Does anyone have experience with pre-fab 'Passive Homes'? Should they cost $500k

[STEMorbust]

Hi all, my wife and I are saving up to buy land to develop and eventually retire to. We're interested (but not committed) to building a "passive house". That is a home that is built in a way that minimizes carbon emissions and requires little heating and cooling. More info here: https://passipedia.org/basics/what_is_a_passive_house

I'm wondering if anyone on the forum has experience going this route. What builder did you use? Did your costs stay consistent with the estimate? Would you do anything differently?

We're excited by the prospect of minimizing our environmental impact in our forever home, but want to iron out the cost of doing so. I'm forever spoiled by MMM building his $30k ADU shed.

[affordablehousing]

A friend built a high quality passive yoga studio, so it included a bathroom but no kitchen. The cost was ~$300K for 800 square feet, no permits. That was a good deal and done about 6 years ago. Any high quality contractor who watches youtube for continuing ed could figure out the insulating and ventilation quirks of a passive house construction.

[Jon Bon]

So south facing and super insulated? 300k for 800sqft 6 years ago is a good deal? I'd like to know a bit more about where the costs are coming from on this.

I just did my addition, triple pained windows, r-19 walls plus r-5 exterior insulation, R-60 in the attic, heat pump etc. I did not pay anywhere close to those prices.

I get most houses are built to "meet code" at the lowest price point possible. They are also not very efficient. As a general rule you can make a house 50% more efficient for maybe 10-20% more costs? But after that you get diminishing returns is my experience in home building.

[joenorm]

Passivhaus is typically way overkill and a VERY expensive way to build. I would look into the Pretty Good House concept(PGH).

Don't get me wrong, lot's of cool concepts. But they take it to an extreme that quickly enters the realm of diminishing returns. 

[Fresh Bread]

We built one! Not pre-fab though, it was custom. It cost a fortune, similar to those above, but I'm in another country and in a very expensive part of that country so builders rates are eye watering. It's my understanding that passive houses should cost approx 10% more, but that's 10% more than a standard good quality custom build, which is not cheap either.

The one area that cost a lot (I'm talking thousands) was outside the build, being the PH certification. The architect did it and the detail the certifier needed required a lot of time/fees, possibly as the architect was reasonably new to it too. That in hindsight is the one thing I might do differently. If we build another I definitely wouldn't bother certifying. I'd still do the blower tests etc though.

We used a few nice finishes like hardwood cladding but the materials were irrelevant compared to labour costs. The builder was also the project manager, but what you spend there keeps things running to schedule if that's important to you. 

We used a very good builder but ours was his first passive house. He did a practice run on an extension at his place and also a course. We had overuns on cost but mostly not to do with the PH requirements, the only exception being that after our first blower test, we had to put membrane on the floor as well as the walls and ceiling.

If you are interested I can pm links to our project.

[Fishindude]

I get most houses are built to "meet code" at the lowest price point possible. They are also not very efficient. As a general rule you can make a house 50% more efficient for maybe 10-20% more costs? But after that you get diminishing returns is my experience in home building.

I would argue than most new homes, even the lower cost stuff is being built to better energy standards than ever.

[Moonwaves]

This thread reminded me about seeing a pre-fab house on Grand Designs once and I thought I'd google to see if that company is still around. It's called Huf Haus (and is still around) but I typed Hupfhaus when googling and was puzzled for a minute as to why I was seeing pictures of bouncy castles. Apparently the German for bouncy castle is in fact stuck in my head somewhere. That's of no relevance to this thread but it made me laugh when I realised so I decided to share anyway. :-)

[PDXTabs]

I don't know the answer to this question. I do know that there are some kit homes using SIPs which I look at sometimes such as the ones from Mighty Small Homes. Eg, The Contemporary. Do SIPs provide enough insulation for your needs? I'm curious.

[Jon Bon]

I get most houses are built to "meet code" at the lowest price point possible. They are also not very efficient. As a general rule you can make a house 50% more efficient for maybe 10-20% more costs? But after that you get diminishing returns is my experience in home building.

I would argue than most new homes, even the lower cost stuff is being built to better energy standards than ever.

Yes they update the codes over time for better insulation.

I guess my point is you can do R-49 in the attic to meet code, or spend an extra $500 bucks and get r-75 plus. r13 in walls or get north of r20 with exterior insulation for a few thousand.

