Poroton - T8/T9
Recommended for energy efficient building
- 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 giving the 425mm wall a 0.18 U-value.
- 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.
- 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 British 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 challenges in Britain are temperature fluctuation, air tightness and humidity. All three are easily controlled with Poroton. 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.
- 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 100mm 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. 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 stone house built using Lime mortar. The wall surface remains dry preventing surface condensation which causes mould formation.
- 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.
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