My house is hot in the southern United States. Trying to add insulation in the attic space during the summer almost killed me last year. The attic was so unbelievably hot. I have developed a roof leak and was thinking about a metal roof on top of my current roof. I was wondering why a metal roof can’t be installed on braces a few inches above an existing roof to function as a roof and shade. The airflow between the two would have to cool the attic, much better than if the heat radiated through straight to the shingles and plywood. We bought a sunshade for our back patio, and I’ve thought about even something as simple as that over smaller homes could drastically help.
In: Engineering
Same reason builders in texas still use single pane windows and put no insulation in the walls. Builders are cheap and there are no codes.
Texas can literally cut its energy usage in half just by making people have double pane windows, R15 in the walls, and R30 in the attic. All house are built like shit in texas.
The attic already insulates your living space (why it’s so hot). Solar panels can help reduce it some more and tall trees can help even more.
Awnings can definitely help heat entering thru your windows. Plus modern ones can be retracted in the winter to let more heat in.
Snow, partly.
The top layer needs to be strong enough to support several tons of fluffy white bullshit.
It’s certainly possible to build a unique design for every environment with tolerances based on the prevailing weather conditions… but that’s a lot of extra work. Easier just to have a single universal design that works 99% of the time.
Wrap around porches and awnings basically do the same thing. Shade the windows and your cooling need drops significantly. It’s basically just an aesthetic choice because they fell out of fashion once AC became widespread.
Depending on climate, you might be fucking yourself come winter, when your roof could be collecting passive heat. In general the house should be sited and designed to work for exposure, climate, and your specific use cases. Of course nobody in the US hires architects, so how your home performs is usually down to dumb luck.
Solar panels over a roof area where you want less heat collection would kill two birds I imagine.
Others have said trees, and they’re not wrong. Though waiting for the trees to grow is problematic. Back in the day, when you wanted to figure out how much cooling and heating was required to keep your house comfortable, it was assumed deciduous trees were on the east/west/south, with evergreens on the north. The idea is that in the summertime, the trees would absorb the sun’s heat, but in the winter, with no leaves on the trees, the sun’s radiant energy could help heat your home.
Forests have the added benefit of lowering the overall surrounding temperature. But this is counter intuitive to building homes nowadays, as one wants to build as many as possible on as little land as possible, in order to earn as much money as possible.
You absolutely can. A very effective compact design is called a double-skinned roof. Here’s [a diagram of how they work](https://www.researchgate.net/profile/Tiantian-Zhang/publication/289694544/figure/fig20/AS:334745717231623@1456821006504/Schematic-of-double-skin-roof_W640.jpg).
And a couple of papers on those and similar approaches:
– https://www.researchgate.net/publication/289694544_The_application_of_air_layers_in_building_envelopes_A_review
– https://www.researchgate.net/publication/362972004_Integrated_Economic_and_Environmental_Assessment-Based_Optimization_Design_Method_of_Building_Roof_Thermal_Insulation
In hot climates an additional shade overlay is not uncommon either. This site has [some photos of them in use](https://2030palette.org/double-roof/), although these are chosen for style.
The main issue is additional cost and maintenance. That cost would be made up over time via the energy savings, particularly in hot/sunny climates, but that upfront cost and additional engineering work, as well as the ‘ease’ of air conditioning prevents these type of things from being widely used.
Similarly, awnings over windows and doors has a significant cooling and energy saving effect, and used to be common, but the advent of air conditioners and changes in styles has made them uncommon now. Technology Connections just released [an episode about awnings](https://www.youtube.com/watch?v=uhbDfi7Ee7k) and their benefits.
I’ve thought about this too. I think the gap would fill with wildlife unless you seal it up with unchewable mesh with holes too small for birds and mice. It may make strange sounds at certain wind speeds and could accelerate airflow the way underpasses do. Overall it’s worth a try imo.
I asked this very question years ago, and I was told it would be too expensive because the under-roof would have to be stronger, and the over-roof would cost a lot too. I wa sfactoring in the reduced cooling costs over years, but thats the answer I got.
Then, I recently saw a “brilliant” project for a school and multi-use building in equitorial Africa. The main buiulding was fairly normal, but…it had an extra roof that covered the entire structure and extended out to form a shaded patio, which also shaded all the outer walls.
The one difference in this project was the over-roof was bigger than my original idea
One thing it didn’t add due to a tight budget, was a full-footprint basement, because basements are very cool year round.
A common way to achieve that is to put an insulation under the roofing iron – a inch of fiberglass bonded to a reinforced foil. It works well to keep the temperature of the ceiling space under control.
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