None of that is very expensive compared to the total cost of a house. This kind of feels like greenwashing. Do the stuff I mentioned, have a super efficient house. Or use a "specialty" and get a fancy certification for 100k more with very little real world benefit.

So in conclusion I have not done a passive home, but making your house 2-3x more insulated might only add 5% to the total cost.

YMMV

[bacchi]

I get most houses are built to "meet code" at the lowest price point possible. They are also not very efficient. As a general rule you can make a house 50% more efficient for maybe 10-20% more costs? But after that you get diminishing returns is my experience in home building.

I would argue than most new homes, even the lower cost stuff is being built to better energy standards than ever.

Yes they update the codes over time for better insulation.

I guess my point is you can do R-49 in the attic to meet code, or spend an extra $500 bucks and get r-75 plus. r13 in walls or get north of r20 with exterior insulation for a few thousand.

None of that is very expensive compared to the total cost of a house. This kind of feels like greenwashing. Do the stuff I mentioned, have a super efficient house. Or use a "specialty" and get a fancy certification for 100k more with very little real world benefit.

So in conclusion I have not done a passive home, but making your house 2-3x more insulated might only add 5% to the total cost.

YMMV

Yep.

As someone mentioned above, my GC literally watched youtube on how to add exterior insulation on the roof and walls. I wasn't going for a LEED house with all the checklists and substitutions though.

[STEMorbust]

Passivhaus is typically way overkill and a VERY expensive way to build. I would look into the Pretty Good House concept(PGH).

Don't get me wrong, lot's of cool concepts. But they take it to an extreme that quickly enters the realm of diminishing returns.

I love this. Wasn't sure if you were kidding about Pretty Good House being a thing. I'm looking forward to watching their two-hour video on designing a PGH. It's right on their homepage if anyone is curious: https://www.prettygoodhouse.org/

The first paragraphs of their summary hit the nail on the head (https://www.prettygoodhouse.org/the-whole-shebang-in-one-reading):

"Key to the PGH approach is balancing expenditures and gains. Where other programs use specific energy-use targets or other criteria, and the building code establishes a baseline (“the worst house you can legally build”), a PGH goes above code until it stops making financial sense. On some new homes, that may be not far above code, and on other projects performance may rival that of a Passive House, but in most cases it will be somewhere in between those two standards.

How do you decide what makes financial sense? One approach is to look at the payback--the time it would take for an upgrade to pay for itself. A better way is to look at the return on investment, or ROI. Energy and maintenance costs are fairly steady and easy to predict, so you can choose what level of return you would like to see. Using a simple formula, ignoring the effects of compound interest and inflation, improvements with ROI of 5% or higher are generally a good investment. Even a 2% ROI may be competitive with secure investments such as CDs. Lower ROIs may not make financial sense but should be considered if there is an environmental benefit, such as lower embodied carbon emissions."

[STEMorbust]

We built one! Not pre-fab though, it was custom. It cost a fortune, similar to those above, but I'm in another country and in a very expensive part of that country so builders rates are eye watering. It's my understanding that passive houses should cost approx 10% more, but that's 10% more than a standard good quality custom build, which is not cheap either.

The one area that cost a lot (I'm talking thousands) was outside the build, being the PH certification. The architect did it and the detail the certifier needed required a lot of time/fees, possibly as the architect was reasonably new to it too. That in hindsight is the one thing I might do differently. If we build another I definitely wouldn't bother certifying. I'd still do the blower tests etc though.

We used a few nice finishes like hardwood cladding but the materials were irrelevant compared to labour costs. The builder was also the project manager, but what you spend there keeps things running to schedule if that's important to you. 

We used a very good builder but ours was his first passive house. He did a practice run on an extension at his place and also a course. We had overuns on cost but mostly not to do with the PH requirements, the only exception being that after our first blower test, we had to put membrane on the floor as well as the walls and ceiling.

If you are interested I can pm links to our project.

I'd definitely like to check it out.

[STEMorbust]

I don't know the answer to this question. I do know that there are some kit homes using SIPs which I look at sometimes such as the ones from Mighty Small Homes. Eg, The Contemporary. Do SIPs provide enough insulation for your needs? I'm curious.

Some Googling tells me that SIPs can be up to R-58 for 12-inch think walls. That'd definitely be sufficient for Northern Vermont. I wonder how much cost those thick panels would add, though. Would SIP be any cheaper than a Passivhaus?

