Renovation & Design
Renovation & Design
Heating cables OK for eavestroughs, rarely ideal
Question: I’ve read your previous article on why you shouldn’t use heating cable on roofs. Wouldn’t it be better installing the heat cable only in the eavestrough, and then running it via the downspout, not putting any of the cable on the shingles?
We had rain, then freezing rain and then temperatures dropped well below freezing, all in a day and a half. That crazy weather didn’t allow much melted snow to drain out of the eavestroughs. After that, these big icicles formed, hanging down from the troughs.
We do have lots of insulation in the attic, so I don’t think that is a cause.
I would appreciate your viewpoint on this matter, as I agree with you about putting the heat cable on the shingles being a bad idea.
— Ralph Nafziger
Answer: Heat-trace cables are among those items I consider a Band-Aid or a last-ditch solution for more complex house issues. While they may work for your suggestion in the eavestroughs, other maintenance efforts may negate the need for these questionable electrical devices.
Home centres and other retailers are frequently full of items that appear to be simple solutions for often difficult to understand home issues. Many of these are inexpensive to use and install, but others are mainly unnecessary, or downright harmful.
Heat-trace cables are electrical devices that provide a moderate amount of heat to help melt ice and snow during cold weather. Most have an integrated thermostat, which only triggers the device when temperatures are below freezing.
I have little idea what the monthly cost in electricity is to run these gizmos, but it is not negligible.
In some older homes with very poorly designed roof systems, electric heating cables may be the only way to prevent the formation of huge, dangerous icicles from hanging down from the eaves, particularly below steep valleys. In those situations, periodic use on the roofing in the bottom of the valleys, in the transition seasons, may be acceptable.
In other buildings, mainly 1½- and 2½-storey homes, they are often used questionably, where improvements to air sealing, insulation and ventilation are the proper methods of prevention.
Also, periodic removal of heavy snow accumulations on the roof will minimize the need for electrical snow melting.
The reason heat cables should not be used on typical asphalt shingles is that the heat will damage the roofing. Heating shingles from the top in the winter will create a large temperature differential between the top and bottom of the roofing. This will cause the shingles to curl and dislodge the protective coloured granules embedded in the top layer. This will reduce the life expectancy by up to half, greatly increasing the chances of leakage. Roofs that leak will allow damage to the eaves, roof sheathing, framing and, potentially, the interior of the home, if they are large enough.
For this reason, anything that allows the top of the roofing, or the underside, to be warm during our bitterly cold winters can cause major moisture intrusion and damage.
Your specific question appears to address a common issue that may occur in the shoulder seasons, late fall and early spring. A freeze/thaw cycle is normally only seen in our area during these times, or once or twice during a warming trend in the middle of winter. So, those may be the only periods when it would be advantageous to use a heating cable in the metal eavestroughs and downspouts.
There are few drawbacks to the targeted use of this system, as long as it is limited. The main problem, other than the costs associated with installation and operation, is possible blockage of the roof drainage system. It can be tough enough to prevent blockage of eavestroughs and downspouts by leaves, twigs and other debris without further jamming an electric cable inside the small spaces. Tree litter can more easily get hung up on the plastic-coated wiring than the relatively smooth metal surfaces of the gutters and pipes.
For this reason, I would suggest removal and storage of any heat-trace wiring components after the spring thaw to prevent blockage during summer rain.
While I agree limited use of heating cables may prevent excessive ice formation during unusual shoulder-season weather, they may still not be worth the effort. As long as the freeze/thaw events are not compounded, these issues may solve themselves as soon as there are a few sunny days. Even in below-freezing temperatures, the warmth from the sun will often be enough to melt ice and allow some drainage before the dead of winter arrives. Conversely, when the spring melt begins, it corresponds with longer days and stronger sunlight, which will eventually melt the troublesome ice naturally.
Because eavestroughs are mostly made from metal, they are good conductors of heat and will help accelerate the melting when in direct sunlight. This is less of a benefit in shady areas, so avoiding installation of downspouts on the north side of the home or behind trees and bushes is also a good idea.
Using a device that requires costly electrical current to melt ice inside eavestroughs and downspouts is a temporary solution, and one that should be used sparingly.
Clearing snow from roofs before spring, and other maintenance items noted, may be better choices to prevent troublesome ice from forming at your eaves.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
Renovation & Design
Sprayed-on poly foam OK for stone foundation insulation
Question: I have been trying to do some research on the risks associated with stone foundations that have had spray foam applied on the interior in the crawl space.
