There are some novel construction technologies that promise a significant upgrade of the building envelope. The simpler methods use 4-in concrete walls that are poured in a Styrofoam frame that remains after the pour, to act as a layer of insulation on either side of the concrete. The benefit of concrete wall construction is that there is no thermal bridging by studs to reduce the effective R-value of the assembly, plus the two layers of insulation help to make the composite R-value R-20 or more.
Some manufacturers claim that when the thermal mass effects are taken into account, the effective R-value of the assembly is on the order of R-50. This is likely an optimistic number, based on a perfect concrete composition, ideal construction methods, and the worst possible weather conditions. However, the R-value will undoubtedly be quite high, though, even if to a lesser extent.
The best news about these concrete construction methods is that they are competitive by cost with wood framing systems. The durability of the concrete structure is a definite advantage, and the thermal mass effects are a big bonus as well.
Also keep in mind that the comfort level is much higher for an interior space surrounded by massive walls, which emit far less radiant energy than for an area defined by wood or metal stud walls. The concrete walls are at a lower temperature than the stud walls, taking all day to warm up because of thermal mass; so the perceived temperature of the space is more moderate, even though the actual space temperature may be identical in either case.
To put some hard numbers to describe heavy-wall construction, a rating scale has been developed to measure a wall’s ability to store solar heat and off-peak air conditioning. The unit of measurement is Btu/ft2/°F. A practical indication is the number of hours a building in a warm climate can go without air conditioning. A well-insulated wood frame house has a thermal rating of about 0.5 Btu/ft2/°F and can last 30 minutes without air conditioning; a building with 8-in blocks filled with grout walls has a rating of 21 Btu/ ft2/°F and will last through 9 hours of heat without the need for artificial cooling.