ᐅ Walls made of aerated concrete

Created on: 22 Jul 2015 19:53

Hello everyone,

I have already read and searched around a bit here, but I am still not quite sure.

We are planning to build a house. It will be a semi-detached house. We have been offered a house with 36.5cm (14 inches) aerated concrete exterior walls without additional insulation. The interior walls are also planned to be made of aerated concrete. Soundproofing boards are to be installed between the wall and the neighboring house.

I have to admit that I am quite a layperson and am slowly working my way through the very conflicting statements and information. We don’t want to build a passive house, but it should be future-proof and reasonably designed. Overall, I would like to aim for a kfw70 house, but that is not solely about insulation...

I have read various information about aerated concrete, clay blocks (Poroton), and also about prefabricated walls. I find it interesting that the U-value of the prefabricated walls is apparently significantly better than that of comparable solid walls (without additional insulation). However, I can’t really grasp what a difference of 0.1 W/(m²K) actually means in reality... I lack the practical understanding of this.

What I think I know:

- Aerated concrete can be installed without additional insulation. But is it any good!? Does it only just meet legal requirements, or is it also sensible to build this way?
- Aerated concrete has poorer sound insulation compared to sand-lime brick or clay blocks. This could be a problem especially for thin interior walls.
- Regardless of what I build (even without extra insulation), a controlled mechanical ventilation system is highly recommended because the houses are very airtight.
- Aerated concrete has poor thermal insulation properties in summer (I still don’t understand why a material supposedly insulates well in one direction – during winter – but not in the other – summer –?!).
- I have often read that the costs of adding extra insulation to a wall do not pay off over a reasonable period (in terms of heating savings – of course this also depends on the heating technology).

Could you help me clarify where I might be wrong? Why is sand-lime brick usually recommended for interior walls instead of aerated concrete? Soundproofing? Less crumbling when drilling? Price?

On the website of the well-known aerated concrete manufacturer, I read that they also achieve low U-values (below 0.2). But these blocks are then less stable, significantly more expensive, and worse in sound insulation... So can you really generalize about aerated concrete or do you need to specify the exact type of block? My supplier only talks about 36.5cm (14 inches) blocks. So I don’t really know which will actually be used... I should probably ask.

Is omitting additional insulation really the “state of the art” and reasonable (does it not pay off in heating costs) or just cheap?

As I said, I don’t want to build a passive house but an economically sensible concept.

Which wall structure would you recommend and why under the above conditions?

Thank you!

Schrimp23 Jul 2015 10:52

#19

BeHaElJa schrieb:
Of course, you can also build monolithically with Poroton. With 48 cm (19 inches) Poroton, you exceed all requirements - with 36.5 cm (14 inches) you meet them.

But you are planning to use aerated concrete, or was that a typo? By requirements, do you mean the legal regulations? Whether that is actually a good choice is a different question.

BeHaElJa schrieb:
Yes and no – Poroton doesn’t have a much better sound insulation value than aerated concrete. Sand-lime brick does, to some extent. There are also some builders who construct interior walls with sand-lime brick. (The heavier the material, the better the sound insulation – it’s best to check the technical data sheets)

Okay, then I will check how the interior walls will be done and whether it might be better to use sand-lime brick. I assume they usually choose aerated concrete because it is easier to work with (especially when it comes to chasing for cables and pipes – right?)

BeHaElJa schrieb:
It certainly improves comfort. Over the past three years I lived in two rental apartments that were more or less airtight (although built in 1997 and renovated) and every time I entered them I was met by a blast of stale air.

We currently live in a “fully insulated” older building. Especially in winter, it is really challenging to ventilate enough (but it is manageable). Now I see it as easier in a 3-room apartment compared to a house with a utility room where moisture likely builds up, but no window, or a guest room that is rarely used. So, would you also recommend it?

BeHaElJa schrieb:
Back to the mass factor – the heavier the material, the more inert it is (the more heat or cold a stone stores). Sand-lime brick takes longer to warm up. Another aspect is the phase shift, essentially the time delay until the heat reaches the inside of the house. For example, if it’s 14 hours, the midday heat arrives at night. Go into a church on a hot summer day – similar principle. Without shading and during prolonged heat waves, there are, of course, limits.

