8valvegrowl t1_j6nnwvb wrote on January 31, 2023 at 4:52 PM

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

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.

SomeConstructionGuy t1_j6nr9ld wrote on January 31, 2023 at 5:12 PM

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.

8valvegrowl t1_j6nzfc1 wrote on January 31, 2023 at 6:02 PM

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.

SomeConstructionGuy t1_j6o1e1o wrote on January 31, 2023 at 6:14 PM

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.

8valvegrowl t1_j6o2406 wrote on January 31, 2023 at 6:18 PM

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.