What kind of masonry should our house be built of?

Thermal insulation and sound-proofing capabilities, heat storage capacity, compressive strength

Author: Tibor Farkas, Zsolt Tóth, Mónika Vértesy
2010-05-17

The most important points of view: the thermal insulation, the sound-proofing and the heat storage capacity. In which proportion should we pair up the thickness of the wall and the insulation layer? Now you will be able to learn the best solution! The theme can be familiar for the participants of the seminars, but now we are offering an even wider range of knowledge, we’ll say a few words about pise and Ytong too!

Brick: withness of millenniums

Tha brick have been serving the human race for millenniums, and not by accident. It is durable, weather-proof with great compressive strength, cheap and it can be demolished or altered easily. But what kind of brick – or to express ourselves in a more exact way -, what kind of masonry material should we use? More viewpoints can appear which have to be considered when choosing masonry. Three of them are the most important: the thermal insulation, the sound-proofing and the heat storage capacity. These are the factors which determine our comfort and how we feel ourselves in our own house, wether we like to stay at home.

The best values are highlighted with the color green!

We do not dare to state that the lowest value is the best regarding the moisture content, as the ability of the wall of picking up a certain amount of the moisture formed inside the house can not be considered as a problem by all means.

What should we mind the most?

The chart above presents the values of three main viewpoints regarding certain masonry materials. The examination of these values makes it clear that – generally – the heavier the material is, (the greater heat storage capacity it has) the better the sound-proofing abilities it has. (and a better sound reduction index too) The same time the heat storage capacity does not have an infulence on the thermal insulation capabilities. So why does it worth choosing a material with great heat storage capacity? Becouse the heat storage mass plays an important role in reducing the temperature variation, so all in all, in the thermal insulation. This is the reason why we do not recommend light-structure buildings, becouse they do not have any heat storage mass – explains Zsolt Tóth, architect and managing director of é z s é design and service Ltd.

Thermal insulation capabilites of houses

The thermal insulation capabilites are usually characterized with the heat transfer coefficient, which was called the k-value before, while nowadays the U-value is its most common form. The current Hungarian standard regarding the facade walls is 0,45W/m²K, which means 0,45W of heat transport through one square meter of wall surface in the case of 1K temperature difference. What does this mean in real life? If the exterior temperature is -5 °C and we heat up the interior to 20 °C, the value of heat loss will be 11,25 W for every single square meters. That is why we have to choose a masonry material and insulation which exceed the otherwise not too strict requirement values. This way our heat bills of the winter will reduce too. The exact reason why a passive house can function without any conventional radiators has the same origin: at maximum, the third of the heat escapes through the walls (0,15W/m²k), and also the windows and slabs are insulated perfectly. In a passive house the artificial ventillation device regains the heat of the outgoing used-up air (heat recovery ventillation), so the interior heat gain (heat dissipation of people, domestic devices) is sufficient to complement the existing loss, already reduced to its fragment.

The old classic: the small solid brick (face brick, 25*12*6.5 cm)

Almost half of the Hungarian family house stock were made of small solid bricks. The advantages are the great heat storage capability and the variable thickness of the wall. (The most common: 25, 38, 51 cm). Due to the relatively smaller size of the elements, the labour requirements are greater, so the expenditures are higher too. An essential parameter of the small solid brick is that a 38 cm thick wall, plastered both sides, built from said material have the thermal insulation capability (U-value) of 1,37 W/m²K, so its performance is way worse than than current – not too strict – Hungarian standard.

solid pise brick

B30 blocks and aerated concrete

The heat transfer coefficient of B30 blocks are slightly better than the small solid bricks. With 30 cm of thickness, also plastered from both sides, it achieves 1,49 W/m²K. Further advantage is the faster construction compared to the small solid brick, not to mention the reduced thickness of the wall. Aerated concrete is also a common masonry material, typically used in the eighties, but it is still frequently met during renovations. Its disadvantage is the subsequent swelling and crack. The plastered, 30 cm thick wall has the U-value of 0,83 W/m²K.

B30 brick

Is there a sure recipe?

