why can’t homes or buildings have a sunshade or second roof above them to shade the buildings and cut cooling costs.

Question

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

Answer 1

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.