Unintended consequences – Renos that make ice dams.

That is a curious result that happens.  Someone finally invests some serious money in upgrading their kitchen (or bathroom), installing beautiful cabinetry, gorgeous ceiling lights, and finally get the attractive and bright kitchen (or comfortable bathroom) that they always wanted.  The following winter, an ice dam forms.  The following year, the ice dam gets worse and the ceiling starts to leak after every thaw.  What’s going on?

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Spray Foam – good or bad?

Closed cell-spray foam used as insulation, has been on the market since about 1979, and has gone through a number of evolutionary steps.  The product is a solid plastic, formed by the chemical reaction of two primary components:  an “A” side which is isocyanate, and a “B” side which is usually a mixture of oils, stabilizers, fire retardants, blowing agents, and colouring agents.  The reaction is exothermic (ie, generates a lot of heat), and the materials form a solid within seconds. The blowing agents are the compounds which produce the low-conductivity gas that forms the bubbles in the foam, and thereby form the primary insulation.

When applied to a minimum thickness of 50mm (slightly under 2 inches), the material acts as  insulation, vapour barrier, and an air barrier.  Newly-installed foam has R-values of R-6 to R-7.5 per inch, but this diminishes to about R-5 per inch over time as the insulating gas dissipates.  Compared to other insulation products like fiberglass bat or mineral wool bats, the product has more insulating value per inch, and resists the loss of heating value that sometimes occurs with loose insulation due to air convection with extreme temperature differences.

The ability to prevent air and vapor movement is generally a good thing, except in situations where moisture can enter a wood structure, and then cannot get out.  Therefore the short answer to the question in the header is “spray foam is good when PROPERLY installed, and BAD when installed in inappropriate places or in an incorrect manner.  There are also issues of the impact on the environment, and potential impact on the health of the people living in the homes where the product is used.  The rest of the post touches on some aspects that inform whether the installation is good or not.

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Condensation plays the same role in “modern” roofing practice as “bad spirits” did in medieval times.  If something went wrong, you blamed the bad spirits.  Nowadays, if a roofing system is not working, it’s due to “condensation”.  So let’s get into it and understand what condensation is, when can it appear in a roof system, and what corrective action you can and should take if condensation is really the cause of an apparent leakage.

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Ice Dams – Cures, fixes and band-aids.

You have  a nice ice dam, or maybe even several.  The overflow is producing big, picturesque icicles on the outside, and leakage on the inside.  If you’re unlucky, the ceiling is showing signs of falling in under the water infiltration.  What to do?

There are actions you can take now, and then there are various methods of preventing the issue, or finding acceptable ways to live with it.  Keep in mind that the nature of the ice dam changes depending on the slope, the roof-line complexity, the roof covering material, and the prevailing climate conditions.  Therefore, the discussion below may, or may not address your specific situation.

The first order of business is to assess whether the ice dam is causing (or is about to cause) damage.  The damage that can get caused includes leakage into the house, overloading the gutters, and forming potentially dangerous icicles.  Leakage can range from a slow leak, to a massive entry of water.

A.    Immediate Action

Obviously, the first thing to do is to get rid of the water accumulating behind the dam, and then remove the dam because more water will accumulated after if allowed.  How you go about this depends on the type of roof cover you have.  If it’s asphalt shingles, you have to be careful not to damage the shingles when you remove the ice.

1.     Asphalt roofs

Asphalt roofs are designed to shed water.  They are not waterproof.  To render at least the edges of the roof able to withstand water infiltration, the common solution is to use ice-and-water shield membrane along the eaves to provide a waterproof layer.  When roofs leak even with this layer in place, it is usually because not enough of the right membrane was used, it was applied incorrectly, and the installers did not verify the seal of the membrane.

Safety is the first concern on any de-icing operation.  If your roof is walkable and only one story high (bungalow, ranch-style), then it is easy to get up onto the roof.  If it is steep or high, then this is better done by people who have the equipment to do this safely.

