Drawbacks preclude exterior insulation

Q: You advise putting insulation on the inside of a concrete-block house. Would it not be better to put it on the outside, thereby including the masonry as part of the interior thermal mass of the house? This would help to reduce the amount of artificial heating or cooling, I should think. Maybe someone makes sheets with durable surfaces so no additional outside cover would be needed. Bruce Morgan Annapolis, Md.

A: Insulation between furring strips on the inside of a block wall is the conventional method. We are unaware of a rigid sheet insulation usable outside that is economical, aesthetically acceptable, has an adequate R-factor, and is unaffected by weather.

Wet insulation loses some of its effectiveness, as you know.

One residential construction consultant employed by a national insulation manufacturer says: ''From a thermal-performance standpoint (heat loss/heat gain) the coefficient of heat transmission (U-factor) is the same for the wall section , regardless of whether the insulation is applied on the interior or exterior of a concrete-block wall.

''There are thermal-mass considerations, but I hesitate to approach this subject because of the immense number of variables involved, such as climatic zone, site orientation, angle of incidence, and so on, as well as the theoretical variables of passive-solar design.''

So there you have it from an expert.