How Much Insulation?

Just like putting on a thicker coat keeps you warmer than a thinner one, more (properly installed) insulation has greater energy efficiency than less insulation—so the answer to the question “how much insulation is enough” is something of a moving target. In the olden days, homes were often built without installing any insulation at all. In the past two decades, however, most state building codes began requiring a certain amount of insulation in the walls, ceiling or attic, and floor. In the past decade, the codes have become stricter and stricter, requiring more and more insulation.

The goal of an exceptionally green house—what we’ve dubbed a “Pretty Good House” in our conversation—should be to exceed code requirements. That’s the “super” in “super-insulation.” The trick is to arrive at an insulation balance somewhere between “more is always better” and common sense, based on the goal of the home: to have much lower energy bills than standard new construction, perhaps as much as 2/3s lower. In Green Building Advisor’s original conversation on the “Pretty Good House” the “R10-R20-R40-R60” rule was posited as best for cold climates. (More R-value means more insulation.)

This rule means going with R10 insulation values underneath slab foundations, (building code often requires none), R20 insulation values in foundation walls (building code requires R10-R15), R40 in exterior walls (building code requires R13 to R20, depending on your climate, with R13 being the maximum R-value you can get with batt of that “pink stuff” installed in a 2×4 wall), and R60 in the attic (building code requires R38 in most “mixed” climates).

In mixed-humid climates, experience has shown me that values can be relaxed some, and I propose that a “10-15-30-50” rule is a good starting point: a minimum value that can be achieved at a relatively good cost payback. If budget and space permits, higher values in exterior walls would still make good sense. Innovations like a double stud wall or a raised heel truss help increase the amount of space one has in which to fit all of this extra insulation.

The Solar Homestead, Appalachian State University’s 2011 entry into the US Solar Decathlon, used super-insulated walls as a strategy to help the home reach “net-zero” performance cost-effectively. (“Net-zero” means consuming very little energy and producing what energy is needed with on-site renewable energy for a “net” energy bill of zero.) Home is built with double 2×4 walls allowing 8″ of space for insulation, double the amount of space allowed for wall insulation in typical construction. While a “Pretty Good Home” is not necessarily aiming to be a “net-zero” home, super-insulation is still a core green design strategy.

Insulation Alone is Not Enough

Most insulation products are only as good as the wall or ceiling in which they are installed—and are designed to be installed uncompressed, evenly, and often in an enclosure that is air-tight. Cramming an R19 batt into space for an R13 batt does not equal R19 walls, and a pile of loose-fill cellulose insulation in your attic does nothing to stop heat loss from any sections that are uncovered. Paying attention to the proper installation for each type of insulation product is absolutely crucial.

Another aspect of the building envelope that is often forgotten in the quest for maximum R-values is the total air-tightness of the home—as warm air leaking out and cold air leaking in are an entirely different source of indoor temperature change that must be corrected with a heating or cooling system. Pretty Good Houses should be exceptionally air-tight, with any and all cracks and penetrations in the exterior of the building sealed. Yes, this kind of detail work takes extra time and attention, but is just as important, if not more so, than the R-values you choose to put into your super-insulation.

Next up in our southeastern climate “Core Green Design” series: “Right-sized” Homes and Outdoor Living Spaces

1. Passive Solar design

2. Insulation values exceeding minimum code requirements

3. A “right-sized” home that incorporates outdoor living space

4. Solid heating and cooling system design

5. Smart water management

I put passive solar design at the top of this list because it is such a simple, easy design principle, capable of reducing energy costs while also being decidedly low-tech. If you’re unfamiliar with passive solar design, the Southface Institute has a great primer in it’s online library. The basic concept beside passive solar design is to use your home orientation, window layout, and overhang sides to harness heating energy from the sun in winter, while keeping that extra heat out of your home in the summer.

A passive solar Deltec in North Carolina uses south-facing windows and deep overhangs to harness heat in winter while shading windows in summer.

And in a climate like Western North Carolina, keeping heat out is the rub.

