OVERHANG.

The photograph shown at the top of this page offers compelling evidence of roof leaks into the soffit of this older home.

A Photo Guide for Inspecting the Building Exterior for Wet Site, Sources of Attic Condensation, & Roof Venting Problems

Here we provide a series of photographs taken of the exterior of buildings, demonstrating visual clues that can predict a problem with ice dam leaks into these homes.

No Soffit Intake Vents on a Roof Means Ice Dams

In freezing climates, as in our photograph at page top, given the age of construction (pre 1900), the brown color of the stains (oils from roof sheathing boards that have been wet), and the shape of the roof edge (probably there was a built-in eaves trough gutter), it is likely that when we inspect the attic interior we'll see that despite the perforated soffit covers, the roof has no intake venting and there has been a long history of ice dam leaks on this building.

Inadequate soffit or ridge venting risks attic moisture, mold, ice dams, as show by these photos

In both heating and cooling climates, insufficient roof ventilation risks attic or roof cavity condensation, mold, rot, and in some cases increased heating or cooling costs for the building. And as we show just below, do not assume that your building has working roof ventilation even if you see perforated panels covering the building soffit underside

Fake Soffit Vents?

Photo of ice dam leaks from a blocked soffit

Too often building exterior renovations include covering an existing, solid, un-vented building soffit or eaves with perforated panels, forming a "faux vent" system since the perforations are not really passing any air into the building attic.

It's easy to spot this condition both by visual inspection and, where accessible, by pressing on the perforated panels - if they are over an open space they will move easily.

In our photograph at left, although perforated panels are installed on soffits of this older home, we see extensive leak stains on that material.

From outside we posit that either the perforated panels were installed over solid wood - there is no actual soffit intake venting for the attic, or the building simply has little or no attic insulation, resulting in lots of heat loss into the attic during winter months, combined with freezing of melting snow at the colder roof edges.

No Soffits so No Soffit Vents Means Ice Dams and Wall Leaks are Likely

Photo of a home with no roof eaves

The home shown in our photograph at left was built with no roof overhang whatsoever - or no roof soffits or eaves extension past the building walls. Not only does roof runoff too often run down the exterior wall surface, inviting rot or insect damage or wall leaks, but also this construction makes it tricky to obtain any roof cavity intake venting.

Special products such as the Hicks (TM) starter vent can be used at roof eaves in this location, but an air path must also be provided inside under the roof decking.

The window at the building right corner tells us that cathedral ceilings were probably installed inside this home - under-roof venting would still be a good step to avoid roof cavity condensation, leaks, mold, or related damage.

See ROOF VENTILATION INTAKE if NO OVERHANG for some suggestions on how to vent this design.

Tiny Gable End Vents can Predict Ice Dams and Inadequate Attic Ventilation on buildings

Gable end vent in a building wall - photo

The photograph shown at left demonstrates a tiny gable-end vent in an older building.

This home combines stone construction, multiple shingle layers, shaded site with (unseen) no other attic intake or outlet ventilation, to make attic condensation problems and seasonal ice dam leaks likely.

Photographs of Building Siding Stains Can Indicate Ice Dam Leaks

This photo shows siding stains caused by roof ice dam leaks into the wall cavity.

Photo of ice dam leaks on siding

Notice that the soffit is un-vented on this older home. Roof leaks into the wall cavity have run down the walls and exited between clapboards, leaving stains and peeling paint.

Roof leaks in this area from any cause, ice dams or work, leaky roofing materials will all produce this effect.

Photos of Use of Heating Tapes on Roof Edges Tells the Ice Dam Story

This photo shows roof edge heating tapes installed by an owner to attempt to melt channels through ice that may accumulate at the roof eaves in winter.

Photo of heat tapes on a roof edge

This is an inexpensive band-aid that may be sufficient if ice dam formation on a roof is rare and/or it is difficult to install good under-roof venting.

This roof has eaves and a ridge that could have been vented.

If a roof shape prevents easy installation of under-roof venting, or if a home is located where building custom excludes under-roof venting, use of an ice-and-water shield product under the shingles at roof edges, or use of metal covering the lower roof slopes are other measures taken to prevent ice dam leaks into the building interior.

See HEAT TAPES & CABLES for ROOF ICE DAMS

for details about the use of heating cables on roofs to prevent ice dam leak damage.