[STEMorbust]

I get most houses are built to "meet code" at the lowest price point possible. They are also not very efficient. As a general rule you can make a house 50% more efficient for maybe 10-20% more costs? But after that you get diminishing returns is my experience in home building.

I would argue than most new homes, even the lower cost stuff is being built to better energy standards than ever.

Yes they update the codes over time for better insulation.

I guess my point is you can do R-49 in the attic to meet code, or spend an extra $500 bucks and get r-75 plus. r13 in walls or get north of r20 with exterior insulation for a few thousand.

None of that is very expensive compared to the total cost of a house. This kind of feels like greenwashing. Do the stuff I mentioned, have a super efficient house. Or use a "specialty" and get a fancy certification for 100k more with very little real world benefit.

So in conclusion I have not done a passive home, but making your house 2-3x more insulated might only add 5% to the total cost.

YMMV

Makes me wonder -- is there any benefit to having certification as a Passive House? I can't find anything obvious for the state of Vermont, but reached out to a local construction company that is listed as having done most of the Passive House projects in the state in hopes that they have additional information.

[nereo]

I don't know the answer to this question. I do know that there are some kit homes using SIPs which I look at sometimes such as the ones from Mighty Small Homes. Eg, The Contemporary. Do SIPs provide enough insulation for your needs? I'm curious.

Some Googling tells me that SIPs can be up to R-58 for 12-inch think walls. That'd definitely be sufficient for Northern Vermont. I wonder how much cost those thick panels would add, though. Would SIP be any cheaper than a Passivhaus?

SIPs are a material used to quickly build exterior walls with minimal thermal bridging.  Passivhaus is a set of standards which outline everything from the insulation to the air-tightness to the heating/cooling loads and solar gain.

Many passivhaus certified homes use SIPs to meet the standards. Many SIP constructed homes come no where near Passivhaus.  As with the building code, it takes into account the region, but wall R-58 would be enough to hit that mark.

There’s also a number of ways to hit passivhaus without SIPs, like double-wall construction.

[Jon Bon]

I don't know the answer to this question. I do know that there are some kit homes using SIPs which I look at sometimes such as the ones from Mighty Small Homes. Eg, The Contemporary. Do SIPs provide enough insulation for your needs? I'm curious.

Some Googling tells me that SIPs can be up to R-58 for 12-inch think walls. That'd definitely be sufficient for Northern Vermont. I wonder how much cost those thick panels would add, though. Would SIP be any cheaper than a Passivhaus?

SIPs are a material used to quickly build exterior walls with minimal thermal bridging.  Passivhaus is a set of standards which outline everything from the insulation to the air-tightness to the heating/cooling loads and solar gain.

Many passivhaus certified homes use SIPs to meet the standards. Many SIP constructed homes come no where near Passivhaus.  As with the building code, it takes into account the region, but wall R-58 would be enough to hit that mark.

There’s also a number of ways to hit passivhaus without SIPs, like double-wall construction.

I have no idea about the cost of SIPs but I think its safe to assume it is a bit more?!

If the goal is a high r-value why not go 2x8 framing, spray foam or fiberglass, and exterior foam panels? Cheap and reliable building products. I feel like that is much easier to achieve then some of the gimmicky products out there. IMO an efficient house is not some mystery that only these highly paid specialty contractors can solve. Its just making your wall thicker!

[nereo]

I have no idea about the cost of SIPs but I think its safe to assume it is a bit more?!

If the goal is a high r-value why not go 2x8 framing, spray foam or fiberglass, and exterior foam panels? Cheap and reliable building products. I feel like that is much easier to achieve then some of the gimmicky products out there. IMO an efficient house is not some mystery that only these highly paid specialty contractors can solve. Its just making your wall thicker!

Well, there's a big "it depends" here.

There are two major advantages of SIPs - 1) they virtually eliminate all thermal bridging (resulting in a higher R value for a given thickness) and 2) they slot together to form load-bearing walls very, very quickly (compared to other construction methods).

