The Context: You’ve decided that it’s time to downsize (or right size) and to do it in Vermont, so now you’re searching for a builder who specializes in high performance / zero energy home construction. You want a builder you can believe in and trust that, when it comes to High Performance construction technology, he knows his stuff. The following 25 Questions (actually 26, including the bonus question) will help you determine whether you should entrust your nest egg to this particular zero energy home builder.
The questions, which we have spread over four previous blogs, are followed in this final summary installment by our answer to each question, which you can consult as you discuss the various topics that are listed with your potential builder.
To summarize our own position on high performance custom home construction, in which we specialize, we believe that the future is NOW when it comes to net zero energy custom home construction. It makes ZERO sense to use old and outdated conventional construction methods in Vermont with the technology we now have at our disposal. These practices will save more money than they will cost, while protecting your investment so that should you ever decide to sell and move on, you won’t end up trying to sell a home that nobody wants to buy and that banks will not loan on.
- How do air barriers differ from vapor barriers?
Air barriers stop air movement; vapor barriers stop vapor movement.
- In what direction does warm air move?
Warm air rises. Heat always moves toward cold – which could be any direction.
- In what direction does moisture move?
Toward dry areas.
- What causes mold?
Moisture and a lack of ventilation.
- Explain how and when you “Air Seal” the outside and inside of a house.
- Special air sealing tapes are applied to exterior joints on the wall sheathing, which is also an air barrier if the correct sheathing is used.
- Windows are also taped to the air barrier.
- On the interior, air barriers are applied to the surface of the studs that allow moisture (vapor) to move toward dry areas, yet keep a solid air barrier.
- What is a Thermal Boundary used for?
It identifies where the insulation is located. Ideally, this boundary is as close to the heated space as possible, but sometimes it makes sense to include unfinished areas within the thermal boundary to allow for heating equipment.
- What is Thermal Bridging?
A thermal bridge is an area of higher heat transfer than the areas around it. For example, in a traditional 2x6 wall, the stud acts as a thermal bridge in the wall construction. The stud is in direct contact with the exterior and interior, while the space between studs (wall bays) are not, thanks to the insulation in the cavity.
- What is a Thermal Break?
Insulation. In the example above, if a layer of rigid foam were applied to the stud, it would break the high rate of heat transfer compared to the areas around it.
- What is a blower door and what is its purpose? How often would you use it during construction?
A blower door is a machine used to measure the airtightness of buildings. It can also be used to measure airflow between building zones, to test ductwork airtightness, and to help physically locate air leakage sites in the building envelope. We use the blower door to test the house at various stages of construction. As soon as the air barrier is complete to a point where we can test we do so. This helps identify minor air leakage in the building envelope and it gives us an opportunity to seal things up before insulation and sheetrock covers everything. We also perform a final test at the end of the project to verify that the air tightness has improved; with results sometimes show as much as 40 percent improvement.
- What is the difference between R-value and U-value?
R-value is a measure of Resistance to heat flow; thus, a higher R-value indicates better insulation, or to look at it another way a higher R-value means better energy efficiency. This value is most often applied to components of a home; for example, attic insulation, or the total insulation of all the components of an external wall of a home, or even the ability of the slab to resist transfer of heat out or cold in. A U-value is most often applied to windows or doors. It is a measure of how much energy is lost or gained through conduction or radiation; thus, a low number is better in terms of energy efficiency.
- What are the advantages of investing in triple-glazed windows?
Triple glazing is worth the extra cost because the two air spaces (versus only one in a double-glazed window) injected with a gas (usually krypton or argon gas) can improve the U-value by 20-30 percent. They are more durable, they’re more comfortable (warm to the touch inside), and they reduce condensation. Properly installed, triple-glazed windows should pay for themselves over time. This is why we recommend them in all our high performance / net zero energy homes, tell our clients why, and let them choose.
- What is a HERS rating, and what is it used for?
The Home Energy Rating System (HERS) Index is the nationally recognized system for inspecting, testing, and calculating a home's energy performance; kind of like “miles per gallon” rating of automobiles. The lower the HERS Index score, the more energy efficient is the home. For example, a Vermont farmhouse built 100 years ago, with nothing in the attic, newspapers in the walls, and single pane windows might score 150 or higher. You can almost see the dollars flying out the windows, doors, and attic in the winter. By contrast, a HERS Index Score of ZERO is a net zero energy high performance home, usually custom made. Our best HERS Index Score so far has been: -9 (9 below zero). For more information, see: https://www.resnet.us/hers-index-score-card. Also, you can watch this video on our website: http://prudentliving.com/homes/.
- What types of Air Exchangers have you used and how do they work?
There are many on the market, but our research and experience has led us to mainly use Lunos e2 air exchangers because they don’t require any ductwork and they operate very quietly. For more information, see: https://foursevenfive.com/wp-content/uploads/2014/05/Lunos-brochure-e2-475.pdf.
