Warm walls

October 25, 2017  •  Leave a Comment

A Better Mouse Trap with Less Money

 

Most of the homes my dad and grandfather built used primarily 2x4 studs for the outside walls.  In the early 1900s hardly anyone used insulation in the walls.  I remember once tearing apart a home built in the early 1940s that was very unusual. It had one single layer of aluminum foil put meticulously in the center of the stud bay held in place by small little lath strips. This might have been a good air barrier but provided little R-value and the time involved putting it in was huge!  

 

In 1945 after the war, my father recalls building 2x4 walls and using a product called balsam wool as insulation. Several years later, dad built our home in 1958 (the home in which I was born) using R-11 fiberglass.  R-11 was quickly replaced by R-13 which fit in the same 2x4 walls. 

 

When I was a very young man in 1976 our company built mostly with 2x4 walls; however, Dad was using insulated sheeting on the exterior walls to boost the r-value.  This stuff looked like it was made from horses hair so we called it, “Punk board”. 

 

By 1980 we began using 2x6’s for walls.  With the added 2 inches, we could get an R-19 insulation batt in the walls.  We thought this was really great! By the 1990s, R-19 insulation was mostly replaced by R-21, a high-density batt that would fit into a 2x6 cavity. Today the building code in our area still allows for R-21.However, homes that contain what I call, “Good bones” and built by superior builders do not stop insulating at code minimum. There are countless ways to increase insulation values and stop air movement in a home.  Thicker walls, foam on the outside walls and so on.

 

So the first question now becomes, “What about longevity and systems that do not allow for wet walls and mold to grow?” and, secondly, how do cost and value play a role?  Like anything, there is a law of diminishing returns on insulation, meaning an R-11 wall will not save twice as much money on energy bills as an R-22 wall.  If I spend $10,000 more and save $200 a year, does this make sense?  You need to look at your goals. If you are looking for a “Net zero-energy home” you will want to go further than someone who wants a comfortable home with reasonable energy bills. 

 

Below is a photo of an R-30 wall that goes well beyond the code minimum R-21. It is quite inexpensive and a good “Bang-for-the-buck”. We are using here 2x6 construction and adding 1-inch of foam followed by a ¾” fir strip.  The foam acts as a thermal break for the stud and the 7.25” cavity allows for an R-30 Bibs system to be installed.

Below is slightly better at a significant more expense with a double 2x4 wall that gives a thermal break on the studs and allows for a 9-inch cavity for an R-38 value.

Many builders are using an XPS or EPS foam on the exterior walls to achieve high insulation values. My main concern with foam systems is in the detailing of the windows, doors and roof- to-wall areas under wind-driven rain conditions.  

 

Design and theory are great, but the important thing in any system is good craftsmanship and care in the assembling of the wall you are building.

 

 

 


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