Construction Progress: Week of Apr 8

Plagued by uncooperative weather this week. The ELEMENT Modules were kept inside all week which means the rest of the insulation would need to be put on hold yet again. Tuesday the 17th should hold the completion of the insulation. Until then, the build team will be focusing on touching up details. These include making sure outlets, plumbing lines, roof drains, and HVAC work is properly sealed and in place. As mentioned in the entry "Construction Techniques: Insulation" one of the most beneficial attributes of foam insulation is its ability to resist air movement. Therefore, properly sealing outlets, plumbing lines, conduit, and all other elements are of extreme inportance in order to get the maxium potential performance out of the insulation.

Mechanical Engineering: Thermal Analysis

Energy simulation played an important role in the design of the house, the engineering team
already had a model before the architects got into the project. From this model, they tried to give
orientation in the design. The main areas that were affected by energy simulation were window

placement, insulation thickness, window construction, indoor air quality, as well as the sizing of the
thermal (heating/cooling) and electric (PV) equipment.

When beginning the design of an energy efficient structure, there are several factors which must be realized. As a starting point, the most energy efficient structure would be a fully insulated sphere without any windows, doors or thermal bridges of any kind. Obviously, this structure would in no way be inhabitable. For sake of simplicity, it can be send that any step away from this structure leads to negative effect on the structure thermal efficiency. So, when the building becomes more rectangular, for ease of construction and livability, the building loses some thermal efficiency. Then, in order for the inhabitants to get into the structure, doors must be added. On top of that, windows must be added to make the space more enjoyable. Now, every time a window, door, or corner is added, we are also adding a thermal bridge. While there are ways to limit the effect of the thermal bridges (as mentioned in “Construction Techniques: Advanced Framing” section) it is nearly impossible to rid an entire building of them. If this concept is understood, it is clear that each of these derivations should be as efficient as possible in order to make the structure, as a whole, perform to it’s the best of its ability.

This is where thermal analysis plays an important role in energy efficient structures. In the design of the ELEMENT, energy modeling brought about a substantial design change in the window-to-wall ratios (WTWR) of the house. Originally, the WTWR was around 30% for the entire building, with the WTWR being around 30% on all four elevations. After the change inspired by the thermal analysis, the south façade still had a WTWR of roughly 30%, but the north was reduced to 13%, the east to 5%, and the west to around 1%.

The energy modeling went beyond this aspect of window-to-wall ratios when considering window
openings.  .  First, the thermal impact needed to be considered; that is, how much heating and
cooling energy would be required. The idea is to minimize these energy requirements as much as
possible. Second, the amount of natural daylight needed to be considered.  In other words, properly
placed windows will bring in natural light and therefore will reduce the need for artificial light and
fulfill the aesthetic requirements of the house.  From the energy standpoint, energy simulation
shows that it would be better to have as small window area as possible.  Windows are energy
holes; although they have some energy benefits, such as relieving some lighting and winter heating
loads, on an annual basis, their net effect is negative, and thus increases the energy requirements.
On the other hand, from the aesthetic and psychological standpoint, there is a strong desire to
want to have plenty of openings from which to view the outdoors and supply natural light.

Screenshot of EnergyPlus’ Computer Model of the Solar House

The design of ELEMENT tried to reconcile both standpoints into one design that has a very low
window to wall ratio but guarantees adequate daylight in all interior spaces. The energy simulation
used to perform the thermal analysis was very dynamic.  It is an annual simulation with time steps
every 15 minutes.  This means that the energy load is calculated every 15 minutes over the course
of one year while also incorporating day lighting into the calculation.

Construction Techniques: Spray Foam Insulation

Spray Foam insulation comes in many styles and mixtures. The most common form of spray foam insulation is rigid polyurethane that comes in a liquid and is sprayed into the building’s exterior envelope. This the same method used to insulate the ELEMENT. The benefits of spray foam insulation are seemingly endless: it helps reduce air and moisture infiltration, helps increase the thermal performance of the building (it has a much higher R-Value per square inch when compared to typical Fiberglass Batt insulation) thus saving on energy costs, it can help add strength to the building’s structure being that it is compact in nature, the fact that the insulation is rigid helps prolong the thermal performance of the building (typical insulation, and also other forms of sprayed-in or blown-in insulation, have the tendency to sag or settle over time leaving insulation voids near the top of the wall, and the insulation also helps to ensure air tight construction which while helping reduce air infiltration will also help keep other harmful air pollutants out of the building.