- Have you ever installed Mini-Splits and other heat pumps?
These products are relatively new, and especially practical in high performance (energy efficient) new homes. They can also be installed in older homes, but are not likely to be as effective in heating or cooling unless the home has been re-insulated and air sealed first. Since our focus is primarily new zero energy, high performance homes, we install mini-splits in all our homes, which rely on them for main heating and cooling, with a helper backup system of some sort to supplement the heating function in extremely cold weather. See the following for more information: http://energy.gov/energysaver/ductless-mini-split-heat-pumps.
- What do you know about Heat Pump Water heaters?
We install these in every house we build. Heat pump water heaters convert warm ambient air in the house into hot water. This results in a rather pleasant cooling effect to the house. This is a great feature in the summer because it’s a double win because the water heater is creating hot water and cooling the house at the same time, but during the cold winter months it can pose some problems as spaces can become too cool, forcing the mini-splits to kick on and replace the cold air produced by the hot water heater with warm. Thus, it is important to consider the location of the heat pump water heater. Fortunately, heat pump water heaters have a switch that allows the heat pump portion to be turned off during the winter. The heat pump water heater becomes a normal electric water heater at that point, which is offset by the power produced by your photovoltaic solar array. See: http://energy.gov/energysaver/heat-pump-water-heaters.
- What do you think about ICF (Insulated Concrete Form) foundations?
We use them whenever budget allows. They are well insulated and designed with built-in systems that provide for fastening other products directly to the ICF. The most recent building codes now require a fair amount of vertical insulation on a foundation wall, so we believe that when you account for the work it takes to set forms, pour, strip and then add vertical insulation, that ICFs could very well cost less than a standard residential foundation.
For more information, see: https://www.icfmag.com/back_issues/2015-11.html; http://www.proudgreenhome.com/news/5-things-you-didnt-know-about-insulated-concrete-form-construction/
- Explain your favorite method of insulating under the concrete slab?
- Vapor Barrier type and method of sealing
- Horizontal Insulation (How much?)
- Vertical insulation
- Slab Edge Insulation
- Vapor Barrier type and method of sealing
StegoWrap 15 mil poly laid over 4” of Styrofoam (approximately R-20) with taping of all laps and joints and penetrations. This provides a powerful thermal break between cool soils and the concrete slab, thus minimizing or even elimination of nasty sweating of concrete slabs on hot humid days. During the winter, the warm insulated slab works for you instead of against you by providing a heat sink that will give off stored heat at night. Without the insulation, the concrete will conduct the cold temperature of the soil underneath into the house, forcing the heating system to work harder to keep you comfortable.
For more information, see: http://www.stegoindustries.com/products/stego-wrap-15-m-1.php
- Horizontal Insulation (How much?)
This depends on the foundation configuration. Minimum 20+ R-value (about 4”), with options for more.
- Vertical insulation
Depends on the foundation configuration, but we usually try to achieve an R-20 level of performance.
There are several ways to achieve this performance level. Our first choice is to use ICFs because they come pre-insulated at about R-23, but we also have to apply a waterproof membrane over the exterior plus a protective one-half inch Concrete Wonderboard, taped at all joints with a brush coat of Thoroseal or similar product. This gives the exterior a clean and durable finish.
A second method is to use conventional forms and achieve our performance in a different manner. We usually only use this method when constructing a house with a double wall x 12 inches thick.
- Slab Edge Insulation
Energy Star Certification requires at least R-15 insulation at the edges of all exposed slabs. This is because most heat lost through the slab is lost through the foundation at its edges. We always build to a minimum slab edge performance of R-15; but often it is higher; closer to 25.
For more information, see: https://basc.pnnl.gov/resource-guides/slab-edge-insulation#quicktabs-guides=6.
- Explain the difference between open and closed cell foam insulation and how one might install each one incorrectly?
Open cell foam insulation allows for air to move through it and whenever air can move through something, moisture can also move through it. Therefore, open cell foam insulation needs an air/vapor barrier applied to it.
- Explain when you would choose foam, cellulose, of fiberglass insulation?
Sometimes we use fiberglass insulation in stud cavities of spaces that are heated only when in use. Such spaces include wood working shops, tempered garages, etc. Fiberglass insulation is the least expensive of all insulation types. We strongly resist any requests to use it in permanently heated spaces, because it breaks down when wet and also allows air to move through it.
- When you use Kraft-faced insulation in a stud cavity, to which side of the wall do you apply the Kraft?
Toward the heated side. Don’t get it wrong!
- What is the best way to ventilate a house?
- Bathroom vents
- Open the windows
- There are several reasons why we believe that the roof on every home should be well ventilated; even roofs that use a form of closed cell insulation; technically referred to as a “warm roof.” This is a type of product which claims that ventilation is not necessary. We respectfully disagree.
