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A Makeover for the Mobile Test Lab

contractor sprays interior walls with low-density polyurethane foam

We’re building a new set of walls in a testing trailer to see how well open-cell spray foam performs in the extreme cold.

The Mobile Test Lab is a trailer with nine wall sections, each a different combination of studs and interior and exterior insulation. Last year we tested wall systems with interior fiberglass insulation and exterior EPS foam board  to see how they handled moisture. We were wondering how much exterior insulation would be needed to prevent the sheathing from reaching dew point (the temperature at which vapor condenses into water). Researchers found that as long as a wall has 65 percent of the insulation on the cold side, the wall cavity stays pretty dry and no mold growth occurs. All of the walls with less than 65 percent on the outside had some degree of mold on the sheathing. We also found vapor barriers made a big difference, as walls with vapor barriers were much less humid and featured only small areas of mold near holes in the plastic. (For more results, read the project Snapshot here.) 

This time we’re testing open cell spray foam to see how it handles cold weather and indoor humidity. This winter we’ll set indoor conditions at 70 degrees, 40 percent relative humidity  and positive pressure (a rather exaggerated condition for homes in Fairbanks, which will force moisture into the walls).

What is bow-roof construction and what can I build with this design?

Q: What is bow-roof construction and what can I build with this design?

Simonson's shed has a clear poly-carbonate roof. The end walls will be conventionally framed and will include doors and vents.

We typically think buildings should be made with vertical studs and gabled roofs.

Yet alternative designs offer many advantages over conventional construction. Common materials can be used in new ways to make a wide range of structures, from tool sheds to insulated cabins.

The gabled-arch bow-roof shed is one of these innovative designs.

Bow-roof sheds are free-standing arched frames that are easy to build, light-weight and low cost. Structural strength comes from the arch shape formed by their bows.

They can be 10 to 20 feet wide and any length. The free-standing frame allows covering with any sort of roofing, including plastic sheeting.

Even the foundation can be light and simple. A sill plate may rest simply on ground stakes or just a row of railroad ties. Concrete blocks with adjustable cradles also work.

Your flooring could be anything from bare dirt to conventionally framed floor joists. Pea gravel offers one low-cost, easyto- build floor. Place plastic sheeting under the gravel to keep moisture and dirt from coming through.

Individual bows are mass-produced on a jig.

They consist of two bent wooden strips separated by wooden blocks. The 1-by-3-inch strips, cut to match the width of the bow-roof shed, are bent around these blocks. The strips are fastened using bolts and screws. When the bow is lifted from the jig, it holds its arched shape.

Each bow stands up on the sill plate and is connected to a top ridge beam. Bows may be placed up to 4 feet apart. The erect bows create the classic Gothic arch. Lateral structural strength comes from horizontal purlins fastened to each bow. You can also attach diagonal supports if the roofing has little shear strength.

You can use almost any bendable, water-shedding material for roofing. For example, clear, UV-inhibited plastic sheeting can make a great cover for a greenhouse. One economical option is thin plywood covered by conventional asphalt shingles. Metal roofing makes a strong, permanent roof for a reasonable price. You only need to consider the snow load when selecting roofing materials.

Once the roofing is installed, the bow-roof shed is a strong, waterproof structure. The final step is closing in the walls on the ends. The end walls are typically framed in with conventional vertical studs, although you can use almost any material since they don’t hold up the arch. Doors and windows can be placed within the walls.

Although bow-roof sheds are typically just storage space, they may also serve as heated living space. The floor, end walls and roof could be insulated using conventional techniques; just be sure to use an inside vapor barrier and provide air ventilation under the roofing if you are building in a cold climate such as Fairbanks.

These Gothic arches provide enough strength to allow you to use lightweight, affordable materials and to get creative with your design.

How to Work the Masonry Heater at CCHRC

Building manager Dave Shippey gives a tutorial on how to operate the masonry heater. The unit is made from 12,000 pounds of local rock and heats 1/3 of the building. It burns at 2000 degrees with 98 percent efficiency, produces almost no smoke or ash, and uses less than 2 cords of wood in a winter. Dave describes how the stone absorbs heat from the fire and radiates it for 12-24 hours.

PS-Watch until the end for an uncut Halloween scene!

 

The Making of the UAF Sustainable Village

The November snow didn’t stop CCHRC and UAF from beginning the early steps of creating the UAF Sustainable Village: clearing the site.
A half-dozen students joined CCHRC designers and builders as well as UAF workers in the field next to the research center this week. Clad in Carhartts and safety goggles, they chopped trees, dragged brush, chipped wood, and flagged land for the future buildings. They aimed to clear enough trees to create solar exposure for the homes but also to impact the habitat and soils as little as possible.

