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Comment by leashless | Hacker News Reader

I have an ambition to live in an insulated metal barn. They’re incredibly cheap compared to regular construction. I would then construct smaller dwelling units inside of it, non load bearing, which could be played around with much like legos. (It may help to know I’m the designer of the hexayurt, a shelter technology popular at Burning Man and eventually bound for the world’s refugee camps.)

Key to this plan is handling humidity. Metal buildings don’t breathe. Humidity condenses on the metal, turns into mould, then you have real problems.

But with humidity sensors and A2A heat exchangers you wind up with the best of both worlds. I think.

Let’s say I’m not going to be building this before I’ve had real analysis from a good hvac engineer or two.

https://www.kitbuildings.com/products/insulated-steel-buildi... For a sense of prices.

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What makes barns cheap is the lack of glass windows, insulation, plumbing, carpets, climate control, decks, etc.

Add that stuff back in and you are just building a house.

> Metal buildings don’t breathe. Humidity condenses on the metal, turns into mould, then you have real problems.

Neither do modern homes made out of timber and wood sheathing. This is a good thing.

Humans need to breathe, not buildings. Buildings need to be able to dry:

* https://www.energyvanguard.com/book-house-needs-breathe-or-d...

* https://www.energyvanguard.com/blog/myth-a-house-needs-to-br...

* https://www.greenbuildingadvisor.com/article/buildings-dont-...

* https://www.youtube.com/watch?v=CIcrXut_EFA

What lets them dry is mostly air movement, which some people would calling "breathing".

The main difference between the "new" and the "old" approaches to this is that the new one calls for much more organized and controlled air movement, while the old one tended to just rely on leakage, well, pretty much everywhere.

There's a lot of variations of prefab sheds, metal roofs, etc in Australia.

    The vapour permeable sarking, separated from the roof sheet by a drainage batten provides drainage of any moisture or condensate forming below the roof sheet.

https://dctech.com.au/products/dct-r01-1c/

is a common housing solution - that's a "runoff sheet" immediately under the metal that allows vapor up to the metal and then catches condensed water and runs it down to the sides and out.

In a hot climate big wide roofs with a good pitch (and a venting cap gap at the ridge line) can heat air under the metal and use the rise of hot air (and out the ridge cap) to draw in air through (say) watered hedges.

You might get some ideas browsing Aussie prefab shed solutions, etc.

https://www.theshedcompany.com.au/barns/american-barns/

https://ams-group.com.au/

> The vapour permeable sarking

I would have hoped that with fairly good knowledge of both UK and US english construction terminology, AU english would have nothing left to confuse me with. But ... no. "Sarking" ?

The UK has a lot of dialects and the north (Scotland) has a lot of Danish hybrids unique to the region - curiously a bunch of those words survived better in the colonies (Australia, New Zealand, Canada, backwards parts of the US) than perhaps they did on UK soil.

    The word sarking is further used as part of the term scrim and sarking, a method of interior construction widely used in Australia and New Zealand in the late 19th and early 20th centuries.

    In modern usage of the term in Australia, sarking refers to a laminated aluminium foil layer, or reflective foil laminate (RFL), that is installed on the roof trusses, beneath the battens, supporting a tile or metal deck roof. It acts as additional radiative (radiant barrier) and convective insulation and provides a condensation barrier.

https://en.wikipedia.org/wiki/Sarking

https://www.bradfordinsulation.com.au/home-insulation/roof-s...

I don’t know where are you located. But I worked in insulated containers in south Germany. The office was being built. It was like sauna in summer and unpleasantly cold in winter. I guess you would need 10 inches of insulation to have acceptable result here.

There's a some research into thin internal wall insulation in the UK, because our housing stock is old and small.

Spray cork seems to come out the winner.

https://www.gov.uk/government/publications/thin-internal-wal...

and for a very recent (last week) US perspective on cork insulation (and siding), here's Matt Risinger (Build):

https://www.youtube.com/watch?v=iXY_f-bJDyA

You wouldn't need to have exterior load bearing construction inside, but I don't think that absolves all structural concerns. What about services (HVAC, electricity, plumbing)? What about interfacing with the outside world, i.e. windows?

