How to Prioritize Energy Upgrades to an Existing Home-Part 2

I purchased my home in the fall of 2018.  I could have decided to build something new or forgo all the maintenance that comes with home ownership and rent.  Instead, I chose to purchase an older home that needed updating, both in appearance and performance.

The 24’ x 32’ home was built in 1952, a Cape Cod design with the normal problems of a Cape Cod, attic knee walls that were both inside and outside the air control layer.  There was some evidence of past water damage and a few old clips on the roof where a heat tape would have been placed, suggesting an ice dam issue.  The high efficiency natural gas forced air furnace appeared to be from the 1990’s, the same year as the electric water heater.  There was also a natural gas fireplace in the small living room.  There was a weird-shaped room on the main level (behind the sun and where the sliding patio door is located, 9’ wide by 24 feet long.  Two bedrooms, and a bathroom were located upstairs, a bathroom on the main level, and an area in the basement that had an egress window well that would support another bedroom.

I purchased the home too late to perform any exterior projects the first year.  I spent that first winter building an office in the basement (where I am currently writing this article) and learning about how the home operated.

Collecting data to prioritize a scope of work

Before I even purchased the home, I conducted a blower door test.  I was expecting something in the high single digits, maybe 8 or 9 ACH50.  I was a little leakier than I expected, 12.3 ACH50.

The equivalent leakage area at 10 Pa (what might be expected during the winter months) estimates a 12” x 24” hole in the home, not something you want in your building enclosure when you live in climate zone 7.  This high rate of air leakage causes indoor humidity level to drop into the single digits during very cold temperatures (below -30°F).  The blower door software also suggests the cost of the air leaks is more than $550 per heating season, I think this estimate is a little high.

Further investigation while the blower door was operating indicated that a lot of air leakage was in the roof.  This was confirmed by the ice dams I experienced that first winter (which were also the result of low R-values).

The cost to heat the home the first winter, using natural gas, was right around $900.  Not overly expensive for my climate but realizing that about half of the cost was the estimated air leaks, I knew air sealing needed to be a priority.

As far as comfort within the home, it varied during the heating season.  Some areas were cool, others were fine.  But if I got close to an outside wall during very cold weather, I could feel the heat leaving my body.  The home can also get uncomfortably warm in the summer.  Improving thermal resistance would be another priority.

I did see some water on the basement floor, dripping from the level above in the spring of that first year.  The water lined up with an interior wall common to both bathrooms, one on the main level and the second on the upper level.  One of the walls in the upper level is an exterior cheek wall for the shed roof dormer.  I think frost forms in that wall during the winter months, then melts in the spring, ending up on the basement floor.  I have yet to renovate any of the bathrooms, which should confirm my suspicions.

After I purchased the home, I disassembled a small area of an exterior wall to determine if the wall was insulated, it was, but with a product I had not encountered before.  A 2”, kraft encapsulated mineral wool insulation batt.  The insulation was stapled to the inner face (warm side) of the exterior wall assembly leaving about a 1.5” air space between the kraft facing and exterior wall sheathing.  This probably resulted in convection loops forming inside these wall cavities.

There were a few windows around the home that had been updated, (I found one during a later window replacement with a date of 1989), other windows were original to the home, single pane with aluminum storms.

The foundation is 8” CMU.  During the build-out of the basement office, I discovered there is no core fill, nor could I find any place where the house is fastened to the foundation, a little unnerving.  The CMU basement leaks but so far, the leakage has been minor.  A couple small puddles after very heavy rains.

As I mentioned earlier, the forced air heating system (natural gas) and water heater (electric) were from around 1990.  The only ventilation in the home was a bath fan in the bathroom on the main level.  The house has a high rate of uncontrolled natural ventilation.  Air sealing the structure would change that, a new ventilation strategy would have to be developed.  I also brought up earlier how the home gets very warm during the summer.  Window AC units were used the first three years, but I installed an air source heat pump in 2022 providing summer AC and spring and fall heating.  The unit is not cold climate, I run it until outdoor temps are consistent at around 20°F, then switch over to natural gas.

The work scope

1. Repair any damage (water) and improper renovations that have occurred over the years.
2. Improve air sealing of the home.
3. Improve insulation levels.
4. Upgrade all windows.
5. Replace aging space and water heating equipment.
6. Install a balanced mechanical ventilation system.
7. Modernize the exterior and interior décor.

The progress

I wanted to have a primary bedroom on the main level of the home.  That 9’ x 24’ room on the North end of the home was the perfect candidate, but the size and shape created a challenge.  I decided to add a small addition to bump out an area where a bed could be located.  The addition was only 3’ wide (all the closer city zoning would allow me to go to the property line without going through the process of a variance) by 12’ long.  I designed a 5’ x 9’ small walk-in closet on the east end of the space, where the sliding patio door is located, and a 5’ x 9’ room on the opposite end that will eventually become the main-floor laundry room (the laundry is currently in the basement).

