Oct 13, 2017: The Snow Shows Where the Heat Goes

A fresh dusting of snow shows where heat is escaping through the roof of this house in Missoula

A fresh dusting of snow shows where heat is escaping through the roof of this house in Missoula.

Greetings (for the last time on this trip) from Missoula, Montana where we woke up to find a fresh dusting of snow on the ground this morning. This will be just the first of many snow falls over the coming long, cold winter. There was one year while I lived here, we had the first snow in October and I didn’t see the grass in my back yard again until April. As you can imagine, good insulation and air sealing are essential for keeping a house comfortable and energy efficient through such an extreme winter. Roof insulation is especially important and a good way to gauge its effectiveness is to watch what happens to snow on the roof.

As you can see from the photo above, this house does not have a well-insulated attic. The snow has melted off most of the roof, except at the bottom and the sides where the eave extends out past the walls of the house. This is a clear indication that heat is being lost through the ceiling of the house into the attic and then from the attic to the outdoors. Apart from adding a lot of cost to the heating bills this can cause serious problems in a house like this. As the warm, moist air from inside the house escapes into the attic it can take with it a lot of water vapour that will condense when it finds the cold surface of the underside of the roof. I’ve seen some horrible mould problems in attics in Montana due to condensation problems.

Dammed Ice

Another issue that often happens with a roof like this is called ‘Ice Damming’. As the snow melts off the upper part of the roof it runs down towards the eave, hits the cold area near the bottom (where the snow hasn’t melted in the photo above) and freezes again. Over the course of a bad winter this ice can build up until it creates a dam that can cause water to run back under the roof shingles and into the attic, potentially causing serious mould, rot and water damage.

Thankfully we don’t have to deal with the worst of these issues in most parts of Australia. But, if you happen to live in a snowy area, it can tell you a lot about where heat is escaping. And, even if you don’t get snow, good insulation and air-sealing between the house and the attic, and good ventilation of the attic are very important for maintaining comfort, health, durability and energy efficiency. The following photo shows the house directly across the street from the first one. Clearly it has much better insulation, air sealing and attic ventilation as the snow hasn’t melted off the roof at all.

No snow melt on a house with good insulation and ventilation in the attic

The Halloween decorations aren’t nearly as scary as the roof of the house across the street

My son Sam’s house (the one I’ve been hard at work renovating for the last couple of months) used to have problems with snow melt and ice damming. This was hardly surprising when I saw the state of things in his attic. Unfortunately all of the ducting from his gas-powered, forced-air central heating system runs through the attic. Ducts in attics are a bad idea at the best of times, even when they are properly sealed and insulated they still lose a lot of heat to the attic. In Australia the problem is the opposite with heat gain due to air conditioning ducts running though poorly ventilated and scorching hot attics (often sitting directly under a dark tile roof that soaks up a huge amount of heat from our hot summer sun) but just as big of an issue.

Ducts in Attics are a BAD IDEA!

Ideally all duct work should be inside the ‘Thermal Boundary‘ of the building (the insulation and air-sealing layer that surrounds the ‘Conditioned Space’). But if the attic (or uninsulated crawl space) is the only possible place to run the ducts, then it is essential they are tightly sealed and well-insulated.

This duct boot has become disconnected and is leaking hot air into the attic

This duct boot has become disconnected and is leaking hot air into the attic

Unfortunately, as you can see from the photo above, this was not the case in Sam’s attic. All of the ductwork was uninsulated and poorly sealed. In fact I found three places where ducts had become completely disconnected and were letting tons of heat escape into the attic. I would guess that a quarter of Sam’s winter heating bill was being lost through duct leakage to the attic.

So I’ve spent the last week crawling around inspecting, sealing and insulating all of the duct work. In the case shown above I reconnected the duct then sprayed foam around where it connects to the ceiling of the house. Then I sealed all of the joints with a special duct sealing compound before wrapping all of the ducts with insulation.

Sealing the joints in the ducts with a special paint-on compound

Sealing the joints in the ducts with a special paint-on compound

I also added vents in the gables of the roof, built a dam around the access hatch (to stop the cellulose insulation from falling on your head when you open the hatch) and built a catwalk (above the eventual height of the insulation) from the access hatch all the way to the far ends of the attic. This is so that, in future, when anyone needs to inspect the attic or do electric or duct work, they can access the whole attic without disturbing the insulation.

Now all that’s left to do is to get our friendly insulation contractor to come and blow more cellulose into the attic. I spoke to him this morning and, with winter approaching, he’s so busy that the only day he can come is the day I fly out to return home. So I’ll be meeting him early in the morning to get him going then I’ll have to leave him to it. But I’ll leave happy in the knowledge that Sam’s house will be much more comfortable, healthy and energy efficient this winter.

Tomorrow Sam and I are heading back out to his family’s ranch to help bring all the cattle down from the forest to the meadows along the creek bottom near the homestead where they will spend the winter being fed all the hay that Sam’s uncle worked so hard to put up over the summer. It should be absolutely beautiful at the ranch at this time of year and I’ll try to post some photos next week.

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