Attic mold/condensation

Mildew growth or water stains on interior of the attic (roof sheathing)

These problems may indicate that your home has inadequate attic ventilation, insulation or that there is faulty roof covering that is causing a leak.

                                                               Attic mold


The major sources of mold in attics are improper ventilation and insulation:

  • Soffits (overhangs) aren't ventilated or they're blocked by insulation.
  • Missing insulation and vapor barrier.
  • Missing/inadequate upper and lower vents.
  • A bathroom's exhaust venting into the attic. Moisture escaping the bathroom hits the sheathing and cold air outside creates condensation inside, creating mold-optimal conditions.
  • Leaks in the roof.
  • Improper chimneys, vents and plumbing stack flashings.
Attic condensation (winter)

Attic condensation

Attic condensation during the winter can decrease the effectiveness of insulation and over time can cause significant damage to structural elements in the attic such as rafters or trusses. And the same factors that cause attic condensation problems also cause ice build-up on roof edges, which can lead to ice damming. If ice damming occurs it often results in snow-melt water entering the home with the potential of causing significant
water damage to the home's interior.

Attics tend to be very inhospitable places (scorching hot in the summer and freezing cold in the winter) so the average homeowner seldom visits the attic to check its condition. Therefore, if an attic condensation problem does exist, it often goes undetected until significant damage has occurred. As mentioned previously, the same factors that cause attic condensation problems also cause ice build-up on roof edges. So if you have noticed that you have lots of icicles hanging from the edge of your roof, it is also probable that your attic has condensation problems.


Attic condensation

Causes of Attic Condensation

The primary cause of attic moisture problems is due to moisture transported from the heated portion of the home into the unheated attic via airflow.


  • Heated air escapes into the attic around unsealed penetrations in the ceiling for items such as light fixtures, vent pipes, chimneys and fans.
  • Bathroom/kitchen exhausts fans vented directly into attic space.
  • Leaky roof (damaged/cracked shingles, flashings and leaky vents).

How to fix attic condensation problems:

  • Clear the space between the rafters that draws fresh air from the soffit.  There should be a 1" space below the bottom of  the roof sheathing so the incoming air will keep the roof cold and supply enough  air to exhaust any warm air that leaks into the attic.
  • Ensure that no holes, air leaks or bypasses of warm air can pass through the house and into the attic.
  • Re-routing exhaust fans from your home appliances and bathrooms to reduce attic condensation. If the fans in your home are vented into the attic, you may want to consider re-routing them to the outside.
  • Improve attic insulation.
  • Install more upper and lower (soffits) vents.
  • Install power vent.




Insulation - amount too little, missing, compressed, gaps/voids.

Common insulation materials:

  1. Loose fill (which can be blown or poured) - cellulose, glass fibers, mineral wool vermiculite and perlite.

  2. Batts or blankets. Fiberglass and mineral wood commonly come in batts or blankets.

  3. Rigid boards. Common board insulation include fiberglass, polystyrene and polyurethane.

  4. Foamed-in-place insulations.

Missing attic insulation


Do I have enough insulation?

No matter what kind of insulation you currently have in your attic, one quick way to determine if you need more is to look across the span of your attic. If your insulation is just level with or below your floor joists (i.e., you can easily see your joists), you should add more. If you cannot see any of the floor joists because the insulation is well above them, you probably have enough and adding more may not be cost-effective. It is important that the insulation be evenly distributed with no low spots; sometimes there is enough insulation in the middle of the attic and very little along the eaves. If your attic insulation covers your joists and is distributed evenly, you probably have enough.



How much insulation should I add?

Insulation levels are specified by R-Value. R-Value is a measure of insulation's ability to resist heat flow. The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.





Ridge vent
  • The idea behind roof ventilation is to get fresh air circulating to the underside of the deck. Proper attic/roof space ventilation will help with energy efficiency (lowering heating and cooling costs), preventing premature failure of the roof and deterioration of floorboards, and lessening susceptibility to ice dams in cold climates and mold in all climates.


  • Industry standard is that for every 150 square feet of attic floor area, you need 1 square foot of intake ventilation and 1 square foot of exhaust ventilation. An even better way to do it is to run continuous soffit ventilation (intake) and continuous ridge ventilation (exhaust). The code permits less ventilation opening area – down to a minimum ratio of 1 square foot for every 300 square feet of attic floor area if a vapor retarder is included on the warm-in-winter side of the ceiling in cold climates.


