When talking about climate change and the need to reduce emissions, living sustainably is key. So what do we mean by sustainably? While there are probably thousands of ways to define this word, the most relevant definition today is “without relying on the use of fossil fuels or other limited natural resources.” So how is the SURE HOUSE sustainable? We will use up to 90% less energy than a typical New Jersey home by adhering to the most stringent building energy standard in the world, the Passive House Standard. This low energy demand combined with our solar array will also make us a Net Zero energy user year round. Now that’s sustainable.
When most people think of a building with low-energy use they often think of the efficient technologies used such as LED lights, low-energy refrigerators or efficient dishwashers. While these things are an important part of the equation, there is no question that in climates with big temperature swings between seasons, such as the Northeast United States, the energy needed to heat and cool a building will always be its greatest single energy demand. Therefore reducing the need to heat and cool a home is the best way to cut down your overall energy consumption, and the best way to do this is to create a building that virtually eliminates the exchange of heat with the exterior climate and holds on to the energy used to condition the interior air. This is the idea behind Passive House and explains why one of the most important parts of this house is its insulation, the material that increases the thermal resistance, or R-Value of a wall, roof, or floor assembly.
In order to reach the Passive House Standard, an energy model of a building must be validated which calculates the yearly heating and cooling energy consumption based on local climate data and all of the specifics of the home. A very important part of this model is the thermal resistance or R-Value of the building envelope, the shell of the building that is in contact with both interior air on one side and exterior air on the other. These values are split up by surfaces, walls, roof, floor, windows and doors and your energy model helps you determine what values you need to hit to meet the Passive House Standard, often 1.5 to 2 times what is required by code. For the SURE HOUSE, we have designed our house to have an R-50 roof, R-37 walls, and R-30 floors. In New Jersey, code requires an R-39 Roof, R-19 walls and R-13 floors. These numbers were chosen because of the results from our energy model compared to the cost to insulate more. While insulating is cheap, there are diminishing returns the more you insulate. Therefore, going from an R-0 wall to an R-50 wall will have a much greater effect on your heating energy consumption than going from an R-50 wall to and R-100 wall.
— We are excited to have started building the SURE HOUSE in a parking lot on the campus of Stevens Institute of Technology in Hoboken New Jersey. “SURE Construction” is a subset of our PopSci blog that we’ll use to chronicle our construction process. Check back often if you want to follow our progress and get a first hand view of how a sustainable and resilient house takes shape.
SURE HOUSE Insulation
The insulation material we are using for the SURE HOUSE is a mineral wool material known as ROXUL. This product was chosen for several reasons. The first and foremost is its ability to dry out when wet to prevent moisture and mold issues. Compared to a typical fiberglass batt insulation which does not do well once wet, mineral wool is designed to dry out before mold can grow. This is essential for an area where flooding could be an issue, but is also very important in humid climates such as New Jersey. When creating a home that is airtight and highly insulated in a humid climate, one major concern that arises is condensation inside the assemblies of the envelope. For this reason, buildings must be designed in order to control this potential moisture issue, and depending on the season, there must be a way for moisture to dry out. ROXUL insulation is the best product for mitigating these issues and for a New Jersey coastal environment, it was a no brainer.
Preparing for Insulation
Before insulating, we first needed to bulk up our framing to make it 100% storm resistant. This meant adding blocking to walls where extra strength was needed as well as attaching our ceiling to our walls with high strength hurricane clips to resist high wind loads.
ROXUL Products of all shapes and sizes were used to get the maximum R-Value out of our floors, roof, and walls. For our ceiling, we used a combination of a 5 ½” Batt and a 3 ½” batt for 9” of insulation. For our walls we used 1 ¼” exterior rigid board, 5 ½” of batt inside the wall and 2 ½” of batt inside the service cavity. For the floor we combined two 3 ½” batts for a total of 7” of insulation.
Due to the flood-proof sheathing installed beneath our floor, we had to insulate the floor cavity much earlier than would be the case in a typical home where one would still have access to the floor cavity.
