How to choose masonry if the sound-proofing capabilites are also an important factor besides thermal insulation?

Author: Zsolt Tóth, Mónika Vértesy
2009-07-08

Which masonry materials should we be interested in?

What sound-profing and thermal insulation values do they have?

How much does the masonry cost including labor?

An old friend of Zsolt came to us with the following needs. He is building a house at Madárhegy, close to the highway, so for him, the sound-proofing capabilities were also important besides thermal insulaton and cost efficiency. We are not the ones who made the design, but we are on the verge of becoming the contractors.

The process of construction plans is in progress. János Pap, the acoustic specialist has the following suggestions related to the masonry material:

• Silka sound-proofing brick
• Porotherm 30 sound-proofing block
• Porotherm 30 tongue and groove block with fiber insulation

To expand the list we added the insulated formwork block and the Ytong too. While we were looking for the optimal solution, we examined the prices of certain masonry materials and their thermal insulation and sound-proofing capabilities.

Acoustic performance

Before getting down to the comparison, let us get to know the concept of acoustic performance. It is a quality of a wall separating two premises which prevents the sound energy affecting the wall from passing to the other premise nearby. So the bigger value it has, the better is. However, this calculation does not take in mind the impact sounds.

The sound does not only spread directly, but also by an undirect manner, so its value can only be measured at the scene. Now we are about to present the values of the weighted sound reduction index, which is measured by laboratory testing and has the unit of dB. The real value after the consturction is always less by 3-4 dB.

We can also state as a general truth that the heavier the material is, the better sound reduction index it has.

Does the thermal insulation materials reduce the sound reduction index?

The solid foam insulations (like EPS) create a vibration and are able to reduce airborne sound insulation even by 5 dB. However, this problem has a solution as each: for example, Austrotherm manufactures a facade insulaton that has good properties of sound insulation. Based on the permit of ÉME, installing this AT-HR thermal insulation to the wall, made of Porotherm products and also by plastering the wall,the value of the sound reduction increases by 7-10 dB. A 20 cm thick layer of this insulation increases the costs of the wall by 1500HUF per square meters in comparison to the non-acoustic insulation with the same thickness. With fiber insulations we win in every case. Besides their light weight, their complex inner structure diverts the sound excellently. Truth be told, their price is not so pleasing (Rockwool).

About the R_w values of the glazing of doors and windows

It is rarely an issue, so it is hard to get data about it. Finally i have found a specialist informator. From Szabolcs Horváth, colleague of OROSházaGLAS , I got to know that the noble gas filling to improve thermal insuation does not have an effect on acoustic performance, and neither the Low-E layer. However, filling the air space with sulfur-hexafuoride (SF₆), improves airborne sound insulation but reduces thermal insulation capabilities. SF₆ can not be chosen anymore as a filling for new windows tough. It was banned in the EU due to its ozone destructive effect.

Other possibility at OROSházaGLAS is the sound reduction foil, which can be used with a two or more layer laminated glazing. In case of windows the two layer glazing is the most popular. For example: the sign 3.3.1 means that two panes with 3mm of thickness are laminated with one layer of PVB foil (0,38mm). The third number in the sign means the number of foils, which can be one (0,38mm), two (0,72 mm), three (1,14mm ) or four (1,52 mm). It is also important that in case of breaking the construction the foil keeps the glazing at one piece, so it does not cause injuries and the glazed opening will not be left uncovered either. The glazing made with this method is also a safety glazing, but to be honest, it is the least we can expect for a price half as big again. This PVB foil also has a sound reductive version (such as 3.3.1 SC), which is able to further improve the R_w value.

Random examples

are all I can publish with the hope that it is more than nothing:

The 3.3.1 – 15 – 4 two layered thermal insulation construction has an Rw value of 35 dB without a sound reductive layer. Keeping in use the slimmest PVB foil while using thicker glazing (4.4.1 -15 – 4), the Rw value rises up to 39 dB. With sound reductive foils at both sides,even the value of 51 dB can be achieved. Still, the lack of exact orders made me unable to get to know the expectable prices if someone desires quiet. The price is an equation with a great number of variables, more that the sound-proofing and thermal insulation capabilities: appearance, temperation, size, etc.

More info about windows:

Special doors and windows
Clear opportunity: you enter or you miss it?

Chart of comparison with a heat transfer coefficient of 0,25 W/m²K *

* In the border of A or A+ class, rather in the A class, if we count in that the required values in 7/2006 regulation are based on the average values of the external walls' heat tranfer coefficient (0,45 W/m2K) and the effects of thermal bridges.

In the charts we did not take notice of the polystyrene thermal insulations at the R_w values, so they only refer to the plastered wallings.

Chart of comparison with a heat transfer coefficient of 0,15 W/m²K **

** fits the thermal insulation requirements of passive houses!

The Porotherm 30 HS can not be found in the chart (becouse of its bad results). This masonry material with outstanding thermal insulation capabilities is so light that is can not be considered as a sound-proofing material (Rw= 39 dB). The Porotherm 25 tongue and groove blocks have a better Rw value: 42 dB. So not always the thicker material is the better in airborne sound insulation.

Searching for the optimum

This decision is quite a serious issue as the mentioned building have a wall surface of 550 m2.

A difference of 2000 HUF (7€) in the price per square meters means a further expenditure of 1100000 HUF (3730€) for the client.

What is the ICF technology and what problems do we have with it?

Probably the word ICF (insulated concrete forms) is not the most commonly known word, but if we present a few manufacturers (IsoteQ, Proconcept, Bauland, Isorast, etc. ), it will become clear that we are dealing with the construction method where the concrete core is surrouded with polistyrene from both sides. Compared to traditional building methods, the ICF technology has a great advantage becouse of its small tihckness, good acoustic performance, not to mention its cheapness which is consisted of several factors: the prefabricated insulation elements are filled with concrete, so the amount of material can be calculated more precisely. Still, we do not recommend the sandwich insulation filled with concrete, as this solution lacks a heat storage capacity. This means that the walls of an ICF house will not be able to reduce the daily temperature fluctuation. Despite the thermal insulation, the inner climate can become intolerable, for example when we would like to ventillate in a hot summer midday. The incoming hot air can not be cooled down by anything and do not forget: the walls are insulated well from the inside and keep the inner temperature like a thermos. Of course, this example is a bit extreme and only happens on rare occasions. The undesired thermos effect is created only if the partition walls are made of drywall and the slabs have an ICF system too. The lightweight constructions have the same disadvantage. If we want a house with cool interior temperature, choose bravely concrete walls, but only insulate them from the exterior (with a quite thick layer indeed)!

Announcement of results

Our choice is the 20 cm thick formwork block and a 25 cm thick thermal insulation if the main concerns are the sound-proofing and the overheating during the summer. An other great advantage of this system is its earthquake-resistance. The second place goes to 25 cm thick Porotherm tounge and groove block with a 22 cm thick insulation layer. The frost-resistent Silka 200 calcium silicate block is also a sympathic choice, which is made by a high pressure press, but we have to dig in our wallet a bit deeper for this solution. Based on its quality, the sound-proofing version of Porotherm is also desirable, even with is slightly higher price than the formwork block.

image source: http://www.autolopasok.hu/images/article/1185.jpg

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