Ick- that trunk looks horrible. Can freezing split the trunk like that? (ignorant So Calif. question)

Cutting the dead stuff out is always a good idea, but when done you're going to have a weird form, and you don't even know if the apples are a good variety. It doesn't seem to be in the greatest spot, either.

I'd plant another apple tree of known variety that may come into bearing sooner than this guy and then try your hand at whacking it. You can take the height down in stages, but sunburn at your altitude is a worry, so paint horizontal branches (if there are any) white.

what I would do: (wait, first off: nice house! congats) OK, so cut away the dead now. But in sections that you can hold the part you are cutting off. Get rid of the whole dead portion. It may get tricky figuring out the final location to terminate that one, just take your time deciding.
For pruning live wood, you can do it now or wait until late winter. Do that pruning based on appearances, since it is close to the house.

Start some new fruit trees in a better location, however this one is a big tree and presumably can give you apples while the others are growing. So, what I would do is try to save this one to be fruiting until the new trees are are fruiting well, then decide what you want to do with this one.

I assume you do not know if there are other apple trees nearby, so maybe this one isn't getting pollinated. So I would get some other varieties to graft onto this tree in the spring. I personally would go easy on the pruning of live wood now, or even wait til late winter to do any. But I would be reading this forum every day until then and learning all you can and keep looking at the tree and getting your mind around the whole thing. then in the spring do heavy pruning and graft on the new varieties. I had better luck grafting a little later then text book. Graft more then you want, you can always cut off if they all take. Don't remove all of the old tree, it may turn out to be an awesome variety, plus the root system needs the developed top for for photosynthesis while the grafts are taking and getting started. Grafts onto this tree should fruit before the new trees you might plant.

Every year you will have to do work on this tree to get it in the shape and condition you want. Although that is true of any tree, just more-so here.

This post was edited by cckw on Sun, Aug 4, 13 at 16:39

After taking out the dead wood, you can start now by removing vertical watersprouts and opening up the middle of the tree where it's overgrown.

In winter, when the leaves are gone, you can get a good look at the basic structure, the major scaffolds, and plan what to keep and what to remove.

Thanks for all the responses.

Given the poor positioning of the tree, I'm keen to get the height under control as soon as possible. It's not easy to see from the picture but the front porch is at about 50% tree height, and extends in to the canopy (see brick line as a guide).

So, for dead wood how close to the main trunk can I go? The big split in picture 3 goes almost to where the branch joins the main trunk. But I don't want to cause any unnecessary damage.

For live wood, what would happen if I remove more than 50% height in one go? Will the tree come back from a drastic approach like this?

In general, planting more fruit trees is probably not feasible without removing other trees. The front or back yards aren't all that big. But I do remember there being fruit on the tree last fall when we first viewed the house. Hopefully this is a good sign, even if there is none this year?