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?

This effect is the result of unintended consequences, and usually, of the renovation contractor not thinking through the entire reno from a systems point-of-view.

The renovation

These problems tend to arise in kitchens that are located below a relatively low-slope roof.  When the renovation is done, it is very common for people to want better light over their working areas, which are usually found as counter-tops along the perimeter of the outside wall.  The contractor will install pot lights into the ceiling, located so that the working areas are well illuminated.  So far, so good.

The result

The ice dams that form in areas where they did not form before, telegraph that the behaviour of the roof has changed, and that more heat is rising to melt the snow along the roof in winter.  How is that heat getting there?  There are a number of possible reasons, including the ones listed below (not in any particular order):

  • the renovation has obstructed the intake air along the soffit, the air channel, or the air outlet,
  • the insulation has been removed, or reduced, or displaced in a way that no longer allows it to work as required,
  • the introduction of the pot lights may have broken the vapour barrier seal, and is allowing new entry of interior air into the cold space above the ceiling,
  • the new pot lights may be generating a lot of heat that was not anticipated in the original design of the roof.

There may be additional factors that influence the way the roof now works, but the items above are the ones we have found to be most common.

The “roof” failure

Since the roof is not being worked on, it is common to not do anything special to the roof at the time of the renovation.  Under normal circumstances, the roofs in our climate will usually have the roof decking covered by a combination of underlayment (usually tar paper), and waterproofing membrane (along the eave).  The practice is to have one width of membrane along the roof edge.  This is usually sufficient if the insulation and ventilation meet the code minimums, and if there are no special features which require additional measures.

When the situation under the roof changes, then the behaviour of the snow on the roof also changes, and increased heat usually means increased melting, which then ends up freezing along the eaves, and pushes the ice dam water level up the roof to the places not protected by waterproofing membrane.

The solution(s)

The cheapest short-term solution is to reroof the roof over the kitchen, taking into account the new behaviour. This means installing waterproofing membrane over the entire surface where water can go, given the presence of a larger ice dam.  In addition, the roofer will have to install additional waterproofing details (flashings, etc.) anticipating the new behaviour.

This solution will have the benefit of keeping the water to the outside of the roof system, and should work for the majority of climate conditions.  However, this approach depends on the weather conditions cooperating, and on the quality of workmanship with respect to the waterproofing.  Under extreme circumstances, there may be still enough water under pressure to still penetrate the protection installed.  In addition such a solution does NOT deal with other unanticipated effects such as increased possibility of condensation on the underside of the roof, contributing over time to possible rot, mold, and providing tasty food for carpenter ants.

A much better, but more expensive solution, would be to rework the attic space above the renovation to eliminate the new sources of heat, and to ensure that the cold space above the kitchen ceiling stays bone-dry.  Although every situation is different, the following steps are some of the ones that could be included in the scope of work:

  • ensure that the vapour barrier layer above the ceiling is fully functional and working
  • ensure that there is no interior air leakage from the living space into the cold space
  • reduce the amount of heat produced by the pot lights by replacing halogen bulbs with LED bulbs,
  • cover any pot light fixtures that are not air-sealed with proper covers that allow full air-sealing,
  • remove any insulation that is compromised by prior water leakage, and replace it with the right type and amount of insulation.  The “type” and “amount” will need to be figured out given the actual space available, and amount of heat expected.
  • ensure that the ventilation is functional and adequate to remove any residual heat that gets past the newly installed insulation.
  • repair the decking damaged by water infiltration, and if necessary, replace by new materials that are more resistant to water damage.
  • install appropriate amount of waterproofing on the new or repaired decking to ensure that no water entry from ice dams is possible.
  • verify that the waterproofing extends up sidewalls (if they are present) sufficient to prevent water entry,
  • Install the appropriate flashings and roof covering that will reduce the amount of snow accumulation.

As can be seen from the above, there is a lot of thought required to ensure that the renovation delivers the expected performance, especially in the areas where the renovation contractor (and the homeowner) may not be focusing on.


When doing a renovation which is below a roof, make sure that the roof system is adjusted appropriately to account for the change in the way the heat (and moisture) can reach it.

If you are a homeowner, and you are getting ice-damming whereas before this rarely happened, it is worth looking carefully at what changed.  When you need to diagnose the issue, give us a call to set up an inspection and a consultation.



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