An Old House Gets a Superinsulation Retrofit
Arlington, MA
Apr 5 By Rob Wotzak | 14 comments
GOOD DETAILS ARE OFTEN THE ONES YOU DON'T NOTICE. The doors, windows, and colors are obviously new, but the home's overall appearance remains relatively unchanged. The biggest differences are the deep-set window and door trim and the new continuous fascia on the right side of the roof. The window details hint at the thick layer of rigid foam insulation just beneath the siding; the fascia alteration was primarily for aesthetic reasons but had the nice side effect of simplifying some flashing details.
General Specs and Team
Location: Arlington, MA
Bedrooms: 6
Bathrooms: 3
Living Space : 3000 sqf
Cost (USD/sq. ft.): $33/sqf
Completed: March 2009
Builder/contractor: Synergy Companies Construction, LLC
Energy consultant: Building Science Corporation
Construction
Basement: ceiling filled with low-density spray-foam insulation (IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick.)
Walls: existing cellulose-filled 2x4 studs; 4-in. of foil-faced polyisocyanurate foam outside of sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
(R-39)
Windows: fiberglass frame, double-pane, argonInert (chemically stable) gas, which, because of its low thermal conductivity, is often used as gas fill between the panes of energy-efficient windows.
-filled, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. (U-factorMeasure of the heat conducted through a given product or material—the number of British thermal units (Btus) of heat that move through a square foot of the material in one hour for every 1 degree Fahrenheit difference in temperature across the material (Btu/ft2°F hr). U-factor is the inverse of R-value.
: 0.33, SHGCSolar heat gain coefficient. The fraction of solar gain admitted through a window, expressed as
a number between 0 and 1.: 0.29, Pella Impervia)
Roof: rafter bays filled with low-density spray foam (Icynene); 6-in. foil-faced polyisocyanurate foam outside sheathing; seams staggered and taped(R-59 total)
Further resources
Mass. Dept. of Energy Resources (DOER) and NSTAR plan to use information gathered from this insulation retrofit to help Massachusetts residents greatly improve the energy efficiency of their homes.
A detailed journal of the project and a complete list of sponsors can be found at Alex Cheimets' blog: superinsulating.blogspot.com
Energy
Heating/cooling: oil-fired steam boiler in each unit
Water heating: main boiler in unit 1; on-demand gas water heater in unit 2 (200,000 Btu, Rheem)
Annual energy use: To come
- All lighting converted to CFLs in unit 2
- Aggressive insulation strategies
Water Efficiency
- Low-flow toilets and showerheads
Indoor Air Quality
- (2) HRVs (Fantech)
- CO sensors on every floor
- Basement ceiling is foamed/sealed to isolate moisture from living areas
- Interior basement access doors converted to exterior insulated doors with weather seals
Green Materials and Resource Efficiency
- Extra materials donated or reused on other projects
- Retained as much of the original structure as possible
A vintage home gets a 21st-century energy overhaul
What started out as a relatively straightforward re-siding project on this 80-year-old duplex in Arlington, Mass., ultimately evolved into part of an ambitious superinsulation pilot program for the Massachusetts Department of Energy Resources (DOER) and the regional utility company, NSTAR.
Upon contacting the state for technical advice, homeowner Alex Cheimets learned that the DOER was in the middle of developing standards for net-zero-energy buildings and agreed to include his home in the research. The state brought NSTAR into the project. NSTAR brought in Building Science Corp. to conduct a study of the building and make recommendations on the overall design and details of the insulation retrofit. Explaining that the project would serve as a model for broader reaching energy-efficiency programs, Alex convinced several sponsors to donate most of the materials, including the rigid foam (Dow), spray foam (Anderson Insulation), roofing (Atlas), and siding (NuCedar). This brought the budget closer to what Alex had initially set out to spend. The hope is that lessons learned on this retrofit could help lower the cost on similar projects in the future.
Save energy before making energy
Rather than adding complex heating systems or renewable energy sources, this project focused on keeping the actual demand for energy to a minimum. More than just minimizing disturbance of the existing home, adding insulation to the exterior would effectively reduce thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel.
through the framing. Plus, with 2x4 walls (already filled with cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.), there was no other reasonable way to get the R-values they needed.
Lots of rigid foam
Contractors from Synergy Companies Construction started by stripping the roof. Then they applied two layers of 3-in. foil-faced polyisocyanurate foam, a layer of plywood sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen.
