These roofs have some pros and cons as explained in the article.
Hot flat roof.
The hot applied asphalt or coal tar pitch blends with the bitumen soaked roof felt and creates a monolithic roof membrane.
The traditional hot tar and gravel roof is built from three or more plies of waterproof material alternated with hot tar and ballasted by a layer of smooth river stone.
While some try to do this with fiberglass or cellulose their efforts are for naught and quite simply it is not allowed by any legitimate building code out there.
Built up roofs are installed using several layers of a special type of roofing felt that has been asphalt impregnated and embedded in bitumen applied with a hot mop.
It s definitely something to consider when re roofing and in a new construction project and you might be able to take steps to cool things down on the roof you already have.
As you might imagine this is the cheapest version possible and good for covering a shed.
The benefits of a conditioned attic.
It may be covered with a granular roll roofing epdm which is smooth surfaced or modified bitumen which may be smooth or mineral surfaced.
Other options to cool your flat roof.
When placed over a cool roof laminate of pvc they will continue to keep your home cool in hot summer weather.
Hot tar and gravel also known as the built up roof bur this type of flat roof features three or more layers of waterproof material mixed in an alternating fashion with hot tar and a layer of smooth stone like gravel.
A system most likely to be found in newly built homes the term hot roof is something of a misnomer as the attic space will only be a few degrees warmer than in a traditional roof.
If you live in an arid region or an older urban area you may have a large flat roof.
You can also add ultra thin solar photovoltaic panels to your flat roof.
These will store energy for you to use in your home and send excess capacity back to the local power grid.
A hot roof is one where there is no ventilation required as the insulation is directly attached to the roof sheathing.
How hot your roof really gets in the summer is a variable you have some control over.
A warm roof is much more straightforward to install and provides a superior thermal performance and is therefore more costly.
A flat roof is usually slightly sloped.
Traditionally the smelly hot physically demanding and sometimes dangerous work of tarring flat roofs has often meant that uneducated fitters of doubtful reputation have done work to a poor standard.
Some flat roofs have hot tar built up roofing which may have a gravel surface.