For Assignment 4 I examined The Center for Energy Efficient Design (CEED), In Franklin County, Va. (20 minutes from my hometown, Roanoke, Va.) After attending a lecture at a church in Roanoke on this local project. CEED is an extension of Franklin County high school, a small school in an extremely rural area of Virginia, with a goal to raise awareness and knowledge on renewable energy technologies and Passivhaus design. This building includes both a classroom and hands on laboratory where high school students study topics like hydroponics, aquaponics, and biodiesel production. This building is not only a tool for our youth but it is also open to the public so that builders and contractors can see Passivhaus systems in action, so that they can more easily apply these in their own work.
In my previous blog post I listed all of the systems and technologies this learning facility includes. Due to the timing of the beginning of this assignment I chose to focus on the thermal insulation of this building. After doing extensive research on the Center for Energy Efficient Design I found that there were no construction or detail drawings of it. For the first portion of my project I attempted a detail drawing of the joint that occurs on the front façade of the CEED between the roof, exterior wall, and bay windows. I had to use multiple sources and condense a large amount of information to be able to create this diagram. There doesn’t seem to be one specific way to insulate a window joint in Passivhaus design but the similarities between other Passivhaus images were enough information. Below I will list the main components of this joint diagram starting at the top of the drawing.
1. Air barrier between roofing material and moisture barrier
2. Fiberglass insulation
3. Rigid board insulation
4. Loose fill insulation in frame
5. Argon gas filled, triple glazing coated glass
This composition of materials aims to prevent the most thermal bridging possible, which is the way most heat is lost from buildings.
Passivhaus certifications incorporate very high standards of insulation. The Passivhaus rating is the highest energy standard in existence ‘with the promise of slashing the heating energy consumption of buildings by an amazing 90%.’ These homes are primarily heated by passive solar gain and internal gains from the inhabiting individuals and electrical equipment. This method works because these homes are insulated so well and because they are virtually air tight. All of the numerical information I could find on these insulation standards were unfortunately in metric units and Euros which makes them difficult for us to imagine, however I found one source very helpful in understanding the difference in heat loss from a typical European house and a Passivhaus house. In the chart below, the U-value, or thermal heat loss coefficient, shows the amount lost through a regularly insulated wall (external wall area of 100 m² with winter temperatures of -12 °C outside and 21 °C). The U-value shows how much heat (in Watts) is lost per m2 at a standard temperature difference of 1 degree Kelvin (inverse of the R-value we talked about in class).
A compact service unit is a system used for both heating and ventilation in passivehaus’s that provide a combined services approach that reduces installation costs. For this type of system to meet the total heat loss of the home the U-value of the walls and roof have to be extremely low. The range of U-values these materials must have to be used in this type of construction is between 0.1 to 0.15 W/(m²K). Any typical construction insulation material is able to meet this level of insulation however the issue is how much of it is necessary. Below is another table from the same source as the one above showing the thickness that would be needed if we were to insulate with some of the materials most homes use today.
As I mentioned above, the Center for Energy Efficient Design didn’t provide any information on the internet about the complexity of the insulation composition it used, which allowed me to infer what I believe they may have used. The model I have made is of a “compound system” insulation system. Termed this because of its use of two major insulators instead of one. This system takes up more space than the latter, but judging by the thickness of the walls in the CEED section I believe more than one main insulation material was used. I modeled a section cut of what I believe the CEED insulation looks like, with a ½” cut away of each succeeding material allowing the viewer to get a larger look at the surface of each. While some materials used in my model were the real thing (wood,fiberglass fill, and rigid foam) others are only visual representations of what the material would look like.
Below I will further explain the labeled layers in my model:
1. Exterior Siding
Exterior siding is used mainly for aesthetics. This material is nailed both to the sheathing that lies directly behind it but also through to the studs in the walls. The sheathing is typically a thin panel of plywood. I have guess that the siding used one the exterior of the CEED is engineered wood. This material is made with wood products but has a uniform wood grain since the finish is man made. Some forms of engineered wood siding are oriented strand board, hardboard, and veneered plywood.
2. Moisture Barrier
Weather resistive barriers are placed in between the exterior sheathing and the structures siding. This layer protects the home from moisture infiltration, and is often times referred to as house wrap. “By keeping building materials dry, a weather-resistive barrier improves building durability, decreases maintenance costs, and reduces the risk of moisture-related problems such as bugs, mold, mildew, and rot.” This layer acts as a drainage plane, draining the water that does get through the exterior siding down through the air barrier that is left between the moisture barried and the siding. To retain system integrity this layer must be installed very carefully by a professional.
3. Fiberglass Fill
Loose fill insulation can be made from materials such as cellulose, fiberglass, and rock wool. This form of insulation is broken down into shreds or granuels which allows the fill to conform to any space. When built by a professional loose fill is applied using speical blowing equipment. This type of instalation helps to lessen the amoutn of gaps that can occur in roll instalation. Fiberglass fill is also very fire resistant.
4. Vapor Barrier
The vapor barried layer that lies between the two major insulation types in this compound system is the second level or moisture infiltration protection. This material not only keeps the exterior moisture out but also keeps the interior moisture in. activities such as cooking, laundry, and bathing all produce a large amount of water vapor. If this vapor reaches the loose fill insulation cavity it can convert to liquid within the insulation and significantly lower the insulations R-value. Without this barrier moisture would collect in the fiberglass layer causing the fill to mat and compact.
5. Rigid Board Insulation
This type of insulation has a higher R-value per inch than fiberglass insulation does. The microscopic closed cell structure of this material gives the foam its unique properties. This rigid foam as we know has very low thermal conductivity but it also has a very high resistance to water penetration and high compression strength.
6. Airtight Envelope
Airtightness is essential to avoid construction damages caused by moisture infiltration. However this layer should not be confused with the vapour barrier. A vapour barrier is a diffusion tight layer. This envelope allows some vapor diffusion. The installation of this layer is extremely tedious and the envelope can only be effective if the layer consists of one undisturbed airtight layer enwrapping the whole volume of the house. This is a separate layer from the insulation because insulation materials are generally not air tight. The accuracy of this amterials correct installation is especially important at joints in the structure, as we know from thermal images in class this is where most buildings loose their heat. This envelope should also not be confused as being an insulation material responsible for stopping heat transfer.
Drywall is a material made of porous plaster and is used for the interior finishes of walls. This material comes in sheets and is nailed to studs behind it.
Other images of my model:
In conclusion, Passivehaus thermal insulation has very high standards but is able to function in an extremely remarkable way, especially when compared to traditional insulation methods. Passivehaus structures use natural systems and resources by capturing and channeling them in the most efficient ways we have discovered instead of relying on predominantly ‘active’ systems as the large majority of building and homes do today. “High performance triple-glazed windows, super-insulation, an airtight building shell, limitation of thermal bridging and balanced energy recovery ventilation make possible extraordinary reductions in energy use and carbon emission.” I found a few different statistics on the price difference between traditional building and it costs a on average a surprisingly small 14% more to build a Passivehaus home than a traditional one. One website claimed as low as 10% more. I have gained tremendous knowledge on all types of insulation for all types of construction methods as well as the most efficient joining systems. I look forward to following the popularity of Passivhaus design locally and genuinely hope The Center for Energy Efficient Design will influence and inspire the rural community of Franklin County Virginia as its designers intended. Not only could these structures change the way we consume energy but also I would love to see more nearby!
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