The single most important thing you can do to reduce your energy consumption and costs is to ensure that you have a tight building envelope -- the building's roof, walls, windows, and doors, in other words the envelope, or separation, that controls the flow of energy between the interior and exterior of the building. Insulation and the building envelope are inseparable components in the analysis of how to control heat loss and heat gain and, consequently, save energy and create a more comfortable living environment. A “tight” building envelope refers to maximizing the integrity of the building envelope to reduce or eliminate heat loss and gain.

Brownstones are particularly prone to leaks and draughts due to the natural settling that would have taken place over the last 100 to 150 years since their construction, causing cracks and gaps to form in the building envelope. Additionally, they are replete with single-pane non-insulated windows that may be just as old, and with exterior walls that may completely lack insulation -- we discovered, for instance, that the rear exterior wall of the parlor floor of 168 Clinton St. was constructed with a 6-inch gap between the interior plaster wall and the brick, with no insulation whatsoever, even though it was apparent that the wall was not original because the lathe was metal and not wood (we know the wall dates back to the 1940s at least).

Frequently, as was the case with the lovely bay windows in our brownstone in Park Slope, there is no insulation in the wood millwork and around the windows which explained why the new replacement windows installed by the prior owner did not eliminate the persistent draughts. 

A typical brownstone which has not been insulated and maintains its original single pane windows experiences complete air replacement about 6 to 8 times per hour, compared to a well-built new home which typically boasts 1 to 2 air changes per hour – this means brownstones are heating all new air 6 to 8 times per hour! On the bright side, starting out with such a bad track record makes for very dramatic results when you institute improvements!

Building green does not have to be sexy. Insulation does not have a lot of flashy bells and whistles, but it is one of the most effective things you can do to save energy. The holistic approach, however, also takes into account indoor air quality – a warm house in the winter and a cool house in the summer is still not comfortable if it gives you headaches or otherwise makes you sick, so choose your insulation carefully.

This Article will guide you through:
The Basics of Heat Gain and Loss
The Basics of Insulation
Insulation Materials Options and Planning
Vapor Barriers
Health and Indoor Air Quality Issues and Insulation
Eliminating Leaks - Sealing Cracks and Gaps
The Role of Windows in the Building Envelope