Net-zero is the new superhero in homes and buildings, and anything less is merely mortal.
“Net-zero” can be defined lots of ways – in terms of energy, water, carbon emissions and waste streams. But for the purposes of this post, I define it with energy use – the energy required to heat, power and cool a home or building is completely offset by energy savings and renewable energy. Thus, netting out at zero.
(Also, I assume, dear reader, that you understand the HERS index and energy modeling. If not, please visit my previous post on this, or go to HERSIndex.com.)
It is absolutely possible to build net-zero (NZ) with conventional sticks and bricks, and I routinely see HERS-rated homes built in the mid- to low-40s. For this article, I created a HERS energy model of 45, and dropped it to zero.
One rule of thumb – if builders did it 100 years ago, it's probably worth considering today. Before builders were able to seal, mechanically heat and cool buildings, they had to work in concert with nature, not oblivious to it.
1) OVERHANGS – Generous eaves and overhangs help shield a home or building from hot summer sun, and as the sun is lower in the North American sky in winter, build so that it passively heats a home’s interior. In my climate zone (Denver, CZ5B), the sweet spot for overhangs seems to be 2 feet (or more) on every side, except the south, which needs 3 feet. If you must skip a side, leaving overhangs off the north doesn’t significantly impact the energy model.
2) LIGHTING – With the drop of LED prices (now below $5 for a bulb), there’s no excuse to skip them anymore. They’re gorgeous, rarely require changing, and can easily be looped into home automation systems. Long the poster child for government interference in efficiency, the CFL bulb was always meant to be a bridge solution. While I do see some clients still use them, most builders and lots of homeowners have made the switch to LED.
3) BUILDING ENVELOPE LEAKAGE – If there is one aspect of green build that makes the biggest difference, it’s “envelope leakage” – how leaky a building shell is. Always work with good contractors to reduce this. Other energy-efficiency fixes usually ride the coattails of reduced air leakage.
THIS IMAGE AVAILABLE BELOW.
4) INSULATING THE “RIM & BAND” – The “rim joists” are the floor supports that sit atop foundation walls, and the “band joists” are the same for upper stories. If you want to head for zero, these critical areas need to be spray-foamed. The rim is usually the leakiest part of a home because it's where mechanical and utility systems enter.
5) WHOLE-HOUSE VENTILATION – ‘Seems counterintuitive to seal a house against air leaks. And then add air. It's all about intention, and the mantra is, “Build it tight – ventilate it right.” High-efficiency ventilation systems like heat- and energy-recovery ventilators (HRVs and ERVs) recycle warmth in a home while exhausting stale, unhealthy air.
6) FIREPLACE – Here and in other cold places, we use fireplaces to heat homes, and there are higher-efficiency ones than others. Check the efficiency ratings or “steady state” efficiencies. And don't rule out electric fireplaces if you don't want to run gas. I've seen some that look great.
7) HIGH-EFFICIENCY HEATING & COOLING – Get the highest-efficiency heating and cooling systems you can afford. They can really drop a home’s energy use - orr eat your lunch. There are LOTS of utility rebates out there to help offset the jump.
8) HIGH-EFFICIENCY HOT WATER HEATERS
Some hot water heaters out there are smokin'-hot in terms of efficiency, including “heat pump” units that operate at 300 percent. But electric models like that also use expensive energy. Also look at high-efficiency gas tanks, or even tank-less. With the latter, you’re not heating a tank of water 24/7.
9) WALLS – The less lumber you use and the more space you create in wall cavities, the more insulation you can install. Talk to your builder about building 24 inches “on center” – center of wall stud to wall stud. What I routinely see is quality builders building this way with thicker drywall (5/8 inch) so framing nuances are minimized.
10) And lastly, SOLAR – If you build the most efficient conventionally framed home today, the HERS rating will be in the ‘40s. Solar makes the rest of a home’s energy use vanish. And that’s the goal.
To write this post, I created a 2,600-square-foot home with high-performing features like in the IMAGE ABOVE. If you’d like an oversize graphic of that house and a copy of the HERS energy model certificate, email me. I’ll send it to you.
And if I can help you with your home’s specific features, reach out.