As a practice generally conceived of in more northern climes, some of the well-known passive strategies for allowing heat in can become a double-edged sword when you are building somewhere that has a significant cooling season. Here are some basic passive solar ingredients in a Passive Solar “Pretty Good Home,” fined-tuned to match the challenges of building in a mixed-humid climate:

1.  Do Have South Facing Windows–But Don’t Overdo It

Many folks understand “passive solar” as a strategy that entails putting a whole lot of glass on the south side of the home. Well-designed overhangs will shade these windows in the summer when the sun is higher, while leaving them un-shaded in winter. South-facing glass is indeed the essential ingredient in a functional, direct-gain passive solar design—but too much glass on the south side can turn a comfortable space into a stuffy oven in fall or spring, or even on a warm afternoon in winter. As a general rule of thumb, south-facing window areas that exceed 7% of your conditioned floor area can start to introduce overheating problems at some point during the year in this climate–unless you start to incorporate thermal mass.

2. Don’t Skip the Thermal Mass

Thermal mass is a dense material in the directly sunlit area that can store the heat that south-facing windows are letting into your home–material such as a concrete slab or tile floor. Often referred to as a “thermal battery”, thermal mass is as critical to effective passive solar design as are south-facing windows, because without it you lose the ability to hang on to a large portion of the heat that your south-facing windows gather.

Home designs that do not have adequate thermal mass planned should be very wary of over-doing their south-facing windows.

3. Avoid East, and Especially West, Facing Windows

No matter what time of year it is, the sun will be low when it rises in the morning and sets in the evening. That low angle sun won’t be shaded by overhangs designed to keep the south-facing windows shaded, and can present an especially uncomfortable situation on spring and summer afternoons in rooms that have west-facing windows. While unwanted heat from low-angle sun makes limiting east and west facing windows a good idea in any climate, in a mixed-humid climate, east and west windows might be best eliminated all-together.

4. Insulation!

South-facing windows paired with good overhangs bring in extra heat at appropriate times, while thermal mass stores that heat in the dense building components of your home. Good insulation serves to slow the eventual process of heat leaving your home, and the more you have of it, the longer you can hold on to that heat. Taking insulation levels above and beyond what code requires, often referred to as “super-insulation”, will be the subject of the next post in this series.

The group of regional manufacturers discussed best practices and current challenges in achieving waste and energy savings at all levels of operations. Participants had the opportunity to speak directly about issues affecting North Carolina’s manufacturing base, and discuss ways they could partner to help improve and expand American manufacturing, including sustainable manufacturing, lean manufacturing and the opportunities for green products.

]]> http://blog.deltechomes.com/?feed=rss2&p=2624 0 http://blog.deltechomes.com/?p=2615 http://blog.deltechomes.com/?p=2615#comments Mon, 19 Mar 2012 00:03:10 +0000 ldickens http://blog.deltechomes.com/?p=2615 Recently over at Green Building Advisor, a great resource for green building knowledge, there’s been a hot discussion around the concept of building a “Pretty Good House.”

Now at first glance, that sounds like a bad deal. Don’t we want to live in a house that’s more than just “pretty good?” Yet the idea behind a “Pretty Good House” is to provide a new type of roadmap for building a green home, one that focuses on cost-effective and common sense energy and durability performance, rather than trying to build to the exact requirements of a green building certification.

Don’t get me wrong, I think that green building certification programs like LEED or Passive House are wonderful, well-thought out ways to create a building with reduced environmental footprint and lasting value for the homeowner, but they aren’t for everyone. Certification means that a widely-recognized green label gets placed on your home—but it also means extra cost in certification fees, and building to a checklist of requirements that may not have the flexibility to match everyone’s budget or design constraints. By contrast, a “Pretty Good Home” is a home that doesn’t certify but that incorporates those green building and energy efficient features that made sense to the project and were cost-effective, enabling homeowners who don’t have the flexibility or funds to go all the way to a Passive House the opportunity to live in a house that functions well and has a reduced impact on the environment.

Since it isn’t a certification, but rather an idea, green building professionals across the country have been given the opportunity to weigh in on what green strategies define a “Pretty Good Home” in their particular climate. Recently, some of my suggestions for a “Pretty Good Home” in a North Carolina climate–what building scientists often refer to as a “mixed-humid” climate–were featured in a follow-up post at Green Building Advisor. Whether you’re building a home that aims to go all the way to Passive House standards or one that merely aims to have some Pretty Darn Green features, these are the most important green strategies that I recommend to customers building in a climate that is cold in winter, warm in summer, and humid for a good portion of the year.

