'Passive house' survives fire in California | Hacker News Reader

'Passive house' survives fire in California

yahoo.com

33 pointstehnub62 comments

This is not a passive house, this was confirmed by a builder on Youtube who contacted the architect.

The features called out that contributed were - Stucco siding - Metal roof with no overhangs - ~4' tall concrete wall - 1 hour fire rated exterior wall assembly

also it looks like this house was not in the depths of the raging wildfire.. the tree's are still there and what we can see of the houses behind it are in tact...

this seems like a very very misleading article.

Passive houses are great, and I support them being a standard. But its not going to make it fireproof.

For folks in the east bay area, the Berkeley fire department gave a great talk on fire risk reduction: https://www.youtube.com/watch?v=0MUh16czYGk&t=239

In the past year, I’ve added gutter guards, removed trees in zone zero (especially fire-prone cypress), and hardscaped zone zero. I need to look into whether we can do more sealing like this passive house- bit tricky with 1950s construction.

You might look into this product https://www.wildfiredefensemesh.com/wdm-products/wildfire-de... for your soffit holes

Reminds me of my home here in Germany. I guess it’s not as sophisticated as the architects where more concerned with energy savings then fresh air. Means in the early years we had to vent the house manually a lot. I friend of mine renovated his house and installed on top an automated air refresh system. I wish my house had the same.

What I mean specifically is that around 2010ish the energy footprint started to be become more and more important. Currently the building codes here are so crazy that building a new house demands quite the upfront costs.

Pretty sure the passive house "movement" started in Germany?

Looks like this type of passive house was a Swedish/German innovation:

> The passive house standard originated from a conversation in May 1988 between Bo Adamson of Lund University, in Sweden, and Wolfgang Feist of the Institut für Wohnen und Umwelt (Institute for Housing and Environment), in Darmstadt, Germany.[13] Their concept was developed through a number of research projects with financial assistance from the German state of Hesse.[14]

https://en.wikipedia.org/wiki/Passive_house#History

See didn’t know that :). Only that we are crazy in Germany not to put any ACs etc into our houses. I mean I don’t complain about my heating system. My house uses water based floor heating. I love it. Newest trend is to put it in the ceiling because the floor radiation tends to reach only the legs or some people feel it that way. But the summers can be rough.

The latest trend is to change your underfloor heating to a air-to-water heatpump system. In theory that can be used to heat and cool. They can also achieve very high SCOP values, meaning you need less energy. Air-to-air heatpumps (aircons that can heat and cool) have the downside that in heating, they disturb the boundary layer around a person, so the perceived temperature is lower. They also have a much more limited SCOP range - mostly because the delta temperature has to be higher.

Edit: I forgot to mention - in some countries installing a heatpump that can also cool does not qualify for government subsidies - so many of them don't have that feature. This seems like a really short-sighted decision IMO.

Yes your last edit is also a thing that baffles me. Heat pumps abilities are mainly advertised with heating applications. That they can run in reverse is too often missing.

I exclusively think of it in the reverse: An A/C that can also heat your home.

One problem of cooling floors this way is moisture. You'll get wet floors if you also don't use traditional air conditioning.

a system with a dew point sensor prevents this, but it does limit the effectiveness

Yes, but as long as you keep it above the dew point, it's not an issue. You also don't want to cool it below that for another reason - it's unpleasant to walk on.

The idea is that you design it so that you have adequate energy transfer with a minimum temperature delta. Then you don't have to go below dew point and the heat pump can run at a higher SCOP/SEER.

That doesn't sound like Passive House design, having proper ventilation is a huge part of the methodology (basically always using mechanical heat or energy recovery ventilation).

Trying to seal a house to save energy but not having mechanical ventilation is just poor design.

I didn’t say it is one. Parts remind me. Triple glazing and the stuff.

Most passive house designs suffer from that.

You guys in Germany have those crazy automated metal shutters on some homes. They would have been a good thing in LA I think (I'm not in LA) or in any fire zone, maybe? I've read many homes burned because windows shattered from heat which then allowed the embers and fire to ignite furniture.

