I'm running solid strips perpendicular to 6' openings between 3 rooms. dining room, living room and foyer. Are T-molding suggested in the 6' stretch? If not I've tried to figure out how to run the boards through and have them line up through each room. Seems too difficult.

That's why I will often start the first row running through those openings by chalking my starting line all the way through those three rooms. This way you have already connected the three rooms openings and don't need to concern yourself with matching up the flooring.

but if you start the first row in the middle (or near) of the room how do you install the strips going backwards? (e.g. how do you access the preceeding tongue)

By inserting a slip-tongue (spline) into the groove. This allows you to change directions. Best way to do this.

I guess that's the kind of stuff that never makes it into the installation manuals Where do you but the spline?

Would it be concsidered "less professional", and by that I mean less resell value, if I used T-moldings across such a large opening?

Actually, I only have 1 room done with the groove end of the boards into the doorway. Could I (should I) install a strip perpendicular and finish the other room just to keep things level? I trid looking at this but it seemed like there might be alot of gaps.

The spline goes in the groove to make a new tongue for blind nailing on a direction change, flooring distributors and suppliers stock them.

If you already have part of the floor down, you are stuck and should install a perpendicular header board. Then keep the rows in the next room even with the existing. It would look better to be all continuous when you have a choice.

Is it ok to install the perpendicular strip even though I will not be able to nail down the tongue? I will either need to float it or face nail it. Will gaps be a problem? Or should I just stick with the T molding?

Are these readily available from Lowes or Home Depot? I don't see them on this web site. Does one size fit all?

Unfortunately, no. Check with a local flooring distributor.

Speaking of Splines, the warehouse I bought from didn't have any. I was just planning to cut my own. Any particular wood I should use or avoid? Unless there is a reason not to, I figured I'd cut them from yellow pine 2x4's.

Also, when reversing direction with a spline, do you put the spline in and then nail through it like you would any other tounge? I assume you would to keep that joint held down, but I'd like confirmation.

I think its best to stay with same species. You can use pieces of flooring and rip your own splines. You need to be a little careful when splining.
Best way I know to tell you is to dry-fit it first and see if the next row fits tight. Pull the spline out and apply some wood glue. The spline should be blind nailed. Use one or two short scraps of flooring and seat them right next to the nailer. That will keep the splines positioned correctly so they don't angle down making the next row a bear to fit.

Back to previous question. I have the 2 rooms comleted with the 6' opening. The lay of the strips is perpendicular to the opening and are sawn off on the groove end. Will a 6' strip fit properly and without gaps or is a T molding the better way to go?

I'm dealing with 1/2" engineered, so I'm not sure what the species of the plywood backing is.

Dave, on my engineered splines I have ripped them out of a sheet of plywood and also paneling. One sheet makes a ton of splines so look far a damaged sheet to save money. You can also use the pine you spoke of.

To determine what size spline, put two boards together, groove to groove, and measure the thickness and width of the space.