Having made sure that you (or your hired help) are safe and properly secured against a fall, it’s probably best to first remove the snow above the ice dam, as this is the “fuel” which will continue to add to the ice dam if allowed.  In doing so, remove the snow down to about 1-2 inches of the roof.  Removing more of the snow, down to the shingles themselves risks damaging the shingles.  We use plastic shovels for this purpose to prevent damaging the roof covering in case the shovel does make contact with the roof.

If there is substantial amount of water behind the ice dam, use a plastic pail or bailer to scoop it out, to reduce the amount of water pressure that is being put on the roof system.

How you get rid of the ice depends on how thick it is.  In the worse case we’ve seen, the ice dam was over 1 ft. thick and the water was about 8” deep.  On that one, we bailed the water, then we used hatchets until we were within several inches of the roof covering.  The last few inches of ice we broke up using hammer blows until we got to the roof covering.

If the situation is not so urgent, you can put de-icing solution on the lower part of the ice dam so that the base of the dam is weakened.  (NEVER put the salt or de-icing solution above the ice dam, as all that will do is make the water that’s accumulating behind the dam even more of a mess, now adding salt and other chemicals to the leakage.)  Once the ice is weakened, then hatchets (used down to several inches of the roof) and hammer blows can break up the ice.

We have seen people try to use hot water, or heating cables, or even propane torches to try and melt the ice dams.  Heat can work, as long as it is applied at the base of the ice dam, and not above the ice dam.  Keep in mind, that if you haven’t removed the water first, and you breach the ice dam, then you will get a large gush of icy water rushing out of its new opening.  If you happened to be doing this standing on a ladder and working on the ice in front of you…  you’re probably now going inside for a change of clothing.

A further issue is what to do with the gutters that are filled with ice, and may have contributed to the formation of the ice dam.  This needs to be assessed on an individual basis, depending on how strong the gutters are, how solidly they are attached, and what kind of material they are made from.

2.     Tar and gravel roof

Tar and gravel roofs generally have a slope of 2:12 or less, and are designed to either allow the water to run off over an eave, or to a drain (or several) located somewhere in the interior space of the roof.  The roof surface is designed to be completely waterproof, and generally there is no need to break up the ice dam, unless the central drainage hole is plugged up and the water cannot drain.  If you DO have this situation, then it’s best to call in professional roofers, who will first remove as much water as possible, and then will try to clear the blockage.  If not done properly, there is the danger that the seals around the drain will be broken, or that the roof covering will be damaged.  In either case, you will have turned a “potential” problem into an actual emergency.

3.     Membrane roof.

Membrane roofs are an alternative to tar and gravel roof, and usually are found on slopes of 3:12 or less.  They are quite delicate, and are not designed to put up with any traffic on the surface.  Membrane roofs should be de-iced only by professional roofing companies that install this kind of product.  However, as with tar and gravel roofs, it is usually not necessary to get rid of the ice dams, as the covering (if properly installed) is designed to be water-tight.

4.     Other kinds of roofs

There are many kinds of materials used for roof covering, such as metal, aluminum, zinc, cedar shakes, clay tile, concrete tile, fiberglass panels, slate, and so on.  The ice-dam removal strategy changes with the type of roof covering, and with the underlying structure of the roof system.  It is usually best to refer this issue to companies that specialize in installing the type of roof covering you have, as they will know the potential dangers and weaknesses of this type of roof covering.

B.    Short-term preventive

Of course, the better strategy is to prevent a problem.  Assuming you have not fixed the underlying issues of insulation and ventilation (more on that in a later section), you can at least approach the problem with the goal of minimizing the problems that an ice dam can cause.

1.     Remove the snow

The simplest strategy is to remove the snow from the roof before it can melt and create an ice dam.  If the roof is not too high and not too steep, it is possible to do this using snow rakes (plastic scoops at the end of a very long aluminum pole), or getting onto the roof and using plastic snow shovels.  Of course, you need to do it immediately after each snow fall, because the melting/freezing starts as soon as there is some snow on the roof.

