Ponti termici

The thermal bridges are such parts of the external boundary of the house structure which heat conduction is much higher than those of other parts of the building.

 

themal bridge _ window

Which of course means that the insulation ability is worse at these places so the amount of heat convection between the heated and unheated spaces are the largest here. If you are to put it into an everday form those point, line or spotty parts are called thermal bridges where most heat escapes out of the structure.  These small „negative” elements could be geometrical thermal bridges like all of the building corners where the heated inner surface is always smaller than the connecting external surface which transmits heat. There may be such structural thermal bridges when materials with low heat-resistance (low insulation ability) interrupts the otherwise properly insulated structure.  Typical example of this is the ferroconcrete  lintel and ring beam in masonry made of hollow or perforated units without insulation (linear thermal bridge) and the hammer fixed anchor with metal nail (point thermal bridge). With thoughtful planning this can be prevented well in advance. The third type could be a human negligence. This occurs when the insulation between the rafters is gappy, when the sealing around windows and doors are not adequate or if we want to use not closed-cell for the insulation of a structure that has contact with the ground.

 

Why is thermal bridge a problem?

 

Thermal bridges

Because the heat that „migrates” from inside to outside significantly increases the heating cost of the house just like, „we would heat the street”. The surfaces inside that we feel cold reduces our comfort sense and the pleasant room temperature can only be ensured by disproportanely high overheating.  Each celsius we could reduce the temperature of the room with, would mean a nearly  6-7% energy saving. The cold side of the internal thermal bridges could result in moisture condensation which can generate mould that could harm our health.

The optimal insulation thickness is a constant question when doing a facade insulation. This depends on the material of the outer walls, on the thermal bridges and on the form of the house, on the desired quality and – first and foremost- it depends also on our financial possibilities. In Hungary there aren’t many masonry units which satisfys the thermal requirements without extra insulation and it only started spreading after the regulation came into effect in 2006. Quasi if my house does not boast such walling, than not only the common sense but also the law requires complete facade thermal insulation. If our masonry is made of old brick (e.g. B30 unit –typical masonry unit in Hungary of the ’80s) or reinforced concrete than the lower limit of the insulation is 8-10-12 cm taking the qualities of an average grade expanded polystyrene or rock wool insulation into account. By using a modern or porous structure insulating block, 5 or 6 cm may be sufficient. In this case it should be noted that by increasing the thickness of the facade insulation only a small proportion of the total labor cost needs to be added to save on the much higher heating costs. If you increase the thickness it does not change the costs of the adhesive used, the mesh,  primer and thin plaster or even the costs of the construction fee or scaffolding.

 

So what should be the insulation of ?

 

It is also a frequently asked question. As a basic rule it can be stated that in case of a solid, massive wall which already has serious vapour proof ability (e.g. concrete, small brick, stone, block B30 etc) polystyrene insulation is recommended, whilst by those wallings that allow rapid vapour migration (e.g. adobe clay walls) rock wool insulation is recommended.

Thermomaster facade insulation system with mineral wool


If we would like to build a wall of aerated concrete elements or modern, hollow ceramic unit than beside carefull vapourtechnic control, in terms of „value for money” polystyrene can be a good and economic alternative. But if we have serious fire or acoustical demands against it, than despite of the 2-3 time price difference we shall choose the rock wool system.