- To keep the roof at or as close to the temperature outside. This will preserve the life and warranty of the shingles. Many shingle companies will not give the same warranty on a warm roof “unvented” as they will on a cold “well-ventilated” roof. The main reason is that the shingles will “bake” or “over-cook” in the hot sun and become brittle a lot quicker than they would if the roof was kept cool.
- To prevent ice dams in the winter. When a roof is not vented correctly, the attic space below it will warm up and melt the snow on the outside. The melted snow then runs down the warm shingles and freezes as it comes into contact with the frozen eaves at the edge. As the water freezes and builds up, it creates a dam that grows thicker and thicker with water backing up behind it until it finds a way into the house from under the shingles. This kind of winter ice dam can grow mold inside the wall cavities without showing any evidence until it’s too late to do anything about it.
- To prevent condensation from building up on the underside of the roof (in the attic spaces or in the rafters). Like the water that finds its way into a house from the outside, this type of inside moisture is extremely bad for the house and also for its owner once the problem is diagnosed. This problem doesn’t reveal itself until the first warm and sunny winter day in late January or early February when the roof surface warms up enough to melt the mass of ice that has built up inside the unvented and usually inaccessible roof edges and rafter cavities. It’s not unusual to get a phone call from a frantic homeowner who claims that even though there is no snow on the roof and the sun is shining bright and warm, that water is coming into the house all over the place and it’s raining inside.
- Is there a time when you wouldn’t ventilate a house?
Our custom built high performance and net zero energy homes are so tight that proper ventilation must be provided. Some say, “A house needs to breathe.” Debates continue over how much a house should breathe. Some say they need to breathe but others assert that a house does not need to breathe. In fact, the question is rightfully asked, “Why should a house breathe?” People need to breathe because they have lungs; houses don’t, and besides, what is in a house that you want to breathe anyway, dead mice? So do we let houses breathe or not breathe? Do we ventilate or not ventilate? Wow! This is tough stuff for tired and weary builders who aren’t sure what’s going on with VOCs or air sealing, stack effects, and CAZ. Their minds are on the cost of gas, getting the mason and drywaller to show up, getting materials ordered and delivered, finding good help, worries about insurance, OSHA’s new 400-page manual, threats from the EPA of lead paint penalties, and endless commercials on TV by injury lawyers and that’s before they start the day. And what’s a CAZ anyway? [Answer: CAZ stands for Combustion Appliance Zone. It includes the area near your water heater, furnace, wall/floor heater, and/or boiler, or your gas fireplace, gas stove, gas oven, gas broiler, and even your gas dryer. If these appliances are not properly maintained or are leaking, and the spaces are not properly ventilated, a danger of unintended combustion can exist. See: [http://www.energyhomechek.com/index.php?option=com_content&view=article&id=8:combustion-appliance-zone-testing&catid=4:residential-services&Itemid=3]
- What is Geo-Thermal technology, and when would you recommend it?
Geothermal technology moves heat from the ground (well water) to the house (or vice versa). Heat pumps are used to transfer the heat back and forth. We don’t use geothermal much anymore, but we do use air to air heat pumps, because they cost less, are easier to maintain, and are nearly as efficient. [see: https://en.wikipedia.org/wiki/Geothermal_heat_pump; and http://www.forbes.com/sites/tomkonrad/2014/01/15/are-air-source-heat-pumps-a-threat-to-geothermal-heat-pump-suppliers/#6e2db4089de1.
- Why is Solar PV a key to net zero energy custom construction in Vermont?
It is a practical solution that provides balance when considering cost. It allows for house designs that people like, while still offsetting the cost of heating with a high performance home. PV systems can be mounted on the roof or on poles nearby, or both. In some cases where a net metering agreement exists between the homeowner and their local utility company, a pole mounted PV array can exist anywhere within that utility’s contract area. [See: http://energy.gov/eere/energybasics/articles/solar-photovoltaic-system-design-basics]
- What are the energy saving advantages of a double-wall house?
Net zero energy custom homes require the highest R-factors, from top to bottom, and in this case the R-factor from double walls can be as high as R-45. Normally, a 2x4 wall has an R-factor of about 15; a 2x6 wall will average an R-factor of R-21.
- BONUS QUESTION: How much do you charge per square foot?
We’ve created a whole booklet on this topic: Understanding Construction Costs. This booklet is available in printed and eBook formats from Amazon.com. Printed: https://www.amazon.com/Understanding-Construction-Costs-Question-Square/dp/1939267439; Kindle: https://www.amazon.com/Understanding-Construction-Costs-Question-Builder-ebook/dp/B01H2AIUT8/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1471554335&sr=1-2#nav-subnav.