, a self-adhesive roofing underlayment, and asphalt shingles. Alex chose the shingles for their durability (50-plus years) and their light, heat-reflecting color.
After the roof was complete and the double-pane, fiberglass-framed windows were in, the crew covered the exterior walls with four inches of rigid foam (2 layers of 2-inch) and taped all the seams. Of course air and weather sealing are just as important as insulation in a project like this, so Synergy meticulously caulked and flashed all windows and doors before the foam went on. Regardless of the choice to replace the existing windows, the new flashing was essential because superinsulated walls dry much more slowly than old, leaky walls.
Furring strips screwed through the sufficiently dense foam provided a sturdy substrate for the new, prefinished cellular PVC clapboards. It did take a fair amount of shimming and tweaking to get everything straight, however.
Adjusting the plan
Even though exterior insulation was deemed the best option for most of this remodel, there were some exceptions. The energy consultants at Building Science felt that the ideal way to address the basement was to insulate the interior surface of the foundation, in order to recapture losses from the mechanical equipment and distribution system during the heating season. The project was already many times larger and more complicated than originally planned, and after careful consideration, Alex Cheimets decided that this was one place where he was comfortable scaling back. The good news is that his choice to isolate the space by spraying foam on the basement ceiling does not prevent him from insulating the walls in the future, should he reconsider.
The same low-density spray foam used below the living space would also give the roof some additional resistance to heat loss (and gain). After stripping a good deal of poorly installed fiberglass from most of the attic, the insulation contractors filled the empty rafter bays completely with foam. This was especially important for bridging the gap where the walls meet the roof.
Additional measures
Although preventing moisture, air, and heat from moving through the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. was the main priority, it wasn’t the only one. New heat-recovery ventilators (HRVs) in each apartment ensure that these now-supertight spaces will have good air to breathe. To further the goal of energy efficiency, Alex converted all the lighting in his apartment to CFLs and switched to an on-demand, gas-fired hot-water heater. One old steam boiler still provides all of the heat for his place, and his downstairs neighbor chose to keep her entire heat and hot water system intact for now. Alex plans to consider upgrading to a more efficient boiler after evaluating a year’s worth of energy data.
With several severe winter storms and a steady flow of reporters, government officials, and product reps, Synergy was still able to wrap up the whole project in about six months. This was far from its first experience with deep energy retrofits, and it only emphasized the company's desire to be a continuing force in environmentally responsible construction.
Measuring success
During the project, Alex had a revelation that should be an inspiration to energy-conscious builders everywhere: "Seemed a shame to rig the house with the best insulation known to man but yet have no idea how much energy the house was using or saving." Data-logging equipment from Onset Computer now tracks his home’s indoor and outdoor temperatures and humidity levels. Two neighbors volunteered to install similar systems in their conventionally insulated homes to collect comparative information. Daily measurements of fuel consumption made by an ultrasonic sensor (from VisiTank) fastened to Alex's oil tank round out the set of data needed to accurately evaluate the home’s performance.
Lessons Learned
Once the ball got rolling, Alex quickly realized that compromises were necessary to keep the project moving— particularly in material choices. If he had had his way, he would have taken more time to evaluate the sustainability and resource efficiency of everything that went into the home.
Exterior retrofits make sense
It depends on the conditions of the particular home, but the consensus seems to be that exterior insulation is the smartest way to boost energy efficiency of existing homes. Other than what Alex describes as a "week of hell" during the basement and attic demolition, the interior remained reasonably undisturbed during the entire process. The place was drafty and cold at times, but that's hardly unexpected when tearing into a house in the middle of a New England winter.
Overachieving doesn't always pay off
Building Science Corp. had specified 4-in. rigid insulation on the roof, but when Alex found out that 6-in. foam was available, he told Synergy, and they decided to go for it. A box of broken, 10-in. screws, a new set of impact drivers, and a week's worth of frustration later, they wonder if it was worth it. In the end, the roof worked out well, but the extra effort and cost were hard to justify.
—Rob Wotzak is associate editor at GreenBuildingAdvisor.com
Image Credits:
- Alex Cheimets
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Apr 6, 2009
2:40 PM EDT
2:40 PM EDT
Attic use and venting,
by GERALD RAND
What was the use of the attic space? I assume it was not ventilated.
