Green Home in New Canaan CT built by BPC Green Builders

(originally published in The Home Monthly, May 2013)

I began this monthly series of columns by taking a look at options for building energy efficient walls and then moved on to attics and roofs.  Now let’s complete our look at advanced thermal envelopes (TE) by checking out foundations.

Most homes in Fairfield County have foundations that include basements, so we will start there.  Foundation walls are built with either concrete blocks or poured concrete, and both have poured concrete slabs.  With an “R” value of 0.11/inch, a typical 10” concrete wall has an R-value of 1.11, which is awful and means that heat is conducted from your basement through the walls and to the ground with almost no resistance, assuming there’s no insulation (Insulation resists energy/heat flow).  With winter-time ground temperatures at freezing near the surface and rising to about 50 degrees at the base of the wall, a great deal of energy – heat –  is lost, if the basement insulation is absent or poor.

I’ve been in many local basements, and it’s typical to find the walls and slab completely uninsulated.  Same for the framed 1st floor deck, as well, although sometimes there is a minimal amount of haphazardly and ineffectually installed batt insulation between the floor joists (batts work best if there is no air flow through them).  There is typically a furnace or boiler in the basement with air ducts or water lines that are either poorly or not insulated at all.  It’s virtually a perfect system for heating the ground, which means it’s perfect for wasting energy and money!  This is a shame because, aside from unfinished attics, unfinished basements represent the easiest and most cost-effective efficiency improvement in a home.

The first decision to tackle is whether to make your basement an “innie” or “outie”, and I’m not referring to navels!  The easiest and cheapest option is to insulate and air seal at the level of the first-floor deck framing, which would make your basement an “outie”, meaning the basement is outside of the TE of the house.  A downside to this option is that you can’t use it for much.  Another is that any heating or hot water mechanical equipment and air ducts and water lines are also outside the TE, which isn’t energy efficient.  If your basement has serious moisture issues, and you can air seal and insulate your mechanicals really well, then this might be the best option for you.  However, if you go this route, make sure you do something to control the humidity, or you may find that you’re growing mushrooms in no time at all, once you stop heating the basement and adjoining soil!

Before you think about how to insulate, it’s crucial that you deal with any moisture problems.  Many basements are built in areas where the seasonal or permanent groundwater table is above the slab.  In other cases, the gutters don’t work, or there are no drain lines away from the house, or the ground is pitched back towards the house.  In such cases, heavy rains result in water that is channeled directly to the ground adjoining the foundation walls.  Footing drains that should conduct this water to grade are often either missing or clogged.  In these situations, even if there is an interior drainage system and/or a sump pump, you need to consider the worst case moisture scenario before you insulate or finish your basement. 

I’m out of space!  Next month I will write about strategies and options to insulate a dry basement and then move on to options for wet ones.

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