ᐅ Which material is best for the structural shell regarding thermal and sound insulation?

Hello everyone,

We are currently considering which material to use for the shell construction. Our goal is to achieve at least KFW 55 energy efficiency, and due to noise levels from the nearby railway, we also need passive sound insulation. External thermal insulation composite systems (ETICS) are not an option for us. Therefore, I see two possible solutions:

- Filled Poroton brick without additional external or internal insulation
- Cavity wall construction with calcium silicate blocks and core insulation

I currently prefer the first option, as I assume it is still more cost-effective than the two-layer masonry and results in a less thick wall. However, I am not sure if the filled Poroton brick will meet our sound insulation needs.

Could anyone share their experiences regarding the thermal and sound insulation properties of the above options?

Phew, building a monolithic Poroton wall to KfW55 standard right next to a railway line—that’s like trying to square the circle.

My parents-in-law built directly beside the ICE railway line (less than 30 meters away) using 1.8 bricks made of calcium silicate. It turned out really well. Soundproof windows contribute at least as much to noise reduction, so you definitely shouldn’t skimp on those. But the masonry itself also needs to be appropriate.

If you choose Poroton, the 36.5 cm (14.4 inches) variant is more of a Pyrrhic victory because it’s borderline for KfW55, meaning you will have to make costly compensations elsewhere. With 42.5 cm (16.7 inches) Poroton combined with a double-leaf calcium silicate wall (11.5 cm plus 17.5 cm calcium silicate plus 14 cm (5.5 inches) mineral wool), the result is practically the same, but you get poorer sound insulation for free. Also, Poroton can’t be recycled later, whereas calcium silicate can.

Just ask your preferred builder what they use most often.

Scout schrieb:

Phew, building monolithic Poroton to KfW55 standard right next to a railway line—now that’s like squaring the circle.

My in-laws built directly next to an ICE high-speed rail line (less than 30 meters away), using 1.8 density sand-lime bricks. It turned out really well. However, soundproof windows are at least equally important, so don’t skimp on those. But the masonry also has to be suitable, of course.

If you choose Poroton, the 36.5 cm (14.4 inches) version is more of a Pyrrhic victory because it’s borderline for KfW55, meaning you’ll have to make expensive compensations elsewhere. With the 42.5 cm (16.7 inches) Poroton plus a double-layered sand-lime brick wall (11.5 cm plus 17.5 cm plus 14 cm mineral wool [5.5 inches plus 6.9 inches plus 5.5 inches]), you end up with roughly the same performance, but you get somewhat worse sound insulation free of charge. Also, Poroton can’t really be recycled later, whereas sand-lime brick can.

Just ask your preferred builder what they install most often.

Thanks for your reply.

Regarding the railway line, we and all our previous neighbors perceive it as less problematic than the assessment assumed in the development plan. These are mostly trams; no ICE trains run on this route. Besides, we will be in the noise shadow of a block building. The distance is 120 meters (394 feet), and a noise barrier is currently being constructed.

We have already planned to install good quality composite windows, and we will definitely include a mechanical ventilation system with heat recovery.

When you mention “worse sound insulation free of charge,” are you referring to the mentioned 42.5 cm (16.7 inches) Poroton or the proposed double-layer sand-lime brick construction? Isn’t the double-layer construction significantly more expensive due to the higher complexity?

DASI90 schrieb:

Are you referring to the poorer sound insulation when comparing the mentioned 42.5 Poroton or the proposed two-shell calcium silicate brick construction? Isn’t the two-shell construction significantly more expensive due to the additional effort?

I’m referring to the Poroton; it simply lacks the density compared to the calcium silicate brick.

How much extra it costs depends, I don’t have exact figures. But if your preferred shell builder usually only uses calcium silicate bricks, then the surcharge for a two-shell system might be relatively moderate compared to an alternative quote for Poroton—not just due to reluctance, but maybe he only trusts one of his several masonry crews with it, or the discount scale for the few pallets of Poroton he orders annually or just for your project is simply very poor, making the material more expensive.

By the way, my in-laws have 24cm (9.5 inches) calcium silicate bricks plus external thermal insulation composite system (ETICS). Together with soundproof windows, it’s top quality—inside, you only hear a soft rustling, while next door in the old brick house, you had to stop talking until the train passed.

I find that impressive.

Poroton blocks are now also available with a lambda value of 0.75. However, it is already possible to build a KfW55 standard house using blocks with a lambda value of 0.9 in 36.5cm (14.4 inches) thickness.

The masonry is not the critical point. Use filled Poroton bricks; they are excellent for sound insulation, 36.5cm (14.4 inches) thick with perlite. This will give you around 48 dB.

Your windows are much more important. Standard triple-glazed windows have poor sound insulation, offering only about 32 dB, and that mainly at high frequencies. Low frequencies pass through almost unimpeded!

So, install soundproof glass with at least level 4. It doesn’t cost much more but has a significant effect.