[Strawbale] Wall Capping

[Stewart Hargrave]

On 1 Feb 2004 at 13:35, Rene Dalmeijer wrote:

> Alex,
> 
> Besides slightly sloping the outside capping to allow water runoff. 
I
> would also do the following move the window out much closer to the
> exterior surface. This does 2 things it avoids possible moisture
> problems in an area that is difficult to inspect and it also 
improves
> the insulation value of the structure. There is less external 
surface
> working as a heat sink. This is a general rule for any type of
> building structure. The less the external exterior surface area for 
a
> given volume the more thermically efficient it will be. Another 
effect
> is that it lessens the effect of cold bridges which are always a
> potential problem around wall openings. Another effect which can be 
of
> some importance is that by reducing the external surface area
> maintenance is also reduced. There is less external surface area to
> deal with which requires the most maintenance.
> 
> The above again should also be considered in some balance because 
when
> pushed to an extreme moving the window flush to the outside surface 
or
> even projecting it out is not a good idea either. A window frame is
> quite a complicated (expensive) structure and also deserves some
> protection so it is a good idea to keep it back somewhat form the
> outside surface. In your case where you have big overhangs this is 
not
> such a necessity and you only need a small setback maybe about 
100mm.

This all makes sense, but don't forget about a sill. This is old 
technology, but very effective. 

The sill is made as part of the frame and overhangs the opening. It 
has a sloping surface to shed water, and a groove or lip running the 
length of it underneath as a drip return, so that drips of water 
cannot work their way back along the underside into the joint between 
frame and wall. 

Also, from an aesthetic point of view, I think a frame with a sill 
looks more 'finished' than one without.

-- 
Stewart H.

Finally visible on www.hargrave.me.uk