Horizontal and vertical seams are taped and spackled exactly the same way. The only difference is whether one is moving sideways or up and down. Whether or not the taped seams are visible depends upon the light source and angle. Let's consider taping either horizontally or vertically on the OPs wall.
16' long by 8.5' tall. Horizontal - using 4' wide x 16' long sheetrock requires 2 horizontal seams (at 4' high and 8' high + 6" filler) That's 32' of seams. Vertical - using 4' wide by 9' (or 10') long sheetrock requires 3 vertical seams 8.5' tall. That's 25.5' of seams..
Four 10 foot sheets run vertically. Wasted will be 1 foot 7 inches off end of each one (one cut each but no horizontal joins) and one piece full length of sheet about one foot wide. There will be no lifting; after cutting each sheet can be stood up with one end on floor. Mudding three vertical seams and the two ends.
Only if you do it the stupid way. The right way is to use wider sheetrock or if not readily available, put the filler seam in the middle. That reduces the horizontal to 16' minus whatever openings are in that wall.
As to taping horizontal vs verticle, they are not alike as anyone who has taped an 8' verticle vs a horizontal well knows. It is far and away much simpler to tape the horizontal.
For me, the debate over hanging a sheet vertically or horizontally comes down to butt joints and weight. I've done it both ways and you can produce invisible joints with either method. On the other hand, it is extremely difficult to hide a butt joint.
You mentioned a room width of 15', which means you would need a sheet at least that long to avoid a butt joint if you hang the sheets horizontally. The longest I have ever seen locally is 14', but they may come in 16' sheets. Even so, do you have the manpower to lift a 15' sheet of drywall 4.5 feet off the floor and hold it there while you screw it to the studs? For that matter, do you have a place to cut a 16' sheet and would you be able to carry it through the house (through doors, around bends, etc.)?
If you hang the sheets vertically, you can easily avoid butt joints. In addition, you can set the sheet against the wall, then use a lever to push it tight against the ceiling. Easy for even one person working alone. I generally work alone or with the help of my wife, and hoisting a
15' sheet of drywall in place horizontally would be quite a chore for us. On the other hand, we installed over a dozen 14' sheets vertically by leaning them against the studs. Much easier.
10 foot sheets would be ideal if you can find them, but with only one wall to do, 12 footers would work just as well and are easy to find at any home center. You only need four sheets, so it might cost you an extra $20 max.
As for getting them home, you can rent the truck at the home center, or rent a Budget truck, U-haul, etc. I have hauled home several really large loads of lumber using a Budget truck. Of course, if you know someone with a pickup or a trailer, that would save you a few dollars too. Remember, you can take a knive and straight edge to the store with you and cut the sheets down to 9 feet on the spot if you can't find a way to carry 12' sheets. If you do cut at the store, I'd recommend leaving a few inches more than you need and then cut it more exact when you get home. It's very difficult to get a clean snap if the piece is 2" or less, so leave some extra.
I look at two priorities: the first is to reduce the total length of ALL joints, and the second is to reduce the total length of butt joints. A third, more minor, priority is to reduce the waste.
This generally means that sheets are hung horizontally, mostly due to the fact that there are not a lot of walls in a residence that exceed 12' in length without a door or window in it (in my house, my living/dining room are separated by a half-wall, leaving the upper wall 29'3" long with no door or wiindow in it, so there are some exceptions).
With thoughtful placement, a butt joint can be placed in the middle of a door or a window (NEVER have any joint be in alignment with the edge of a door or window - you are just asking for eternal cracking problems!). This means that the butt joint is not the full width of a sheet, thus reducing the total length of butt joints.
One of the few places where I would hang drywall vertically is where the stretch of wall is less than four feet wide, though occasionally I have hung it horizontally in these situations where priority #3 made sense.
Taping a horizontal joint that is at or near waist height is far easier than a taping a vertical joint.
The one place where I broke with my "tradition" and hung all drywall vertically was in our basement. We built our home with an ICF (Insulated Concrete Form) foundation. This means that the walls have styrofoam on their surface, which must be covered by code. The walls are 9'4" in order to leave 8'2" beneath any beams so we could later (actually, now) finish the basement with 8' ceilings. With the floor poured, the walls that had to be covered with drywall were exactly 9' tall, so using 9' sheets was a breeze to put up.
I am surprized that some have mentioned the difficulty of ordering 9' sheets, they are not special order in our area (even at Home Depot).
Good points all. The butt joints in a normal room will all fall above/ below doors/windows. Even if one does a poor job of taping there it will never be noticed.
My addition, where I got my education, was 18x30. There was only 1 section where 12 footers would end up with a verticle butt joint and it fell behind a tall german style 'schrank'.
Personally, I don't think taping regular tapered joints is that big of a deal. A few extra feet will only take a few minutes at most.
But it takes a lot more practice and time to get a butt joint to turn out nicely. Not to mention, a butt joint will ALWAYS leave a bulge in the wall. You may not see it, but things like trim, cabinets, etc. will be a pain to fit nicely over the bulge.
We have several 14 foot walls in our house. In my case, it was easier to climb up and down the ladder to tape them vertically, than it would be to move the ladder back and forth to tape a horizontal seam at 10' off the floor. We had scaffolding, but even that limited us to about an 8' wide section at a time.
I hung sheets vertically in my garage too. 28' long walls, 8' high, no doors or windows. No brainer. :)
Of course, the garage ceiling is 24'x28', so I had butt joints there no matter what size sheets I used. That's where I got lots of practice taping butt joints. :)
Our kitchen/dining wall is 24' wide x 14' high. Easier to hang sheets vertically.
Our living room walls are 16' wide x 12' high. Easier to hang sheets vertically.
If it is done via the "sprung end" technique and tapered, so slight as to be a non-problem. The problem here is we're talking DIY'ers who, for the most part, do only a few seams at a time at best and are learning as they go...
That's why the pros wear stilts...if doing a full house or even several rooms, renting a pair and learning to wear them is well worth the initial effort/frustration.
These are places where I would have broken my usual practice as well.
Every situation is a bit different and sometimes a better result or simplified action can result from staying from the rules of thumb.
In the basement renovation we are doing, I had one section of wall that was only about 40" wide. Under my "rules", that would normally call for the vertical sheet with no seam at all, but in planning the requirements, it was more economical to use two cut ends from elsewhere to do this an have a horizontal seam.
Yea, ceilings is where butt joints are almost always present. Our family/ dining room is that 29' length with a 14' width, and the largest room in the basement has an open area of 33' by about 16', so butt joints are only reduced by the use of 12' sheets, but are far from eliminated.
I didn't bother with them for our basement reno, but when I built the house, I hired a subcontractor to do the drywall finishing (just couldn't do that myself in the timeframe available!). My sub used stilts, even though is is against the regs in our jurisdiction.
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