Ah, okay, that definitely makes sense again. Thanks.

BeHaElJa schrieb:
I think it depends on your perspective… whether 14 cm (6 inches) or 16 cm (6.3 inches) of mineral wool from the hardware store makes a big difference is questionable – but if the supplier wants to hit your price point and splits the layers into 2 cm (0.8 inch) increments with hefty surcharges, then it certainly does. If you plan to apply exterior insulation composite systems (EICS) on Poroton, it’s generally not worthwhile.

As I said, it will be aerated concrete. But if I understand you correctly, you also confirm the opinion that adding extra insulation on aerated concrete is not economical, yes? (I’m just assuming there is not a big difference between Poroton and aerated concrete in this regard).

jupartner schrieb:
That is a good goal and can be achieved quite well with 42 cm (16.5 inches) walls without additional insulation. That includes the roof, windows, and basement ceiling/floor slab – everywhere you should aim for U-values of 0.17 to 0.2 W/m²K, and windows no higher than 0.9 W/m²K. The heating system should incorporate 15% renewable energies. Ultimately, you’ll need someone to perform an energy saving regulation calculation (such as EnEV or local equivalent) for your home to verify the achieved standard. This calculation is also required for both subsidy and building permit/planning permission applications.

If you apply this year, you can still get funding. The KfW has just announced that from April 2016 the Efficiency House 70 standard will no longer be supported.

Thanks for the advice. Right now, the wall thickness is planned as 36.5 cm (14 inches). The windows of course will be triple-glazed. Roof and floor slabs will be insulated. I don’t yet have the U-values, I still need to get those. Currently, only a solar system for domestic hot water is planned. I would have liked a ground-source heat pump, but I’m starting to think that I won’t be able to justify the extra costs compared to a gas condensing boiler in the long run. So, roughly estimated, 36.5 cm (14 inches) aerated concrete without additional insulation combined with a gas condensing boiler plus solar might not be sufficient, right? Also, a controlled mechanical ventilation system will presumably be installed, as I find it difficult to ventilate everything properly by hand, as I mentioned before… even though you often hear horror stories about “ill health caused by controlled mechanical ventilation.” I still can’t really judge that.

Bauexperte schrieb:
No responsible builder would even consider that.

So you mean the partition wall to the neighboring property shouldn’t be made of aerated concrete? How about the homogeneity of the wall if I have the one wall made of sand-lime brick? I had understood that all walls, including the partition wall to the neighbor, would be made of aerated concrete (according to the offer). And just out of curiosity, how does the price of an aerated concrete wall compare to sand-lime brick or Poroton?

Bauexperte23 Jul 2015 10:52

#20

Hello,

Schrimp schrieb:

Sound insulation panels are to be installed between the wall and the neighboring house.

And what exactly is that?

Schrimp schrieb:

I have to admit at the start that I am quite a layperson.

So there are indeed engineers who know that outside their field they don’t really know much.

Schrimp schrieb:

I just can’t grasp what a difference of 0.1 W/(m²K) really means in reality... I lack the practical experience to imagine it.

Me neither; it’s just another number game used in advertising.

Schrimp schrieb:

- Aerated concrete can be used without additional insulation. But is that effective!? Is it only enough to meet legal requirements or does it make sense to build like that?

We have been building monolithic walls for years, using either aerated concrete or clay blocks. Meeting legal requirements requires more than just choosing one material.

Schrimp schrieb:

- Aerated concrete has worse sound insulation compared to sand-lime brick or clay blocks. Which could be problematic for thin interior walls.

That’s why many suppliers who build with this material offer lightweight interior walls in the attic. Quite a few builders also opt for sand-lime brick. I always wonder why sand-lime brick is chosen – have potential homeowners been so disturbed by “noise” from children in their previous rental apartments, or is it just trendy to jump on the supposed “noise disturbance” bandwagon?

