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Twigglesnix OP t1_j6ndqrh wrote

Reply to comment by SomeConstructionGuy in Really want to build a house like this. Passive home stays at 70 degrees in Maine w/o furnace. by Twigglesnix

Would love to know your approach if you think passive isn't worth it.

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SomeConstructionGuy t1_j6nik64 wrote

I’m a big advocate of net zero. Its basic goal is to have a house that’s net energy input is zero. This is achieved by building a tight envelope, being realistic with size requirements and using efficient heating where the energy can be generated on-site. Site generated energy is usually solar with possibly a small woodstove to cover below zero days.

This allows you to look at energy consumption over a year not day or week as with passivehaus. Because you’re actively heating the house you drastically lower then envelope requirements but at the same time on a yearly basis you’re a net zero consumer of energy.

The solar/minisplit/woodstove/tight envelope compliment each other very well while still being reasonably priced.

For envelope I’m a big proponent of simple rectangular houses and double 2x4 walls with dense pack cellulose. With a little planning it’s easy to air seal effectively and costs much less than foam for the same r value. Im also a fan of still foaming rim boards as it’s just so much more consistent.

Ventilation is easy as sizing an erv based on house volume. If you want to splurge the zehnder system is a very elegant way to get even balanced air exchange.

Edit: spelling

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8valvegrowl t1_j6nnwvb wrote

Exactly this.

I looked into Passivhaus design when I started planning for my new place, and given our climate and the overall costs, I decided net-zero should be my goal. I took about 4-5 years of research and planning before I even broke ground in 2019.

I built a 1500 sq ft timber frame house, R24 SIPS for the exterior walls, R38 SIPS for the roof. Roof aligned with the south and my main windows on the south wall. 4 zone minisplit system and a small woodstove. SIPS have virtually zero thermal bridging except on wall penetrations, the insulation doesn't degrade, or pack down, and can be made into large panels, they just really seem like best envelope you can make, whether stick-built, or timber frame.

It isn't fully net-zero yet...I need to install a ERV system, then size my solar appropriately (waiting to install the ERV and possibly a Level 2 car charging setup before I size my panels), but it's all designed with it in mind.

I use 1.5 to 2 cords of wood per winter (most of which I can harvest on my land), and the house is a nice 70 all summer and a nice 75 all winter. My electric bill is stable at $150/mo year round with no solar at the moment. The only fossil fuel on-site source is my gas cooktop, which seems to use about 20 gallons per year.

I'm very pleased so far.

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SomeConstructionGuy t1_j6nr9ld wrote

The timber frame/sip combo is a great setup.

With recent spikes in foam prices were getting r40 walls and r60-80 ceilings for similar or lower cost than sips. In our experience with sips it’s been very easy to get a decently tight house but hard to get a very tight house. Getting to 1 ach50 seems easy but getting below .33-.5ach 50 hasn’t been consistently easy. The double stud alsogive a lot of benefits such as being able to run plumbing in exterior walls.

Overall we’re so much better at this than 10 years ago. Being unsatisfied with 1 ach50 was nuts in the US 15 years ago.

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8valvegrowl t1_j6nzfc1 wrote

For sure...I seem to recall my house fell in the 0.5-0.75 ACH50 range, which is pretty tight. Interesting to know that foam prices have risen so much. We paid as much for the SIPS as we did for the timber frame (About $30K for frame and $30K for SIPS in 2019 prices)

Is the double stud scheme staggered? It's pretty fascinating how much the state of the art changes in building tech...seems like so much is pretty much built using legacy techniques still.

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SomeConstructionGuy t1_j6o1e1o wrote

That’s still a very tight house, nice work!

It depends on the builder/architect/engineer. I like to treat the interior wall as non load bearing and stagger it from the exterior. More thermal break makes me feel good and then we can make the stud layout an even 16” from one corner on the inside so drywall and trim are easy. Realistically if the wall is 10” thick you still get an r12 break wirh aligned framing and the total r value is only knocked down by 5% or less.

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8valvegrowl t1_j6o2406 wrote

Yeah, makes sense. Good stuff. I know in the future if we have an addition made for a first floor bedroom, we may consider stick built on a slab, so great to hear about options for construction! Thanks for all the info.

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recyclopath_ t1_j6p5u4k wrote

The US has a Passive House standard, the above commenter used the German spelling, that is much better aligned with US climate zones. Getting your home Passive House Certified is likely a bit over rated, like many certifications unless they open up funding.

You can absolutely build a Passive House without getting it certified which is totally worth is.

That being said, there are freaking excellent green building experts in Vermont with loads of experience who can guide you on what approach is right for you.

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