Re: Re: New Part L Revision re Applications lodged after Nov 201

@onq wrote:

Here’s a great detail – a construction stuffed full of insulation – http://t.co/v8d1Hcx1

100 Interweb points for guessing where the interstitial condensation is most likely to occur.

Hint condensation that occurs within the insulation can reduce its effectiveness.

There is a theoretical point beyond which insulation cannot go.

Thus the emphasis on sealing, but its not understood.

Unless you seal the sandwich perfectly it starts to get wet internally.

Realizing this was impossible the powers that be suggested controlling “air quality”.

People get confused between oxygen levels and humidity levels, both of which need control for “good air”.

you picked a very bad example to make your point

that detail, while not perfect… is specifially designed to reduce thermal bridging as much as possible. the roof construction is created as a warm roof type (see gutex wood fibre) with a breathable felt over. In this construction vapour will only condense into liquid over the felt and into a ventilation layer and exhausted away. the dew point in this detail occurs outside the insulation layer
condensation in the wall construction will occur at the cold face of the cavity insulation, and is allowed to exhaust through the external blockwork.

Investigations into the condensation point can be done with software such as wufi, which gives a dynamic rather than static view of where condensation will occur.