Schrimp schrieb:

- No matter what I build (even without extra insulation), a mechanical ventilation system with heat recovery is strongly recommended since the houses are all very airtight.

I agree; yes – the upcoming energy saving regulation 2016 will reinforce this. If you read the forum’s posts about mechanical ventilation with heat recovery, you will see that it also offers a major comfort increase. Whether central or decentralized ventilation is one of the “Jehovah topics.”

Schrimp schrieb:

- Aerated concrete has poor thermal insulation in summer (I still don’t understand why a block supposedly insulates well in one direction – in winter – but not in the other – in summer).

Because anyone can write whatever nonsense they want on the internet.

Due to many small air pores, aerated concrete has very good thermal insulation. Its low thermal conductivity means that in winter, as little heat as possible is lost to the outside. Conversely, in summer it helps keep the interior comfortably cool despite high outdoor temperatures. This results in a pleasant indoor climate throughout the year.

However, if we in Germany have a stretch of +30°C (86°F) or more, only an air conditioning unit helps. We have 40 cm (16 inches) clay bricks (old building) and sweat just like everyone else.

Schrimp schrieb:

- I have often read that the cost of adding additional insulation to a wall does not pay off in a reasonable time (in terms of heating savings – of course this also depends on the heating system).

If you decide on insulation, you should, in my opinion, really look into the type of insulation. And yes – more insulation does not automatically mean lower heating costs; mechanical ventilation with heat recovery is key.

Schrimp schrieb:

Can you give me some guidance on where I’m wrong? Why is sand-lime brick always recommended for interior walls instead of aerated concrete? Sound insulation? Less crumbling when drilling? Price?

“That was always done that way” – people who say that often forget that no block can do without special screws or anchors. Otherwise, I already wrote something about this above.

Schrimp schrieb:

Is foregoing additional insulation really “state of the art” and sensible (does it not pay off in heating costs), or is it simply cheap?

What should be problematic about sound insulation with a 36.5 cm (14 inches) block? Personally, I consider aerated concrete plus exterior insulation system to be a “cheap” solution. It should be cost-neutral compared to a monolithic wall – at least it should be – but building companies often choose it because surface settlement cracks can nicely be hidden behind the cladding.

Schrimp schrieb:

Which wall construction would you recommend and why under the above assumptions?

Only you can decide that; there is no “better” or “worse” among exterior wall options. There is no single “best” block – if there were, the world would be pretty monotonous. It depends on many factors – location of the construction site in Germany, seismic zone, soil conditions, to name a few. And also on your budget – a concrete facade wrapped in polystyrene is cheaper than a monolithic exterior wall.

Best regards, Bauexperte

Bauexperte23 Jul 2015 11:03

#21

Schrimp schrieb:

So you mean the partition wall to the neighboring house should not be built from aerated concrete? What about the uniformity of the wall if I have one wall constructed from calcium silicate masonry?

If the party wall is the same thickness, 36.5 cm (14 inches) – which reduces the living area – as the other external walls, that is not a problem. Otherwise – I once “borrowed” this, saves me typing:

"The party wall must not only serve the purpose of sound insulation and fire protection but is also an essential part of the load-bearing structure of both adjacent buildings. Therefore, a party wall must remain in its original position even if the adjoining building (for whatever reason) no longer exists in its original form, for example due to demolition, renovation, or fire damage. This also highlights the particular challenge of a party wall: it is effectively jointly owned by both property owners, as it forms the single-leaf dividing wall between the two properties. Another major issue is usually the poor sound insulation, because party walls – especially in older buildings – are often not made from sufficiently heavy materials (e.g., solid bricks or heavyweight concrete blocks) and frequently have installations (such as water and wastewater pipes) embedded within them, which further reduces the sound insulation.

Fire protection of a party wall is also problematic. To prevent or at least delay the spread of fire from one unit to the immediately adjacent one, no combustible building materials (such as wooden beams) may be embedded or pass through the party wall (although this is often the case). Slots or openings for water and – even larger – wastewater pipes reduce the party wall’s fire resistance. Renovations may have also caused further weaknesses, for example through the installation of electrical or heating distribution systems inside the party wall. This not only significantly reduces the fire resistance duration of the party wall but also greatly worsens the sound insulation."