1. Passive Solar design
2.Insulation values exceeding minimum code requirements
3. A “right-sized” home that incorporates outdoor living space
4. Solid heating and cooling system design
5. Smart water management

In follow-up posts on this blog, I’ll go into each of these design principles in more detail.

Energy Star is a certification available to new homes constructed under certain guidelines that intend to make them at least 15% more efficient than a standard new home. The EPA recently released their “Designed to Earn the Energy Star” program for pre-designed homes, and Deltec, which provides floorplans and an energy efficient building shell, has been able to assist customers in certifying their home under this label.

The requirements for an Energy Star certified home are many, but well-installed insulation and air-tight construction are two of the most important. One of the tests a home must pass is a blower door test, which measures how air-tight the entire home is. The more air-tight a house is, the less energy it uses, because it isn’t constantly having to heat or cool air leaking in from the outside. Deltec’s green department videotaped the Stilwell’s blower door test, which was performed by VandeMusser Design.

To achieve the required blower door test score, the Stilwells used spray foam insulation in the ceiling, a material that blocks air movement in addition to providing insulation. Their builder was also very dilligent at applying caulk where the components of the home fit together. We’re pleased to report that the home passed with flying colors!

The Stilwells have a blog of their own where they’ve shared their experiences in constructing a very green Deltec home. Bloomberg Television’s host, Lee Patrick Sullivan, recently visited the Stilwell’s and interviewed them for the program EnergyNow, for an episode covering energy-efficient home building methods. On the same day, Sullivan toured the Deltec Homes plant in Asheville, North Carolina, and visited two other owners of  Deltec homes. The program is scheduled to air Saturday, January 7 at 5:30pm, and Sunday, January 8 at 9am and 1:30pm.

Deltec recently began offering its employees a ‘weatherization program’, whereby participating employees spend less than $100 on materials and a few hours of elbow grease at each others houses to tackle common energy efficiency shortfalls in existing homes.

A few months ago we worked on the engineering director’s house, sealing up leaky spots in his semi-finished basement and tightening up his home’s duct-work. This time around, it was the sales director whose home we put in the spotlight.

Our work began with inspecting underneath the registers, those vents in the floor that allow the heated/cooled air to circulate in your home. Often the ends of air ducts don’t fit perfectly within the hole cut for the register, allowing some of the air meant to heat or cool your home to escape back down into the basement or crawlspace.  Sealing the perimeter of each register boot in your home to the floor can help make sure more of the air you’ve already heated actually makes it into your living space.

Joe using caulk to seal the duct-work in the register to the floor.

Materials needed: one or two tubes of caulk and a caulk gun

Time required: one hour or less to do the work, plus an hour or two to let caulk dry before replacing register covers

Our next stop was to tackle a particular problem in the attic:  In Joe’s house, as is common in two-story homes with a basement, a long shaft called a chase serves to enclose the duct-work that runs from the furnace in the basement up into the attic and over the second story of the house. This chase is about 4×4 feet in size, large enough to fit several large ducts.  However, as is often the case, in Joe’s house the top of this chase was not capped off, leaving a hole in the floor of the attic. Covering this hole keeps warm air inside the house from escaping into the attic, and creates a surface for attic insulation to rest on so that it doesn’t fall down the hole.

Steve in the attic, using rigid foam insulation to seal off the top of a chase.

Materials needed: rigid foam insulation, measuring tape to measure the hole, something to cut the foam to size, mastic and a brush to seal it in place.

Time required: one hour or less.

We still had some more work to do in the attic. When holes are cut in a ceiling for water pipes, bath fans, or electrical wires, those holes are generally a little bigger than they need to be, thus allowing some air from the home to escape into the attic.  In addition, where the tops of interior walls intersect with the ceiling sheet-rock there is often a small crack where the two materials are not installed completely flush to each other. We dug through the insulation to find as many of these holes and cracks as we could, and sealed them with mastic.

Leigha raking insulation back into place after sealing various small holes in the attic floor.

Materials needed: mastic and a brush, mask, gloves, and a rake

Time required: Two to three hours to dig through insulation, find things to seal, let the material dry and then rake the insulation back into place

When working in an attic with insulation, it’s a good idea to wear a mask and gloves to avoid irritation by fiberglass insulation.  Be sure to watch your step and to stand only on rafters, as a sheet-rock or plaster ceiling cannot support a person’s weight.

