Home > Uncategorized > Heat Loss and Attic Problems

Heat Loss and Attic Problems

              
If you’re like most homeowners, you have rarely (if ever) entered the attic space in your home.  This is a good time for a brief inspection.  When the cold December and January temperatures roll in, it’s possible to see signs of problems that are not visible during the warmer months.  Most of you have heard of “ice dams”, but few people seem to understand why they form.

The primary source of ice dams is air leakage into the attic space.  Besides the obvious waste of energy, heat loss can cause problems inside the attic space, as well as lead to ice dams on the roof.

If you find frost buildup inside your attic, it indicates that house air is finding its way into this space.

Small amounts of frost on nail heads is common, but if the frost buildup becomes significant, problems can occur.

When significant frost buildup occurs regularly, the continual saturation of the roof decking will likely cause the plywood to delaminate / decay.

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When frost melts, it also wets the attic insulation, which lowers the R-value (insulating value).  This leads to more heat loss.  Moisture from melting frost can also stain the interior ceilings.

Ice Dam Cutaway

This pattern of heat loss into the attic can also lead to ice dams, which appear as icicles at roof overhangs.  A small amount of this is generally no cause for concern, but when the ice buildup becomes significant, larger problems can occur.

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Older homes are much more susceptible to ice dams for multiple reasons: 1) They tend to be inadequately insulated, 2) They tend to have far more thermal bypasses (air leakage sources) into the attic, and 3) The roof design often does not allow for proper venting of the attic space.

Image 1

How Ice Dams Form

Ice dams can occur on your roof for the same reasons that frost occurs in your attic.  In most cases, the heat loss into the attic space is to blame.  As the heat enters your attic space, it warms the roof surface.  This melts snow, which then travels to the soffit area.  The soffit area is colder and if it is below 32 degrees, ice will form.  As the ice grows, water is prevented from draining off of the roof.  Then, water held up by the “dam” starts to back up, eventually finding cracks in the roof covering. 

Knee Wall Diagram

When water backs up below the roof coverings, leakage into the home will likely occur.

While eliminating ice dams at older homes is not always possible, modifications to the attic should at least reduce the problem.  Most people assume that the answer is to simply add more insulation to the attic spaces, but attics should be air sealed prior to adding insulation.

Stopping the flow of house air into the attic is the best way to reduce the problem

Attic bypasses are simply gaps, or passageways that allow house air to leak into the attic.  As I mentioned above, older homes tend to have far more bypasses than modern homes.  The following images are taken from actual inspections:

This first image shows a kitchen exhaust vent that terminates inside the attic space, rather than at the house exterior.  Notice how the heat from the exhaust air is warming the surface of the roof.  This will melt snow and will likely cause an ice dam to form at the soffit below.

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Attic hatches are almost never insulated in older homes – and in modern homes, the insulation is rarely secured to the back side of the hatch.  The resulting voids allow large amounts of house air to leak into the attic space.

Hatch Insulation

Small gaps exist where circuits enter the attic space and these openings are rarely sealed – particularly in older homes.

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This infrared image shows how much heat loss occurs at these small openings.

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If you have a masonry chimney, you can bet there will be a large gap at its base.

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The infrared image clearly shows this heat loss.

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Large gaps also exist at the base of plumbing vents.

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Even larger gaps will be found around exhaust flues.

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 Modern homes will also have bypasses and some of the most common offenders iclude vents that have simply disconnected from their roof penetrations.

In this example, the dryer vent has separated, which allows most of the hot, moisture-filled exhaust air to vent into the attic space.

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The same problem is occuring here – even though the dryer vent appears to be properly connected.

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The vent below has completely separated.  This is very common in modern homes and the separation often occurs during re-roofing jobs.

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 Kitchen and bathroom soffit areas are another common leakage source.  In older homes, there often is no drywall covering the openings to these spaces – from the attic side.

SoffitVoids2

The cold attic air is clearly visible in this infrared image.

SoffitVoids2IR

 From the attic space, the opening above this soffit area is obvious.

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Here’s the view with infrared.  Notice the obvious heat loss into the attic space.

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This diagram shows this problem more clearly.

DroppedCeiling Bath

Here is the recommended solution.

Dropped Ceiling Sealed

The image below shows a common wall in a 1980’s built 4-plex townhome (this wall separates the units from inside the attic).  In this case, a large gap exists at the base of the wall.

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The infrared image shows the heat loss occuring into the attic space.

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(the following link provides a detailed source of information regarding air sealing attics)
http://www.homeinvestigator.com/xSites/Inspectors/homeinvestigator/Content/UploadedFiles/Attic-Air-Sealing-Guide.pdf

When you decide to make improvements to your attic

If you have decided to make improvements to your attic, it is best to first talk to a specialist.  While it may seem simple to seal air leaks, it is not easy to find them without specilized equipment.  Additionally, there are other factors that need to be accessed prior to proceeding with your attic improvements:

For example:
* If the attic has active knob and tube wiring, it must be rewired prior to the attic being air sealed and insulated.

* If the house attic has vermiculite insulation, then professional advice should be obtained.  The vermiculite insulation may contain asbestos and must be tested prior to the attic being air sealed and insulated.

* If the attic has bathroom fans vented into the attic, then bathroom fans must be vented to the outside prior to
the attic being air sealed and insulated.

* If the attic is not vented properly, this must be improved.

Ventillation

For attic ventilation to be effective, outside air should enter the attic at the eave / soffit areas and exit high near the attic ridge areas.  This cyclical effect keeps the attic cooler, which helps prevent the formation of ice dams.

Proper Air Flow

Some roofs have minimal or non-existent overhangs, which prevents the installation of traditional soffit vents. However, there are still ways to remedy this situation.  Two recommended methods are: 1) low gable vents located near the attic ceiling (but above the top of the level of the attic ceiling insulation) and 2) “eye-brow” vents that can be located on the top of the sloping roof surface near the soffit area/eave.

If Ice Dams Continue, Even After Making Repairs

If air sealing, and improving insulation and ventilation does not eleiminate your problem, you can always have a de-icing system installed.  This is essentially a heating cable that is secured to the roof in ice dam-prone areas.  The cable must plug into a hard-wired outlet (usually at the soffit area).

de-icing-system

Raking snow from the roof edges with a special “roof rake” is another way of preventing problems.

roof-rake-in-use-250w

 

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Categories: Uncategorized
  1. James Jackson
    January 29, 2013 at 3:37 pm

    This is phenomenal information. Thank you for sharing! I’m off to buy a roof rake this evening!

  2. davidlloydnelson@comcast.net
    January 29, 2013 at 11:18 pm

    Thanks Tim.  I can’t believe I just got all that good information for free.  Damn, priceless information.  I’ve been seeing quite a few issues with my attic inspections.  More than normal.  Must be the weather?   

  3. lea
    December 31, 2013 at 6:26 pm

    I heard that roof raking was actually bad.. Roofer told me that you are just pushing the ice dam back further. Said you should remove all or none at all

    • December 31, 2013 at 7:23 pm

      it’s true that raking can cause ice dams to form higher than usual, but this practice does prevent ice dams at a majority of homes. Ultimatley, it will depend on the style of home that you have. For most traditional (gable, or hip roofs), roof raking is an effective method of preventing ice dams.

      Tim

  4. March 8, 2014 at 12:24 am

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