Schrimp schrieb:

And just a basic question, how does the price of an aerated concrete wall actually compare to calcium silicate or porous clay brick?

An answer to that won’t really help you, as each supplier/general contractor handles it differently.

**Source: LKG Technical Terms

Regards, Bauexperte

Schrimp23 Jul 2015 11:12

#22

Bauexperte schrieb:
And what is that supposed to be?

Well... I would need to ask about that.

Bauexperte schrieb:
So there are indeed engineers who know that they know nothing (outside their own field).

Yes, of course... "Know that you know nothing."

Bauexperte schrieb:
Me neither; it’s just another numbers game as part of marketing.

Hmm... okay, that doesn’t make it any easier for me. If even the professional can’t give a clear answer, there’s no point for me to try.

Bauexperte schrieb:
We have been building monolithically for years; choosing between aerated concrete or clay blocks. Meeting legal requirements requires more than just choosing a material.

Okay, and I guess you have good experience with that. I still remember years ago when everyone went crazy about wrapping their houses in expanded polystyrene insulation. And now, with much higher requirements and expectations, suddenly that’s supposedly unnecessary? I didn’t think the bricks have evolved that much.

Bauexperte schrieb:
That’s why many suppliers who build with this material offer lightweight interior walls in the attic. Quite a few builders actually choose sand-lime bricks. I always wonder why sand-lime brick is chosen — have potential homeowners been so disturbed by their children’s “noise” in their previous rental apartments, or is it more trendy to jump on the supposed “noise nuisance” bandwagon?

Honestly, I don’t quite get that. Why do they then build lightweight walls in the attic? Well, I thought sound insulation in modern houses is actually worse than in older buildings. And if you turn the volume up, you don’t want the neighbors right on your door... Otherwise, I might as well stay in an apartment. I was told that no sound insulation has yet been invented that can block out children’s noise.

Bauexperte schrieb:
I see it like this: yes — the upcoming Energy Saving Ordinance 2016 will boost this even further. If you read the forum posts about mechanical ventilation with heat recovery, you will see that controlled ventilation also provides a major comfort benefit. Whether centralized or decentralized is one of those “Jehovah’s Witness” topics.

Yeah, I suspect we won’t get around it. Without heat recovery, it probably doesn’t make much sense, right?

Bauexperte schrieb:
Because anyone can write whatever nonsense they want on the internet.

Due to the many small air pores, aerated concrete has very good thermal insulation. Its low thermal conductivity means that in winter, as little heat as possible escapes to the outside. Conversely, it helps keep the interior pleasantly cool in summer despite high outside temperatures. This results in a comfortable indoor climate throughout the year.

However, if we in Germany have several days over 30°C (86°F), only an air conditioning unit helps. We have 40 cm (16 inch) bricks (older building) and sweat just like everyone else.

Okay, that’s reassuring to hear.

Bauexperte schrieb:
If it’s insulation, you should, in my opinion, deal with the type of insulation. And yes — more insulation doesn’t necessarily mean lower heating costs; that’s what controlled mechanical ventilation is for.

Okay, I have no problem skipping insulation if I’m sure I’m not building a garden heater.

Bauexperte schrieb:
["It was always done this way" — people who say this always forget, among other things, that no brick can be installed without special screws or anchors. Otherwise, I already wrote something about this above.

Now you’re onto something… If I imagine hanging a kitchen cabinet on an 11 cm (4.3 inch) aerated concrete wall, my knees get a bit shaky… But people tend to underestimate walls and anchors.

Bauexperte schrieb:
What should be problematic about sound insulation with a 36.5 cm (14.4 inch) block? Personally, I find aerated concrete with external insulation systems to be a "cheap" solution. It should be price-neutral compared to monolithic walls, but building companies often choose it because external cracks can be nicely hidden behind the facade.

Okay, the company offering the quote does not want to use external insulation systems. I’m also concerned about soundproofing the interior walls, because, as I said, if it’s only an 11 cm (4.3 inch) wall… I don’t know if that still provides much insulation.

