Insulation in Basement

Q. I think I heard you recommend to use UNFACED insulation on the outside concrete walls of a basement, rather than kraft faced insulation-TRUE? I am covering the walls with plasterboard attached to 2 x 4 studs.

Is it all right to use kraft faced insulation on the inside walls inside the basement to deaden sound? These are free-standing walls not against the concrete outside walls.
Finally, I am adding heating to my basement when it is finished. Is there a formula to use for adding heat vents and cold-air returns?

A. First, (on a dry foundation basement wall) clean & coat the concrete foundation walls with UGL Dry-Lock or a moisture block paint product on the raw concrete wall. Then build your stud wall and insulate the stud cavities with unfaced batts with NO vapor retarder and definitely no plastic vapor barrier. The walls need to be able to breathe as the humidity changes. St. Louis relative humidity is often 90% in the summer so the general air is often loaded with water vapor even in "dry" basements.

Interior walls can be insulated with any type of batts or faced insulation for sound. Sound insulation is better with higher density so the "heavier" the sound insulation the better. Rock wool is a great sound batt. We often sound insulate the ceiling of finished lower levels if noise is a problem. The insulation attenuates or "muffles" the sound but does not block the sound.

Heating and cooling is a science of air flow, BTUs, and air changes per hour. Heat loss/gain calculations and CFM (cubic feet per minute) air flow volume balancing is absolutely essential to ventilate and keep the air dry in the St. Louis climate and especially basements. Mosby Building Arts installs new furnace systems and ductwork in almost ALL finished basements to move the air, dry the air and remove any musty smell of stagnant, humid air. Heating and cooling contractors can provide this design, but the results will very often indicate another system for areas that exceed 400 square feet of added area.

Cutting holes into the existing ductwork in the basement is similar to cutting holes in the bottom of a water bucket. The more flow that goes through the bottom ... the less is effectively delivered to the floor(s) above. This effect is to starve the main floor and especially the 2nd story of two story houses by taking air flow from the existing basement ductwork. The existing ductwork was designed to effectively serve only the original floor plan at construction ... and most existing ductwork systems are ineffective by today's standards and maybe your current comfort standards.

Please be thorough with your air flow for the sake of indoor air quality, your health, moisture management, and simply protecting the investment in your lower level.

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