More insulation alone won't prevent ice dams.
We were recently called to a home for leaking from ice dams. The winter of 2013/14 saw unusually cold temps with slightly above average snowfall. This led to a lot of ice dams on homes and businesses. A little background on this home. It was built in the 1980's. It was on its second roof (the original had been removed at the time of re-roofing). The front side (facing north) was difficult to ventilate because of the soffit construction and knee walls inside. The back side (facing south) had typical construction with a soffit that could ventilate into the attic space. There was a ridge vent in place that ran continuously. The attic had just had new blown in fiberglass insulation added. There was a minimal amount of proper vents (the styrofoam baffles that allow air to flow from the soffit to the attic. There was a large drop down attic access hatch that was poorly sealed. The picture to the right shows the new insulation in the attic. It is taken from the attic access hatch.
Why didn't the additional insulation prevent the ice dams?
The intended purpose of the insulation in the attic is to prevent heat loss from conduction. Insulation offers little resistance to the movement of air. So, can or recessed lights, bath exhaust fans, and other penetrations in the attic allow air to move through them and the insulation does not stop that movement of air. The attic access also played a role in the problem. When the homeowner had pulled down the attic access stairs, light from the attic could be seen all around the base of the cover supposedly built to prevent the air from escaping. The access doors are notorious for air and heat loss. To be fair, the insulation contractor did offer to install a zippered cover and the customer declined the added cost. But that contractor did not explain how this was contributing to ice dams and higher heating and cooling costs. (Don't know the effectiveness of these add on covers - the best are constructed out of rigid insulation and physically sealed with gaskets and a means to compress the cover to the gasket). So, the customer got extra insulation and did nothing to address the real problem. That money could have been spent on sealing of the attic bypasses. This is something that is little understood by most homeowners. Because of that, it is not difficult for the 'blow and go' style of insulation contractor to influence homeowners to bring their home's insulation up to today's codes (and conveniently do not emphasize air sealing). 'Blow and go' insulators are also interested in selling product - air sealing is often done with some caulk and canned spray foam.
Wouldn't venting have solved this problem?
Venting is designed to move air. Difference in temperature is required for that to happen. Many imagine that if you add venting at the soffit and balance that with venting at the ridge that there is this magical breeze that baths your attic in fresh, cool, ice dam preventing air. The reality is often different. We are not saying that venting is not required or important (although we have written previously in our blog on that subject). What we are saying is that without proper air sealing techniques, roof venting will not keep up. Sure you could create a literal breeze up there with a powered ventilator. That may have solved the condensation issue (debatable), but it would have also dramatically driven up heating and cooling costs. Why? The make up air to replace what was being drawn out would have come from the inside conditioned air.
If insulation isn't the answer, what would have solved this ice dam problem?
The customer should have started with air sealing. We recommended a competent home performance contractor to completely evaluate the homes problems. Homeowners rarely start with this, but it is essential to truly understand what is needed to improve your homes performance. This will result in lower heating and cooling bills and prevent attic condensation and dripping. Because these services have a cost, homeowners often think that it can be sidestepped. After what we have seen this winter, please consider a home performance evaluation. Contact us - we can make a recommendation.
Yes, we do sell and install heat cable systems that are quite effective at solving ice dam problems. We were called out to solve this one. We didn't sell them on what we do. The customer remarked "Why are you being so nice to us?" Their experience up to this point had been contractors selling them what they did rather than solving their problem. That is not what we are about. If our system is not what is needed, we won't talk you into it. If another contractor would be better suited to solve your problem, we will tell you that. Hopefully, this good will comes back around. But, if not, we have still done the right thing.