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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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