2.     Install de-icing cables

If the roof area is too dangerous to go onto, or too high, then removing the snow becomes impossible, and the second strategy can be used, which is to use de-icing cables or heating tape to melt channels into the forming ice dam.  This has to be done ahead of time, before the snow season starts.  This method CAN work, IF done properly.  However, most installations of de-icing cables do not accomplish their job and end up contributing to the problem.  So what are some of the common failures?

  • The gutters are not included in the de-icing strategy.  The meltwater then runs into the gutter, freezes, and backs up.  The cables need to be placed along the gutter, and down the downspouts.
  • The cables are placed horizontally and not vertically.  The point of melting channels in the snow is to allow the water to use these channels to run off the roof.  Therefore, they should be arranged more vertically than horizontally.  As well the cables should go into the gutter, to intersect the cables running along the gutter base – this way the water has an open channel to escape.
  • The cables are place too low, and the ice dam forms above the cables.
  • The cables are placed too far apart, and the space in between forms many small ice dams.
  • The cables are not secured properly, and snow movement causes them to come off the roof.

When using de-icing cables, you need to arrange them to provide for a water flow path from above the point where the ice dam can form, all the way down to the gutter, and down the downspout.  De-icing cables work, but they are an expensive band-aid.

C.     Fixing the causes

The best way to deal with ice dams is to make sure they don’t form in the first place.  If you’ve read the article “What’s an ‘Ice Dam’?”, you’ll know that the primary issue is that there is insufficient insulation which therefore allows heat loss to the attic, and with insufficient ventilation, the warm attic then melts the snow that accumulates on the roof.  The meltwater runs down the slope to the eaves, and once it is over the roof above the soffits, there is no more warmth to keep the water liquid, and it freezes.  To fix the problem at its source, you need to address both the insulation and the ventilation issues.

1.     Insulation

How much insulation is “good enough”?  The building code minimum depends on many factors, but the general recommendation is to have attic insulation between R40 and R60.  In our own work, we have observed that roofs with real insulation value of R30 or less almost always have serious ice damming issues.  Roofs with real insulation value of R40 or more almost never have ice dams.

Notice I wrote “real” insulation value.  The insulating value of various materials depends primarily on how much air they can hold without movement.  Still air is an excellent insulator.  Moving air, however, is not.  Therefore, to get the maximum value of insulation from any insulating material, it must be installed in a way that prevents movement of air through it.  It is not uncommon to find lots of insulation in an attic, but arranged in such a way that the effective value is less than half of what it should have been.

The insulation value also depends on the insulation being dry.  Wet insulation has effectively no insulating value.  Therefore, if one has had leaks in an attic due to ice dams, and those leaks soaked the insulation underneath, then the attic has even less ability to prevent heat transfer – enabling more heat to escape and melt more snow – a vicious cycle.

One very common source of heat in the attic, is the use of poorly installed and insulated pot lights or ceiling lights.  The boxes containing these lights are normally placed above the ceiling and displace a portion of the insulation that would have normally been there.  These lights generate a lot of heat, which then easily escapes into the attic (due to minimal insulation) where it is then transferred to the roof.

Different materials have differing insulating values.  To get R40+ insulation using fiberglass bats, would take about 13 inches if they were well installed with no air gaps between them, and no possibility of air movement through them.  If, the same bats were poorly installed, you’d need at least 26 inches to get R40.  The same R40 requirement can be achieved by 6” of polyurethane closed-cell foam.  Therefore in some areas of the attic where space is limited, it is worth thinking of mixing different types of insulation to achieve the goal of having at least R40 in the attic.

2.     Ventilation

Once the heat enters the attic, whether due to poor insulation or other cause, it will warm the air in the attic, which then rises to the roof decking, and warms the roof.  The effects of poor insulation can, to a certain extent, be reduced by good ventilation – that is, the movement of air from the soffits along the eaves to the outlets located near the top of the roof at the ridge.  In practice, we have observed that good ventilation reduces the effect of poor insulation, but does not completely prevent the heat transfer.  In addition, due to the complexities of construction of many homes, the ventilation air flow is not very linear and consistent, with many spaces that have no effective ventilation.

