So I'm in the planning phase of a new home I'm going to build, mostly by myself, for my family and I was wanting some opinions. As an insulation contractor that specializes in spray foam, I know the value of a tight, energy efficient home. I'm not a very big proponent of the whole "tried and true" method of doing things, as that has not really worked out to our advantage. My plans are to build an 1800-2000 sq. ft. house. Even though I can get spray foam at cost, I am still leaning towards ICF walls, with a closed cell spray foam lid. The layout of the house is fairly simple with few 90 degree angles. I have thought about consulting with a company called energy wise structures, but not sure if it's worth the extra expense. I'd really love to go the extra mile and shoot for Net Zero or Passive house standards, but it's probably not going to be cost effective...i know..i know. Anyway, what I was hoping to learn about is some of the musts and must not's when building an ultra tight home. I'm planning on an ERV and I would really like to learn more about the best heating system. How does a ducted Mini split system stack up vs hydronic? Thanks

Where will this home be built?

Foamer,

EnergyWise Structures provided us a Man J and recommendations for our planned ICFhome. They are strong proponents of proper energy efficient construction and accurate sizing of HVAC system including ductwork. I'd highly recommend using their services. And Richard Rue and his staff are readily available to answer your questions. Dave

How much closed cell do you intend to use (and why?)

"Cost effective" and "closed cell spray foam" don't generally belong in the same sentence at R values greater than R10-12. Judicious use of closed cell foam CAN be useful in air-sealing a house, but it's no panacea, and there are usually other methods. Closed cell is more useful in adjusting vapor retardency or protecting wood if used in just the right amounts & places, but it can also trap moisture and cause problems where it might otherwise not have occured.

Also, at high-R the lifecycle greenhouse gas potential of the HFC blowing agents are worth decades (or even centuries, at very high-R) of the energy use it avoided. This is not the case with open cell foam, EPS, polyiso, or cellulose (but it is also the case for all XPS made in the US.) So even if you're buying it "at cost" in dollar terms, it's cost in environmental terms are significant. The air-sealing qualities of closed cell foam aren't particularly better than with open cell foam when looking at code-min attic insulation R-values, but the vapor retardency is MUCH higher (for both good or ill, depending on the assembly stackup and climate.)

Air sealing isn't rocket science, it's goop-science- taking the time to define which elements in the stackups are on all 6 sized of the cube, and making sure they meet at the edges/corners, and are properly lapped and sealed to each other every step of the way. This goes from the vapor-barrier under the slab, up the walls (taking care to define what's-what at the window & door openings/flashings), to the roof/attic, etc. While spray foam is sometimes useful, it's by no means an absolute necessity. ICF walls are a good start, since monolithic concrete doesn't leak much air, but there are at least 1001 ways to defeat that inherent air-tightness, and they don't automatically beat pretty-good stick-built on air-tightness- somebody has to play Air Sealing Czar to hit PassiveHouse type air-tightness, starting with the architect's prints, and following up on all of the critical details. It's neither hard nor expensive, but you can't get there if you wait until it's all up and finished, then run around with a dripping can o' foam during a blower door test.

Mini-split performance is climate dependent. Hydronic system operating costs may be lower or comparable if it's a cheap fuel and a cold or VERY cold climate, but the up-front system costs of hydronic systems are much higher than with mini-splits. But any successful heating system starts with a room by room heat load calculation. On a custom high-R house it pays to do that early, and multiple times as you adjust R/U values and window sizes/types/locations, etc. Most NetZero homes don't need ducted mini-split systems if designed iteratively with point-source heating in mind. (One mini-split head per floor is typical.)

You might try BEopt or similar program so you can try different designs.

If you want to use a CC spray foam "lid" for air sealing, I would consider spraying a thin layer from the attic down on the joists and drywall (assuming a cold climate, vented attic, cellulose overlay). At least your vapor retarder is then on the right side.

Thanks for the replies, sorry for the delay getting back to this. The house will be built in Nebraska. I'm fairly sure that we will end using Energywise for an energy analysis/HVAC layout. Dana, my plan would be to use no more than 2" of closed cell directly on the attic lid, with the exception of a vaulted living room, and then use blown in on top of that to a min. of R-60, maybe higher. I would like to use a raised heal truss as well. Would you lean more towards the ductless mini split then? I haven't done a lot of research into them yet, but I love the idea.

The efficacy/sanity of a ductless solution depends upon the climate, the floor plan, and the room-to-room heat loads for doored-off areas.  

That said, they are fully modulating systems with good turn-down ratios, and unlike gas-fired equipment, are easily matched to the loads of low-load houses like PassiveHouse or NetZero homes.  There's a PassiveHouse bigger than your proposed house about 5 crow-miles from my not-so-insulated house also located in climate zone 5, heated with a 2- head multisplit, one-head per floor where the 99% outside design temp  is ~+5F, which is similar to design temps in Nebraska.  It spends most of it's time in cooling mode, even at the beginning & end of winter.  There are many Net Zero homes heated with mini-splits in southern New England as well, with whole-wall R values much lower than what it takes to do a PassiveHouse in this climate.