The shutters are actually pretty common , even not motorized ones. Not sure what the availability is in the US, but purchase and installation in NL is under €1000.

I'd love to know more about the windows. The architect's thread on Twitter mentioned that the windows are made of tempered glass, but I don't know if that's significant because they withstood impact damage better, or rejected heat better, or for some other reason.

Often there are flammable interior furnishings close to windows in a home (e.g. fairly flimsy cloth curtains). I wonder if the radiant heat of a nearby structure or vehicle fire is sufficient to ignite them through a typical residential single-paned window. In other words, is there a fire danger even when the window pane doesn't break and embers or hot gases stay on the outside?

> Though still a fairly new trend on the market

Passive Houses are a thing since the seventies or so and fairly common since the nineties. Does that still count as a "new trend" in real estate?

I’d say so.

Houses have been around for a very very very long time, but the technology around them doesn’t change all together that much.

I've head that fire resistance and earthquake resistance work against each other. That the things that make a house fire resistant - stucco/metal roofs - are bad for earthquakes and the things that make earthquake resistance - flexibility - are bad for fire resistance.

Reading just a bit it seems like the question is how you get that flexibility; the easy way would seem to be building with wood which is tricky with fires.

Any truth to this?

I’m not an engineer/have no formal training in this area. My hunch is that your statement is perhaps true at a scale of a house. For large builds like sky scrapers you’re definitely able to include fire resistant and earthquake resistance features. I think ultimately it comes down to cost. It’s possible to get treated lumber that is fire resistant, but it’s going to cost much more than traditional lumber

Reminds me of this story about this hurricane-resistant house left standing in Mexico Beach, FL after Hurricane Michael:

https://www.nytimes.com/2018/10/14/us/hurricane-michael-flor...

How does an airtight house work day-to-day? If I don't open a window, how quickly am I poisoning myself?

Not knocking the idea, I've heard of them before and experienced the joy of triple pane glass (both in insulation and noise protection)

They have heat recovery ventilation systems which bring in fresh air and send out stale air, capturing the heat in the process. But yeah, I am not sure what happens to air quality if the power goes out - I suppose you have to crack a window.

But yeah, I am not sure what happens to air quality if the power goes out - I suppose you have to crack a window.

So much for being "passive" then...

"Passive House" is a well defined term. It's a house that gets almost all of its heating from "passive" sources like insolation, or the appliances that run in the house.

I'm going to err on the side of caution and say that they were making a joke, as if the task of "occasionally opening a window" was enough to invalidate the entire concept of passivity from a passive house.

I was more referring to the fact that a "passive" house seems to actively require power to remain inhabitable.

They still have windows that you can open

The article mentions "Heat recovery ventilation", which means things like air exchangers [0] which pre-heat or pre-cool incoming air.

It is an active ventilation though, so you better run it periodically, even if you do not need heating/cooling. Your thermostat will have special setting for that, don't turn it off.

[0] https://www.productcleaningsolutions.com/blog/what-is-an-air...

Going off Wikipedia: When outside temperature is good natural ventilation is used, otherwise a heat recovery ventilation system is used to replace all inside air every ~2 hours. So to answer your question: you don't need to open windows for ventilation.

Moderately well sealed houses still exchange quite a lot of air, but if it wouldn't be satisfactory, they often have a fresh air vent usually with a heat exchanger to maintain heating and cooling efficiency. The HRVs and ERVs mentioned in the article are these kinds of devices.

I've had problems with some apartments where I had to have at least one window open 24/7 to keep the CO2 under 800ppm which is double the outside value. I feel a little unfocused at that level (standards say that starts at 1000ppm, I think I may be a little worse off with a broken nose).

Levels of CO2 which have detectable effects are easy to attain in a well sealed home. Levels which will result in a medical emergency (tens of thousands of ppm) are very hard to reach unless your house is sealed like a submarine.

I connected the dots at an office from a few years back about why I couldn't get anything done after lunch. CO2 levels were near outside numbers first thing in the morning and >1500ppm in the afternoon because HVAC was poorly done.

I suspect they set the recirculation as high as they legally can, to reduce HVAC costs.

Do you turn the HRV off during a wildfire to stop smoke intrusion from destroying the house?