Four 4-bedroom homes will be constructed on the land this spring. It will serve as a living and learning center, housing students and providing research fodder for them, along with CCHRC scientists and UAF faculty. The homes will demonstrate cutting-edge sustainable building, with passive solar design, energy-trapping thermal mass, and a custom foundation that won’t disturb the permafrost underneath. The project will cost $1 million, showing that a super-efficient 4-bedroom home can be built in a subarctic climate with private financing for $250,000–a stride toward high-performing affordable housing.

Five students will join CCHRC architectural designers this winter to plan the village, after winning a design contest hosted by UAF.

Why look at the Whole Wall R-Value of your wall?

You might think you have R-40 walls, but have you factored in your studs and windows? With the recent emphasis on home retrofits and energy efficiency, many homeowners are defining their walls by R-value.

The whole wall R-value factors in the R-values of the insulated wall, stud, and window.

For instance, if you have 2×6 walls filled with fiberglass batt insulation (R-19), plus drywall and plywood, you probably consider your overall R-value to be R-21. But that only counts the insulated portion of the wall and ignores the weaker parts, such as windows, doors and structural framing (or studs), that provide primary paths for heat to escape. Just as water and electricity seek the path of least resistance, heat flows through the weakest thermal component of the wall assembly.

To see how much studs and windows affect the performance of your wall, CCHRC calculated the “whole wall R-value” for a hypothetical 2×6 house with 11 percent of the wall area taken up by studs (24-inch on center framing) and 15 percent taken up by double-pane windows.  The original R-21 wall is reduced to R-18.3 when you factor in the studs (R-8.8). And the whole wall R-value is further diminished to R-8.2 when you factor in windows with a U-value of 0.5 (standard double-pane windows).

How can this information help you improve the energy efficiency of your home? First, it gives an accurate picture of the overall thermal resistance of your wall. (Though there are many other components of a house that impact efficiency, such as the attic insulation, heating system, and ventilation system.) Second, it reveals the extent to which thermally weak points can counteract stronger points in your wall.

And third, it illuminates retrofitting options, each with their ups and downs. Replacing windows, for example, may achieve a greater whole wall R-value, but it can be pricey. Adding exterior foam, on the other hand, can be a cheaper way to cut heat loss through the insulated wall and the studs. But you must be careful to add the right amount of insulation, and possibly extra ventilation, to avoid moisture problems within the walls.

The best way to weigh these costs and benefits and make the most of your retrofit is first get a home energy audit.

 

Integrated Heat and Ventilation

Research engineer Bruno Grunau installed a diesel heater to the HRV supply air in the CCHRC lab.

CCHRC researchers are testing an integrated heating and ventilation system that warms up ventilation air without running up electric bills. The system adds an in-line, sealed-combustion diesel heater to the HRV supply air and will be installed and monitored at a CCHRC prototype house in Anaktuvuk Pass this winter.

Electric resistance heaters are often added to HRVs for the same purpose: to warm up outside air before blowing it into your home. But depending on your source of electricity, this can be inefficient and expensive. In rural Alaska, for example, electricity is generated by burning diesel and costs up to 80 cents a kilowatt-hour. The diesel heater burns fuel oil directly, which is much more efficient than converting diesel into electrical power and transmitting it to your home.

The small truck heater burns fuel oil and can produce more than 17,000 BTUs per hour, more than enough to heat ventilation air on even the coldest day in the prototype house. The system uses a microcomputer with an electronically commutated motor that controls both the amount of fuel used and the blower speed.

Once installed, CCHRC will study the fuel consumption and power consumption of the system and see how it affects indoor CO2 and humidity levels.

A Novel Way to Preheat HRV Air

Thorsten Chlupp's passive solar home in Fairbanks

CCHRC is working with Fairbanks builder Thorsten Chlupp to research a novel ventilation system that could improve energy efficiency in homes across Alaska. The project looks at a new HRV and ground loop-based air preheating system. CCHRC is researching whether the design could address a common complaint against HRVs: that they are unable to warm incoming air fully to room temperature and allow cold drafts indoors. The HRV under study is a three-stage system that uses a glycol ground loop to preheat incoming air before it reaches the air-to-air heat exchanger.

CCHRC will be monitoring the performance of the HRV using BTU and flow meters, humidity and temperature sensors, and electric-use sensors. The data will help answer the following questions:

A temperature and humidity sensor connected to an air duct of the HRV.

1)  How effective is a ground loop for preheating the air?

2)  How does the ground loop affect the ground temperature?

3)   How much electricity does the HRV system use compared to a traditional HRV?

4)  What is the temperature of the air entering the conditioned space?

A technical report will be created that documents project methods, instrumentation, results, and findings.

