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
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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.


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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 remarkable materials.

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 winter months.

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 polyiso insulation.

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 will see.

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.


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