In general the material costs are much greater than 2x4 framing (but less than 2x8 framing when we priced it out in our neck of the woods).  The cost of freight and a crane rental (if you are doing a SIPs roof and/or very large panels) can be considerable, depending on your location and site.  But increased material cost can more than be made up for with the decreased labor costs relative to traditional stick-frame homes. I've seen SIP homes go from a slab to a completely water-tight envelop in three days, with the glazing taking about as long as installing the panels. A similar stick-framed house might take 3 weeks, providing all the subs show up and all the materials are on site.  If you are building a 1-story home it's possible for 2-3 relatively unexperienced DIYers to

As for being 'gimmicky' - they've been around for almost a hundred years, and heavily used over the last 30+.  There's a reason why a higher percentage of high-end homes use them over stick framing.

One downside to be aware of - it takes a lot more thought to modify the exterior envelope of a SIPs home than stick-frame construction.  If you decide you want to widen a doorway or add a window somewhere that's pretty straightforward with 2by construction.  It's also very important to make sure the seams are properly sealed - a lot of early failures with panels came when the exterior plywood rotted due to water penetration, and because it's laminated to the foam it's not as straightforward as simply replacing the wood as you would replacing the shear panels.  You also have to consider where your electrical and plumbing chases will go during the design phase - you aren't going to run another circuit inside that wall ('through' penetrations are fine though).

[STEMorbust]

I have no idea about the cost of SIPs but I think its safe to assume it is a bit more?!

If the goal is a high r-value why not go 2x8 framing, spray foam or fiberglass, and exterior foam panels? Cheap and reliable building products. I feel like that is much easier to achieve then some of the gimmicky products out there. IMO an efficient house is not some mystery that only these highly paid specialty contractors can solve. Its just making your wall thicker!

Well, there's a big "it depends" here.

There are two major advantages of SIPs - 1) they virtually eliminate all thermal bridging (resulting in a higher R value for a given thickness) and 2) they slot together to form load-bearing walls very, very quickly (compared to other construction methods).

In general the material costs are much greater than 2x4 framing (but less than 2x8 framing when we priced it out in our neck of the woods).  The cost of freight and a crane rental (if you are doing a SIPs roof and/or very large panels) can be considerable, depending on your location and site.  But increased material cost can more than be made up for with the decreased labor costs relative to traditional stick-frame homes. I've seen SIP homes go from a slab to a completely water-tight envelop in three days, with the glazing taking about as long as installing the panels. A similar stick-framed house might take 3 weeks, providing all the subs show up and all the materials are on site.  If you are building a 1-story home it's possible for 2-3 relatively unexperienced DIYers to

As for being 'gimmicky' - they've been around for almost a hundred years, and heavily used over the last 30+.  There's a reason why a higher percentage of high-end homes use them over stick framing.

One downside to be aware of - it takes a lot more thought to modify the exterior envelope of a SIPs home than stick-frame construction.  If you decide you want to widen a doorway or add a window somewhere that's pretty straightforward with 2by construction.  It's also very important to make sure the seams are properly sealed - a lot of early failures with panels came when the exterior plywood rotted due to water penetration, and because it's laminated to the foam it's not as straightforward as simply replacing the wood as you would replacing the shear panels.  You also have to consider where your electrical and plumbing chases will go during the design phase - you aren't going to run another circuit inside that wall ('through' penetrations are fine though).

Thank you for the detailed information. I've gawked at some incredible SIP builds on Netflix series but never grasped the implications of going with one. I'll look to chat with a builder that does both styles of construction and can give a sense of the cost and trade-offs. This would be a fairly rural area so I expect SIP to be at a premium.

[joenorm]

Sounds like you are interested in high performance buildings. Check out greenbuildingadvisor.com

lots of good stuff there.

[Jon Bon]

There are two major advantages of SIPs - 1) they virtually eliminate all thermal bridging (resulting in a higher R value for a given thickness) and 2) they slot together to form load-bearing walls very, very quickly (compared to other construction methods).

I agree with both of these statements. The thermal bridging is a big deal. The speed of construction is nice, but less important for most people.

As for being 'gimmicky' - they've been around for almost a hundred years, and heavily used over the last 30+.  There's a reason why a higher percentage of high-end homes use them over stick framing.

I guess my point is that SIPs in of themselves are fine, but the increased cost is substantial. The Gimmick is that you need a fancy outfit to achieve such results. I have also seen things like "t-studs" and insulated zip sheeting. I am sure they work, but the price premium is just ridiculous. They are the building equivalent of the new EV hummer. Yes it works, but there are much cheaper options.

