In our city, all buildings are insulated to ensure that heat is kept in but even a small break in the insulation can actually affect performance of these insulations by as much as 20% since the heat goes out of the gaps. The NYC energy code actually requires insulation to be continuous but code interpretation has allowed various metal and concrete components that allows heat to penetrate the walls/insulation.
These days though, we will be seeing a lot of changes as the new interpretation of the codes shows that most buildings with exposed slab edges and continuous shelf angles will no longer be considered as compliant with prescriptive code insulation requirements and with DOB to strictly enforce the provision, the energy loss through the gaps in the walls can now be averted.
What Was Done Before
Previously designers of high-rise buildings have been able to use exposed slab edges as well as continuous shelf angles that disturb insulation. These metal shelf angles provide support for brick façade just like the exposed slab but isn’t noticeable from the outside and while the exposed slab edge may look like it shows a more substantial thermal disruption, the thermal conductivity of the steel actually has the same flimsy thermal performance as that of the exposed slab edge.
2014 Code Changes
The examples noted above cannot represent continuous insulation and the DOB has confirmed this and as such, the code now requires for wall sections to have a truly continuous insulation. The slab should be fully insulated and the shelf angle be cantilevered away from the slab by brackets and doesn’t break the insulations’ continuity. The brackets show an acceptable example of how it should be done, there may well be other ways to do it as well, but the main consideration will be the continuity of the insulation to prevent heat loss due to the gaps.
Looking Ahead
We must keep in mind that unlike appliances or automobiles, buildings constructed today will impact energy consumption up to a 100 years from now or perhaps even longer. Making sure that building energy codes are complied upon to facilitate energy efficiency is very important.
Lowering energy bills and lowering energy generation demands help by controlling greenhouse gas emissions as well as air pollution. Updating these energy codes to make them more efficient for easy compliance and enforcement is a very important aspect in reducing energy use of the building’s life.
It might be realized that in time, as efficiency requirements of building energy codes are improved, zero net energy buildings or ZNEBs – buildings which produce their own required energy - will be the recognized standard of new buildings/constructions.