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Varieties of insulation

An introduction to insulation: II

Local architect, insulation specialist and sustainable building expert, Ken Davis offers HOT readers more helpful information on insulation. Essential for maintaining warmth in the home. I have heard this many times from numerous sources, writes HOT’s Zelly Restorick – that it is no use having the best heating system if you don’t have good insulation, for maintaining the heat in the house. 

The last brief article about insulation concluded that the choice of which insulant to use – and where to use it – involves both knowledge of the building construction into which the insulant is being placed for both the on-going health of the building itself and its occupants. The diagram below repeats the point about very different thermal conductivity of materials but shows that insulation cannot be seen in isolation (as it were!) because it must work with other parts of the construction.

conductivities-1Comparison of thermal conduction properties of different materials:

 

Mineral wool: low density, good thermal insulator.

  1. Brick: high density, poor insulator.
  2. Glass: high density, poor insulator.
  3. Partially filled cavity wall of about 10-15 years ago….better, but not good enough.

In order to understand that relationship we have to consider how to work out insulation values for materials of different conductivities and thicknesses combined together such as the cavity wall shown in diagram d. These insulation values are known as U-values (and the lower they are numerically the better) but rather than explain how they are worked out here I will just give some comparative values so that the effect of insulants can be appreciated. (For simplicity I will ignore surface resistance of materials).

The U-value of a typical 9 inch (225mm) brick wall (many Hastings houses but ignoring possible internal lath and plaster) i.e b in the above diagram, is around 4.0 while a typical insulated cavity constructed perhaps 10-15 years ago would be around 0.28 (d above). A zero energy house would have a wall value of 0.1 or less i.e around 40 times better than a 9inch brick wall!

You can see from these simple comparisons just how much improvement is possible …..and necessary, if we are to turn around global warming. Similarly if a solid brick wall is about 4 then it is not hard to imagine just how much valuable and expensive heat is leaking out of single glazed windows; probably about 70 times worse than a brick wall!

The picture at the top of this article show a variety of different insulation materials, there are many others! We will consider some of them in the next article.

Posted 17:42 Wednesday, Dec 6, 2017 In: Energy Wise


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