Exterior insulated sheets and spray foam with trinational stick framing can achieve the same results with a much lower cost. This can be done by "regular" subcontractors. Its not difficult of complicated. Now would SIPs still be 1-10% more efficient? Probably? But I cant see how that is worth 50% more. So many people are subjected to marketing that is heavily greenwashed, and SIPs are a fantastic albeit expensive method. I just want OP to know there are options.

[joenorm]

Arguably the cheapest way to get good R-value is to build with 2x8's for the walls with dense packed cellulose or blown in fiberglass as insulation. You can even use "advanced" framing techniques which minimize lumber use and reduces thermal bridging.

For the roof build a standard gable with a reasonable pitch and fill the attic floor with a thick layer of insulation, maybe R-80.

This combined with paying close attention to air sealing the envelope and using decent and windows and not too many of them can get you far along the road to Passiv Haus at a much better price.

Air sealing is likely the most important part. All the insulation in the world doesn't stop cold air infiltration. And remember as the house gets tighter and tighter you'll have to introduce fresh air for breathing, so you'll want to design in an ERV/HRV of some sort.

[nereo]

There are two major advantages of SIPs - 1) they virtually eliminate all thermal bridging (resulting in a higher R value for a given thickness) and 2) they slot together to form load-bearing walls very, very quickly (compared to other construction methods).

I agree with both of these statements. The thermal bridging is a big deal. The speed of construction is nice, but less important for most people.

I think the speed of construction is a core consideration, not just a "nice to have". Simply put 'faster' means 'less labor', which goes a long way towards balancing out the cost equation. With traditional stick-frame you've got a crew framing the walls, followed by sheathing, followed by house-wrap.  Meanwhile plumbers and electricians are drilling holes through the exterior walls to run the services before you can put up drywall. So materials cost less, but labor costs go up.

People look at the cost of SIP and think "hell, I could do that at 1/3 the cost with traditional materials" - and often they are right. But if you are paying a few hundred labor-hours to do all that the cost 'savings' quickly evaporates for anything but the most basic, built-to-spec homes. With SIPs you are paying for the factory to do most of these steps, and the installation costs are just a fraction.

Which puts us back to "it depends".  Sloped, wooded site with a two-story insulated roof requiring a big-ass crane and three-states from the nearest panel manufacturer for freight... yeah, it's going to be expensive as hell.  But for lots of houses in lots of places the cost premium is not what it appears to be.

Arguably the cheapest way to get good R-value is to build with 2x8's for the walls with dense packed cellulose or blown in fiberglass as insulation. You can even use "advanced" framing techniques which minimize lumber use and reduces thermal bridging.

For the roof build a standard gable with a reasonable pitch and fill the attic floor with a thick layer of insulation, maybe R-80.

This combined with paying close attention to air sealing the envelope and using decent and windows and not too many of them can get you far along the road to Passiv Haus at a much better price.

Air sealing is likely the most important part. All the insulation in the world doesn't stop cold air infiltration. And remember as the house gets tighter and tighter you'll have to introduce fresh air for breathing, so you'll want to design in an ERV/HRV of some sort.

Air-sealing is paramount, and for whatever reason gets lost in the chatter whenever people are discussing high-R values. A home which meets PassivHaus air-tightness guidelines but has 'just' modern-code insulation levels will have a lower heating and cooling load than one that goes much higher on the insulation but doesn't get the building envelope as tight.  On paper the jump from R-60 (upper threshold of 'recommended' by EPA) to R-80 in the attic is a 33% reduction for heat loss through the roof, but in reality it's going to be almost immeasurable, because at that point most of the thermal leakage is elsewhere.

In some places and during 'normal' times 2x8 framing may be the cheapest. It wasn't when we priced it out in our region.  It was actually much cheaper for us to do 2x4 and 2" of continuous exterior insulation. A 2x8" with blown cellulose gets you around R24 in the bays but around R-9 for the framing. Meh. The 2x4 will (obviously) have much faster heat transfer in the bays but less around the framing, and be tighter. In the real-world they seem to perform roughly the same. Of course an even better solution is 2x8 with advanced framing and then 2" (or more) of exterior insulation with seam staggered.  But at that point it's certainly not the cheapest build option, and also no longer the cheaper option over SIPs.

And one frustration I have with 'advanced framing' - I'm completely behind the idea. We've got over a century of data showing that 24" OC is plenty strong for everything a home experiences, particularly when stepping up to 2x6 or larger framing.  But I've had argument after argument from construction folks about it's viability. ok, /rant...