I have a two story house in Puerto Rico that gets unbearably hot during the day (Especially now in mid-summer). If you don't know anything about construction in PR, basically it's just a block house with no insulation and a flat roof with reflective white coating. At night when we go to bed, we can feel our walls radiating heat to the inside. I would like to hear your ideas on how we can make the house more tolerable. Are there any cost-effective ways to retrofit insulation into a house built like this? Are there shade trees that will grow quickly and potentially be providing partial shade within a couple of years? Right now we have ceiling fans running all the time and shades pulled on our hottest windows/doors, and the downstairs is comfortable enough but the upstairs where all bedrooms are, is a sauna. We often have to resort to using AC at night which is very expensive. I look forward to hearing your ideas on what we can do to improve our situation.

The mass of this type of house can be used to your advantage.... Could you take temp readings inside and outside for a normal day like every half hour?

You can retro-insulate with foam or Rockwool panels.
You can then place furring strips and side or coat the house however you want and the furring strips will provide you with an air gap for drying.
If you have a flat roof with parapet and scuppers, they make foam roofing kits that allow you to insulate and slope properly for drainage.
If you have no parapet/scuppers and it's just direct drainage off wherever it comes off...you could probably use shims to create a minimal slope to direct drainage.
Then 2+lb sprayfoam for a couple inches on the roof.
Then finish it off with the white reflective paint to prevent UV damage to the foam.

As for picking shade trees, take a look at this PDF.

https://www.srs.fs.usda.gov/pubs/gtr/gtr_so027.pdf

@newbostonconst - I will order some thermometers to take the readings. I'd be interested to hear your ideas on what we can do without spending a ton of money.

@Dilettante - We do have a flat roof with parapet and scuppers. However our roof also has a cistern, solar water heater, and a few air conditioning units. I'd be interested in hearing more about these roof insulating kits for flat roofs. I tried googling it but came up short. Additionally, because of hurricanes, we need to be able to securely attach things to the roof. How does this work with these kits? My wife and I are very intrigued about the roof insulation. In discussing our options, we came to the realization that our bottom floor is pretty comfortable, while the upper is not. And that's because the roof of the upper floor is absolutely radiating heat out. The walls are warm too, but the roof is scorching. I think insulating it could give us a major boost.

Thank you!

Tapering foam insulation kits: Here's a couple to look at.

https://www.achfoam.com/Insulation/RoofInsulation/Tapered-Roof-Insulation.aspx

https://www.insulfoam.com/residential-home-roof-insulation/ (Pics on the site depict a product like SIPS panels. But this isn't the only way to get it.

https://www.cellofoam.com/BuildingProducts/taperedeps.html

You can also just spray the roof with 2-3 lb spray foam, have the sprayer manufacture a high point. And then trim out around the scuppers.

As for hurricane proofing, I'd talk to the vendors about that.



Also, take a look into radiant barriers for the underside of your roof.
Some people swear by them.
Some people swear AT them (and claim they do jack squat).
Just remember that they need an air gap for ventilation beneath them if you're going to insulate.

https://youtu.be/Y5oK-n-A_bM