The addition allowed for an opportunity to correct issues from a prior renovation that were hiding behind the exterior wall “sun”.  I discovered that area used to be a side entrance into the original kitchen location.  The rough framing for a door and window along with some very risky electrical work were located behind the “sun”.  There was also a wall cavity return air duct in the exterior wall providing a return path from an upper-level bedroom to the basement, where the furnace is located.  I’m sure that building cavity duct was pulling more air from the outside than from the upper level.  The addition also gave me the opportunity to improve the water control and air control layers from the outside.  The original cladding and WRB (#15 felt) were removed on both the North and West (street facing) sides of the home.

Because I removed all the interior finish in this area, I was able to update the electrical wiring, change the R-7 insulation product to a mineral wool R-15 insulation, and further improve air sealing by installing a class II vapor retarder treated as a secondary air barrier.

During the demolition phase of the street side elevation (west facing), I found an area where the board sheathing and rim joist were damaged, caused by a concrete step that had settled.  The step pitched towards the home allowing water to wet the building materials behind the step, a common problem.  Carpenter ants had made this area their home.  Removing the concrete step and repairing the damage was a little unexpected work, but not hard to do.

Because the home is sheathed using board sheathing, I chose a self-adhered WRB which acts as both the water control layer and primary air control layer.  I contemplated adding continuous insulation but without a roof overhang on either of the gable ends, and not wanting to rebuild the roof, I decided against that improvement.  I added 3/8 strips of plywood as a rainscreen, improving the drainage and drying of the exterior wall.

Windows were updated using a builder grade window with better glass and an insulated frame.  U-.30 is common in my market.  The double pane, casement windows I chose are U-.27.  Installing the flanged windows with a self-adhered WRB required a bit of a learning curve.  The first few windows I installed, I followed the WRB manufacturer’s installation instructions, the window was installed over the self-adhered WRB, creating a reverse lap at the window head.  The window was taped using Henry’s butyl flashing tape and a bead of Henry’s Crystal Clear 212 sealant tooled at the top of the tape to create a belt and suspenders approach to water management in that location.  As I moved around the home, I modified that installation.  I now leave the SA WRB off above the window head, install the window per the window manufacturer’s instructions, then install the last strip of SA WRB.  This creates a traditional shingle lap of the WRB.

Interior Improvements

My most recent interior renovation happened over the winter.  Demo revealed frost accumulation in the wall cavity after removal of the R-7 kraft-faced mineral wool batts.  The frost forms from interior air leaking into the wall cavity and condensing on the cold wall sheathing.  These photos were taken in December, the early part of winter.  I wondered what they would have looked like had I taken this room apart in February.

This interior renovation included upgrading the insulation to Rockwool’s ComfortBatt R-15 and the installation of Siga’s Majrex, installed as both an air and vapor control layer.  This project was also my first use of Siga’s Twinet, a double-sided tape used to adhere an interior membrane to framing, eliminating the need for staples.  The double-sided tape takes a little bit to get used to, it has an aggressive adhesion.  You need to start the membrane correctly; repositioning can be difficult.

Because I demoed the space down to framing, I had access to the roof eave and the attic knee wall area of the Cape Cod design from the main level.  I had two choices of how to improve this area.  One, insulate and air seal the knee wall and first floor ceiling, or two, locate the insulation and air barrier at the roof, making the attic knee wall a conditioned area inside the home.  I choose the latter strategy.

I added ventilation chutes to the underside of the roof sheathing, which will eventually extend all the way to the roof peak.  I could then insulate between the 2×6 roof rafters, but with only an R-15 batt.  Not nearly enough for my cold winters.  After the batt insulation was in place, I extended the Majrex air and vapor control layer from the wall, up the roof.  This required a lot of taping around the floor joists for the second story.  Once the membrane was fastened and sealed, I added a layer of ridged mineral wool insulation (a layer of continuous insulation on the interior), secured to the bottom of the roof rafter.  I’m still only at an R-23 roof insulation value, but a major improvement over the R-7 that was originally installed.  At present, this insulation and air sealing improvement has only been extended to the knee wall of the upper-level bedrooms.  A renovation to the bedroom spaces is planned for this winter, the improvements will extend the air sealing and insulation through the rest of the roof.

The work at my home still has a long way to go.  I’m self-performing everything, solo, which results in slow progress.  Living in a constant renovation isn’t enjoyable, but I do like the work and find a lot of satisfaction in seeing the improvements.  So far, the blower door number has been reduced by 25%, and I still have the majority of the roof improvements that need to be completed.  Costs to heat the home have decreased as well, from $900 in 2019 to less than $550 in 2023-24 (some of the reduction was the result of last winter’s very mild temps in our region).

There are a lot of old homes that could benefit from improved water management details, air sealing and insulating, and updated heating and cooling equipment (along with a ventilation strategy).  Whether the improvements are part of a shallow energy retrofit, deep energy retrofit, or a simple room renovation, having a smart plan to provide a pathway for these improvements is key.  It’s also important to note that changes to the home can have a detrimental effect on how a home operates (increased humidity levels causing a decrease in air quality as an example).  Pre and post testing of the structure should be included in the scope of work.  Having a trained workforce that understands the building science behind the improvements is also very important, finding these workers is the current challenge.  A discussion for another time.