Working towards a future of almost non-existant heating and cooling bills!
The western side of my 1975 raised ranch house. Standard consruction
for the time. Two-by-four walls which had some celluose blown into
them at some point in the last 10 years.
That makes an R-15 wall, or as we say in the super insulation game:
not very good.
So what does the deep energy retrofit encompass?
I heard a great story from a builder friend of mine, Ward Smyth. He said he was working on a job and happened to be
watching a roofer put shingles on a roof. He stopped the guy and asked him what he was doing. The roofer looked at
Ward as if he was crazy and said, "Whadda ya mean? I'm puttin' shingles on the roof." Ward smiled at the man and asked
again,"No, really, what are you doing?" The roofer, still puzzled and thinking Ward is a bit strange said, "I'm shingling
this roof, what does it look like I'm doin'?" Ward said,"What you are doing is making the roof water resistant. That is what
you are doing, and that bit of shingling you did there was backwards which would cause the water to run into the wall
and ceiling of the house."
Ward was talking about the meta meaning of putting shingles on the roof. What is the effect we are looking for from the
putting on and layering of shingles? Making the roof water resistant (any builder will tell you that waterproof doesn't
I bring this up because it is the question I asked myself when beginning this project. What am I doing?
January 15, 2013
Deep Energy Retrofit in Jericho, Vt!
Part 3 - The Little Dig part 1
Increasing the insulation on the house to make it more energy
I am wrapping the house in an outer layer of insulation to
remove any thermal bridges that may exist), or at the very least
to minimize the effect they have on the energy performance of
the house (see last blog post on chainsaw retrofit).
To attain this goal the house needs to be examined and we need
to look at where we need to insulate, what kinds of insulation
each of these 'where's require for their environment. We also
need to look at the house as it now stands and ask what about
how the house is now that needs to change to allow for this
blanket of insulation to be brought onto the house.
In Passive House design we strive to get the air barrier, moisture barrier and thermal barrier well defined early in the
design process. Using this as one of the overarching design strategies saves time and effort later on. Good barrier design
is time consuming and costly if it has to happen later in the project. Plans need to be redrawn, strategies for ventilation,
plumbing, electrical and other services may need to be re-drawn.
This careful planning is something you do when you are building a new house. With an existing house you don't have the
luxury of getting these design ideas into the construction process at an early stage. The house is already built. You are
stuck with whatever the design originally was. This causes retrofits to be costly, usually twice as expensive as if you were
adding these energy saving ideas in a new house.
So we have a house that is already built. How do we get from a house that is using 112,000 Btu/hr (somewhere around
$3500/year to heat, depending on the severity of the winter)?
1) Thermal Barrier - we want to create a thermal barrier that is continuous around the entire
house. The design of this barrier should be done carefully to minimize thermal bridges.
2) Air Barrier - infiltration losses are one of the biggest losses a house can
have. Infiltration is the uncontrolled ventilation a house gets from air that
passes between gaps in the construction of the house. This usually
happens at conjunctions of walls and roof, or walls and walls, or walls and
foundation, around windows and doors, etc.
Designing where the air barrier is going to be and how you are going to
achieve it are a big part of making a house energy efficient.
This house was tested with a blower door test. The results showed that
when a 22 mph wind was blowing on the house (50 Pascal pressure
difference between inside and outside of house) the air in the house was
changing 8.25 times per hour! This is given as 8.25 Air Changes Per Hour
at 50 Pascals (ACH50).
For the sake of an example lets say the temperature of the outside air is
14 F. This means that when a 22 mph wind is blowing the entire house is
flushed with 14 F air 8.25 times PER HOUR! This is air that my heating
system must warm up - and which is then replaced by more 14 F air which
also needs to be warmed up. This repeats every 7.27 minutes for as long
as the wind is blowing at 22 mph. If it is blowing at 50 mph then the air is
chaning faster than every 7.27 minutes...more than twice as fast.
This is why infiltration is such an important part of energy efficiency. The
detailing of the penetrations, that is where windows, doors, plumbing,
ventilation ducts, etc. go through the air barrier is of the utmost
importance. These must be air sealed as good as possible.
Focus on Three Barriers:
3) Vapor Barrier - It is important not only to keep the cold air out, but the
moisture in air, water vapor, can transport huge amounts of water into a wall
assembly, making the wall insulation less effective as well as increasing the risk
of mold and wood rot.
Water vapor moves, in a similar manner to heat, from an area of higher
moisture to an area of lower moisture. The difference in humidity (water vapor
in the air) between one space and another creates what is called the vapor
Vapor drive is the pressure that moves water vapor through a wall, roof or
floor. It is most common to find this in moist rooms like your kitchen or
bathroom, but can happen from outside to inside as well.
A house needs a good vapor barrier to insure that this moisture doesn't get into
the wall OR it needs a wall that allows for moisture to easily move back out of
the wall if it gets moisture in it. It is almost unavoidable to get water in a
wall...and if it does get trapped there then mold and wood rot are often the
How we handle moisture in our walls is of the utmost import, especially when
we make our houses very air-tight.