 

Hot roofs, cold roofs, and common roof problems

Cold roof on the CCHRC building.

In severe cold climates, roofs face two important challenges; retaining heat effectively, and controlling moisture trying to escape from the living space.  The colder the weather and the longer the winter, the more pronounced the issues can become.  Deficiencies and poor building practices that are overlooked in a more forgiving climate become very apparent here in Fairbanks.   A basic understanding of your roof system and the challenges it faces can help to identify the sources of problems.


Roofs fall into two categories: “cold” and “hot.”  They can suffer from the same ailments.


 A properly constructed “cold” roof maintains a continuous air space between the underside of the roof and the insulation. This air space is designed to do two things.  To some degree, it allows an exit path, through vents, for moist air that has leaked from holes in the ceiling vapor barrier into the insulation cavity. The space also creates a thermal break that helps prevent escaping interior heat from conducting directly to the roof’s underside, where it can cause the snow above to melt.


A “hot” or unvented roof relies on high levels of insulation to slow down heat transfer to the exterior.  The other critical component in a hot roof system is a near-perfect vapor barrier that keeps moisture-laden air from entering the roof cavity, where it can become trapped.

If either type of roof fails to retain heat, one result is ice damming, a fairly common sight in Fairbanks in mid-winter. The classic symptoms are large icicles hanging off of eaves and exposed spots on the roof where snow has melted away. Roof problems are more pronounced in our climate because we have an increased “stack effect.” Rising warm inside air will try to exit the building through leaks at the ceiling level. To replace it, dense, cold, outside air is drawn through cracks in the bottom of the house like a chimney. The greater the temperature difference between inside and outside, the stronger the stack effect, amplifying the heat loss.

Water vapor abides by similar laws. During winter there is a huge imbalance between moist, heated indoor air and extremely dry, cold outdoor air. Because water vapor molecules by nature try to reach equilibrium, they will move through any vulnerable areas (including solid wood) to balance the moisture levels. This is called vapor drive. The greater the temperature difference, the more intense the vapor drive. When a house has high indoor humidity, the combination of stack effect and vapor drive can cause severe moisture problems inside the roof if it is poorly sealed.   Gone unnoticed, this can lead to structural damage as well as mold and its accompanying health issues.

Whether your roof is hot or cold, three elements will keep problems at bay: good indoor moisture control, adequate insulation, and good sealing.

Expanding Sustainable Housing in Rural Alaska

Another prototype house is underway in Point Lay, on the northwest coast of Alaska, that addresses a serious building challenge in parts of the arctic—subsidence, or sinking earth, caused by thawing permafrost.

This is part of the CCHRC Sustainable Northern Communities program, which designs test houses for rural Alaska that match the culture, climate, and soil of individual villages. Our mission is to help villages achieve energy-efficient, durable, affordable, and easily repeatable housing.

The Point Lay design has r-60 walls with spray-foam insulation, metal studs, metal siding, and metal roofing (similar to our Quinhagok prototype).

It is now under construction by the regional housing authority, TNHA, as well as several local students and an instructor from Ilisagvik College in Barrow. They are building one three-bedroom and one two-bedroom home for the very overcrowded village.

The most unique feature of the design is the foundation, which is tailored to the unstable soil conditions of Point Lay.

As permafrost thaws in arctic regions, the soil previously held up by ice collapses. In Point Lay, this has caused the ground to crack in a polygon pattern, with ice wedges in between the cracks—very tricky to build a foundation on. While building on higher ground would mitigate the problem, the only sites available at Point Lay happen to be on low-lying polygons.

ground in Point Lay cracks in a polygon pattern

Typically builders cope with this problem by building on thick gravel pads or on long wooden piles (think stilts).

But piles exacerbate subsidence because they disturb the ground cover, which allows the permafrost to thaw further. Pools form around the piles, are warmed by the sun, and further erode the ice. Over time, these structures become unstable.

So we looked for a way to build on the ground, and yet prevent heat loss from the house from further thawing the soil. The ground contains ice-rich permafrost (beneath 12-18 inches of active layer), which will provide a stable foundation if we can keep it frozen.

pools of water form around piles under a house in Point Lay

While a thick gravel pad is one option, gravel is not available in Point Lay and is very expensive to import. So we decided to build a foundation out of spray foam that would insulate the ground from the building. We worked on a modeling program with UAF to determine how much insulation would be needed to kep the house from affecting the soil below, and found that 18 inches of spray foam (with an r-value of 118) was enough to keep the ground frozen for at least 50 years.

“Everything around it will still be thawing and subsiding. The house will eventually be higher than everything around it, but not for a long time,” said CCHRC architectural designer Judith Grunau.