January 6 was the coldest day in the past 10 years here in rural Ridgeway.
A newly-named weather phenom, known as a polar vortex, had descended on the Driftless Area. In downtown Dodgeville, -22F was flashing out front of the Wells Fargo Bank – and a brutal wind produced a plummeting wind chill as the day dawned.
It warmed very little during the day and got almost as cold the following night as the wind began to die down.
Underhill House is just over a year old. We were curious and a little nervous to see how our home would perform in this kind of cold. 
Saturday and Sunday we hastily sawed and split extra firewood, and jamming it under the loft ladder next to our wood-burning stove. Though we’ve never had a fire for more than an hour or two in the evening, we feared that we might have to burn wood constantly – as opposed to our usual hour or two in the evening.
We watched the temperature drop and went to sleep listening to the cold wind howl. Monday morning dawned clear, but before the sun rose over the hill, we both had to venture out. We wanted to experience the coldest air we’d known in a long time, and we had chores out there.
Doug made an early morning foray out to the barn and two hikes down to the highway to put out the garbage and recycling. We weren’t actually sure it would get picked up in such bitterly cold weather, but our intrepid trashmen came through.
Meanwhile I ventures out on a mission of mercy for the birds. Doug and I decided last summer that we would not put out bird feeders this year and work instead on turning the land around our house into the best bird habitat we can. We are planting various dogwoods, viburnums and other bird-friendly shrubs to provide natural food and shelter.
However, the day before the cold set in, I began to fear for my feathered friends and determined they could use a little immediate help finding fuel in this intense cold, so we made a last-minute trip after dark for sunflower seeds and suet. So there I was in the first light, shoveling an area to spread seed and trying to wire up a suet feeder without taking my gloves off – that proved impossible, and my fingers immediately began to burn. I got out my phone to take a photo of the sun rising, and it immediately froze.
Less than half an hour out there gave me a great appreciation for those creatures who find their winter shelter and food where they can. ( All day, we saw no creature of any kind venture out into the teeth of the windstorm. In fact, it was a couple of days before the animals began to appear.)
We came in and warmed up with hot tea and steaming porridge, but we held off lighting the fire. The sun was just hitting the solar panels and starting to spread out on the surfaces inside our house.
We designed this place with:
- Straw bale insulation
- Passive solar design
- Over-insulated foundation walls
- Thermal mass
- Solar hot water infloor heat
We wanted to see what Underhill House could do.
The backup propane boiler turned itself off at 9 a.m. — almost as soon as the brilliant morning sun started to shine through the windows. By 10, the solar hot water panels were replenishing the heat in the 160-gallon storage tank in the mechanical room.
By lunch time, we were down to t-shirts as sat in our loft watching the snow glisten and the trees toss. On many a sunny winter day, Underhill House has warmed us to t-shirt temperatures with its one-two punch of passive solar heat pouring into the house through the windows and the heat collected in the solar panels coursing through our concrete floors, but we weren’t sure it could kick such extreme cold.
It could!
No propane use, no wood stove fire – indoor temperatures near 70, and water coming off the panels and into our basement storage at 130 degrees.
We didn’t start a fire in the wood stove for almost two hours after sunset, which allowed us to coast comfortably through the evening on the main floor. Meanwhile the stored heat in the tank kept the downstairs (which receives little passive solar input) in the low 60s. We let the fire die down and went to bed about 11. The residual heat from the day’s sun and the wood fire kept the upstairs thermostat above 60 all night long – except for our bedroom and the front hall, which we keep cooler.
The only propane we used, heated our downstairs offices starting about midnight.
Bottom line? We had a 5-hour-long wood fire and perhaps 7 hours of propane used to heat less than a quarter of our living space in the coldest 24-hour span in the last decade.
No compromises. We were cozy through the bitterest cold our climate is likely to throw at us.
Cozy and a bit bemused by the whole experience.
Categories: Eco architecture, Underhill House
Digging in the Driftless 
Wonderful news, and what a triumph of thoughtful design! I had been wondering how you were faring.
In the photo of Doug stoking the fire it looks like you don’t use curtains on cold nights. Are your windows sufficiently multi-paned to avoid significant radiant heat loss? Without curtains, the dark glass seems to suck heat from the room. Even a thin curtain makes a noticeable difference.
Trial by cold in its extreme. Glad to hear it passed with flying colours. My one concern would be cooking, as we would be more likely to use a wood fire for cooking and I wonder if the over insulation would make that difficult. I would rather not use grid power for cooking in the middle of winter as it has a tendency to go off here in Latvia.