Study Reveals Why Certain Homes Survived the Marshall Fire While Ones Around Them Did Not

One of the free lectures associated with the Oct. 1st tour of “green” homes was a fascinating presentation by Paul Kriescher of Bowman Consulting based on a study of the few homes which survived the Dec. 31st Marshall Fire while the houses around them burned to the ground. Click here for a PDF of Paul’s PowerPoint slides.

You’ll recall that it was the hurricane-force winds that were responsible for the fast spread of the Marshall Fire. Flying embers were what caused homes to catch fire in rapid succession. According to Paul, there’s a simple reason why those embers didn’t torch certain houses. It was because they didn’t get inside the homes or their attics.

The standard developer-built homes are “leaky” and built with ventilated attics. As I have explained previously, the standard procedure for finding and sealing the places where air can enter your home is to conduct a “blower-door test.”  (See graphic.) This involves installing a computerized fan in a doorway and sucking the air out of a house. The computer on that fan will tell you how leaky your house is — how many air changes per hour your home can expect during a certain wind speed. While that fan is operating, the technician can go through your house and determine all the places where air is coming into your home so that they can be caulked or otherwise sealed.

Many of those places are going to be around windows or on the rim joist — where your floor joists rest on the concrete foundation.

The goal is to get your home to a degree of air tightness at which you achieve two air changes per hour or less. Once you achieve that degree of air tightness, you then install an energy recovery ventilator (ERV) to bring filtered outside air into your home while expelling air from your home.

Making your living quarters more air tight can keep burning embers from entering your home. Combine that with having non-combustible exterior siding, decks and landscaping, and you go a long way toward preventing burning embers from being sucked into your home — and to keeping ash and smoke from making your home unlivable if it doesn’t burn down.

But the most critical area to seal is your attic. Your home probably has an attic which is vented. Blown-in insulation sits on your attic floor to keep your living quarters warm in the winter, while soffit vents combine with roof vents to draw outside air through your attic. This controls moisture buildup but is also ideal for drawing burning embers into your attic which can then light your entire house on fire.

Some builders have switched to building homes with “conditioned” attics, meaning that the underside of the roof is insulated and all vents eliminated. Thus, the attic itself is heated and cooled like the rest of the house. With no vents in your attic, those flying embers blow past your house instead of entering it.

There’s a subdivision in Arvada built by Meritage Homes called Richards Farm. It’s on the north side of 72nd Avenue, across from the Apex Center. Our agents were invited to tour it while it was under construction, and the builder showed us their conditioned attics. The reason the attics were conditioned had nothing to do with fire prevention. They were running heat ducts through the attic, and by insulating the attic, it made the ducts more efficient. But now we know the most important reason for conditioning an attic, and I suspect we’ll see building codes changed to require conditioned attics.

I learned another disadvantage of vented attics from participating in the 1994 Jimmy Carter Work Project, which built 30 Habitat for Humanity homes on the Cheyenne River Sioux Indian Reservation in Eagle Butte, South Dakota. Those one-story homes all had vented attics. Within months of completing those homes there was a blizzard which filled the attics of those homes with snow, which entered through the soffit vents. The snow then melted, causing the drywall ceilings to fall, causing immense damage. The homes had to be vacated and rebuilt on the inside the very next summer. The reservation had no building codes to follow, but if it did it would probably not have allowed vented attics for that reason.

What Are the Steps You Can Take Toward Making Your Home Net Zero Energy?  

I don’t know anyone who doesn’t like the idea of saving money, which will happen when you convert your home to “net zero energy.” So, what are the steps you can take to get there?

Net zero energy” means that your home generates more energy than it consumes. With “net metering,” your electric meter runs backwards when your solar panels generate more electricity than you’re using (on a sunny day), then runs forward at night, resulting in zero (or less) net consumption of electric power.

Solar power gets more affordable every year. When I purchased my first 10-kW solar photovoltaic system 15 years ago, the cost was over $60,000, but Xcel Energy gave a rebate of $4.50 per watt, so I got a check for $45,000 from the utility, reducing my net cost to $15,000. Nowadays that same system would cost as little as $15,000 with no Xcel rebate but a 26% federal tax credit.

While you can generate your own electricity, you cannot generate your own natural gas, so terminating natural gas service is key to achieving net zero energy. This involves some major system changes if you are currently heating your home and your water using natural gas, cooking with gas (including with a gas grill) and have a gas fireplace.