We have had an inspection done on a house that had this applied and the inspector raised this issue.
Thanks.
— David Lee
Answer: When relatively new materials or procedures are used in homes, it may be difficult to fully determine their effectiveness or problems for many years.
Spraying polyurethane foam insulation on the inside of a stone foundation should not create any serious issues, but any problems related to moisture may not show up for several years, making speculation about potential pitfalls largely theoretical at this point in time.
Before answering your question, my opinion on insulating most stone or rubble foundations is they should be left uninsulated and uncovered, if possible.
I know this is not practical for several reasons, mainly energy efficiency, but basements built with this type of foundation were not designed as living space — the basement was simply a cellar to store the mechanical systems, and other items, for the home.
It didn’t matter if there was a little seepage through the foundation walls, as there was little to become damaged before this water ran harmlessly to the floor drain.
So, leaving the walls uncovered on the interior allows for periodic inspection and repointing of mortar in between the stones.
This is important to prevent excessive leakage, and to prevent movement in the stones, which can lead to serious structural issues.
Regardless, if you are going to insulate the inside of this type of foundation, sprayed-on high-density polyurethane foam is the best choice.
With many older houses, various dilemmas arose when we started adding large quantities of thermal insulation.
Insulating attics and foundation walls created a good environment for condensation and moisture to develop.
This occurs because most traditional insulating materials do not stop air movement, they only slow it down and trap air to improve their performance.
Because of this, moisture dissolved in the air will cool, and often condense when it hits the cold foundation wall surface, or cold attic space.
Because of this property, moisture damage and mould growth are major concerns.
To counteract this issue, the use of air/vapour retarders has become necessary in conjunction with the insulation.
The most common type is a layer of polyethylene sheathing, often stapled to the framing around the insulation.
While fairly effective in preventing air leakage into the insulation, this plastic can also trap water vapour, which may arise from condensation of air that does get past the barrier.
It is critical to seal this poly around the perimeter, at each framing member, and around any protrusions, to prevent excessive air leakage.
Regardless, it is still nearly impossible to prevent, so problems with using traditional fibreglass batts for foundation walls are common.
What makes it even worse with a stone foundation is the added possibility of wet insulation from seepage.
The reason I have described the traditional basement insulation method is to make the point that even though there may be some issues with installing sprayed-on foam to the inside of a stone foundation, they are much less possible than problems with more traditional batt and poly methods.
The two main concerns often raised in discussions are moisture-related issues and lowering the temperature of the foundation.
Both are somewhat theoretical, as they may not be visible once the entire inside surface of the foundation is covered with spray foam.
Moisture concerns are often related to collection of moisture behind the foam, which may lead to hidden mould growth.
The theory is that any seepage or water vapour that migrates from outside to inside will provide an ideal environment for mould growth.
Since there is dirt and debris on the surface of the stone, and also materials in the mortar which can provide a food source, two of the three major factors for mould are present.
The final component, heat, may not be an issue in the winter, but could certainly be a factor in the warmer months.
While this may be a legitimate concern for many older stone foundations, my opinion again is that it is much less of a concern than with batt and poly applications.
The foam insulation is moisture-resistant, so it may even help prevent some moisture migration due to this property.
Regardless, most mould issues with foundations occur from condensation of warm house air leaking into the insulated wall cavity, not from outside seepage.
Having insulation on the inside that has an excellent, integral air/vapour barrier, like spray foam, will certainly prevent this from occurring.
Also, spray foam conforms beautifully to all surfaces, even uneven stone and mortar walls, so air gaps and voids common with batts and wood studs are virtually non-existent.
Less gaps for air to leak into means less places for mould to grow.
The last concern is that stone foundations were designed to "breathe" on the inside and allow moisture trapped in the mortar to evaporate into the basement.
The concern is that insulating the interior surface tightly, by spraying foam, will prevent warm house air from contacting the stone, allowing it to freeze in the winter.
This could cause the damp mortar to expand and become damaged, without being visible.
While this may occur, it could be years or decades before this theoretical problem occurs and would still be possible with any other type of insulation installed on the inside.
There may be much speculation on this subject available, even by knowledgeable inspectors and building scientists, but only time will show us if they are true, or not.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
