Stacking turf...

i stack grass to grass then soil to soil etc. i put it in an out of the way place in the garden and leave it for 6 months and usually its loam by then. if there are dandelions etc in it [sure yours wont have spritz] i pull those out by hand.
are you extending a border?

Grass side downwards, try to make it a squarish stack, takes ages to rot down into something usable though, however you stack it. I just used to leave mine in a dark corner behind everything, uncovered, and ignore it for some considerable time.

So do we have to water it if the weather's dry?

Sbg - I am crazy, I am digging a new bed! A huge one. :-)

as bamboo says, grass side downwards, but i have also seen it grass to grass too, all the way up.

You can water it a bit if we have really hot, dry weather, but if it's a fairly big stack (and it sounds like it's gonna be) it'll stay damp for ages anyway. Lucky you - all that new planting space.

will it be ready for next years open garden? lucky you all that new planting to plan and resource.

Depends on how deep is your stack as to whether to dampen it or not. It doesn't really matter how it is stacked, it will still eventually all rot down and you will have some wonderful soil. I would suggest putting either old carpet or sheeting of some sort over the stack it helps to warm it up hence rot more quickly.

Thanks, everyone!

Yes, Sbg...I shall 'blog' it eventually as I'm taking loads of photos!

Put grass to grass and sprinkle carbonate of lime on the grass as you go, it will neutralise the nitrogen as it rots. This applies if you are putting lawn mowing in as well. Cover the top of the heap with a sheet of polythene.