Ventilation types:

  • Top hat or can vents.
  • Ridge vents – A ridge vent runs the entire length of the roof peak. A ridge vent with external baffles and an internal weather filter, combined with soffit venting, is the most efficient system you can install.
  • Gable vents are louvers with screening that are installed in the gable walls of the attic.
  • Turbines are extremely effective if and when the wind is blowing; otherwise, ventilation is limited.
  • Power vents – work great, but they are mechanical devices and when the motor fails, it is out of sight, out of mind.


Common issues with soffit ventilation include the following:

  • Missing, inadequate vents.
  • Soffit vents obstructed by insulation.
  • Vents obstructed by dust or dirt.
  • Painted vents (restricted air-flow).
  • No baffles in the attic.




Common steep roof covering - glass fiber shingles, wood shake and shingles, clay and concrete tiles, slate roofing, metal shingles and sheets

Shingle problems

Cracked shingles
  • Cracked, curling or buckling shingles – these problems could be signs that your home has inadequate roof ventilation or that your shingles have reached the end of their useful lifespan.


  • Missing granules (dark spots) – missing granules is often a sign that it is time for a new roof. Some granules will come loose as part of the installation process, but visible dark spots on the shingles, piles of granules in gutters or at the end of downspouts are signs of shingle deterioration.


  • Algae growth – algae growth causes dark brown to black discoloration of the shingles on your roof. It is caused by air-borne algae deposits on the roof. Removing algae growth can be difficult, but can be chemically treat the roof and thereby extend the life of your roof.

Asphalt shingles. Asphalt shingles are the most common type of roofing material found in United States, especially on steep-sloped roofs. These are usually reinforced by organic or fiberglass material. There are wide variations asphalt shingles. Asphalt roofing shingles have come in grades with an expected life of 20-50 years, depending on the weight of the shingles, slope of the roof, exposure to the sun, color, and weather and climate conditions.

Deteriorated flashing
  • Fastener back out or nail popping – this occurs because the deck is in poor shape, the nails are too short, or there is severe building movement resulting from the foundation settling or roof structure problems.


  • Leaks after heavy rain – leaks following rain could mean that you have deteriorated flashing somewhere on the roof, preventing your home from being sealed properly. Leaks could also indicate the shingle and shingle underlayment is damaged or inadequate.


  • Leaks after driving snow – leaks following a heavy snow could be caused by inadequate or improperly-installed shingle underlayment allowing water from ice dams to leak into the attic. Clogged vents, poorly-installed gutters, or an improper balance of static and soffit vents can also lead to post-snow leaks.
Wood shake and shingles. These types of shingles are generally made from cedar or redwood and occasionally southern pine. The difference between roofing shakes and roofing shingles is that shingles are machine-sawed; whereas shake are handmade to look rougher. The life expectancy of wood shake and shingles is shorter than most other roofing products, lasting between 8-25 years, with proper maintenance.
Attic mold
  • Damaged flashing around chimneys, vents, skylights, and walls – damages can be caused by improper installation, deterioration over time, or settling of the structure. Replacement of the damaged flashing and surrounding shingles usually corrects the problem.


  • Missing shingles – missing shingles are usually caused by improper installation and/or strong winds. Generally, if the roof is otherwise in good condition, missing shingles can be replaced and loose shingles sealed with roofing cement. However, missing shingles can be a symptom of poor installation, and a warning of future roof problems.

                Missing shingles                                              Old roof covering

Metal roofs. Metal roofs have become a popular alternative to traditional roofing materials. This is due to the fact that metal is lightweight and durable, and can be manufactured to give virtually any look imaginable (even imitate other types of roofing). Metal roofs come in either shingles or panels, both with a life expectancy of over 30 years.



Roof structure problems

Sagging ridge and rafters. Sagging may be caused by -

  • Rafters overspanned or/and undersized.
  • Too many layers of roofing materials (more than 2).
  • Excesive loads - snow drift and roof-mounted equipment.
  • Poor connections at hip and valley rafters.
  • Cracked rafters and ridges.
  • Poor rafters end bearing and weak connections.
  • Ineffective intermediate supports, including - collar ties, ridge posts, knee walls and purlins.

                  Sagging roof ridge                                              Cracked rafter


Sagging roof sheathing. Sagging may be caused by -

  • Overspanning.
  • Inadequate edge support.
  • Excess load.
  • Deteriorated wood and improper material.
  • Rot and insect damages.
  • Mechanical damages and splitting.
  • Attic moisture and mold.