Apr 7, 2009
11:24 PM EDT
11:24 PM EDT
Attic use and venting
by Alex Cheimets
Attic is 60% living space with 3 bedrooms and a bathroom. The balance are crawl spaces. The attic is not ventilated. At the risk of mis-stating the consultant's report.......they recommend a "compact roof" which is unventilated. They also recommend that all barriers be on the same plane (water, vapor, insulation) meaning on or under the roof.
Apr 8, 2009
9:24 PM EDT
9:24 PM EDT
Furring Strips
by John Brooks
Alex, I have been looking at your blog.
This photo of the icicle seems wrong...it looks like the furring strips are in the wrong place...creating a cold channel between the outsulation and the weather barrier...and there apears to be no furring strip between the siding and the outsulation.
http://4.bp.blogspot.com/_krzeS_nEpwk/SccUu4q3xMI/AAAAAAAAAxs/zihmaPHR5F...
Warm moist air from the house may be leaking into the channel..condensing and freezing.
Apr 9, 2009
7:32 AM EDT
7:32 AM EDT
oops
by John Brooks
Alex, I see the drainscreen furring strip now. It was out of frame on my screen.. so I had to pan to the right to see it.
Did you use any kind of insect screen at the bottom of the drainage channel?
Apr 11, 2009
7:33 PM EDT
7:33 PM EDT
iso on exterior
by mark galezo
Do you see any issues with the iso on the exterior as a vapor barrier? Wouldn't this trap moisture in the cellulose and create a problem eventually even though cellulose is tolerant to moisture? i assume the principle is the assembly will dry to the inside??
Apr 12, 2009
7:40 AM EDT
7:40 AM EDT
Re: iso on exterior
by Rob Wotzak, GBA Advisor
Mark, this seems to be a question that many people are concerned with, as is evident in many of the discussions on our website. If you browse through the building enclosure overview in our Green Basics section you wiil find plenty of useful information. This envelope of this particular project closely resembles work Building Science Corp. did in one of their own buildings. The principles of how the wall assembly works are covered here.
Apr 13, 2009
1:21 AM EDT
1:21 AM EDT
Answers from Alex
by Alex Cheimets
John, There is a plastic insect screen at the bottom of the wall assembly.
Mark, the thickness of the polyiso insulation is such that the vapor barrier will be too warm for the vapor to condense. As Rob indicated, this is Building Science Corp's SOP. That said, this was the issue that kept me awake at night the most, and I'm not using that phrase as an expression. Awake! That said, I discussed this concern with the Mass Dept of Energy Resources, and other green developers and energy modelers and they all agreed with the BSC design. And so here we are.
Apr 13, 2009
6:56 AM EDT
6:56 AM EDT
What about the Network of cavities?
by John Brooks
Alex,
I understand the outsulation concept for new construction where you can create an almost perfect air barrier from the inside to the outside. It seems like the spray foam at the underside of the roof deck will take care of things in your attic..but what about the walls? How did you achieve an almost perfect air barrier in the existing walls? What were the blower door results?
The icicle photo from your blog is still a little disconcerting. It looks like the ice is forming between the sheathing and the WRB not between the WRB and the outsulation.
Did you ever confirm the source of the icicle?
Agreed that the outsulation in theory will keep the WRB "warm enough"... but what about the network of cavities between the polyiso panels?
What keeps cold outside air out of those cavities?
I know that the panels are taped on the face..what about all the edges near windows and at the top and bottom of the wall? Why is this any different than The SIP failure problem in Juneau Alaska?
Apr 13, 2009
9:45 AM EDT
9:45 AM EDT
What's your biggest concern?
by Rob Wotzak, GBA Advisor
John, maybe Alex will have something more to add, but what are you most worried is going to happen? I don't see how Alex's insulation compares to the SIP problem you mentioned. With the multiple drainage planes, even if there were some leaks, most of the moisuture would find its way downward out of the assembly. Also, there's no OSB (or other moisture sensitive materials) in a place where moisture would be trapped as in the SIP roof scenario. Alex also pointed out that, even if he hadn't replaced the windows, he still would have pulled all of the old windows to re-flash and air seal them to work with the new wall assembly.
Apr 13, 2009
1:25 PM EDT
1:25 PM EDT
What me worry?
by John Brooks
I know..I worry too much and ask too many questions... Jeneau Alaska is an extreme climate and an extreme example and the fact that this project does not involve OSB is a good thing.
My understanding is that the Jeneau SIP failures were do to air leakage and moisture accumulation.
The network of cavities between the sip panels was not a large area... but large enough to cause damage.