Actually, I'm wondering why not more houses are build out of a metal-insulation sandwich contruction, one downside, no nails on the outside walls (but this can also be solved with a regular installation zone out of plywood, here is an example from one who built his own home out of a metal sandwich contruction: https://www.youtube.com/watch?v=brcGQZWbeLI according to him it was really cheap (don't know how it compares to wood framing with insulation)

wondering how prefacb metal sandwich construction compares to prefab wood framing (which is quite common here in germany)

Wood beam construction is really fast, cheap, and easy to insulate or modify.

People argue for all kinds of alternatives but the cost to construct a wood frame is only around 5% the cost of the home. Swapping to something else just doesn’t buy you much and most alternatives have significant downsides.

Barndominiums are really popular depending on where you live. I see them all the time in the United States, really popular for new construction custom home.

Interesting, but I don't see the massive cost advantage.

$150k for a 150 m2 kit. That's before you have constructed the outer shell or the internal dwelling(s). What am I missing?

The most expensive kit on the site (for me) is 50x15x7,3m which comes out to 750 m2 and it is 2 stories high, so that comes out to 1500 m2.

Flexibility to change things without massive costs maybe?

A drywall is then a solution. It can be build almost anywhere and removed within hours again.

You basically want balloon framing, in spirit if not in execution.

In old balloon framed houses you'll often find all the interior walls are not structural -- they were often built after the sheet rock was put in on the exterior walls and ceiling. That leaves you free to shift them however you please without compromising the stability of the house.

Buildings don’t need to breathe. They need some way to dry out, because there is essentially no such thing as perfect waterproofing.

I suspect the condensation problems in a barn like that are due to insufficient insulation or insufficient control of air movement. 50mm of polyisocyanurate is less than R10, which doesn’t come close to even the code minimums, and is totally inadequate for a roof of a house anywhere remotely cold. Separately, if it’s cold, then the interior surface of the metal will be cold, and any humid interior air making it to that surface will condense. A real house would do something to minimize that movement of warm interior air outward through the insulation.

Co2 build up and indoor pollution is a thing.

The building doesn't need to breath.

The building needs to have a supply of fresh air.

Both are true.

Indeed. You want fresh air (possibly filtered, heated, cooled, humidified and/or dehumidified) to enter the living space. This is not the same thing as air flowing through the walls, roof, etc.

In-laws have gone this route. I helped them install dense-pack-cellulose in the walls (like 8" of it or so). They have plenty of windows and tall ceilings. Doesn't feel dark or dank. I'm not sure what they have done in terms of indoor air quality but I'd definitely recommend an ERV.

I don't think they've had a mold issue, but it's only been a couple years. (I think with a lot of insulation there won't be condensation on the metal, but suppose bridging could still cause a way around this.)

Put a vapor barrier inside of the insulation--this is very typical in any cold climate construction. Then humidity inside doesn't matter, because it never touches a cold surface.

… but be careful when layering moisture barriers.

If you stack two moisture barriers with any void space or (other material) in between, you can create a space that moisture can enter … but never escape.

You will live in the dark :/

I guess cell phone reception would be an issue too.

Cell phone repeater tech isnt hugely expensive if you want to do it.

More expensive the bigger the installation. Some carriers offer basic units.

If your carrier supports wifi-calling then that can do most of it if you have decent internet.

Lies, all lies!

We have metal siding, and get bitten by RF issues over and over again. The back of the house is in a cell phone shadow. The WiFi access point on the roof has all sorts of unpredictable deadspots outside. The 900MHz weather station display has to be placed within a 2" square spot indoors. Also, the solar panels and batteries drop into "call installer" mode a few times a week when their mesh network collapses.

And so on. The internet of things will only make this worse over time.

People who understand wireless technology use wires.

That sounds like a way to get locked in by a particular carrier.

With how popular barndominiums are these days I don't think handling humidity is going to be that much of an issue. I have even seen some more like you described where they build the actual home on the interior of the metal structure instead of adopting the metal structure as the homes walls.

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