“WINTER IS COMING”. A MESSAGE OF WARNING AND CONSTANT VIGILANCE
Winter is coming
For those of you who watch the HBO series Game of Thrones[1], "Winter is Coming" is the motto of House Stark. The meaning behind these words is one of warning and constant vigilance. The Starks, being the lords of the North, strive to always be prepared for the coming of winter, which hits their lands the hardest. The deeper metaphorical meaning is that even if things are good now ("Summer"), we must always be ready for a dark period when events turn against us ("Winter").
With last winter’s polar vortex there was a significant rise in winter season property damage claims. Burst pipes, wet floors, leaking ceilings, cracked chimneys, settled porches and foundations, roof collapses are just a few of the numerous forensic investigations we had to perform. This past year, ice damming was cited by the insureds as the cause for the leak in the roof or the ceiling/exterior wall, peeling paint and stained/rotted wood framing or the collapse of the gutters and so on. Because winter is coming and the forecast calls for an equally bad winter as the last one, below you will find information about roof failures, ice dams and how to prevent the costly property damage they can cause.
Failed roof due to the weight of snow and ice. Structural deterioration due to lack of proper maintenance and wear and tear were additional contributing factors leading to the failure
What is an ice dam?
An ice dam is a frozen barrier to the free flow of rain and melting snow and ice. It can form when melting snow and ice from the roof refreezes at the gutters and eaves or gutter-stored rainwater freezes in these areas. When temperatures rise and ice and snow on these unheated edges of your roof do not melt as fast as the heated areas that cover the other parts of the roof, then this melting water will be backed up by the ice dam that was formed along the gutters. Unfortunately, this causes water to drain improperly and unpredictably, finding its escape routes through the home, mostly through the joints around the chimneys, roof/wall intersections, windows, and so on. The end result is damaged ceilings and walls and, if left unabated long enough, significant structural damage and potential loss of life or property. See image below from one of last winter’s casualties.
What causes ice dams?
The ice dam is a warning sign that something is wrong with the design, construction or maintenance of the roof, the attic, the ventilation of the home, and the drainage system along the roof. A poorly constructed roof or inadequate insulation or improperly directing heat to the attic can result in significant heat transfer to the roof. The heat transfer results in enhanced melting of the snow and ice on the roof, while the ice that had been formed along the gutters will not melt as fast because it does not receive much heat from the attic. So this roof meltwater or melt off will accumulate behind the ice barrier located along the gutters, soffit or other non-heated areas of the roof. Then you have your ice dam that will force this accumulated meltwater to find openings in the roof to enter the structure.
Due to so many differences in temperature levels involved and the different structural elements and materials (such as brick chimney, asphalt shingle, wood, metal, etc.) we get different expansion and contraction rates in the roof material that leads into the creation of openings in the roof: joints between the chimney and the roof, connections between the roof and the exterior wall, etc.)
A better view that shows how this issue happens – in this case it is further exacerbated by the soffit venting which helps cool the area even faster.
Schematic showing the process of ice dam formation
A picture from this past winter’s inspections showing the water entering the soffit vents and forming icicles is shown below.
Note the icicles coming through the soffit vents. The ice dam is further exacerbated by the soffit venting which helps cool the area even faster.
How can you prevent ice dams?
As was explained above, ice dams occur after heavy snowfall when warm air in the attic causes the roof to warm and the snow to melt. Water running down the roof refreezes when it reaches the colder roof edge, forming a mound of ice. The ice traps meltwater, which can seep back up under shingles and drip through the roof into your house, causing wet and stained ceilings and walls, and peeling paint and rot. Based on what we said earlier, you should focus on increasing the ventilation of the attic, eliminating the warm-air bypasses (they are numerous!), increasing the attic insulation and clean the gutters prior to the winter time.
Clean the Gutters and Remove other Obstructions – Make sure that the gutters are free from leaves and other debris. You would be surprised what we find inside gutters every time we do these investigations. When the gutters drain freely, it reduces the potential for accumulated rainwater to freeze and cause ice damming; also, when the gutters are clean, the melted water has a nice route to drain away from the home.