The Icicle photo from Alex's Blog made me wonder if the Walls were airtight.
Perhaps the icicle is the result of improper flashing or a plumbing leak..but what if is not?
Was there a plumbing leak? Alex..did you find a plumbing leak?Or did warm moist air from the basement or house find its way to an interface with a cold crevice between the panels or a cold zone between the panels and the existing wall?
It is not clear to me from the article or the Blog if any measures were taken to make the walls airtight before the tyvek and Polyiso were installed.
If the walls are airtight ..and if the icicle is the result of a plumbing leak..then I have no concerns.
Apr 14, 2009
7:35 AM EDT
7:35 AM EDT
Great Blog
by John Brooks
Alex, I really enjoyed your blog.
http://superinsulating.blogspot.com/
Thank you for documenting your project and your thoughts.
Apr 20, 2009
1:24 PM EDT
1:24 PM EDT
More Blog Questions
by John Brooks
Alex,
Concerning the photo from December 2008
http://4.bp.blogspot.com/_krzeS_nEpwk/SeP_yYBN7iI/AAAAAAAAA0k/p65IX2I44B...
Was the 4 inches of rigid foam in place when that photo was taken?
Concerning the basement photos:
http://4.bp.blogspot.com/_krzeS_nEpwk/SeKtbFSD-NI/AAAAAAAAAz0/jUOXUcco4a...
Why did you choose to not spray foam on the underside of the floor joists and encapsulate the joists like you did in the attic?
Concerning the HRV in the basement: Why is there no insulation on the duct that supplies the fresh preheated air to the house? It seems to me like you are "exchanging" the heat with the basement that you just paid to recover.
Apr 22, 2009
6:59 AM EDT
6:59 AM EDT
SIPs Original Built and SIPs retrofit
by Karla Eldridge
Thanks for posting and look forward to reading the details. I built a SIPs home in 2004 It is an Urban in-fill, two-family, "green", SIPs & Universal Design - Age-in-Place home. Now I have to buy an additional home at a new job location to live in during the work-week. I am "Spoiled" by SIPs construction and thought I would have to build again to get what I crave. Now seeing that retrofitting is possible - I can look at normal houses on the market and dream of changing them.
OF course training the construction crew is often the toughest part.
May 6, 2009
10:20 AM EDT
10:20 AM EDT
Very Late Answers
by Alex Cheimets
Sorry guys for these late answers. I did not know this was continuing.
Answers to Mr. Brooks:
1) Icicle
The icicle was another one of those sleepless night issues until I realized that it was located where the outdoor water spigot once was and would return. The old spigot was cut off during construction, and the inner valve was 99.8% closed. That 0.2% formed the icicle until the pipe extension and new spigot were attached. Problem solved.
2) Cavities beween Polyiso Panels
Fine! Another thing to keep me awake! :-) Actually firring strips lock down the panels squeezing out the air between panels. The taped seams makes air entry difficult, but the fasteners and firring strips eliminates venting between the panels. Beyond this explanation, I'm not qualified to answer.
3) Air tight walls.
The walls inside are plaster on lathe. Not airtight. The other walls are polyiso on tyvek on sheathing. There is no inner vapor barrier. The foil faced on the Polyiso is the outer vapor barrier.
4) Moisture Management Windows and Doors
All the windows and doors have been reflashed. The window (jam, frame?) boxy thing extends from the current window out and manages the water out. The reality is that I'm relying on the skills of the contractor and the background work of the consultants.
5A) Foaming Photos: Attic
In the photo referenced, the 6" roof insulation was already installed, but the crawl space window in the photo was to be removed so the 4" of exterior polyiso was not yet installed on this particular outer wall.
5B) Basement foaming
The foaming was mostly, though not entirely, used to seal leaks, so encapsulating the beams was not necessary. Further, encapsulation would have had problems of burying water lines and wiring, and reducing head room.
6) HRV Ducting Insulation in Basement
That is an excellent question, and you have a great eye. You're good. Sitting at my computer, I think we would want:
-pre-HRV incoming air to be through an un-insulated duct (basement is warmer than air)
-post-HRV incoming air to be hmmm. Not sure
-pre-HRV outgoing air to be in insulated duct (air is warmer than basement)
-post-HRV outgoing air to be un-insulated (unimportant).
Perhaps the other issue is simply convection, losing heat to the basement through the duct, so everything should be insulated. I'll bring the question up with the contractors.
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