About 3 years ago, I had what I call a minor existential crisis, in someone else’s living room. My neighbour Tom had been talking nonstop for months about “the craziest efficient house” his cousin Sarah had built in the hills near Bath. When we visited for a weekend getaway with the kids, he insisted we go check it out. Honestly, I was thinking we were headed to some kind of hippie commune with composting toilets and solar panels plastered everywhere.
It was February (one of those winter days that isn’t brutally cold, but it is cold enough that you’re bundled up and dreading the minute you have to leave your warm car). We drove up to what looked like a completely normal house, nice, but normal. No signs of weird eco-features or zany architecture that screamed “I’m saving the world”. It was simply a standard, two-storey house that could’ve fit into any housing estate around Bristol.
When Sarah met us at the door, it started to feel unusual. She was wearing a light jumper. No coat, no multiple layers like I had on, just a plain cotton jumper, like it was a mild spring day. The kids rushed in before us and in about five minutes my 7-year-old was peeling off her jacket. I turned to Sarah and asked, “Is your heating system just super powerful or something?”
“Have we ever turned the heat on yet this winter?” Sarah responded.
I stopped dead in my tracks. “You mean to tell me you haven’t turned the heat on all winter.”
She laughed again. “Nope. The thermostat is set to come on if it drops below 18°C, but it hasn’t kicked in. The house just keeps itself warm.”
I literally didn’t know what to say. It was probably 2°C outside. I’d been running our heating constantly since December and watching our energy bill rise every month. Here was this woman telling me her house kept itself warm. I assumed she was messing with me.
However, as we walked around the house, I realised she wasn’t having me on. Every single room was comfortably warm. There weren’t any cold spots, draughts, etc., no need to sit next to the radiator to stay warm. The bathroom, which is always freezing in my house during the winter, was just as warm as the rest of the house. I tried to touch the window with my hand, expecting the cold to radiate through, but the window was room temperature.
“It’s called a passive house,” Sarah explained when she saw me prodding the windows like a lunatic. “The whole house is designed to lose hardly any heat, and gain hardly any heat. Very well insulated, very tight, special windows, and a ventilation system that captures heat from the air that is leaving and uses it to warm the air entering.”
I nodded as if I understood what she was saying, but in reality, it sounded like voodoo to me. Houses that heat themselves? Get out of town.
The big reveal came when Sarah handed me her past winter utility bills. I am talking about a 230 square metre house and her total heating bill for the entire winter was less than I spend in a typical month for electricity alone for my much smaller house. I was so shocked, I asked to see them twice.
This visit stuck with me. Started me down a rabbit hole of researching about passive houses that took up far too many nights after the kids were asleep. Passive house standards aren’t some sort of fringe eco-nut movement, they are a very specific set of building criteria developed in Germany that produce incredibly energy efficient buildings. In short, the goal is to build the shell of the house so tight and well insulated that you will need little to no mechanical heating or cooling.
The requirements are fairly detailed: the house needs to have a heating load below a certain amount per square metre, and overall energy consumption below another threshold, and it needs to be so airtight that typical construction methods appear to be nothing more than a screened-in porch.
Most UK houses, including mine, leak air like it is nobody’s business. We are essentially heating the outdoors through all the holes we don’t even know exist in our houses.
Finally, after months of learning about this stuff and becoming increasingly fed up with our winter heating bills, I decided to see what we could do to improve the efficiency of our house. Not full passive house, which is primarily for brand new construction or massive renovations we can’t afford; but maybe some small changes that would make a difference.
Step number one was to hire a company to perform a blower door test to determine how leaky our house actually was. This bloke comes to your house with a large fan contraption, attaches it to your front door, and sucks all the air out of the house to determine where it is leaking back in. He then goes around your house with a thermal imaging camera and shows you all the places that your house is leaking heat.
Honestly, it was disheartening. There were areas of our house that were losing heat everywhere, around windows, at joints in ceiling and walls, and gaps in the skirting board I had never noticed. The technician was professional about it, but I could tell he thought we were throwing money away by running the heating.
“Look at this purple area on the camera?” he pointed to what appeared to be a cold river running along our living room wall. “That’s a thermal bridge. Heat is simply passing straight through from inside to outside.” “And see this,” he walked to the front door, “you’ve lost the same amount of air as if you had a 15-centimetre hole in the wall.”
We were basically heating the neighbours’ houses.
The inspection report was 12 pages of things I had no idea existed. Not enough insulation in the loft, no insulation in the basement, gaps everywhere that needed sealing, ductwork running through unheated areas of the house, etc. The quote to fix everything correctly was more than we paid for our car.