There are electric alternatives to all of these uses of natural gas, and you’ll appreciate that eliminating natural gas also eliminates the possibility of a gas explosion and of carbon monoxide poisoning (unless you have a gas powered car).

Heating your home with electricity used to mean installing baseboard resistance heating units in each room, but that is so 20th century. Nowadays electric space heating is done far more efficiently (and evenly) using heat pumps.

Gas forced air furnaces and water heaters are considered to have a 15-year life expectancy, so when yours fail, think of that as an opportunity to adopt heat pump technology for both functions. And a heat pump eliminates the need for a separate A/C unit, since it heats and cools.

Gas furnaces and water heaters generate heat by burning gas. A heat pump moves heat, similar to what A/C does. (How heat pumps work) It cools your home by moving the heat out of your house. If you put your hand over the external compressor unit while it’s cooling your home, you will feel the heat that was moved from inside your home. In heating mode, the process is reversed, and the heat pump moves heat from outdoors into your house. It may surprise you to know that when it’s freezing outside there is actually heat that can be moved from outside to the interior of your house, but it’s true. (Heat pumps work in extremely cold climates) Our office has been heated solely by heat pump since November 2017, and ever since there has never been a day when the system failed to keep our office at 70°F or warmer.

A simple one-unit 12,000-BTU, 29.3-SEER ductless mini-split system from Fujitsu can be found online for $1,961. That’s a small unit, suitable for one room or a garage (a great application!). For our office, we bought a Mitsubishi system in which a single compressor drives three separate wall units, each with its own thermostat.

A heat pump water heater (which I installed at our home) has the compressor built into the unit, above the tank. You can feel cool air emitting from it when it is heating water. I suggest putting it in a wine cellar where it’ll keep the room cool without buying a separate A/C unit.

For cooking, you’ll be amazed and delighted by the induction cooktops that are now widely available. I saw them used on a cruise ship for both cooking and warming surfaces, and the chefs loved them. (Modern cruise ships have eliminated natural gas because of the fire hazard.)

An all-electric home will, of course, demand more electricity, but Xcel Energy now allows you to install enough solar panels to generate double your electrical usage over the prior 12 months. That is more than enough to cover your new electric space heating, water heating and cooking needs, with capacity left over to charge an EV, too.

An important first step in pursuing net zero energy for your home is to reduce your need for energy, and the easiest and cheapest way to do that is to improve your home’s insulation. I had Dennis Brachfield of About Saving Heat blow cellulose insulation into the exterior walls (not just the attic) of a 1940s bungalow I owned, and I was astonished at how much more comfortable the house became. Even if your exterior walls have batt insulation in them, there is still space in the walls to blow in cellulose. (How to insulate an old house)

I learned something interesting from that experience. We all know that walls can radiate heat, such as a brick wall in bright sunlight. Well, walls can also radiate coldness, or suck heat. The air temperature in my bungalow before and after blowing in insulation was the same, but I felt warmer and burned less gas.

You can go beyond improving the insulation of your exterior walls and attic. There are numerous places that allow cold into your home, especially around your windows. Whether or not you install triple-pane Alpen windows, as we did at our office, caulking around the window frames and elsewhere can reduce the energy needed to heat your home.

A blower door test done by a contractor will identify the air leaks in your home. Insulating your attic with blown-in cellulose and your crawlspace with plastic sheeting will also reduce your home’s energy needs whether from gas heating or your new heat pump. (Insulating crawl spaces)

Of course, many homes, especially in older neighborhoods, can’t benefit from solar power because of shading from trees or insufficient south-facing roof area, but you can purchase community solar. (This is also a good solution for condos which have no roof at all.)

The way community solar works is that you invest in solar panels that are part of a solar farm in some distant pasture. The electricity generated by your panels in that remote location is credited to the electric meter for your home or condo. One advantage of community solar is that when you move, you only need to change which meter gets credited with your solar production.

Other ways of reducing energy use include replacing CFL or incandescent light bulbs with affordable LED bulbs and “daylighting” your home or office. (Batteries + Bulbs sell 8-packs of 60W LED replacement bulbs for $6.49, tax included, after $15 instant rebate.) We have “sun tunnels” in our home and office to bring daylight into interior spaces. In fact, on a sunny day we don’t need to turn on any lights in our office. It’s great— and saves energy. We had Design Skylights of Evergreen install Velux sun tunnels at both home and office.

Would you like one of us to visit your home for a private consultation about the sustainability possibilities in your home? Email me at