A crash course in wall construction

Now is the time for me to seriously begin thinking about some of the details of how I’ll make our new eco-friendly home as energy-efficient as possible. My wife and I have our hearts set on a design that we like for our new home, now I am starting to plan the nuts and bolts of how we will lower the energy costs of our home and reduce its carbon footprint.

One major way that I plan to do this is through smart construction of the building envelope. I’ve learned through my research and experience that a tight building envelope would allow me to have more control over conditions inside the home, reduce heat loss during the winter time, and reduce the amount of energy I need to consume in order to run the systems inside of my home.

Advanced framing is the foundation on which we’ll make find our balance between being eco-friendly and having a comfortable, livable space. This is probably one of my favorite parts of the project, because the details we come up with in our meetings with the architects will be a lot of fun to implement later on when construction begins. How we insulate the home is very important too - in this episode, I speak with the architects about several different insulation methods - all of them have their respective benefits and drawbacks, so we’ll be looking for the one that really fits the bill for our new home.

No framing method or insulation method is going to be the uniform best choice for every house in every climate, and fortunately we have a lot of options available to us. If you have had any experience in this area or want to give some feedback, I’d love to hear from you. Leave a comment below and let us know what you think!

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Dave Sweet commented 2016-06-06 17:30:22 -0700

As for your other comments, Bob I think your comment is a good one. The 50/50 rule could be useful as I go forward in my homebuilding process. I’m fully aware of dew point issues, that’s why I plan on using 4 inches of polyiso outside (R20-23) and 5.5 inches of cellulose dry pack in the wall cavity’s (R 20). I think insulation can do more than just keep us comfortable – it can also save us a lot of money on our energy bills.

Gene, thanks for the reference material! I’ll definitely take a look at it… the more I know before I choose which insulation to use in the wall construction method we pick, the better off we’re going to be in the end.
Dave Sweet commented 2016-06-06 17:23:44 -0700

Graig, I agree completely with your statement – that’s why I plan to use a vapor permeable ridged insulation; closed cell polyisocyanurate (polyiso) foam fiber reinforced facers on each side. This is more vapor permeable than XPS insulation.

When it comes to advanced wall construction, I kind of live by the idea that there is no perfect framing system, otherwise I think we would all be using the same; they each have pros and cons. I think it also depends a lot on environmental factors too – I am trying to take everything into consideration when picking the right way to go.
Gene DeJoannis commented 2016-05-27 21:26:14 -0700

Bob Brunhnke has good advice; Dr Joe has great information on Building Science in that book. Also see the buildingscience.com website for some of his articles on envelopes. A good one to start with is “The Perfect Wall”. BTW, the 50/50 rule that Bob mentions is 50% of the wall’s R-value, not just insulation thickness. It has to do with insuring that at the vapor retarder the surface temperature is always above the dew point.
Bob Bruhnke commented 2016-05-27 20:39:38 -0700

Building in a cold climate? Pick up “Builder’s Guide to Cold Climates” by Joseph Lstiburek. Excellent information. The wall assembly needs to account for the dew point at the inside relative humidity into consideration. This will determine what type, if any, vapor retarder will be needed. A good rule of thumb for your particular climate would be the 50/50 rule. 50% of the wall insulation in rigid form on the outside of the sheathing. 50% or less in the wall cavity. No dew point problems. Latex paint on the inside walls for vapor semi-permeable. The wall is designed to dry to the inside, which is desireable in a ‘tight’ house that will most likely have some form of heat recovery ventilation system.
Graig Pearen commented 2016-05-27 10:55:45 -0700

Placining a moisture barrier such as foam insulation on the outside of a wall can be problematic. The vapor barrier is placed on the warm side of the insulation, usually just under the drywall. Placing a second impervious layer on the outside of the wall can trap moisture within the wall structure. I know it has been done many times but any imperfection in the primary vapor barrier installation or damage due to renovations or hanging pictures or shelves has the potential to cause future problems.

With the double stud wall with staggared studs and an insulated gap between them, it is possible to put the vapor barrier on the back of the inside wall. I have never done that but apparently it is an approved method. That way, the electrical wiring and plumbing do not penetrate the vapor barrier!

PS. With standaed 2×6 walls, with studs on 16" centers, about 10% of the wall is only about R6.