The R-value of insulation that a particular home needs depends on its location. First, evaluate what insulation you currently have in your walls, attic, basement and crawl spaces. For finished walls this is tricky but not impossible. You can start by removing outlet covers so you can see into the wall, or drill a small hole in a hidden place such as a closet, and then identity the substance and measure its thickness. Multiply the R-Value per inch in the table below corresponding to the type of insulation you have, by the number of inches you have in your application to calculate the actual R-value of the insulation currently in your walls and elsewhere.  Unfortunately the R-Value of a particular kind of insulation material produced by different manufacturers varies, so the chart shows a range of R-values to be used as a guide. 

 Type of Insulation  Material                      R-Value per inch
 loose-fill  cellulose  3.1 - 3.7
   fiberglass  2.25 - 4
   mineral wool  2.4 - 4.0
 blankets or bats  fiberglass  3.4 - 3.4
   mineral wool  3.1 - 3.4
   high density fiberglass or mineral wool  4.0
   cotton  3.7
 rigid board  expanded polysturene beadboard  3.5 - 5
   extruded polystyrene  5
   polypolyisocyannurate (foil faced)  5.4 - 7.5
   rigid fiberglass  4.2
 blown-in insulation  cellulose  3.2 - 3.7
   fiberglass  3.2 - 4.1
   mineral wool  3.4
   polyurethane foam (from petrochemicals)  5.4 - 7
   soy (open cell foam)  3.7
   soy (closed cell foam)  5
 small particle, pourable substances**  vermiculite**, perlite and polystyrene beads, foam plastics   4 or more
** Some vermiculite contains naturally occurring asbestos, so if your insulation is a type that looks  pourable then have it tested before you disturb it.  If it is vermiculite that has traces of asbestos then have it abated by a licensed asbestos abatement professional.
©Ecobrownstone 2008 All Rights Reserved.

Next determine the recommended R-Value for your house -- the Department of Energy map and chart below indicates the recommended R-value of insulation in different climate zones, and the DOE website also has a nifty zip-code finder that will help you pinpoint the R-value insulation level best suited for your home based on its location, the kind of house it is and the type of heating system in use, however the DOE notes that its recommendations are meant to be cost effective levels based on information it has on local fuel and materials costs and weather and may differ from building codes. New York City is in zone 2.

A.  R-18, R-22, and R-28 exterior wall systems can be achieved by either cavity insulation or cavity insulation with insulating sheathing.
For 2 in. x 4 in. walls, use either 3½ in. thick R-15 or 3½ in. thick R-13 fiber glass insulation with insulating sheathing.
For 2 in. x 6 in. walls, use either 5½ in. thick R-21 or 6ΒΌ in. thick R-19 fiber glass insulation.

B.  Insulate crawl space walls only if the crawl space is dry all year, the floor above is not insulated, and all ventilation to the crawl space is blocked.
A vapor retarder (e.g., 4- or 6-mil polyethylene film) should be installed on the ground to reduce moisture migration into the crawl space.

C.  No slab edge insulation is recommended.

We will be reviewing every kind of insulation for application to our brownstone renovation at 168 Clinton St., and we will need various kinds because we’ve got some rooms where interior walls will not be taken down, one gutted room where a spray insulation is feasible, and no attic requiring specialized insulation for the roof, so check the 168 Clinton St. blog, or subscribe to an RSS feed.