                     Sagging roof sheathing                                    Cracked rafter




Roof ice damm


An ice dam is a problem of house and building maintenance in cold climates. An ice dam can occur when snow accumulates on the slanted roof of a house with inadequate insulation and warm air leaks into the attic at penetrations for plumbing stacks, wiring, chimneys, attic hatches, recessed lights, etc.

These warm air leaks are known as attic bypasses. Heat conducted through the insufficient insulation and warm air from the attic bypasses warms the roof and melts the snow.  Meltwater flows down the roof, under the blanket of snow, onto the eave and into the gutter, where colder conditions on the overhang cause it to freeze.


Eventually, ice accumulates along the eave and in the gutter. Snow that melts later cannot drain properly through the ice on the eave and in the gutter. This can result in:

  • Leaking roof (height of leak depends on extent of ice dam).
  • Wet, ineffective insulation.
  • Stained or cracked plaster or drywall.
  • Rotting timber.
  • Stained, blistered or peeling paint.

Under extreme conditions, with heavy snow and severe cold, almost any house can have an ice dam, whereas a house that is poorly insulated with attic bypasses will have ice dams during normal winter weather. Giant icicles hanging from the eave are one indication of a poorly insulated attic with many attic bypasses.


To fix attic moisture and ice damming problems, three factors need to be addressed:

  • Prevent warm air in living spaces from infiltrating into the attic with a good air barrier between the heated portion of the house and the attic. Properly finished drywall or plaster on ceilings provides an adequate air barrier. But significant air leakage occurs wherever there are penetrations in plaster or drywall ceilings. Most insulation products are not effective air barriers, so even well insulated attics can have significant air leakage problems. Plumbing vent pipes, chimneys, recessed lights, and attic access stairs are examples of penetrations that need to be carefully air-sealed. The typical homeowner does not have the expertise, equipment or experience to adequately do this job. Therefore, it is advisable to seek the services of a professional to find and seal air leaks.


  • Prevent conductive heat loss between living areas of the home and the un-heated attic by making certain that attic insulation levels are adequate and that insulation is correctly installed. The US Department of Energy recommends that ceilings have insulation levels rated at R-49. A 15-inch thick layer of cellulose insulation or a 27-inch thick layer of fiberglass insulation is required to obtain an R-49 insulation level. Few attics are insulated to these recommendations. Doing so can significantly reduce home heating bills. Combining proper levels of insulation with air-sealing will prevent both attic condensation and ice damming problems.


  • Provide ventilation on non-heated attic spaces. Even with sufficient insulation levels and a good air seal between the attic and heated spaces below, some heat may escape. Attic ventilation is suggested because it can draw this heat from the attic before it can accumulate and begin to melt roof snow. It also keeps the roof cooler in summer. In addition, building codes often require attic ventilation. Open attics should have 1 square foot of vent area for every 300 square feet of ceiling area. Cathedral ceilings should have 1 square foot of vent area for every 150 square feet of ceiling area. The most effective attic ventilation strategies divide ventilation is equally between soffit (roof edge) and roof peak areas. Correctly installed soffit ventilation allow air into the attic area, but also protects insulation from the negative effects of wind washing




Benefits of flat roof construction:

Flat roofs are very convenient, easier to build, and cost less than pitched/sloped roofs. In some cases, a flat roof is the only way to go, for example, when you have a large size building. Building a reliable pitched roof in those cases will require extra engineering to accommodate for additional structural weight. Flat roofs are also convenient for installing large HVAC equipment that otherwise would have to be installed on the ground. You can also use flat roof as a roof-top deck, patio or penthouse.


Limitations and disadvantages of flat roofs:

Flat roofs also have a number of disadvantages. The main one is the fact that there is no slope and all the water/snow sits on the roof. While water can be taken care of with proper drainage, snow will sit on the roof until it melts. This requires the engineers / architects to implement building components with a higher structural load. Another disadvantage that haunted flat roof installations for over a century is ponding water. Until the invention of single ply membranes such as an IB roof, there was no effective and economical way to eliminate the leaks caused by ponding water. That had to be taken care of in the initial design/construction stage. Creating a slight pitch and multiple drains was required, and still ponding water caused over 75% of all flat roof leaks.