Provide better insulation in the attic – Inspect the attic and check the depth of your attic insulation. Building codes require about 12 to 14 in. of fiberglass or cellulose insulation. Add more if you have less than 8 in. and have had ice dam problems in the past. It should be noted though, that the United States Department of energy recommends that ceilings, both cathedral and regular, have insulation levels of R49. That’s a 15″ thick layer of cellulose or a 27″ thick layer of fiberglass. Blown-in cellulose and fiberglass are usually better than hand-placed batt, because they fill more tightly around rafters, joists and other obstructions, leaving fewer gaps. When renovating rooms, consider removing and replacing older insulation in your ceilings. Some preventative renovation is easier than costly ice dam damage repair or replacement.
Ventilate Your Attic Properly and Adequately - Good insulation, air-tight ceilings, low humidity levels in your home and proper ventilation usually will keep a roof cold enough to prevent ice dams from forming. Start by making sure heat does not escape around chimneys, pipes, skylights, attic accesses and vents. Then address any ventilation issues your current roof might have. A well-ventilated attic continually replaces warmer air in the attic with cold outside air. Research suggests that maintaining an attic air temperature below freezing when the outside air temperature is in the low 20s can help reduce the occurrence of ice dams.
Reduce or eliminate all attic bypasses– Attic bypass leaks can cut the effectiveness of attic insulation by 30 to 70 percent. Based on our inspections, we have found that ALL homes plagued by ice dams have a significant number of bypasses. Some examples are shown below. Typical culprits include: furnace flue or furnace vents openings; spaces around masonry chimneys; recessed lights; electric conduit openings; and many-many others.
Attic bypass around vent pipe
Bypass around furnace vent
Remove accumulated snow from your roof – This is the least preferred method of preventing ice dams and should only be attempted in emergency situations, using an appropriate roof rake. Avoid using salt or chemical snow-melt products to melt ice on the roof. These can erode shingles and gutters and potentially void the roofing manufacturer's warranty. It should be noted though that partial removal of snow can cause ice dams to occur on other areas of the roof, away from eaves and gutters.
When comes to ice dams, an ounce of prevention could weight its weight in gold.
Attic Condensation, Ice dams and Mold
Attic condensation can cause a variety of issues in your home. These issues, if not addressed promptly and repaired properly, can be very detrimental to the structure of your house as well as the health of you and your family. Condensation during the winter months help create an environment conducive to the formation of Ice Dams, where ice and snow on the unheated edges of your roof do not melt as fast as the heated areas that cover your attic space. Once an ice dam has occurred, water tends to backup under roofing materials and infiltrate into attics and living spaces. These Ice Dam leaks account for a large percentage of roof and structural damage to homes every year. Roof leaks can also severely degrade the R value of your attic insulation as well. The United States Department of energy recommends that ceilings, both cathedral and regular, have insulation levels of R49. That’s a 15″ thick layer of cellulose or a 27″ thick layer of fiberglass. If these insulations get wet, they become compacted which degrades their insulation effectiveness. Another destructive as well as dangerous product of Attic Condensation is mold, specifically Black Mold. It is common knowledge that molds are the main cause of allergies. Most every chronic sinus infection (37 million Americans) can be linked to mold spores. Molds are now classified as one of the leading causes of allergies. Attics with condensation issues and bad ventilation are prime breeding grounds for molds to grow rapidly. And where molds flourish, sickness closely follows.
The major cause of attic condensation is due to moisture escaping from the living portion of your home and migrating up into the attic. The average household of four generates anywhere from two to four gallons of water vapor per day, from everyday activities such as cooking, laundry, showering and washing dishes. These activities should not cause an excessive amount of condensation in your attic, unless your living space is not properly venting these vapors out. There should be exhaust vents in your kitchen and bathroom to vent vapor out of your house. Sometimes builders when building houses will vent bathroom and dryer vents into attics, crawl spaces or over hangs, and not out onto the roof. This is a very bad corner cutting procedure common in the construction industry today. Penetrations in your ceilings and walls (such as ceiling fans, outlets, and attic doors) are great entry points for water vapor to enter your attic.
If you suspect that you have an condensation issue with your attic, there are several things that you can do to diagnose as well as help eliminate this issue, including:
· Look for wetness on the nails piercing through the wood deck.
