Building for heatwaves and blackouts (without adding to their root causes)

We build houses that stay cool in heatwaves even when the power goes out.  Interested?  Then we’re going to have to talk about insulation, thermal mass, and passive systems.  I know those are boring words but put them together right and they get very sexy results.  Talking about electric engines is boring, driving a Tesla is sexy.  So buckle up and come for a drive with me…

The recent heatwave in the North West has woken many people up to the new realities of a changing climate.  In places that are not accustomed to 100˚+ heat, a prolonged heatwave is miserable and even dangerous.  Buildings with poor insulation, no radiant barriers, and bad ventilation offer little shelter and can even make the situation worse.

Even in places where hotter temperatures are the norm, like here in inland San Diego County, many homes still rely on electrical cooling to function.  And if everyone is relying on the air conditioning, that puts a huge strain on the power grid which can lead to blackouts, rendering the AC useless and the homes uncomfortably hot.

As the climate gets more erratic, more people will want to have the option of turning on the AC.  Of course, this will lead to more strain on the power grid, elevating the chances of blackouts.  It will also mean more energy use, which likely translates to more greenhouse gas emissions…which leads to more climate change.  AC is an ineffective and counterproductive “solution.”

Wouldn’t it be wonderful to be comfortable in our homes when it’s hot out, even if the power goes out?  It’s a luxurious and downright sexy idea.  To get there, we have to talk about some effective but not-very-exciting strategies.

Insulation.  Did your eyes just glaze over? Come on, stay with me for the payoff.  Think of insulation as the puffy, down sleeping bag you take camping.  Insulation prevents heat or cool from moving from one place to another, such as from the cold night air into your cozy sleeping bag or, in the opposite direction, from the blazing outdoors into your comfortable home. 

The higher the insulation value of a material, the longer it takes for heat to get through that material.  Good building code require R-19 insulation in walls and at least R-30 in attics for this climate.  Most homes were built before good building codes and many have almost no insulation.  My house was built in the 1950s with zero insulation.  I’ve been able to add about R-5 in narrow space in the walls but there’s nothing in the cathedral ceiling yet.  Without the AC running, it only takes a few hours for the heat of the day outdoors to get indoors.

If my home had R-19 insulation in the walls and R-30 in the ceiling, it would probably take most of the day for the house to heat up.  With its unshaded South-West facing windows, it would certainly be hot by the time I got home at end of the day. So like all of my neighbors, I would turn on the AC until the cooler nighttime temperature started to get indoors. And hopefully, the power would not go out as we all tried to cool our homes down at once. 

If my home had R-30 insulation in the walls, R-60 in the roof with a radiant barrier (as do the homes my company builds), the heat coming through the walls or ceiling would be so minimal that it would not be an issue.  Heat coming through windows would still matter, so we orient our homes for maximum shade during the warm months.

So insulation can make a big, sexy impact, but the other key to building comfortable homes is an idea we’ve almost lost in the construction industry: thermal mass.  Did you nod off then?  Pinch yourself, I promise it’s worth it. 

If insulation is the sleeping bag, what is thermal mass?  It’s some ye olde gadget like a hot water bottle.  In the olden times before central heating, people would sleep with a hot water bottle under the bedcovers.  Water has good thermal mass – the ability to absorb and store heat – so the bottle of hot water would stay warm after the fire in the hearth died out and the air temperature dropped.  Thermal mass can also be understood by cooking in a cast-iron skillet: once the skillet is hot, it stays hot after you turn the heat off under it.  Or a tile floor that stays cool underfoot even as the air temperature warms up.  These are all examples of thermal mass, something we desperately need more of in our homes because it can act like a battery and a fly-wheel for maintaining the right temperature.

What if you had the best of both worlds:  the down sleeping bag and the hot water bottle to keep you toasty all night?  What if your house had insulation and also had mass, maybe in the concrete floor and the plastered walls?  It would mean that once your house reached a good temperature, say 72˚, it would be easy to keep it there no matter what was going on outside. Maybe in the winter, you’d need to run your heating once in a while to get the house from 69˚ back up to 72˚.  Maybe in the summer, you’d need to open some windows at night to catch the cool breeze and bring the house from 74˚  back down to 72˚.  Wouldn’t that be nice? 

A well-insulated house with good thermal mass is a beautiful thing that only requires small inputs of energy.  But give it too much energy and it will overheat and hold onto that heat.  Unshaded South or West-facing glass walls could create a greenhouse effect so ensuring the house has the correct passive solar orientation for its climate is important.  When we build here in inland San Diego, we build for shade and passive cooling.

The idea of passive systems is the last snoozer I will bring up to get us to our sexy Tesla house.  What will happen if the power goes out in your super-insulated, high-mass house oriented for shade?  Not much. You will notice very little difference in your thermal comfort.  The temperature will not change.  Say it’s 72˚ degrees inside and 100˚ outside.  You’re feeling happy, maybe even a little smug, but then you have to open the door for a minute.  Oh no!  A blast of hot air comes in, some of your precious cool air goes out… and then your amazingly sexy house absorbs that heat and cools the air back down to 72˚  through the magic of thermal mass.  You do not miss the AC because you are comfortable.  And your home will be comfortable for a few days, probably long enough for the power to be restored.  Even if the power is out for a crazy, hot week, your house will only get a few degrees hotter each day and you may be able to cool it enough by opening windows at night.  Wouldn’t that be nice?

Yes, in a power outage you’d still have all of the other inconveniences of being without power (unless you had some of those voluptuous Tesla PowerWall batteries) but you’d be relatively comfortable, surprisingly resilient, and feeling happy in your sexy, super-insulated, high-mass, passive home.

We’ve arrived at our destination, thanks for coming on this ride with me.  Maybe next time we’ll head out and explore how this same type of home can actually combat climate change by locking up carbon in its walls.  Or maybe consider that they have better indoor air quality because they have fewer toxins built into them and they regulate their own humidity.  Or how remarkably well they resist wildfire.  So many interesting places we could go…