Old houses can be made super energy efficient as well!
Post: February 22, 2013
Deep Energy Retrofit in Jericho, Vt!
Part 5 - A Warm Wooly Blanket for the House
West wall of the house. Here the first layer of the
repurposed polyisocyanurate insulation board is being
attached to the house. It is one of two 3" layers that will be
added for a total of 6".
The day is finally here. The stacks of polyiso insulation that have been
sitting in my backyard are finally going to be attached to the house.
The house should be instantly warmer with each added panel of
insulation. The fuel use should be instantly reduced.
It took the crew from Caleb Construction (Cambridge, Vt.) a little more
than a day and a half to get this side of the house completed.
Eco Houses of Vermont, LLC
Copyright 2013 Eco Houses of Vermont, LLC
Chris West is a Certified Passive House Consultant
Affiliated with the PHIUS and PHI 2013
One of the details that has required the most thought is that around the
windows. We decided not to replace the windows during this renovation
because they were bought new just two years ago and it wasn't in the
budget to replace them all with high efficiency triple glazed insulated
windows, like I would like to have done.
Instead we are leaving the windows where they are. The solution for
bridging the gap between the window and the new outside plane of the
wall is to build a window buck.
How the buck is to be built and attached was the subject of some
discussion. We decided to go with a PVC buck. This will reduce
maintenance and the possibility of rot. It does have a poor thermal
resistance and it's waterproof qualities means it doesn't let moisture
move through it, so we need to give any water that does get behind it a
path to the outside. More on these details in the next blog.
Part of the plan here is to wrap the house in an intelligent membrane.
These new membranes are imported from Germany and are quite
The membranes are made so that they have a variable vapor diffusion. That means that they change in how open they
are to letting vapor through. The standard construction practice for years was to wrap a house in plastic. This plastic
didn't allow any vapor through. Good idea you may think. Yet this has caused many a problem in many a house. Just ask
energy retrofit contractors like Jim Bradley from Caleb Construction. He has seen lots of houses where the plastic house
wrap has caused moisture that has gotten into a wall to sit and cause mold and rot damage.
The concept behind these variable vapor open/vapor closed house wraps is that when there is vapor pressure from the
outside (like from rain or other high humidity conditions) the membrane has a high resistance to vapor (a perm rating of
4). Yet when there is moisture in the wall, where the vapor pressure is from inside (like in the winter where you are
cooking and heating your house and water vapor moves into your walls) these membranes open up to allow this
moisture to escape instead of being trapped in the wall.
The idea is that this type of membrane allows the wall to breathe. Creating a wall that can keep most moisture out and
allow any moisture that will get into the wall to escape.
Why don't we just keep the moisture out of the wall altogether? That would be ideal, but it is unrealistic. All good
builders will admit that even the best flashed windows will leak at some point. It cannot be avoided. Therefore we need
to design the window penetrations (where the window makes a hole in the wall) to be resilient and allow that moisture to
get out of the wall/window.
A Window Is Born
The South wall of the house is the gable end. This means it is shorter
than the East and West walls. One of the results of this orientation is that
there isn't much room for windows on the South face of the house...and
that isn't good.
Proper orientation of the house for maximum solar heat gains would
suggest putting the largest wall facing the South with a good number of
big windows to allow for lots of sunlight for maximum solar heat in
Oh well. Part of retrofitting an old house is taking the orientation you are
given and living with it. The views out of the living room window are
amazing. I understand why the builder made the house this way.
To try to make the best out of a bad situation I decided to add one more
window to the south face of the house. I already said that it wasn't in the
budget to get lots of nice, fancy new Passive House type windows. What
was in the budget was to go to the local window place and look through
their 'bone yard'. This is a place in the warehouse where the lost and
forgotten windows, the orphans, are kept.
Filling in the gaps
Since the window has been installed the light available in the room on the South face is just fantastic and will add to those
solar heat gains. I do regret that it isn't a Passive House window, but I made a decision to put the money into the shell and air
tightness. At some point the windows will be replaced, when the money is there.
There are places that the insulation panels don't meet perfectly. To maintain the thermal insulation these
gaps have been filled with one part insulation.
Here is a picture of the window (lower left) after being
installed and then the rest of the house wrapped in the 6" of
The frame is a different color than the rest of the windows but
can be painted to match the others.
Some details: New electric service connection
Penetrations through the new thermal envelope/air barrier need to be carefully looked at and details developed to keep the
thermal qualities as well as air tightness in order.
There is very little hope to get this house down to the Passive House Enerfit air changes (1 Air Change/Hour at 50 pascals
pressure). There are just too many double hung windows to allow for this. Still the original blower door test was 8.25
ACH50 which is way too much. With a bout of air sealing in the attic and the planned insulation and house wrap the
expectation is that the new blower door test will be at least 50% better. I am hoping to get it down to 2 ACH50, but we
In any case, as part of the renovation the house will be getting a Heat Recovery Ventilation (HRV) system as well as an
Air-To-Air heat pump, all of which need 220V power. My old 100 amp electrical box is full. There just isn't any room for
more power to be drawn from this old box. An upgrade to 200 amp service is the only answer. It also means a major
penetration of the air barrier and thermal layer.
In the pics you can see the new service box being mounted on the outside as well as the cable that is going into the house.
Not only will there be one cable going through, the main service line. We are also having a generator power coupling
mounted under the electric meter. This will allow us to feed our home's electrical system if/when the power goes out. We
can attach our (still to be purchased) backup generator and run the water pump, heat pump and the ventilation system
when we loose power.
So both of these penetrations need to be looked at. All of the other penetrations as well.
This week Jim Bradley's crew was able to get three of the four walls completely
covered with the 6" of polyiso. Next week (week of Feb. 25th), the bay window
will be removed and a new, flat bay window will be put in as the replacement.
This will make the detail around this window much easier to deal with. It will also
cut down on maintenance - bay windows are water traps that rot after time.
Putting the window into the plane of the wall will remedy this problem.
The crew will also be wrapping the house in the high performance membrane. I'll
ask Jim to take pictures so I can post them as I am out of town for the week. That
tells you how much I trust Jim, leaving for a week in the midst of a major retrofit.
These pics don't show the taping of the main cable through the plywood sheathing
but I assure you it is there. Before I do the final rockwool insulation I will pull it
out again and take a look at how I taped the penetration with Tascon tape.
These pics are also before the generator plug and cable were installed.