Thread by @energysmartwv

Some wonder why we don't advocate more for external wall insulation (wrapping a new wall around the outside of a house). This is why.

A 🧵

https://twitter.com/AdrianHiel/status/1571829859315220482

Our last house was a beautiful 1835 home outside Cleveland Ohio, I figured it would be $70K-100K to do external insulation on.

How much did it save? It modeled $250/year. That would be closer to $500/year now, but that's a 140-200 year payback.

That's not uncommon.

Ugh.

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That house had a gas boiler with hot water radiators like most of the UK/EU.

I tested what water temperature it needed to keep the house warm on a design day (5F/-15C). It was 180F/82C. 3

That's a problem because heat pumps currently on the market top out at about 150F/65C, and that's pushing it, probably don't want to count on getting beyond 130F/55C.

So it was a REALLY hard electrification. 4

I figured a full electrification done the way I wanted it would be $150-200K.

We sold the house for $200K.

If I'd spent that, it would have pushed our retirement back 5-10 years. There's no resale value from it, the upgrades have no predictable resale value. 5

Spending a huge amount of money on building shell (insulation and air sealing) to get nothing back is capital destruction - that money is gone from the system, it never gets to be used again.

This is seriously foolish. 6

As far as the boiler goes, there is a solution, but it's also expensive: replace all the radiators with larger ones.

Those radiators were purposely built into the baseboards, so there would be an aesthetic penalty that frankly I wasn't willing to take. Nor was my wife. 7

There were two electrification options: ductless mini splits (which have horrible indoor air quality capabilities), or 1-2 ducted heat pump systems.

The mini splits would have been much more reasonable for that home, probably $25K vs $50-60K for ducted in that case. 8

Back to the walls though:

Not only is exterior wall insulation expensive, but it creates a great deal of moisture risk: homes can rot in the middle of those walls and it's not immediately apparent. 9

We call water a patient and potent foe: it always wins and it's willing to wait.

These moisture failures typically take 10-20 years before they are noticed, and fixing them can cost tens of thousands of dollars. 10

There are two big challenges:

1. It's easy for moisture to get in the middle of the wall.

2. Once in, that moisture can't get out easily, there isn't enough warmth to help it get out, and it can't dry into the air.

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On the first issue, when you bump out a wall, you have to replace the windows or "buck" them out.

It's very easy to make small errors here and allow water into the middle of the wall between the old wall and the new one.

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You also lose a bunch of the roof overhang which helps keep rain off the wall.

Dr. Joe Lstiburek of Building Science Corp found that water in walls was directly correlated to the size of roof overhangs: the bigger the overhang, the less water intrusion in walls. 13

Pushing the wall out 4-8" means you lose that much overhang which may tip the house to where it gets wet and makes rot more likely than it was before. 14

Which brings us to the second problem: moisture can't get out.

By building another wall on the outside, air can't get to the inside wall anymore to dry it out, and now it's relatively cold in the middle so there isn't much heat to dry it out anymore. 15

Plus if you aren't absolutely perfect in reinstalling the windows and flashing every small detail so water flows to the outside of the house (newsflash, perfection is impossible), those walls are getting wet. 16

Once that water gets stuck in there, it starts to create mold and rot.

Remember, it's nearly impossible to do this perfectly. 17

The risk can be mitigated to a degree with good assembly and materials choices along with very careful details, but guess what, those cost a lot. 18

So in the end we have a VERY expensive solution that carries high risk of destroying buildings within 10-20 years. And it saves relatively little energy. 19

So what's the solution?

More energy.

Sometimes problems are worth throwing energy at. This is usually one of them. 20

Seal the top and bottoms of the home (attic/loft and basement/crawlspace, respectively), and put in the right HVAC for the home.

Add a battery for handling the cold morning peaks and solar if appropriate. 21

Also, if you want to see more insulation and air sealing projects, publish energy use.

Without this, cold climate shell retrofits are going to struggle unless energy costs are very high. They never stay really high, so this is a failed business model. 22

After years of watching, if we want to scale #electrifyeverything for homes, there are 3 key factors:

1. Business model - make it better than BAU

2. Publish energy use at resale - creates value

3. Make heat pumps the default choice (3H in US)

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We've been actively trying to make these happen:

1. Business model: HVAC 2.0

2. Publish energy use - been talking about it for years, currently starting a paper

3. Make heat pumps the default choice: pay OEMs to stop making one way ACs - Hybrid Heat Homes program

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All this comes back to that wall insulation: it's a silly way to spend money for the vast majority of homes and buildings, it's better to put more heat pump capacity in and make more electricity. Whenever you can make energy cheaper than an upgrade, make energy. 25

That last point isn't just pontification, we modeled a number of our projects to see what it looked like, it didn't save substantial amounts of energy, it adds a lot of moisture risk, it's very hard to do perfectly (and perfection is often required), and it's expensive. 26

It's good to look at a lot of homes, you get to look for patterns and see what upgrades almost never make sense. Exterior insulation and windows almost never make sense in our experience, or at least they are the last things to get done and are cut for budget reasons. 27

If we want to see #electrifyeverything scale, we have to look for the best opportunities, and those will vary from home to home and client to client.

The clients have to be convinced they are taking the best path, so it's more of a sales problem than a technical one. 28

Plus, if we want contractors to switch from business as usual to a new way, it has to be so attractive to them that they don't slink back to their old ways. 29

And lastly, if we focus on extremely labor intensive measures like exterior wall insulation, we simply don't have enough people to do the work, nor are we likely to be able to train them. 30

So overall the lessons for #electrifyeverything are:

1. Business model - make it better than BAU

2. Publish energy use at resale - creates value

3. Make heat pumps the default choice

If we don't make all three happen, expect difficulties.

31/End

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