Poroton House
Due to the unique shape of the honeycomb holes and their porosity, Poroton exterior wall clay blocks achieve extremely good thermal insulation values. The latest T8 block filled with perlite has a lambda value of 0.08 W/m2K.
The “secret” of the thermal insulation of Poroton clay blocks is the air trapped in the many small pores. At the brick plant, the clay is prepared and sawdust is added. The clay is shaped, dried and fired at approximately 1000 °C. When the sawdust burns away it leaves countless tiny holes. These enclosed air pores provide thermal insulation. The porosity of the clay blocks and a carefully designed hole geometry intelligently reduce the flow of heat and thereby heat losses through exterior walls. The latest T8 block filled with perlite has a lambda value of 0.08 W/m2K giving the 425mm wall a 0.18 U-value.
A Poroton clay block wall absorbs heat from the sun and Solar Gain from the house during temperature peaks. This stored heat is later released back into the room when temperatures drop. Temperature fluctuations are balanced out by the absorption and release of heat, in the winter your house remains comfortably warm, in the summer your house remains pleasantly cool. By absorbing solar heat and buffering temperature fluctuations Poroton can deliver the average Irish external temperature (13-15 degrees) into your home lowering the heating requirement. This effect is not calculated by the U-value calculations so its an added extra. The biggest house heating challanges in Ireland are temperature fluctuation, air tightness and humidity. All three are easily controlled with Poroton.
Lets compare a Poroton block wall with a traditional partial filled cavity wall both with similar 0.25 U-values. To compare like with like we need to calculate the Cold Bridges. The 4 inch uninsulated Cold Bridge between the walls and * floor brings the traditional build U-value to 0.36, add the CB around the windows/doors and it jumps to 0.47, then add the CB between the walls and the roof (cavity closer block on the flat) and you get 0.58. Now calculate the loss in insulation due to "Thermal Looping" where the insulation in the cavity is not tight against the inside block. British tests have calculated that on average 33% of the U-value is lost due to "Thermal Looping". So the actual U-value of the traditional build jumps to 0.75. On the other hand the Poroton clay block does what it says on the tin, no Thermal Looping, no Cold Bridges and you get all the extras, breathable walls that sweat, no fungus or mould, no temperature fluctuations and a wall that picks up heat from the sun and delivers it into your house hours later when it's cold.
Internal walls are built with high* density Poroton blocks that help to control temperature peaks and troughs. High room temperature reached through solar gain is absorbed/stored in the walls. This heat is slowly released back into the room as the surrounding temperature drops. The dual capacity of Poroton to thermally store and insulate keeps a Poroton construction cool in Summer and warm in Winter.Poroton has the lowest natural moisture equilibrium of all building materials and is vapour permeable. It naturally regulates internal humidity levels. Porotons high hydroscopic action enables it to absorb water vapour, which it then rapidly transports hydroscopically to the outside without condensing, just like an old Irish stone house built using Lime mortar. The wall surface remains dry preventing surface condensation which causes mould formation.
The Poroton building system totally eliminates "Cold Bridging" which is the Scourge of Irelands traditional building method. Cold Bridging is the cause of major heat loss in Irish houses and is one of the main reasons why our houses cost double the European average to heat. Internal water vapour condenses on these cold spots inside your house causing fungus and mould growth. With the Poroton system this is avoided.
Poroton build options
The monolithic external wall | The cavity wall with facing bricks | The cavity wall with a plaster façade | The external wall with additional |
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Poroton clay blocks have ideal moisture control properties. The countless pores in the brick favour the exchange of humidity between indoor and outdoor environments, thereby guaranteeing an excellent storage capacity and outstanding vapour open diffusion. Clay blocks absorb interior moisture and release it again quickly keeping the internal Relative Humidity at around 55% which is ideal for human health. This keeps the wall surfaces dry in every season and ensures a comfortable room climate.
A Poroton clay block wall absorbs heat from the sun and Solar Gain from the house during temperature peaks. This stored heat is later released back into the room when temperatures drop. Temperature fluctuations are balanced out by the absorption and release of heat, in the winter your house remains comfortably warm, in the summer your house remains pleasantly cool. Poroton is an Insulating material with Thermal mass, this makes it 10 times better than concrete at storing/releasing heat.
Of particular importance for thermal comfort is the surface temperature inside the external walls. A wall that is significantly colder than the room air temperature result in an uncomfortable feeling which makes you want to turn up the heating. If your walls are 15 degrees then you need to turn your heating up to 25 degrees to reach the comfort zone, if your walls are 19 degrees then 20 degrees is sufficient for your heating. The excellent thermal insulation properties of Poroton clay blocks result in higher room-side surface temperatures and therefore superior thermal comfort.
During warm periods a well-insulated house with good Thermal Inertia remains pleasantly cool during the day and maintains a good temperature at night. When temperatures rise concrete block walls with high specific heat capacity absorb a lot of heat, but because concrete has a bad U-value this heat quickly dissapears away through the wall and gets lost through Cold Bridges. To achieve good thermal inertia, the external wall must have a high specific heat capacity to absorb large amounts of heat and also be insulating so that the heat does not pass quickly through the wall.
With a large Decrement Delay the effect of the midday sun is * felt in the evening. * This can only be achieved if the material used is both insulating and heavy. A "pure" insulation" material has a very low mass and cannot store up the heat. In fierce sunshine, this then gives rise to the "caravan effect", whereby it quickly becomes unbearably hot in the house. Poroton has the properties of an insulation material but also a considerable mass (between 400 and 700 kg/m2). It therefore satisfies all the conditions for creating good thermal inertia.
Traditional Irish Building
Drylining only insulates 90% of the wall because you are not insulating where the internal walls and floors meet the outside walls. Drylining moves the "Dew Point" of the wall internally to the point where the insulation meets the wall. This is where you get mould and fungus growth due to condensation at the "Cold Bridge" points causing health problems.
Scandinavian building regulations state "If at all possible insulate on the outside preferably with a breathable insulation, if it is impossible to insulate on the outside only then consider drylining".
Partial fill cavity walling has been scrapped as a failed technology in every country in Europe except here and England due to "Thermal Looping" and "Cold Bridging". The Polish and Baltic builders working here think it's hilarious that we are still using this archaic building system in modern Ireland that was scrapped there 50 yrs ago because it doesn't work.
Here is an article by Joseph Little, Orizon Architects that was in Construct Ireland last year highlighting this huge problem that is being ignored by the Government and Homebond. Thermal Looping.