Nowadays it is an essential viewpont that how deep we have to dig in our wallet when the heating season comes, so we not only have to focus on deploying an up-to-date heating system, but the heat storage capacity of the wall also comes into view. In any case it is worth choosing a layered wall, becouse this way it is possible to take advantage of the best qualities of each layer, like the mass of the load-bearing structure and the thermal insulation capability of the insulation. The Hungarian population mostly thinks in thick wall-thin insulation layer combination, partly becouse of the brick-manufacturing companies. It would be time to change this.

New songs of the new era… or: thin wall, thick insulation layer

Following our heart we would recommend the Porotherm 20 N+F tongue and groove blocks with 16 cm of insulation. This construction has a U-value of 0,21 W/m²K and a sound reduction index (RW) of 46 dB. It may be the easiest to make acceptable for the layman user, becouse all in all this is also masonry block, only thinner. The only serious obstacle is the lack of testing as an exterior wall in Hungary.

PTH 20 N+F

Compressive strength

A lot of factors have to be taken into consideration during the static calculatios, and of course, every single construction must be dimensioned with a safety backup. These are complex calculations which are not published now in a detailed manner. We made a comparison tough, which clearly points out the main differences in the most decisive static charachteristics of certain masonries, namely in the compressive strength.

The compressive strength is expressed by the N/mm² value, as we also show it in the chart. However, it is a much more communicative value if we examine the load-bearing capabilities of a 1 meter long section of the wall with given thickness.

Regarding the data above, we wonder that the 20 and 25 cm thick Porotherm blocks can not be used as exterior walls for reasons unknown, while the weak Ytong aerated concrete block is fine. Take a look at it! From a static - load-bearing - point of view, a 2 cm thick Porotherm masonry, or even a 3 cm thick concrete formwork block masonry has the same capabilities as a 30 cm thick Ytong P2-05. It is an other question tough, that even it is permitted, it is still not considered as a great idea by our structural engineer to start a construction with this material. Even in the case of family houses, it is possible to have a beam where the concentration of the loads rise so greatly near its edges that it could cause the crack of the aerated concrete. It is not by accident that certain standards exist regarding the number of stories which can be built from certain masonry materials.

The concrete formwork block is also recommended

The formwork block is also a remarkable building material, not only becouse the mentioned compressive strength. (Which can be even greater by using built-in reinforcement) This large-scale component is filled concrete. The most often it can be found at fences, basements of family houses and footings. However, nowadays the people treat the concrete with prejudices, especially here in Hungary. This does not have any real basis, it is possible tough that the bad memories of the large-panel houses of the previous decades are still haunting. A masonry consisted of a 20 cm thick concrete block and a 16 cm thick insulation layer has a heat storage capacity of 395kg/m² , a heat transfer coefficient of 0,224 W/m²K, and a sound reduction index (R_W) of 67dB. These values are considered to be really good.

concrete formwork block

So formwork block kor Porotherm?

The question could come up in the case of the formwork block (as we are dealing with concrete): is the masonry colder from the inside? Raising the question stands to reason, as our thermal comfort can be crushed by cold surfaces. (We will dedicate a whole other article to the theories of thermal comfort – the author) Let us compare a plastered formwork block wall with 16 cm of polystyrene insulation and a Porotherm 30 block wall with 12 cm of EPS insulation, which has the same U-value as the concrete block wall. The result: the temperature calculated on the final surface of the interior plaster is almost the same in both cases. Presuming -2 °C as exterior temperature and 20 °C as interior temperature, the interior side of the wall has the temperature of 19,39 +/- 0,01 °C. So leave our disapproval of concrete behind our backs and let’s use this material bravely! Furthermore, take into consideration that the wall built from concrete block is more resistent to earthquakes than any other of the examined masonries!

What about pise?

The pise is beloved by many, mostly becouse it is a natural masonry material with great traditions. We are not arguing with that, moreover, we think that is is a great thing to live in a house built from pise until we are capable of protecting it from moisture very carefully. Pise tends to hydrate and lose its material strength becouse of moisture.

Kapcsolódó témák:

Mit kell tudnunk a telekvásárlásról, mielõtt házat építünk?
The declaration of construction
Kell-e kiviteli terv a családi házakhoz?
Mit ellenõriz az építésfelügyeleti hatóság?