A Test of Three Different Insulation Methods Set Up By the Insulation Company

However, there are some downsides to the use spray foam insulation. In most cases, such as is the case with the ELEMENT, the spraying can be very hazardous to the health of present during the spray. For this reason, spray foam insulation must be installed by a trained professional and in a well ventilated area. Because the spray foam has a chemical base, when it is sprayed it also releases these chemicals into the air. There are several spray insulation methods which use water as the base compound which makes the installation much safer for the environment; however, these tradeoffs typically results in a lower R-Value per square inch of insulation. Also, most spray foam insulation is very dangerous when on fire (in some cases it is impossible to extinguish with household fire extinguishers or water). For this reason, proper fire protection must be incorporated into the envelope design when using this type of insulation.

When looking at the insulation installation used in the ELEMENT, there are several problem areas that came about through the design and detailing of building’s exterior envelope. The first problem area came about when detailing the electrical and plumbing systems. To keep the tubing and conduit out of sight, they were placed inside the walls; the majority of these walls being exterior walls. The greatest issue which will likely arise from this detail will be the fact that the energy models of the building have no way of accounting for this reduction in insulation thickness. While there are ways to designate a specific reduction in the amount of insulation, it is very difficult to model the unique thermal bridge which will occur from the conduit running through the envelope.

Running Plumbing and Wiring Through Building Envelope on the Bedroom Module

Conduit Running Through Exterior Wall After Insulation Has Been Sprayed In

The second issue arose when the insulation was physically sprayed in. To make the installation easier for the professional insulators, the interior sheathing was installed first and the exterior sheathing was left off. This way the insulators could simply walk around the outside of the building spraying as the go. The problem can be seen when this process is looked at more carefully. When the insulation is sprayed out, it hits the back side of the interior sheathing as a thin film which then expands very rapidly (typically to 100 times its volume in roughly 8 seconds). This is a fact known by the professional insulators, so they spray very quickly and move on so that the insulation does not expand too much past the wall studs. In a perfect the world, the insulation would expand exactly to the outmost point of the wall studs and stop. This way the exterior sheathing could then easily be installed over the insulation. Obviously, this is not possible so the insulators spray in the foam insulation so that it does not reach the outmost point. If the insulation would expand beyond this point, it would need to be cut off. This process is very labor intensive and the insulation often breaks away in chunks, not a clean line. This too will become a problem in the computer modeling of the house. The model assumes that the insulation fills the entire wall cavity. Unfortunately, it does not. Again, there are ways to compensate for this lack of insulation; however, as you can see in the image below, the insulation is not uniform in shape. If there was a discrepancy in the thickness of the insulation, ideally it would be thickest at the wall studs and other areas where thermal bridges occur. However, it is almost completely reversed in this case.

Spray Foam Insulation after Installation, Notice the Corner Where Insulation is Hardly Present

Another Example on the South Wall Where Insulation Is Severely Lacking

The easiest method to avoid this issue comes in the planning stages of construction. If these facts are known, there effects can be minimized. One method to limit this problem would be to install both interior and exterior sheathing before the insulation is sprayed in leaving a hole in the exterior sheathing where the insulation can be sprayed down into the cavity. This method is clearly more time consuming for both the insulators and the builders. However, if the building’s systems rely heavily on computer modeling, this is one of the most effective ways to ensure a uniform insulation thickness when using spray foam insulation.

Detailed Section Sketch Showing this Process with Both Interior and Exterior Sheathing Installed Before Insulation is Sprayed In

Construction Techniques: Advanced Framing Techniques

Advanced Framing involves a variety of construction techniques aimed at reducing the amount of lumber used in the framing of the building envelope. This process leaves more room for insulation and helps reduce the number of thermal bridges in the wall assembly. These are a few advanced framing techniques as illustrated by the US Department of Energy:

Many of the techniques show above where incorporated into the framing of the ELEMENT. However, in several situations, mainly due to the placement and direction of the exterior openings, these techniques could not be used so that the building could maintain its structural integrity. This brings to light an important subject: the integration of design and thermal performance of a building. As the chart above clearly demonstrates, using advanced framing techniques can greatly increase the thermal performance of the building. A more efficient building envelope will lead to a decrease in the energy load on the building and hence lower the energy consumption of the entire building.

To illustrate this point, an energy analysis program called the Passive House Planning Package (PHPP) was used to retool the framing (and thus the window / door placement) of the house. This scenario was set up to see the net effect of the façade design on the building’s performance. The building’s envelope already had a structural system comprised on 2 x 6 studs placed 24 inches on center. Therefore, any opening in the building’s envelope would now be placed on this existing grid.