For passive ventilation to exist, it needs to enter the attic at a low point (typically the soffits), move through an air channel (minimum 2” according to the building code) into the attic, from where it exits through a ventilation outlet located hopefully near the top of the structure.

Some of the reasons why ventilation is NOT working include:

  • Blocked soffits (vented soffits installed over solid wood, vent holes in soffits covered by paint, insulation blown into the soffit cavities, etc.)
  • Insufficient air channel (insulation is too close to the roof to allow easy air entry from the soffit cavity into the attic).
  • Poor location of both intake and outflow vents, creating ventilation short-circuits,
  • Poor balancing of intake and outflow – too much or too little outlet or intake.
  • Internal attic obstructions that prevent the movement of air.

It is not enough to place a number of outlet vents and consider the ventilation issue to be “solved”.  There is a science behind this, and the amount of ventilation required can be calculated quite easily, if you know what you are doing.

D.    Preventing damage

If you cannot fix the problem at its source (namely by improving the insulation and the ventilation), then there are other things that you can do so that the ice dams don’t cause serious damage.

1.     Ice-and-water shield membrane

The most common solution is to install a width of ice-and-water shield membrane along the eaves, the valleys, the endwalls, and all other places where it can be expected that water from ice-dams could penetrate the roof covering.  For this protection to be effective, the right product needs to be installed in the right way, at the right time, and at the right place.  In another post (Dec. 8, 2013), I discussed some of these issues.

Ice-and-water shield membrane needs to be installed at the time the roof is being constructed, or at the time of re-roof.  It needs to be installed high enough up the slope to ensure that the worst ice dam will not breach the defenses.  It needs to be applied directly to wood, so that it can bond with the wood.  It needs to be properly overlapped to ensure proper sealing of membrane-membrane joints, and be properly primed if the membrane is contacting surfaces like metal or brick.  There are a few more “needs to” or “should” instructions, but it is clear that if not properly installed, the ‘miracle’ stuff won’t work when you really need it to work.  And yet,when we are asked to diagnose a roof failure this is where we find a large number of short-cuts taken .

2.     Ice belts

Ice belts are horizontal bands of smooth metal that are installed along the eaves (usually over the soffit cavities) to allow snow at the roof edges to slide off, and thereby removing one factor that can help the formation of the ice dam.  They work, kinda.  The real problem is that often times the belts are not high enough to ensure that no snow sticks to the roof and contributes to the ice dam formation, and under certain climatic conditions, the ice belt doesn’t prevent the snow from sticking to the roof.  However, being made of continuous metal with few joints, there is much less chance for water to enter through one of the joints.

Using an ice belt is a good way to reduce the chance of ice dams, but it doesn’t prevent them.  Again, an effective ice belt requires proper installation, proper waterproofing, and proper protection of the roof deck below the metal.

3.     Smooth metal roofs

Expanding on the idea of the ice belts, you can cover the entire roof with a smooth metal (in the form of panels or shingles), which will allow the snow to slide off the roof.  This is one reason why historically most roofs in the heavy snow regions usually have some kind of metal covering.  So why not install metal roofs everywhere?  There are several reasons why:

  • Metal roofs typically cost anywhere from double to as much as four times more than the common asphalt roofs.
  • Smooth metal roofs do shed the snow, but not always when you want the snow gone.  Under some circumstances the snow may stick to the roof, accumulate, and form a thick ice crust at the base of the snow, before finally conditions change and the entire mass avalanches off the roof slope.  Depending on where it ends up landing, you could have some serious damage or injury.  Therefore, smooth metal roofs need to be designed to allow snow descent in the right areas, and prevented from doing so in areas where injury or damage can be anticipated.  Not all contractors worry about these kind of niceties.
  • Smooth metals roofs have their own esthetic appearance.  Some love it, some don’t.
  • Metal roofs usually require a different level of expertise to install properly, compared to asphalt roofs.  These skills are not common, and are usually specific to the type and brand of material being installed.  Therefore finding good installers is somewhat more challenging.
  • Not every metal product is appropriate for every situation.  It requires some expertise to ensure that the strong points of a particular product are fully utilized for a specific installation, and that the corresponding weaknesses (and all products have weaknesses of one kind or another) have been adequately covered.

