On Fri, 12 Mar 2010 06:40:34 -0800, jamesgangnc wrote:
You need to use pt lumber where it contacts the concrete.

Yeah, good call on that - I think when I roughly priced things up last
year it was for 2x6" PT (decided to wait until the weather got warmer - I
didn't feel like fitting a new exterior door in -30 temps :-)

A plastic moisture barrier is fine if you beleive there is not one
under the concrete.

I can't see an obvious one, but the concrete doesn't seem to allow
anything through - but I don't believe it's expensive to lay one down, so
I may as well just in case.

If you use 2x6 that is really 5 1/2 so you are left with 1 1/2
inches. A 3/4 ply plus another 1/2" or so for tile and mortar brings
you close.

Yep, it's pretty tight. I'm not sure what common practice is for framing
direct onto concrete, given that there's some very slight variation in
the concrete surface; do folk normally put a little cement down (and fit
the frame before it's dry) to pick up the slack, or it is possible to buy
some kind of flat shim for that purpose? I think I'm looking at about
1/8" max variation in the concrete height, so need something if I'm going
to put the frame down directly on top of it.

I assume there is a door transom between the two rooms so
exact matching is not needed.

The porch must have been added much later, so there's actually what would
be once been the rear step for the house between the two rooms. That
means I can be out height-wise by 1/4" or so without it looking (or
feeling) strange, although obviously I'd like to get the heights between
the two as close as I can get.

I would frame 12" on center instead of 16" to place the tile directly
on the 3/4 subfloor.

Yeah, good idea. I was going to go with 16" only because I have some 16"
insulation rolls already, but I've got a later project in mind that can
always use those, so I wouldn't be wasting anything.

The porch isn't big at all, around 7x8', so it's not going to be a
particularly expensive job.

thanks for the tips!

Jules