On Sun, 14 Nov 2010 13:06:22 +0000, Andy Wade
wrote:

That's a half-brick thick wall, "one brick" being the stretcher length,

I had a look at the wikipedia entry you pointed me to. Thanks. yes, my
wall is just one row of stretchers, so although it is one brick thick
the terminology is a half brick wall, no wonder I was confused!

The only place there are headers are buttresses. There are three of
these along the length of the wall.

then add on the air boundary layer resistances for the two faces. The latter -
which you have to look up - depend on whether the faces are internal
(sheltered) or external (exposed) and whether the heat flow is
horizontal, upward or downward.

Thanks. The celotex calculator had these figures and I wondered what
they were all about, now I know.