External Insulation - Before and After Thermal Images 

Condensation in single-leaf concrete wall upgrades

The first issue I will discuss is the  problem of condensation in single-leaf concrete wall upgrades due to inappropriate knowledge, installation or material selection.

Typical drylined hollow block construction

Hollow block buildup:

The typical buildup of a typical drylined hollow block wall is shown above, as can be seen the two faces of a hollow block each about 40mm wide are linked by three cross members of 35mm thick. When built the resulting large hollows of each block become vertically linked. Given that moisture can penetrate through the outer 40mm of hollow block in driving rain conditions, it is a saving grace of their design that the air movement that occurs encourages evaporation of this moisture. However this air movement also reduces the thermal performance in that any warmed air will rise naturally to be replaced by cooler below.

Typical Drylined block walls:

In a typical buildup of a drylined hollow block wall treated timber studs are mechanically fixed to the hollow blocks wall. Mineral wool insulation is then friction-fitted between the timbers and a sheet of polythene is stapled to the studs to act as a vapour barrier. Where required a "hole in the wall vent" or a back box for a socket etc. breaks through the vapour barrier all contributing to a very leaky membrane. Water vapour can move with relative ease through the plasterboard into the insulation zone and condense where the temperature drops sufficiently. 

Overcoming the problem:

The typical approach could be improved if the following steps where followed, firstly a fibrous insulant more resistant to sag and better able to absorb moisture without collapsing such as hemp wool as used, next an intelligent vapour control layer (VCL) such as "intello" could be installed. The membrane could then be separated by a services zones from the plasterboard, a limited amount of insulation can be installed there and services be run through.

Hygrothermic study of drylined walls:

The image below was generated in a specialist simulation software called "WUFI" which looks at temperature and moisture fluctuations (In this case in a drylined concrete block wall) this new kind of simulation can go beyond considering a wall buildup of dry materials, it can investigate the performance of that wall under different design scenarios, if the simulation shows that the resulting moisture content reaches a critical level or simply grows year on year we can be sure that we will have some level of building failure on our hands, it can test for reduced thermal performance, structural damage or even mould growth.

Dynamic display of moisture movement in the wall

Conclusion:

The external envelope of any building is a place of seasonal and at times weekly change in temperature, moisture content and vapour movement. In certain cases of inappropriate knowledge, installation or materials the thermal performance of the insulation can change and so to can the likelihood of that building element hosting mould growth. Designers and builders need to build with far more awareness of moisture movement to ensure the structure and the occupants health are safeguarded. In some cases it may mean clients need to pay more, in others there would be no cost difference gut the pay off for their health should be clear.

Welcome

Welcome to my Blog about Retrofit Insulation Technology. I will be investigating the benefits and drawbacks of all types of retrofit Insulation.