Signs of Roof Ice Dam Problems Can Be Seen in Any Season

Photo of gutter damage from ice dam chopping Shingle damage from ice dam chopping

In addition to our photos showing missing roof intake or outlet venting, roof leak stains, and similar clues, you may be able to spot evidence of attempts to remove roof ice dams by chopping at the ice itself.

Usually attempts to remove roof ice by chopping at it results in damaged roof shingles and sometimes holes in nearby flashing or gutters as shown in this photo.

You'll also spot chop or cut marks in roof shingles at the lower roof edges when this procedure has been attempted.

This article is part of the series ROOF VENTILATION SPECIFICATIONS - topic home,

and part of our discussion of ATTIC CONDENSATION CAUSE & CURE - topic home.


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Comments

danjoefriedman (mod) · Feb 16, 2021

PS:

Several roofing vent manufacturers warn that if the roof venting system is not properly-balanced between air intake openings and air exhaust openings there may be problems of blown -in rain or snow.

In my OPINION, because balanced ventilation is calculated based simply on vent area, providing equal intake and exhaust areas may not actually work as fantisized in the "real world" in which, depending on building structure, eaves overhang dimensions, terrain shape and features that affect wind flow, such balance may not occur and additional vent opening might be needed, creating an un-equal vent area at ridge-outlet or eaves-intake.

danjoefriedman (mod) · Feb 16, 2021

Kathleen:

It is possible that the roof sheathing cut is too wide. For example a CertainTeed ridge vent cutout opening is at a width allowing just 3/4" of opening on either side of the ridge board; If we allow 1 1/2" for a typical ridge board thickness, that's a total of 3" cutout opening width.

To know if your ridge vents are properly installed we would need to know

- the actual dimensions of the opening (I estimate from our photo that it is about 3 to 3 1/2" in width)

- the recommended cutout width for the specific brand and model of ridge vent that is installed

But most-often when I see a lot of wind-blown snow or rain entry at a ridge vent it's a design issue such as use of a plastic or metal ridge vent that lacks adequate exterior baffles or flanges to deflect wind-blown water or snow that is pushed up the roof slope by the prevailing wind direction.

Or the installer omitted a mesh screen recommended by the manufacturer.

More details are at

RIDGE VENT, ATTIC INSPECTION

inspectapedia.com/ventilation/Ridge_Vent_Inspection.php

Kathleen · Feb 16, 2021

We just purchased a spec home from a builder. We had a recent snow storm with high winds. In our plat of around 90 homes, 90% are experiencing snow in the attic. Not a little, a lot. The melting snow has seeped into the drywall damaging the ceilings in several areas of living area. The ridge vent seems to be the problem as the snow was built up under the ridge vent from the from to the back of the house. When I look at pictures, it seems like our venting and/or plywood under was not properly installed. It looks like the gap is too big. Also we have slash marks that can be seen in the ridge that out neighbors don’t have. Can you tell by the picture if the basic install was done correctly? If not, what do we do?

Thank you, Kathleen

danjoefriedman (mod) · Oct 28, 2018

Burn

Take a look in your attic - if you look up through the vents, or at the roof underside below where the vents are visible from outside, and if you don't see daylight then most-likely the vents are blocked.

Best venting on most roofs is continuous inlet along the soffit or eaves and continuous outlet along the ridge via a ridge vent - something easily added from outside atop the roof. Interval-vents will virtually never vent the entire underside of a roof.

danjoefriedman (mod) · Sept 24, 2017

From inside the attic you would look into the vent opening and see that there is just screening and they like. However unless you have adequate Eve's or soft intake venting and continuous Ridge Outlet venting the attic venting is likely to be inadequate. A few spot friends will not correct the condition.

Jim · Sept 23, 2017

Even though I have 6 circular attic roof vents - my attic is always extremely hot. How does one inspect tehse vents to insure they are not blocked?

Burney · Oct 27, 2018

@Jim,
Hi, I had my roof changed last year. The company doing the job added 1 more roof ventilation cap making it 4 altogether with the previously existing 3; it also added 2 goose neck vents. However, whenever I openned the attic opening board, a small wind (bad) air always flows into my home now rather than out of my home into the attic strongly as before the roof was replaced. I thus suspect something has gone wrong. Perhaps most of the vents have been blocked and not connected with the attic at all. How can I solve this problem? Thanks!

 

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