The Current Framing Design An Advanced Framing Design

As one can clearly see from the sketch above, the current framing design uses a great number of studs in order to support the interrupted window placement. With the current framing, the wall in the lower left corner (north wall of the living module) is made up of 23.9% wood studs which act as thermal bridges. By removing the “panoramic windows” and replacing them with windows also placed at human eye height, but more importantly, within the designated framing grid, the wall using advanced framing techniques yields a 23% reduction in stud use and an 8.7% increase in the overall R-Value of the wall assembly. Another advanced framing technique not used in the current framing design would be the use of hangers instead of cripples to transfer roof loads around window and door openings. While the overall effect of this method is not as largely significant as window placement, it can still yield close to a 5% increase in insulation area in the building envelope. To fuller illustrate the importance of proper window placement, one can examine the effect of window trim. While windows have an overall negative effect on the buildings thermal performance, they are undoubtedly any important feature of any building. This being said, the window frames have absolutely no positive attributes when it comes to either energy performance or aesthetics. Thus, it is important to minimize the frame area when looking at the overall building envelope (this also makes the windows cheaper to purchase). Looking again to the sketch above, the framing in the upper left corner shows the current framing of the south wall of the living module. By replacing the three small windows with one large window and placing it in the framing grid, the wall experiences a 47.4% reduction in window frame area. As mentioned earlier, troubled spots for air infiltration and exfiltration occur mainly at windows, doors and corners, therefore, it is important to reduce the window framing area and likewise the chance for energy loss.

If this process of the placing windows and doors within the structural grid, which must exist, is taken around the entire envelope of the ELEMENT, a 36.4% reduction in energy consumption is possible. This method, however, did come with some sacrifices to the current design. For example, while the windows on the south façade experienced a small increase in area, the overall window area was reduced by 10 square feet, essentially one whole window (the majority of this reduction came from the north façade). This reduction would likely have an adverse effect on the lighting load. However, 36.4% reduction in the total energy requirement would likely make up for this relatively small increase.

Corner Framing Detailing, Notice Window / Door Interruptions on Left Side

Advanced framing techniques produce several methods to deal with the effects of thermal bridging. Perhaps the easiest method, at least in terms of overall wall design and detailing, would be to add an extra layer of rigid insulation (commonly expanded polystyrene otherwise referred to as EPS) to the exterior sheathing of the wall assembly. This method is also quite useful in retro-fit projects because nothing has to be done to the wall assembly, the rigid insulation is added to the exterior after which stucco or siding can be installed.

Sketch of Heat Transfer Through Typically Framed Wall and Same Wall with XEPS Added

Construction Progress: Week of Apr 1

Work this week has been put on hold for the insulation to be sprayed and set. For more information about the insulation installation in the ELEMENT see “Construction Process: Week of Mar 25.”

Also, for more information on spray foam insulation, please see “Construction Techniques: Spray Foam Insulation.”

North wall of the living module with foam insulation sprayed in

Construction Progress: Week of Mar 25

This week the house is being prepared for insulation which will be sprayed in at the end of this week. This preparation includes running electrical outlets and conduit, installing pipes for plumbing and calling out details on the roof for proper insulation installation.

Being that the roof is one of the most critical areas of the house envelope in terms of heat and energy loss, the insulation detailing is of extreme importance in the overall performance of the ELEMENT. The roof insulation is also made of polyurethane and is beneficial for several key purposes: One, roof penetrations can be more adequately sealed and insulated to avoid rapid heat loss when compared to standard practices. Two, rain, snow and other debris is much more easily displaced when compared to a standard flat roof system. Three, the obvious shape for filtering water and other debris off the roof is also the optimal location of insulation. More precisely, heat and energy loss will occur through the roof most rapidly at the corners where the roof meets the wall.

Roof parapet without insulation

Roof parapet with insulation

The 2 x 6 studs used in the exterior walls also provide several advantages when compared to standard construction practices. For example: a 2 x 4 stud (actually measuring 1.5” x 3.5”) provides only 3.5 inches of depth for insulation and the studs need to be spaced at a distance of 16 inches on center (in other words, measuring 16” from the center of one stud horizontally to the next stud). However, using a 2 x 6 stud (actually measuring 1.5” x 5.5”) provides two more inches of insulation depth and the studs can be placed 24 inches on center. This, on average, leads to a 5% increase in insulation. In other words using 2 x 4 studs spaced at 16 inches on center, on average, 12% of the insulation area will be lost to the studs. Whereas, using 2 x 6 studs spaced at 24 inches on center, on average, 7% of the insulation area will be lost to the studs. As mentioned in the posting “Construction Progress: Week of Mar 11” this loss of insulation area can be reduced to almost nothing (on average 1% - 2% because of support needed at the corners) using Structurally Insulated Panels (SIPs).

This week came to an end with the professional insulator coming to the construction site. All three modules were pulled out from the warehouse so that the insulation could be sprayed out in the open air and also so the process could be viewed by the interested public. Unfortunately, rain put the insulation installation on hold after only a portion of one module could be completed. The insulation should be completed by the end of next week.