Thermal insulation. Do you need it?

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Thermal insulation. Do you need it?

The thermal insulation is mandatory for the blueprint of new houses, and in the recent years it has become a priority also for the old buildings. For residential buildings, houses, blocks the most common ways of insulation are wall-cladding with polystyrene (extruded or expanded) and assembling of tight fitting woodwork (with rubber seals) with PVC window.

A little theory about the principle of the thermal insulation

A good insulation means a heat transfer as reduced as possible. When we talk about a house the heat transfer is realized through three ways:

– heat conduction through walls, roof, windows – this is the reason that we isolate the walls and we use PVC profiles with lots of rooms or aluminum with thermal break;

– radiant heat, especially through windows (between the glass sheets) – and, to have losses as low as possible, we use Low-E windows;

– effective exchange of air masses between inside and outside – and, to stop the air flow transfer, we have a series of gaskets and seals for doors and windows.

Imagine against all reasons, a house with insulated walls of 50 cm polystyrene, with 3 rows of triple PVC windows, with perfect gaskets of doors and windows.

It is this a well-insulated house?

Obviously yes! It is even a passive house, where a comfortable temperature environment can be achieved without having a heating system (inside, the heat produced by people, lamps and various devices is enough).

Is this a solution for a house?

No, although we get a perfectly insulated house, it is also very tight, because there is no ventilation. In other words, it is vital to ensure a quality atmosphere of the interior through a regular intake of fresh air.

Central ventilation with heat exchanger .  How is the ventilation done?

The easiest way: Open the window! For short time, but often, no matter how cold (or hot) is outside; unfortunately, with the ventilation substantial losses of warmth are produced, warmth which we tried with so much effort to maintain.

A more complicated way but also more efficient is a central ventilation with heat exchanger. It produces air exchange between interior and exterior, but also it makes an exchange of heat between the two air flows (for example we use the heat of the used air that should be evacuated to heat the fresh air introduced from outside). Obviously that the heat transfer through the central ventilation will not be complete and there will be some loss of heat, the efficiency of the central is more than 80%. However, the heat losses will be much lower than in case of ventilation by opening the window.

Conclusions:

A well-insulated and airtight house is predisposed to condensation indoors, if it has no sufficient ventilation. Simply, the humidity developed during living inside (breath of people, cooking, washing, etc.) is trapped inside and because of the lack of ventilation it increases to values at which it condensates on surfaces that are only a few degrees cooler than the interior air temperature. The described phenomenon can happen in any house which is insulated with polystyrene, but it appears mostly in houses where the construction technology gives to the house a very good tightening – ex. ICF’s Amvic, IsoteQ, Isorast, Argisol, etc.

Unfortunately, the humidity is just the tip of the iceberg. In reality, the humidity, the condensation, the mold, are only the exterior signs of a flowed, vitiated, air. If we have a well-insulated and airtight house and we do not ventilate, we would breathe a highly vitiated air, and if we only ventilate the house by opening the window, we lose heat.

A thermally efficient house and also ventilated it needs a ventilation system

The passive house, promoted by sellers / manufacturers of ICF’s (Amvic, IsoteQ, Isorast, Argisol, etc.), is a myth as long as it is not accompanied by ventilation systems with heat recovery.

It is true that a wall covering done with materials which are permeable to air and water vapours, such as mineral wool plates, will allow a transfer of air through walls (you might have heard the expression of “breathing  walls”, or about the polystyrene that is not good because it does not breathe). In my opinion (I have not seen a study to show me the otherwise), the amount of air transferred through walls is not sufficient to maintain the high quality of interior atmosphere, although the inside relative humidity is lower than the sealed insulation. In addition, there are other disadvantages such as the price and sensitivity to water (by moisturising, the mineral wool diminishes radical its thermal properties).

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