However, I figured we should try to do something. So, I started with the easiest wins, add insulation to the loft, seal any obvious gaps with caulk and draught-proofing strip, add insulation to the basement walls. My wife Sarah thought I was nuts about the whole thing and worried I would spend every Saturday afternoon at B&Q buying supplies for projects that would never get done.
Well, can’t deny she was right about the B&Q part. I did end up spending more Saturday mornings than I care to admit standing in the insulation section trying to figure out the difference between 100mm and 150mm batts and why some insulation cost three times as much as others that were virtually indistinguishable.
The loft was relatively easy. Just blow in a lot of cellulose insulation, plug up some holes, install baffles to help ensure there was still airflow. Messy and itchy, but not difficult. The basement was a bit harder since our house is on a crawl space that is only slightly taller than I am and every time I went down there I discovered new issues that previous owners had let slide.
Still, even these minor fixes seemed to make a significant difference. After the first winter after we had insulated the loft and plugged up the big holes, our heating bills fell by approximately 30%. More importantly, the house felt warmer. Fewer cold pockets, less of that draughty feeling when sitting near exterior walls.
That got me totally hooked on the efficiency thing. Began reading about heat pumps, better windows, wall insulation options, etc. My browser history started to include a bizarre combination of building science articles and YouTube videos about vapour barriers. I began to bore friends and acquaintances at neighbourhood barbecues with reasons why thermal bridges matter.
The kids thought it was hilarious that Dad had become obsessed with the house not losing air. They began to point out places they found, “Dad, there is a crack by the light switch!”, and assisted with some of the easier sealing jobs. We even turned the process into a game of who could find the most air leaks.
Approximately two years later, we replaced the old heat pump with a more efficient version and installed new windows on the north side of the house where we were losing the most heat. Not to the extent of a passive house, but sufficient to drop our energy usage by more than 50% from where we started.
I think about Sarah’s house more often than not, particularly on the coldest days when I’m still running the heating system that she doesn’t need. It isn’t just the money saved, although that is considerable, it’s the concept of living in a space that is inherently comfortable without needing to give it any additional consideration.
Most of us expect to be somewhat uncomfortable in our homes during extreme temperatures. We wear coats indoors in the winter, run fans in the summer, tolerate rooms that are too hot or too cold, pay exorbitant amounts for utilities, and accept this as normal. However, there is nothing normal about this, it’s merely a function of building practices that prioritise lower initial costs above longer term performance.
Construction of new homes is the ideal application for passive house standards. The premium for building to these standards from the beginning is typically 5 to 10% more than traditional construction, while the potential for energy savings can be 80 to 90% for decades. Regardless of the environmental implications, the financial implications are clear cut.
I have seen a couple of new passive house homes around the South West lately and what struck me was how normal they look. No wacky features or obvious eco-signalling, just good quality houses that just happen to use nearly zero energy for heating and cooling. Residents I spoke to raved about the comfort level and utility bills, but also mentioned items I wouldn’t have guessed, such as how quiet their homes are due to the airtight construction and high performance windows.
For homes already constructed (like ours), a full passive house retrofit is usually not feasible or cost effective. However, applying some of the principles, i.e. better insulation, air sealing, efficient windows, can make a tremendous difference in terms of comfort and running costs.
Overall, the whole experience has dramatically altered my perception of buildings. A house is more than just walls and a roof, it is a system that either works with the laws of physics, or fights against them. Most conventional construction is essentially fighting a losing battle with thermodynamics, using mechanical systems to counteract poor building envelope designs.
Passive house flips that formula. Rather than relying on heating and cooling equipment to maintain comfort in spite of a leaky, poorly insulated building envelope, you construct an envelope so good that maintaining comfort becomes almost automatic. The house does most of the heavy lifting, not the mechanical systems.
Not rocket science, just serious building techniques. Once you have experienced what a well designed building envelope can accomplish, whether it is a full passive house or a substantially improved existing home, returning to draughty, inefficient construction seems absurd.
I imagine my kids will likely grow up thinking it is normal for houses to be uniformly comfortable throughout the year and have reasonable utility bills, provided we continue to make improvements over the years. That is how progress occurs, what appears to be revolutionary to one generation becomes the baseline expectation for the next.
At times I ponder what Sarah’s passive house will be like in 20 or 30 years when passive house construction is widespread. Will my kids view our current house as I view the old farmhouse where my father grew up, draughty, inefficient, uncomfortable, but acceptable based upon the standards of its time?