Maybe? But at least air coming in the HRV is filtered, unlike all the air that leaks into traditionally built homes.

I'm curious what temperature its contents reached.

The house is airtight, and air is a great thermal insulator. I wouldn't be surprised if the interior remained a comfortable temperature the whole time.

couldn't houses be clad with something like Space Shuttle heat tiles?

Fitting a house with them would push it into mansion price ranges. The per-tile costs I could find when searching look to be around $1000.

Many of the houses in the PP are already worth 7 or 8 figures.

weren't these called "superinsulated" just a few weeks ago?

"other construction material more fire resistant than plywood box held together by spit and prayer"

How interesting.

In all seriousness you could make a home from almost anything else and it would end up being more fire resistant. The flammability of your average US suburb has to rank somewhere near 1944 Tokyo.

We have two different building codes in the US, one for single family buildings and one for multi-unit buildings.

The single family code is optimized for cost, cheapness, ease, and speed. The multi-unit code is optimized for expense, difficulty, and making sure as little gets built as possible.

That means that even though the US suffers far more deaths from structure fires than the rest of the world, common-sense multi-unit designs like single-staircase that are present in safer countries are illegal in nearly all of the US.

How do you know it’s optimized either way?

It could be semi-random, based on a lot of events, motivations, etc., that occurred or didn’t occur by chance.

The earliest authors of the codes were very clear about these motivations, in books from the time, which I do not have handy. So, take that as you will from a random internet commenter.

But I think that even without the motivations being written out, it's pretty clear in the nature of their differences.

> The flammability of your average US suburb has to rank somewhere near 1944 Tokyo.

Funfact: in large parts of Central Europe (ex austrohungary), wooden homes were banned after a series of large fires in the 1800’s. Brick was considered to give people a better chance.

Although it turns out that’s really bad for earthquakes …

You can use reinforced masonry in earthquake areas. Unreinforced masonry is prohibited in California building codes. Probably can't retrofit that though.

Seen from western europe, that kind of cheap house construction looks absolutely insane.

I've seen videos of houses being built in the US and I'm not sure my local construction workers would believe it if I show it to them.

Wooden building construction for single-family homes is not unusual here (Germany) either, especially for prefabricated buildings. It's cheaper than bricks or premade concrete elements and easier to insulate. From the outside you usually won't see a difference.

I've never seen that on my side in France, the only way you would get a wooden house is some cottage in the middle of the mountains and even that, they are usually only coated wood and are actually made of concrete or rocks behind.

The old houses are made with rocks and the new ones with concrete. The wood is usually just a decoration on top.

Considering that cladding/siding is independent of the construction method, it may not even be visible. Even prefabricated buildings made from wood might have plaster outside, just as concrete buildings could be clad with wood.

Yes that's possible, however the usual fashion is to have the top of the house plastered wood and the bottom left in concrete or rock so you can guess how it's made.

One thing I'm curious about is how the CO2 levels in these "passive houses" look. If there's limited indoor to outdoor air exchange, wouldn't they build up? Is there a scrubbing mechanism?

I answered elsewhere: They have heat recovery ventilation systems which bring in fresh air and send out stale air, capturing the heat in the process

Yep. These make the air quality a lot better as well, since you have control over most incoming air.

Of course, if you build a house with a tight envelope and reduce air circulation, you can easily have poor indoor air quality. You still need a strategy for this, and in my opinion, it’s very overlooked.

https://www.researchgate.net/publication/273588438_Building_...

Yes, and the article mentions the HRV and ERV systems these homes typically come with.

Air exchangers are one of the key HVAC considerations for passive houses... not sure how that could be considered overlooked.

> Balanced Ventilation with Heat & Moisture Recovery

> With an airtight enclosure, continuous, balanced ventilation is absolutely critical to indoor air quality (IAQ). Passive buildings continually exhaust air from bathrooms, kitchens and other areas with stale air and supply fresh air to living and working space

https://www.phius.org/passive-building/what-passive-building...

It is not - IRC (International residential code) requires whole house mechanical ventilation (like the forementioned ERV/HRV) if a house is measured at < 5 ACH50.

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