· Check for condensation or moisture on rafters and wood decking.
· Look for water stains on the roof decking that normally indicate a leak. If you find a leak mark it with electrical tape so that you can show your roofer if you call for a repair.
· Look for mold on the structure of your attic. If you find mold, you can kill it with household bleach. Dead mold can still make you sick, so be sure and add a coating of kilz (easily found it at your local Hardware store) to the affected area to seal the area up.
· Check your attic for exhaust vents and make sure that they are properly vented through the roof.
· Check all penetrations in your ceilings such as light fixtures and make sure there are no excessive gaps between the fixtures and ceiling.
· Make certain all drywall is finished properly with no gaps or cracks for moisture to migrate through.
· Consider installing an insulated zip cover onto the entrance of your attic.
· Check for soffit vent and make sure that it isn’t blocked by insulation.
· Check for roof ventilation, such as power vents, louver vents or ridge vents. If you have ridge vents, you shouldn’t have any other roof venting systems, except soffit vents, which work hand in hand with ridge vent.
Roof Failures from this past winter’s Snow and Ice Loads
Public works garage roof buckled Feb. 8, 2014 apparently under accumulated weight of ice and snow.
This past winter we had a very significant increase in failures of the roofs. The insureds claimed that the weight of snow and ice caused the roof failure. Certainly the snow and ice accumulation on the roof likely contributed to failure of a truss. This is just one example of a structural collapse in the Northeast (especially in New England) following a series of severe snowstorms and freezing rain that have made accumulated snow denser and heavier, especially in southern New England.
Of the 200 distressed roofs Metropolitan has assessed in the past year, we found only a few buildings where the total weight of ice and snow was approximately equal to or slightly above design code requirements. Most collapses are related to details of design, structural deterioration or building modifications. Property owners should be cognizant of any structural changes and assess whether they have proper drainage to avoid refreezing of any melt off. If an owner builds a new roof, they should be sensitive to issues that can affect the total load on the roof during the snow season.
Both New Hampshire and Vermont, which have received mostly light powdery snow, have experienced only a handful of collapses, including many barns. However, in Massachusetts, which received wetter, heavier snow, 172 roof failures were reported to state emergency officials from Feb. 1 to Feb. 9, including 98 commercial or industrial buildings and 10 institutions, including schools and churches.
Most collapses in New England have involved structures with long-spans, including web-joist structures with flat roofs; modified designs or older abandoned buildings. Existing building codes are adequate if designers allow for a factor of safety. But we recommend designers make proper allowances for snow accumulation such as when designing roof structures near parapet walls, especially those that are four feet or higher. We’ve had many roof collapses this year involving accumulation of snow on roofs when snow builds against the parapet. You have to design for these kinds of snow loads.
Multi-level roofs with steps instead of roof flashing can also be problematic with snow accumulation on a first-story portion, for example, piling up against the second story. It’s best to avoid stepped designs unless you design for them. While an average of 40 psf may be adequate for designing most roofs, designers should allow 60 psf to 80 psf for the parapet wall. Mountainous regions may require twice as much strength for the roof structure.
Solidification of Several Layers of Meltwater
While state building codes address snow drifts with requirements for the shape and slope of a roof, this year’s record snowfalls and ice accumulation with little thawing has led to a greater number of collapses. Even two feet of freshly fallen snow or more totaling 16 to 20 lb/sf was not a danger to buildings. However, invisible loads caused by accumulation of ice have been a serious problem since ice weighs 7.5 to 8 times more per cu ft. than snow. In many cases, even before reaching two-foot snow loads, we were in excess of 30 pounds because of the ice.
This occurs when two layers of ice form in the snow from solidification of melt off when the temperature drops at night. One layer of ice can form during a cold but sunny day in the upper section of snow from melt off that penetrates into the snow and the other forms at the lowest level while the building is heated. This invisible load has been overlooked by many property managers, since this has not been a typical problem in prior winters with time for snow to melt between storms.
We recommend developing an educational program to educate building owners about unusual situations involving snow, wind and ice.
Metropolitan Engineering, Consulting & Forensics (MECF)
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