Bauexperte schrieb:
This decision only you can make; there is no “better” or “worse” among exterior walls. There is no single “best” block; if there were, the world would be pretty monotonous. It depends on many factors — the location of the construction site in Germany, seismic zones, soil conditions, to name a few. And of course, the budget — a concrete facade insulated with polystyrene is cheaper than a monolithic exterior wall.

Okay, thanks. Then the only remaining question for the exterior walls is whether the wall next to the neighboring house needs to be built differently...

Schrimp23 Jul 2015 11:18

#23

Bauexperte schrieb:
If the party wall has the same thickness of 36.5 cm (14 inches) – to the detriment of the living space – as the other exterior walls, it is not a problem. Otherwise – I once “borrowed” this, it saves me typing

Ah OK. Yes, as far as I understand, it would be a completely standard exterior wall like all the others. Also, the two houses each have their own walls (so no shared wall). Then I don’t need to worry about it. Thanks

Bauexperte23 Jul 2015 11:49

#24

Schrimp schrieb:

OK, and I guess you have good experience with that.

Yes. I would never voluntarily apply an external thermal insulation composite system (ETICS) with oil-based products; but that’s just my personal view and by no means the only valid one.

Schrimp schrieb:

I still remember how years ago everyone went crazy wrapping their houses in polystyrene insulation. And today, when requirements and expectations have clearly increased, suddenly it’s supposed to be unnecessary? I didn’t think masonry blocks had evolved that much.

The houses you describe were mostly built hastily after the war. Exterior walls (EW) of 12 or at most 15 cm (6 inches) thickness were not uncommon. When central heating replaced fireplaces in the early 1970s, owners might as well have thrown their money out the window. To prevent this—and with the help of subsidies—the oil industry profited substantially.

Schrimp schrieb:

Honestly, I don’t quite understand that. So why do they build lightweight structures in the attic then? Well, I thought sound insulation in modern houses is usually worse than in older buildings. And if you turn up the volume on the amplifier, you don’t want your neighbor standing at your door... Otherwise, I might as well live in an apartment.

You can—and should—not mix all materials due to different drying behaviors. That’s why providers—including myself—use lightweight partition walls in the attic. They have many advantages, especially better sound insulation (e.g., separating bedrooms). Also, they can be removed more easily later on, with less mess, to create a new room layout when the kids have moved out (which usually happens sooner than expected).

Calcium silicate blocks combined with aerated concrete are less critical in this regard; so that combination is also an option.

Schrimp schrieb:

I’ve been told that no sound insulation exists against children’s screaming.

Exactly.

Schrimp schrieb:

I guess we won’t get around it. Without heat recovery, it probably doesn’t make much sense, right?

If you want to stick with gas, in my opinion that’s where it’s heading. Regarding the so-called heat recovery, I’m not sure (and I’m no engineer) if it’s mostly just proven on paper through calculations. But you will probably need it to meet KfW 70 standards (building permit / planning permission level).

Schrimp schrieb:

Now you mention it... Just thinking about hanging a kitchen cabinet on an 11cm (4 inch) aerated concrete wall makes my knees shake a bit... But people tend to underestimate walls and anchors.

With the right anchor, that’s not a problem.

Schrimp schrieb:

Ah OK. Yes, it would be a completely normal exterior wall like all the others as far as I understand. Also, the two houses have separate walls (so no shared wall). Then I don’t have to worry about that. Thanks.

I can hardly imagine that—better ask explicitly again!

Usually, party walls between semi-detached houses are made of calcium silicate blocks (lightweight aggregate concrete is also possible). Between these walls, there is an air gap of about 4 cm (1.5 inches). Usually, you won’t find the standard exterior wall thickness (36.5 cm (14 inches)) here, since that would further reduce the already limited buildable area of a semi-detached house. Normal exterior wall thickness is only chosen if it cannot be guaranteed that the neighbor will also build in the foreseeable future.

Regards, Bauexperte

ᐅ Walls made of aerated concrete

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