thermal mass - roofing

tldr: Looking for suggestions for a high thermal mass roof

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Hello everyone, my apologies if this is the wrong forum to post in, it seemed the most general and wasn't sure if any of the more specific forums were more appropriate.


My wife and I with 3 kids live in high(ish) altitude tropics. Day temps do not vary from 22c to 28c year round (cloud cover depending). With night temps about 14c to 18c. However, my wife is from the hot, humid lowlands and doesn't like the cold (<20c  = cold


We have lived in this area for a couple of years now and are looking to build our own home using more sustainable / natural building (I am assuming sustainable and natural mean mostly the same thing - non / minimal cement). However, the various houses we have lived in have varied extremely in temperature.

1) An adobe brick house (single floor)
Although this was adobe, it was a self design and a bit - lets say strange. Originally two separate rooms joined by a big covered outside living area which was eventually enclosed, but still vary open (gaps around wall to roof. Roof was basically a tin roof.

This house was freezing. In the evenings, my wife would be sat indoors with a coat and scarf on.

2) A type of brick / cement block house (two floors)
Warmer than other house, didn't get much sun, downstairs was always cool, the rooms that got some sun better, but heat didn't remain. Roofing was a kind of fake tile thick sheeting which is popular here (sorry no idea of correct terms). Upstairs was toasty in the day, but temps dropped quickly


3) A cement block house, with a solid cement roof (eventually they plan to build another floor, but for now is one floor)
This house is warm and comfortable year round.  You can sit indoors in just a pair of shorts (me more than my wife). When you come in after being outside all day, as you enter the house, you can feel the warmth. This house is in a good position to get sun all day.

The only reason I can figure out (after some research) is the cement roof is a good thermal mass. Going on the roof on a sunny day, the roof is almost too hot to touch. This then radiates into the house throughout the night.



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Now the issue is (and I know the above comparisons are apples to oranges - or more like apples to watermelons) we like the heat from the cement house but that is completely the opposite of what we hoped to build. With the reading I have done, it is said adobe is also a good thermal mass (although out experience with it says otherwise - but that could be down to the bad design / layout of the house.


Now assuming adobe is a good thermal mass, my hypothesis is the heat for the cement house comes mostly from the roof. We get 12 hours of day (sun up and sun down at 6am to 6pm), 365 days a year and the sun, due to being close to the equator is over head 365 days a year. So the roof is getting most of the sun rays, not the walls.

so my question is, what roof options do we have for a good thermal mass roofing using natural techniques? I have not found any substitute for a solid concrete roof using natural techniques, so am open to suggestions


Cheers

A flat roof requires waterproof material like concrete (including perhaps some type of coating). If you give the roof some pitch so it drains quickly, you have many more options for material as long as you have water-shedding surfaces on top. Brick arched vaulting with clay tile on top is a commonly done example. How much rain do you get? How often, and for how long at a time, does it rain? Is there a rainy season? The less heavy, extended rain you get, the wider the options for natural, non-concrete mass structure.


Your adobe house was designed backwards for your purposes. The tin roof would have largely shaded the adobe walls, so that the mass would never get hot. If you have enough rain that a tin roof makes the most sense, putting it over an earthen masonry vault, either in contact or with a little air space, might transfer enough heat from tin to vault by radiation to warm the roof mass. I would want to test a small sample on a shed or something to see how that worked.

Thing to 'overheat' your house.
1) Make the house airtight esp at the roof.
2) Have as little roof overhang as possible
3) Remove any nearby trees/structure that could block the sun at any time of the day
4) Orient the Windows to the sun path