Energy Efficiency Round 1 - Install lots of insulation

There are many different aspects to having an energy efficient house, but some of the key components are: 

1. 
   Figure 1 -  Rafter extensions to existing 2x4 rafters add an additional
   7.5" of space to install lots more cellulose insulation to the roof 
    
   Very tight air sealing to prevent conditioned indoor air which you already used precious energy to heat or cool from escaping to the exterior.
    
2. High insulation levels to prevent unwanted heat loss (or gain) from the walls, roof, and floors to the exterior
    
3. High quality windows that incorporate items 1) and 2) above so that they are as air-tight and well insulated as possible, while still providing excellent visual transmittance (light) and appropriate solar heat gain for the circumstance.   A really good window can be a net positive if it gains heat from the sun in winter time and doesn't create overheating conditions in the summer.
    
4. Energy-efficient and water-efficient appliances to save energy and resources for common household usages.  This includes clothes washers, dishwashers, stoves, faucets and more.
    

Today's topic is on how to achieve high levels of insulation in a 110 year old farmhouse that was never designed to be insulated in the first place.  BTW, there is a good chance that you will find the rest of this post super-dry, technical, and only fitting for a true energy nerd.  Apologies in advance.  You can always come back to this during an insomnia episode and it will fix you right up.

Figure 2 -  Rafter extensions in the attic 
 

There are lots of ways to build a super-insulated house if you are starting from scratch and building a new home, but it gets harder when you are retrofitting a building designed before we cared about insulation.  All of the walls and roof rafters in our 1900 Victorian farmhouse are made from 2"x4" lumber, and that doesn't allow us to install lots of insulation in wall or roof cavities.  One or more other approaches must be used.

Our approach is the following:

Build out our roof rafters to be close to a foot deep so that we can add much more insulation to the roof assemblies.  We designed what we will call an "insulation truss" or "rafter extension" to install additional 2x4 material in parallel to the existing rafters to add an additional 8" of insulation space.  See the two images on the right of the roof rafters in the master bedroom and attic. Our plan is to spray 4 1/2" of high-density closed-cell polyurethane spray foam insulation (at R6.7 per inch)against the roof sheathing to achieve a very tight air-seal and a high initial R-value, and to finish the roof insulation by blowing in cellulose insulation (which is made from recycled newspapers) (at approx. R3.8 per inch) into the remaining 7 1/2" of space.  The R-value of the closed cell foam is R30 and the cellulose is an additional R28 to achieve a total R-value of around R58. 

For our walls we are adding lots of insulation on both the inside and outside of the building. On the outside, we will install 4" of rigid foam insulation boards over the existing lap siding and then install new siding.  That's a gross simplification since there are about 5 other steps involved to also air-seal everything really well, but that's the basic idea.  The rigid foam boards are a material called polyisocyanate which offers a really high R-value per inch -- R6.5 -- while not producing any hardful ozone depleting gasses.  By installing these foam boards on the outside of the wall framing (i.e. studs), we eliminate something called thermal bridging, or heat transfer passing through the framing to the exterior.

Figure 3 -  Double-stud walls create 8.5" deep wall cavities, achieving R60 walls 
 

In addition to adding approx R26 to the exterior, we will also insulate the wall cavities with more cellulose insulation.   We hope to install the cellulose in the walls using a method called "dense packing" which means that the cellulose is blown in at high enough density that it can't settle and create uninsulated spaces.  Putting cellulose in our 4" walls would add an additional R15 to the R26 of the rigid foam to achieve more than R41.  We are also building many of the walls in the house to be extra thick by framing them as "double stud" walls, i.e. having a second interior wall inside of the original load-bearing wall to allow room for extra insulation.  Our double-stud walls are 8 1/2" thick and would allow R32 of cellulose for a total R-value approaching R60.

The floor needs to be handled just like the walls and roof and needs to be both very air-tight and well insulated.  We're doing pretty much the same thing under the floor as we are doing with the walls, which is to add lots of rigid foam under the floors and then fill the floor joist cavities with lots of dense pack cellulose.   We'll add 4" of rigid foam under the floor joists  and blow 6" of cellulose in the floor joist cavities to achieve approx. R50.

Since the house has had a number of different sections added on after the initial construction, each of these becomes a special case for how we insulate them.  We have walls that are old-style 2x4s (i.e. really 4 inches), 2x6s, and 8 1/2" double-stud walls, and roofs sections that are 2x4s, 2x6s, and 2x10s, and so on.

More on air-sealing, windows, and energy-efficient appliances down the road.

Comments

[Diana Reddy]

I confess that I did scan the specifics rather quickly, but it's no wonder you haven't been focusing on posting on your blog. This is incredible work, and it's going to be so rewarding. It'll be interesting to compare the difference in internal temperatures during summer and winter extremes after such an effort.