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Comment by zdragnar | Hacker News Reader

Insulation does matter, but American insulation is also pretty strange- it is all rated by R value, which is only meaningful if you have a really good airtight seal. Any drafting ruins the insulative value very quickly.

Aerated concrete doesn't have that issue, because the concrete cells are closed and don't draft. If you end up with a poorly fitted window or 50+ mph winds, it doesn't let air through.

OTOH, totally agree about wood. Cheap(er), plentiful, and most importantly, everyone already knows how to work it and has the tools to do so.

Masonry work is physically harder, requires a sounder foundation that won't settle at all due to the increased weight, and there are fewer people willing to do the work. Getting anyone to do foam or aircrete is impossible- you have to watch a bunch of YouTube videos and DIY it yourself.

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> Insulation does matter, but American insulation is also pretty strange- it is all rated by R value, which is only meaningful if you have a really good airtight seal.

You're not wrong, but IMHO the two should be handled separately. The fact that airtightness has been less stringent in the US is mostly an accident of history, which is being improved with recent building codes. It's just that in the past it was easy for people to simply buy some fluffy stuff and stuff it into the walls: doing blower door tests is a lot more complicated.

Building science has also progressed quite rapidly in the last 2-3 decades, and we now 'know better' in many areas than in the past.

> Aerated concrete doesn't have that issue, because the concrete cells are closed and don't draft. If you end up with a poorly fitted window or 50+ mph winds, it doesn't let air through.

First: what's the carbon footprint of concrete? What is footprint of wood framing?

Not letting air through (in or out) is actually what you want. The structures of buildings should not pass any air at all ideally, and all air exchanges should be done primarily via mechanical means:

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

I should edit that- I meant that even with a poorly fitted window or 50+ mile winds, the closed cell nature of the concrete doesn't let air circulate through it, while fiberglass does.

Such is, my point was that foam boards and concrete are compared to blown / rolled fiberglass, even though the fiberglass has more failure modes for insulating. A poorly fitted window will seriously compromise the R value of the surrounding fiberglass.

As for the carbon footprint of cement, solid is pretty high, foam not so much. I don't know about commercial stuff, but most DIY'ers seem to use a little under 100 lbs portland cement to make a 55 gallon barrel's worth once the foam is mixed in. Rough math puts a 55 gallon barrel of concrete at about 1000 pounds.

Edit: I just realized that 10% seems low, so what I saw may have used a 55 gallon barrel but not completely filled it. In any case, depending on the structural integrity that you need, the weight reduction (and therefore carbon footprint from curing) is significantly reduced.

We're living in an airtight, concrete, triple glazed house in europe with mechanical ventilation with heat exchange, plus heat pump on a ground source for heating amd (moderate) cooling. It's amazing, temperature is great 24/7 year round.

Having said that, your point about footprint holds and building with wood is coming 'back' here especially because of that, using cross laminated timber from sustainable forests.

> First: what's the carbon footprint of concrete? What is footprint of wood framing?

Carbon footprint of wood framing is terrible, because its mostly made of engineered wood with a lot of oil in it.

> mostly made of engineered wood with a lot of oil in it.

[citation needed]

Certainly LVL and LSL products are more processed, as is OSB, but those have the advantage of using 'off cuts' so they can use up some of raw materials that might otherwise be thrown out.

Even with all that processing I find it hard to believe that it would be worse than concrete, given the amount of (fossil fuel?) energy needed for cement kilns and other things.

* https://en.wikipedia.org/wiki/Environmental_impact_of_concre...

... is the oil burned?

Insulation in the UK at least is also rated by R-value (or U-value, where U = 1/R). Can't speak to the rest of Europe.

Standard Assessment Producedure (which is used for household energy ratings) incorporates both this and some fudge factors for draftiness and local wind speed.

In the United States, masons and concrete (including aerated) are quite common; rarity doesn't factor into it. DIY is not necessary.

  You misunderstand building construction. American insulation is, indeed, rated by R value, its resistance to the conductive flow of heat. *Any* draft will bypass insulation of any material. A leaky window will leak air, regardless of the construction material of the wall. American wooden buildings are sealed with sheet plastic, Tyvek, etc. to prevent drafts; all part of the insulation.

Tyvek: https://en.m.wikipedia.org/wiki/Tyvek

Looks like you did not understand that comment. Concrete will not let a draft through no matter where the wind hits. For fiberglass and others, one bad fitting means a current can form through the material. This is why you need tyvek to begin with.

How does concrete stop a draft that is going between a window frame and the wall itself?

I've never had a draft through a fibercement/wood/fiberglass/drywall wall, in any case.

A poor fit, minor damage, or any defect allows convection within the fiberglass. R-value assumes zero air movement, which is why it is far less useful comparing fiberglass to foam or aerated cement. In real world settings, aerated cement will outperform fiberglass.

The same thing can happen when concrete cracks, which is quite common. All of this a question of basic building maintenance rather than the building materials chosen.

Cracking is why single family homes generally avoid concrete walls in the permafrost.

You are misunderstanding the American building system. We don't use fiberglass insulation by itself. You're picking a small part of a greater system and complaining it doesn't work in isolation. There are multiple layers to our construction and it's effective.

As for the wall material stopping drafts in a window frame, that makes no sense at all.

Exactly, the critique is that you need multiple layers, and if one fails, the R values you thought you had go out of the window. Whereas a concrete, wattle and daub etc wall will tolerate less-than-perfect fitting and maintenance. Of course if you assume construction is flawless, there will be no issues, and that’s the usual case.

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