Metal roofs are an excellent roof covering, but they don’t make the ice dam problem go away.  There are many fewer opportunities for ice dams to form on a metal roof, but they still can happen.  And when they do happen, the other protective measures need to be in place.

E.     What NOT to do!

Having seen many attempts at removing ice dams, there are a few words of wisdom that come from such observations:

  • DO NOT put your de-icing solution on the snow or ice above the ice dam.  This will just enlarge the pool of water , and cause the water entering to be carrying the salt or chemical in the de-icing solution.  This can be very difficult to clean up after the ice dam is long gone.
  • DO NOT get on a ladder and start chopping away.  If the ice dam breaches, you will be on the receiving end of a lot of water, ice chunks and other stuff.
  • DO NOT try to do the de-icing by yourself.  This is pretty energetic work, and if you’re not used to this level of exertion, bad things can happen to your heart.  If something happens, who will find you, and when?  In addition, a ladder in the snow is not the most stable platform.  If you want to do the de-icing yourself, at least have someone at the bottom making sure that the ladder doesn’t move.
  • DO NOT try to work on the roof without using proper fall protection.  The falls aren’t the problem, it’s the rapid stop at the end.  Or, if you just tied a rope around your waist, you’ve created a situation where your spinal cord can be broken if you fall.  An ice dam is not worth becoming a paraplegic over.
  • DO NOT try to remove all the ice dam – some of the ice is between the shingles, and removing that little final coat of ice will also remove some of the shingles that are encased in that ice.

There are probably quite a few more that could be added to this list, but the point is – if you’re going to do either de-icing, or snow removal, do so in an intelligent, well-thought-out way, using the safe methods and the right tools.  Because your life may depend on it.   Or, hire people who know what they are doing.  Like us.

(c) 2013 Paul Grizenko

F.     Links:

CMHC article on insulating your home:  http://www.cmhc-schl.gc.ca/en/co/grho/grho_010.cfm

Jon Eakes article on insulation levels: http://joneakes.com/jons-fixit-database/793-WHAT-ARE-THE-RECOMMENDED-INSULATION-LEVELS

Definition of R-value:  http://en.wikipedia.org/wiki/R-value_(insulation)

Natural Resources Canada publication: 2012 Energy Start for New Homes Standard:  http://publications.gc.ca/collections/collection_2012/rncan-nrcan/M144-237-2012-eng.pdf

G.    Request for feedback

If you have found this information useful, let me know via a comment.  If you found the information inaccurate or misleading or simply not correct, please contact me to let me know why you think so.  If you have experienced an ice dam and had it resolved, how did you do it?  I’d love to read your comments.

When is a roof leak not a leak?


We were asked to investigate this leak.  It turned out to be due to condensation.  The pot lights were added much after the construction of the house, and the installer did not use an air-tight insulated box for each light.  As a consequence, warm and humid interior air entered through the pot-light enclosure  into the ceiling cavity, and with minimal insulation left (because it was mostly removed to make room for the pot lights), there was a LOT of condensation.

The do-it-yourself remodeller also made similar mistakes elsewhere in the house, piercing the vapour barriers, and not allowing any air circulation above the insulation.  As a result, the interior air infiltrated the cold spaces and almost “rained” condensation into the interior.

In the section https://prsconsulting.wordpress.com/links-and-useful-information/, there is a link to a very good article in Fine Home-building Magazine which discusses ventilation issues and has some nice diagrams showing show how the ventilation should work.

We also have had reported leaks in bathroom fans, which turned out to be condensation, and other “leaks” which turned out to be condensation from poorly insulated air ducts conducting cold air (in summer, obviously).  So when you spot a “leak”, it may not be what you think it is.  Time to do a little sleuthing.

(c) 2013 Paul Grizenko