What is Thermal Mass and how does it affect the heating and cooling of my home?

Q:

What is Thermal Mass and how does it affect the heating and cooling of my home?
A:

Thermal mass describes how certain building materials can help flatten out temperature swings. Masonry is probably the best example. If you're adding a bank of south facing windows to your home, a thick tile or brick floor next to the windows will soak up solar energy during the daytime, helping to keep the house from becoming overheated. At night, it will let that heat out slowly, helping reduce the load on the furnace or boiler.

When contractors talk about the thermal mass of concrete they are talking about its ability to hold and store heat and radiate it back out. In walls like ICF or Insulated Concrete Forms even though the wall performs at an extremely high level because of its thermal mass it has a lower R rating based on the foam that is attached to it. These walls have less R value than conventional stick framed walls but have a much greater thermal mass. So when you are building with a product like ICF you are building a wall that out performs it's R value rating.

When buildings are being designed a lot of time and effort is put into the R value of the walls and ceilings. Little to no planning is placed on the thermal mass of the exterior walls. People will spend thousands of dollars upgrading the R value in their new home and never consider that upping the thermal mass of the outside walls will do the same thing for sometimes less money.

In short thermal mass will have a more dramatic affect on your heating and cooling costs, more of a dramatic affect then the level of R value in the home.

Rob Abbott
Operations Manager
Village Builders Inc.