This program was a great way for employees to have a little fun while working hard, learn a thing or two about their houses they might not have known, and spend only a little time and money to tackle some “low-hanging fruit” items that can make a big difference in their energy bills this winter.

“The team’s passion and enthusiasm were contagious,” said Terri Jones, Solar Decathlon Communications Contest official. “The People’s Choice Award is a popular vote, and I believe the Solar Homestead house and team appealed to people on many levels.”

The Solar Homestead is a self-sustaining, net zero-energy house inspired by original homesteads established in the Blue Ridge Mountains. The Solar Homestead integrates this concept with a highly energy-efficient home, incorporating renewable resources and innovative technology into a prototype that is adaptable, self-sufficient, rugged, affordable, and attractive.

Appalachian State also won second place in the Communications Contest and third place in the Architecture Contest.

Deltec Homes is honored to have worked with such a dedicated, enthusiastic, and creative team. Their passion kindled a true feeling of excitement at our company, and reminds us all why building sustainably is so important.

Now Deltec is unveiling our own Zero Energy Home design—a home featuring all of the benefits of living in the round that is designed to produce as much energy as it consumes with an on-site solar array.

A net-zero home features more than just solar panels.  The high performance of these homes starts with a well-designed building envelope—and Deltec has always excelled in producing a very energy efficient building shell.  With wall insulation at R40, roof insulation at R60, and high efficiency heating and cooling and electric design, the energy efficiency features of Deltec’s Zero Energy Home cut energy use by 2/3rds.  The remaining third is provided by on-site renewable energy.

More information on the Zero Energy Home will be available on our new website coming soon.  If you have any questions, please give us a call at 800-642-2508.

ASU's entry in the 2011 Solar Decathlon

Yesterday we had a wonderful opportunity to get a sneak preview of the 19 zero energy homes at this year’s solar decathlon in Washington DC.  The competition is already underway, and the homes are open today to the public.

Deltec is proud to be a sponsor of Appalachian State’s Solar Homestead. Their project combines the flexibility of the traditional homestead with cutting edge technology.  It showcases an ultra high-performance building envelope built in Deltec’s facility, along with plenty of solar energy and excellent outdoor living spaces.

There is an amazing variety of technology, architecture, and creativity on display here – most definitely an inspiring journey if you are in the area.  Click here to see a video of all the innovative projects we toured.

Last Sunday we took on the home of our Director of Engineering, where, even having only one weekend morning to work, we found and corrected two all-too-common energy efficiency shortfalls:

1.  Leaky Band Joist

This basement, like many basements, is built of cinder block walls. The wooden components of the house above;  the floor joints and wall framing, sit directly on top of these concrete walls, often with nothing at all installed between wood and concrete.   This makes for a junction that is far from airtight, and in many places we could see light from outside through the gap between wood and cinder block.  Not only was this gap allowing cold air into the basement in the winter, making downstairs TV watching far more chilly than necessary, it was letting in that cold draft right underneath the floor of the house upstairs.  The homeowner had commented that the floors near outside walls sure were cold in winter!

The area where the wooden floor joists of a house rests on the cinder block walls of the foundation is called the “band joist.” In some cases, we could see daylight through the gap between the wood and the cinder block.

The fix was relatively simple: we sealed the gap between wood and concrete around the entire perimeter of the basement with silicone caulk.

2.  Leaking Air Ducts

Duct-work is designed to bring warmed or cooled air from your mechanical unit and into the living spaces of your home.  You would think duct-work would be extremely air-tight, the better to deliver as much warmth or coldness as it can.  In reality, most duct-work is anything but airtight, leaking as much as 25%–one quarter–of the air it carries.  Most of these leaks occur at joints in the sheet metal that make up ducts.

Sheet metal duct work leaks out a lot of the air it carries. That’s because it is made of multiple segments joined together, with nothing to seal the joints.

In this house, we covered these seams with a special kind of fiberglass tape–NOT duct tape, which loses it’s stickiness throughout several seasons of temperature swings–and painted over the tape with a good thick layer of duct mastic.  Duct mastic comes in a tub at a home improvement store and looks and feels like putty–but dries into a tough but flexible air-tight material.

Stay tuned for more home energy efficiency projects we will do for each other.