Wall Cavity Wiring.

I suspect an odd length of T and E won't make that much difference, it is scarcely a good wicking material.

It's not the wicking effect that's the issue, but forming a bridge that's downhill from outside to inside along which drops of water can descend - a nice smooth impermeable surface (like a cable sheath) is far more efficient in that respect than an absorbent material. For sure there are a lot of variables - if you're in a sheltered part of the south east where the local venacular is to have the roof oversailing the walls by a considerable distance so the walls are usually kept dry you're most unlikely to have problems. But around here where the rain comes in off the Pennines horizontally on a good day and roofs typically stop promptly at the top of walls (to stop the edges of the roof being lifted by the wind), it's quite common to have the outer leaf completely saturated. Indeed there was a trend in these parts, going back well into early Victorian times, if not earlier, to build outer walls with a significant air gap in the middle - connected by a few carefully chosen 'through stones' in lieu of wall ties. The text books might still classify them as 'solid walls' as they don't quite meet the standards for a proper cavity wall, but mostly the intention and effect was the same. I can't see builders going to all that effort if they weren't convinced of the benefits.


    - Andy.

I suspect an odd length of T and E won't make that much difference, it is scarcely a good wicking material.

It's not the wicking effect that's the issue, but forming a bridge that's downhill from outside to inside along which drops of water can descend - a nice smooth impermeable surface (like a cable sheath) is far more efficient in that respect than an absorbent material. For sure there are a lot of variables - if you're in a sheltered part of the south east where the local venacular is to have the roof oversailing the walls by a considerable distance so the walls are usually kept dry you're most unlikely to have problems. But around here where the rain comes in off the Pennines horizontally on a good day and roofs typically stop promptly at the top of walls (to stop the edges of the roof being lifted by the wind), it's quite common to have the outer leaf completely saturated. Indeed there was a trend in these parts, going back well into early Victorian times, if not earlier, to build outer walls with a significant air gap in the middle - connected by a few carefully chosen 'through stones' in lieu of wall ties. The text books might still classify them as 'solid walls' as they don't quite meet the standards for a proper cavity wall, but mostly the intention and effect was the same. I can't see builders going to all that effort if they weren't convinced of the benefits.


    - Andy.