House construction

The houses you're talking about are basically a concrete construction.
A concrete slab is poured on a previously made foundation and the steel for columns is already attached to the steel in the slab.

Next the columns are made (with steel and a plywood mold).
I've seen two ways: one where the columns are made first and the cinder block walls are done later, another where the walls are erected first and the the columns are poured in the gaps that are left for it. The latter method results in stronger walls.

After the columns are there (with or without cinder block walls) the molds for the beams and the flat roof are made. Beams and roof are poured in one go.

Especially in rural areas these houses are built by two-man teams. They do everything: making the molds, mixing concrete for columns, installing water, electricity and waste water lines, doing tiles and plaster/stucco, installing bathrooms and kitchens and paint the house.

They all use the same concept: columns every 10', six rebars in a 12"x 6" column. Roof and slab thickness is known. I guess that sometime in the past an engineer developed this basic building and many houses are built like that. This construction type is strong enough for two floors.

I'm pretty sure that many people don't have official drawings and permits. You can just buy a lot and start building your house. To get the electricity connected you need a stamp from a licensed electrician - that can be bought for a couple of bucks. I personally know a couple of guys who build houses like that. Most of them want to be paid per day, payable every Friday and the future house-owner pays for the building materials. A 2-bedroom house can be built for 60, 70 Grand. This is a basic house of course but everything is included: closets in the bedrooms, one and a half baths, a basic kitchen, tiles on the floors. It's even painted for that money.

In towns I'm sure things are slightly different. You will need a permit and official drawings. No problem, there are architects one make a drawing for a couple of hundred dollars and you can still have the same two guys build your house. After the house is ready you get your use permit from ARPE (the gvmnt. agency responsible for this) and you're all set.

These concrete constructions are really strong and will survive a strong hurricane. You have to make sure though that your construction guys use steel rebars in the cinder block walls, If not you might lose the wall in a storm.

This Youtube video, well, it's a slide show actually, gives a nice impression of how a PR house is built.

Thanks Gary, great write up. It was interesting to watch the YT slide show.
I now have a better apprecation for why the "cookie cutter" approach to these dwellings.
So, yep, it looks like a second unit could be constructed on the roof at a later date, plumbing issues notwithstanding.
I thought it was rather clever on the sloped side of the foundation to just follow the contour down, then level off the top of the slab by the carport.

What I thought about as I viewed the septic tank construction was, "Is there a drain field or any lateral lines put in?"

DocRob wrote:

So, yep, it looks like a second unit could be constructed on the roof at a later date, plumbing issues notwithstanding.

Plumbing would be be no biggie - the main drain line will leave the first floor somewhere and be visible. A T-piece and a pipe up to the second floor is easy. A false column around it will hide it from view. Many houses have a water lines up to the roof to fill the water tank anyway. Electricity is no big deal either.
This construction type is so straight forward that it's pretty easy to work with - BTDT.

I found a nice set of photos of a second floor construction on a house in Vieques: Second floor construction
As you can see the the rebars from the columns of the first floor are still visible - that makes the construction a lot easier.
If that's not the case one has to measure where the original columns are and open up the roof and part of the beam underneath with a chipping hammer to connect the rebars to the existing construction.

DocRob wrote:

What I thought about as I viewed the septic tank construction was, "Is there a drain field or any lateral lines put in?"

Most of the times there is a drain field.

"...I found a nice set of photos of a second floor construction on a house in Vieques:..."

Nice! Can you say 3rd floor observatory with a hot tub?
The YT slides made me think that they were probably getting in the dry after 6-8 weeks from dirt work inception with another 4 for finish out. Sound about right?