Roof slope

The slope of your roof system plays an important role in how effectively your roof sheds water. The biggest problem with most commercial or flat roofing systems is caused by poor roof slope. Imagine a roof that has very little slope and many areas of ponding water. The ponding water is caused by a roof slope that is inadequate to overcome irregularities in the roof surface. When this roof begins to develop leaks, the leaks will be much more severe than they would on a roof that is shedding water quicker and has minimal ponding water. Simply put, a roof should shed water not retain it (like a swimming pool). While many older flat roofs have performed satisfactorily with slopes of barely ⅛" per foot, it is typically recommended that the roof slope be a minimum of ¼" per foot. This will minimize the chance of stagnant water (ponding) on the roof surface and will minimize the chance of water damage when the roof begins to fail.
Most roof slope deficiencies can be easily corrected with the addition of tapered insulation. Not only can existing roof slope be increased, but it is also possible to change slope direction completely. For example, a roof that sheds water toward the front of a building could be modified to shed water toward the back of the building. Pre-formed tapered insulation is commonly available in ⅛", ¼" and ½" per foot slopes.

Roof drainage

The drainage system on your roof plays an important role in how your roof eliminates water. As roof slope pertains to "shedding water", roof drainage pertains to "water disposal". The performance of the roof drainage system needs to be properly matched to the size and slope of the roof. As the roof slope increases, the volume of water (in a given timeframe) that is routed to the drainage system will increase. Deficiencies in your roof drainage system can be easily corrected. A roof with undersized gutters & downspouts can have larger gutters & downspouts installed. A roof that has an insufficient number of internal drains can have more drains added. The same principal applies to roof scuppers and other drainage locations.

Structural deficiencies of the deck


Structural deficiencies will be defined as irregularities in the roof structure or roof decking. For example, a wood framed roof might have joists that have bowed in the middle from years of constant load. This "bow" might cause water to pond in the middle of the roof. The roof might have odd decking elevation changes from previous additions or other types of construction and remodeling. It is important that the aesthetic and functionality aspects are considered when replacing the roof system. If a roof structure has deficiencies and a new roof system is being installed over an existing one, the new roof system will also mirror the deficiencies. If the existing roof system(s) are being removed down to the decking you will most likely have the best opportunity to address the structural issues.


Common flat roof coverings:

IB roof (PVC roofing) – IB roofing membrane is one of the best low-slope and completely flat roofing products available. IB roofs still feature the same chemical formula as its original design, and with hot-air welded seams, will maintain complete water-tightness over your roof.


Epdm rubber roof – a widely used flat roofing material, mainly popular among contractors because of its low price and no special equipment needed to install the rubber roof. Still, rubber roofs are very prone to leaks, as the seams are glued together, and adhesive tends to break down within 5-7 years.


TPO roofing – a single ply thermoplastic roofing membrane similar to PVC roofs from a first glance. But as you start digging, you’ll find numerous problems with TPO roofs, mainly as a result of manufacturers skipping on adding important ingredients into formulation of the TPO membrane, and as a result, quietly scrapping as many as three major generations of the product.


BUR/tar & gravel torch-down - multiple-ply roof where each ‘tar-soaked’ ply is applied with a torch or hot mopped (preheated tar transported to the roof and applied with a mop). Gravel goes on top of this ‘sandwich’ mainly as a protection layer from foot-traffic and sun’s devastating ultraviolet rays. There are many deviations from the above procedure, but they are all within a close range of similarity.


Modified Bitumen - it is also applied with a torch in a similar manner described above. It is however a different material than tar. Modified bitumen has rubber and elastomers added into the formula, so it is stronger and more flexible. 

Rolled Asphalt - similar to asphalt shingles – tar paper is saturated in asphalt, with crushed stones glued on top of it. Rolls are installed in an overlapping pattern, with cold-mop application and nails to attach it to the roof deck. Overlapping seams are sealed with tar.


Roof covering problems

  • Mechanically damaged - (foot traffic, equipment moved across or installed on the roof, wind, falling objects.
  • Patched - patches are usually the result of prior leakage, and may be weak areas, likely to leak again.
  • Multiple layers - it is common for new layer to be added over old one. This is not recommended practice because it adds weight to the structure below.
  • No protective surfaces.
  • Blisters - may be caused by air or water trapped between the roof sheathing, and the membranes. When the roof heats up with yhe sun, the gases expand and bubble up thtough the surface, or expand to form large bubbles or blisters.Gravel erosion.
  • Ridging and fishmoutsh - may be caused be due to excess asphalt moisture, felt slippage or differential thermal expansion. Membrane movement or splitting.
  • Openings at seams and flashings 
  • Blisters - may be caused by air or water trapped between the roof sheathing, and the membranes. When the roof heats up with yhe sun, the gases expand and bubble up thtough the surface, or expand to form large bubbles or blisters.Gravel erosion.
  • Ridging and fishmoutsh - may be caused be due to excess asphalt moisture, felt slippage or differential thermal expansion. Membrane movement or splitting.
  • Openings at seams and flashings