Wall-Floor Thermal Barrier
Two layers of 3 ½” batt were used in the floor to achieve an R-Value of 30. In order to decrease heat losses at the perimeter of the floor, extra ROXUL was added to try and maintain a thermal barrier from the floor to the insulation in the walls to be installed later.
Thermal Bridge Avoidance
In order to maintain a high R-Value wall assembly, every corner or intersection between exterior and interior walls was treated carefully. This is because of the increased amount of conductive material (wood) that can create a heat sink or what is known as a “thermal bridge”. Here, specially cut pieces of ROXUL fill the space between studs where an interior partition wall blocks access to the wall cavity, requiring us to insulate here before installing the wall sheathing. At the bottom of the wall, stainless steel straps attach the wall to the floor to resist against the flood and wind loads from a storm. Finally, behind this a strip of our air barrier was installed before the partition wall was constructed, giving us the ability to create a continuous air barrier that wraps behind and above all of our interior partition walls.
Wall & Ceiling Insulation
The majority of the ROXUL used in our house was the 5 ½” ComfortBatt sized for 16” on center wood stud walls. One layer of this was installed in all of the walls and ceiling, with an additional 3 ½” added to the ceiling.
After transporting the correct size and amount of ROXUL inside from the storage yard, we went to work unpackaging the insulation with a team of people opening and distributing batts. This way we kept the process moving quickly and efficiently.
Fitting in the Field
Although the batts are sized to fit 16” on-center stud bays, there are always bays that need some custom fitting. Luckily, ROXUL is easily customizable on site. All you need is a big serrated kitchen knife and a tape measurer and the batts can be easily cut and shaped to fit any cavity.
“No Cavity Un-Insulated”
Our motto for the day was “no cavity un-insulated” and we stuck to it. Every small cavity required a carefully modified piece in order to completely fill the space without compressing the insulation. Even though it is often tempting to compress more insulation into a small space, this actually reduces the R-Value of the insulation and needs to be avoided. The “fluffiness” of the batt and the air trapped inside the material is what gives it the majority of its thermal resistance, so squeezing the conductive material of the insulation together increases the transfer of heat, leading to more heat losses and potential condensation issues.
Speed + Precision
In order to achieve a balance of speed and precision, it was often easiest to modify batts in place. This way less time could be spent measuring and more time could be spent installing, often with greater precision. Here you can see the two thicknesses of insulation put in the ceiling, the 3 ½” batt on the left and the 5 ½” batt on the right.
One great quality about Roxul is that once the right sized piece is cut and installed, no additional clips are needed to keep it in place. The friction between the batt and the studs holds the batt in place, making install quick and easy.
Once all the insulation is installed on the interior, the walls and ceiling are checked for gaps and compressed areas, making sure that the highest amount of R-Value possible is achieved.
One way to add insulation to a wall with maximum efficiency is to install a layer of exterior, rigid insulation. For this we used the 1 ¼” ROXUL ComfortBoard on the outside of all of our exterior walls. The reason why this layer is so efficient is because it is practically a continuous layer as opposed to the insulation in the walls which is broken up by wood studs. This creates a complete thermal break with the outside air, covering the wood studs and stopping the transfer of heat through what would be thermal bridges. While the ComfortBoard typically does not need to be penetrated for install, over our floodproofing layer a blocking system complete with caulking was used to make sure all penetrations were fully sealed and water-tight.
After the ComfortBoard was in place, vertical battens were installed, serving the dual purpose of keeping the insulation in place while providing a structure to eventually hang our cedar shakes on. These battens provide separation between the insulation and the finish siding giving the insulation the ability to dry out when it gets wet, keeping the cedar shakes from getting damaged.
Working our way up the house, the sequence of installing battens and then insulation made for a clean and simple install and allowed us to kill two birds with one stone.
Without adding framing to the house which is costly and can decrease performance, the rigid board offers a continuous a thermal break around our entire house, stopping the transfer of heat through the conductive material required to provide structure to our flood-proof home.