The most modern walls are being made vapor open, either on one side (either
towards the outside or inside) or on both sides. This allows for moisture that
gets into the wall to dry out when the vapor drive reverses (usually with a
change of seasons).
A vapor open design often uses an intelligent membrane. A very high tech
membrane that opens up to let moisture move out of a wall but is also able to
be vapor closed to keep moisture out of the wall.
We will be using these membranes in our project.
How will we be approaching these three barriers in this project?
Addition of 6" of Poly Isocyano Board (R-value 6.2/inch) to outside of house
Mentos D - Intelligent Air Barrier outside of the Poly Iso board
Intello - Intelligent Air Barrier inside ground floor walls
Both Membranes will be taped using Tescon Acrylic Bonding Tape
The above mentioned air barriers are vapor variable membranes
Both are vapor closed in cold weather - keeping the moisture out of the wall
and are vapor open in warm weather, allowing moisture trapped in the wall
to migrate out of the wall.
Steps of the project:
This project will be broken down into a number of phases.
Testing the house for air tightness before starting the work.
The preparatory work will be done first. For this house it means moving some structures away from
the house (the deck and the front steps are in the way of putting 6" of insulation on the outside). It
also means removing some old wooden cladding on the East side of the house.
The prep work is something I will be doing myself. Saving a bit of money and getting my hands
The second step will be to have some air sealing done. I hired a professional, Jim Bradley of Caleb
Construction in Cambridge, Vt) to do the blower door test and infrared camera scans. He is also the
contractor I hired to do the air sealing as well as the exterior poly iso, membrane wrapping and
window buck work (a window buck is the building out of the window to accommodate the new 6"
The third step is to insulate the house. There are two levels that need to be insulated. A raised
ranch has approximately three feet of the ground floor below grade. This is a cinder block wall.
This cinder block wall needs to be insulated with a different insulation material than the frame walls
The below grade (below ground) walls will be insulated with 6" of Expanded Polystyrene (EPS -
styrofoam) insulation board. This type of insulation is what Insulated Concrete Forms (ICF) are
made of and a great product for below the ground. This EPS will be protected from moisture by a
bituminous membrane specifically designed for EPS called Soprema.
The above grade (above ground) walls will be insulated with the Poly Iso board, then covered with
the air sealing and moisture barrier membrane.
The vinyl siding, which will be removed before the above ground part of the insulations is put on
will be replaced when the Poly Iso board has been placed and the window bucks and insulation
board have been wrapped and flashed with the membrane.
Finally, I will get to put the front steps back up and to set the deck up we will be done with the
The last part is to put the mechanicals in. Heat Recovery Ventilation and Heat Pump.
Once done the house will be finished. For now.
In addition to all of this work the house will be fitted with a monitoring system from E-monitor.
This will data log temperatures, air quality and equipment efficiencies throughout the house for at
least the next two years.
Monitoring is a crucial part of this type of work because it gives us feedback on how the project is
functioning in real time.
If you are going to make a house very air tight and very well insulated then
you need to look at keeping the indoor air quality good as well as possibly
changing your heating plant.
Going from 8.25 ACH 50 (Air Changes per Hour at 50 Pascals - like a 22
mph wind blowing against the house) to 4 ACH50 or even 2 ACH50 (my
minimum goal) then you need to look at how you are getting fresh air into
Before the house was air tight the wind blew fresh air through the walls.
That was the ventilation system. Wind.
After the air tight work and the insulation work is done the house will need
an artificial lung to make sure that the air quality is good and maintained. To
this end a HRV will be put in. HRV stands for Heat Recovery Ventilation. For
more information on HRV's click here.
The HRV chosen for this project is the Zenhder Comfort Air 350. It is 93%
efficient with heat recovery and uses 0.71 watts to operate - very low
The heating plant in the house is currently a mixture of a 55 kBtu wood
stove and a 112 kBtu oil boiler. The modeling of the project shows that after
all of the insulation is put on then the house will go from 112 kBtu to 16
kBtu. Because of this dramatic reduction in usage the oil boiler will be
replaced with a 22.5 kBtu Air-to-Air heat pump. These heat pumps are
250% efficient (COP 2.5) down to 5 F and 200% efficient (COP 2.0) down to
The heat pump is backup heating - supplementing the wood stove. At least
that is the plan. We will see if we want to keep heating with wood after the
insulating in done. We may decide to go with the heat pump as primary
heating in the end. Lower CO2 output, better efficiency.
Wall detail showing 6" Insulation on South wall w 2x6 studs.
Eco Houses of Vermont, LLC
Intello variable vapor membrane.
Image from 475 High Performance Buidling Supply
Copyright 2013 Eco Houses of Vermont, LLC
Chris West is a Certified Passive House Consultant
Affiliated with the PHIUS and PHI 2013