Corbett walks you around Venice, Italy on a recent trip, and teaches the implications of building science on this beautiful city that’s being torn apart by seawater. Incredible case study of a lovable place where you wouldn’t want to own a home:

Capillary action is the phenomenon of water soaking upwards, like in the roots of a tree. The same happens with buildings that are founded in the sea- the moisture damage to brick, wood, and plaster can be easily seen here:

And once the moisture damage has torn these homes apart, they have surgery to keep them held together for the next hundred years:

HIGHLY RECOMMENDED as a vacation spot, and the buildings are beautiful to see- but be careful what you invest in while you’re there!

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To keep most people in first world countries comfortable, you need at least two things: an enclosure to hang onto heated or cooled air, and an engine to make the air that way. ALWAYS FIRST: create an enclosure at is relatively airtight and insulated. Now for the engine: the HVAC- air conditioner, furnace, heat pump, etc.
Chris McTaggart with a 20 SEER 4 Ton A/C
The question is: how much heating or cooling should I install in this home so it’s both very comfortable and cost-effective?

Great question! There are very precise calculations for this (spelled out in ASHRAE Fundamentals and in Manual J from the Air Conditioning Contractors of America. You take detailed information about weaknesses in the home’s enclosure (window size and orientation, how much air leakage exists, etc) and put it into a computer.

Doing an HVAC load calculation by hand isn’t good enough in most homes because you need an hour-by-hour look at the effect of the sun and weather on the home. This calculation gives you a very specific amount of heating and cooling that a home needs. You don’t need to add anything to this, because the calculations were written by engineers, who are very cautious and conservative people- they’ve added all the safety margins already to make sure you’ll be comfortable.

Next question: how are we going to deliver the warm or cool air evenly everywhere in my home? Wow, that’s a great question! Guess what? There’s a calculation for that!

Again, ASHRAE Fundamentals or Manual D will tell you exactly how the ducts should be designed and installed so that every single room feels comfortable and refreshing, which is possible for every home, in every place, new and old alike.

Now that we know exactly how much heating and cooling each home needs, we have to buy an engine that can make it. Here’s where most people make a big mistake: they buy an engine that’s too big. These people may think that they need a little extra power for when the weather is really crazy. In fact, many of my clients have twice as much machinery as their home actually needs. That’s like building an escalator and installing a V8 engine to run it- it takes you where you need to be super fast, but it’s also uncomfortable, really loud, and slightly nauseating. So you pick an air conditioner, furnace, or heat pump that fits the home like a tailored suit.
Duct testing with Corbett Lunsford and John Bergman
Last step: we test the tightness of the duct system. A duct system is plumbing for air- you do not want it leaking. You might think if the ducts are all inside the envelope and they leak air here or there, it’s not such a big deal. It IS a big deal, and here’s why:

If we spent time and energy calculating exactly how much heating and cooling this home needs, exactly how the duct system needs to be designed and installed, and picked out the perfect heat pump or furnace, all of that gets flushed down the toilet if the conditioned air doesn’t actually go to the rooms where you need it!

Proof Is Possible, and careful planning and performance testing are the keys. Your home won’t need rescuing if you do it right the first time.

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Building Performance Podcast with Corbett LunsfordToday we talk with Kristof “Handsome” Irwin, founder of Positive Energy in Austin Texas, about why your air conditioner is probably an idiot (bless its heart) and HVAC heaven that you might not have heard about.

Hear all the podcast episodes at

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This week’s minute means Corbett is squeezed into a client’s attic, testing the unspeakably awful forced air furnace and air conditioner there. If you haven’t been inside your own attic, PLEASE GO THERE RIGHT NOW and see if it looks like this one!

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Ice Dams troubling a client of Green Dream Group in ChicagoDespite good intentions, most media coverage on ice dams is misguided, and can actually make problems worse

MARCH 11 2014 – CHICAGO – This winter has been a record-breaker, but few homeowners know what they can do about it. Roof snowmelt re-freezing at the eaves (called ‘ice dams’) is a problem for many homes. It causes structural damage to roofs and walls every winter. And with more snow on the way, the immediate question is, what can a homeowner do about it?

Misguided sources, including NBC Chicago’s Nesita Kwan and PBS’s This Old House, say that ice dams are made when hot air escapes from the home into the attic because of missing insulation, and artificially warms the roof. This is only half right– since warm air rises, it does indeed push up through the ceiling, into the attic or roof cavity, but insulation cannot, and does not, fix air leakage. The only thing that can fix air leakage is airtight materials, which insulation is not.

Air leakage from home into atticConsider your furnace filter, for example: air goes right through it, and filters out particles that could damage the furnace or air conditioner… AND it’s made from fiberglass, just like insulation. So really, the air that pushes out of your home into your attic will be the cleanest air in the whole house, if you have a well-insulated attic. But the big problem remains; warm air will still leak out.

Solving ice dams once and for all with Air Sealing is the only solution. Luckily this is very affordable, needs no maintenance or replacement, and doesn’t consume energy (unlike the ridiculous heat wires you can string along your eaves as a band-aid). Never install more attic ventilation before the attic floor is air sealed- this just accelerates the leakage of air from the house to outdoors. And never add more insulation before air sealing- this only makes the attic colder, so the warm air leaking into it condenses everywhere, which can lead to mold. Hire a Home Performance Contractor for air sealing, not just any contractor. Home Performance Contractors test before and after their work with a blower door, to prove you got what you paid for, and to prove that the problem is actually solved. The best part of Home Performance is that proof is possible.

Smart homeowners are opting for a comprehensive home analysis with performance testing, before investing in improving any part of their home. This ensures that home improvements are prioritized, cost effective, and that each improvement makes the home more comfortable, durable, healthy, and energy efficient. It also ensures that you never flush money down the drain guessing at fixes. Home Performance Contractors are easily found through the Illinois Association of Energy Raters & Home Performance Professionals a not-for-profit organization dedicated to guiding homeowners to certified professionals.

To see a demonstration of attic air sealing, watch this:


For a crash course in how to think about your home’s performance, check out this 5-minute video from the IL Association’s executive director Corbett Lunsford:


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