ENERGY STAR Certified Home in Grant Park – Atlanta, GA

Recently, this house in the historic district of Grant Park, Atlanta, was certified through the ENERGY STAR New Homes program at the EPA. The final inspection revealed an air tightness of 0.77 ach50, which is near the maximum acceptable air infiltration level of the aggressive Passive House program (0.6 ach50). The final HERS Index was around 64, which means (among other things) that home should perform at least 36% better than a similar home built to meet the current energy code.

Certified Energy Star, Integrated Design Front Elevation

The home is 2,350 square feet with 4 bedroom and 3.5 baths. Ceiling heights are 10′-0″ on the first floor, and 9′-0″ on the second. It is built on an encapsulated crawlspace, and has an encapsulated attic where some of the HVAC equipment is.

Oak floors throughout, and the custom stained glass featured in the home was made by the builder’s mother.

Certified ENERGY STAR, Integrated Design Dining Room

Certified ENERGY STAR, Integrated Design KitchenThe construction drawings included critical air sealing, water management and thermal boundary details, energy models, heating and cooling load calculations and a complete HVAC design (ACCA: Manual J, Manual S and Manual D) that guided the builder and his sub-contractors to exceed the guidelines of the ENERGY STAR program. All of this was in addition to the standard drawings required for construction. It was one of the first Designed to Earn the ENERGY STAR projects that I completed, and a great example of how integrated design

Certified ENERGY STAR, Integrated Design, Encapsulated Attic

The entire building envelope, from the foundation to the peak of the roof, was filled with an open-cell spray foam insulation that contributed to both the thermal boundary and air barrier. All of the exterior wall (2×4) cavities were filled with the foam (R-13), and roof structure (2×6) was filled to provide a minimum R-20.Certified ENERGY STAR, Integrated Design, Band Joists

In multi-story framed homes, and those built on a crawl space or foundation, the band joist is a critical point where heat loss and infiltration (especially) can happen. Completely filling the cavities with the foam is one of the simplest ways to effectively control both.

Certified ENERGY STAR, Integrated Design, Insulated Header

To minimize thermal bridging, details were provided for advanced framing techniques like this insulated header. The 1/2″ layer of foam replaced what is normally a sheet of OSB sheathing or plywood. Below shows an opening in a load-bearing and non-load-bearing wall to show that it’s not necessary to provide structural headers in every opening. It’s common to find interior wall openings that have no load whatsoever built with 2×6, 2×8, or 2×10 structural headers, when simple cripple studs will do.

Certified ENERGY STAR, Integrated Design, Advanced Framing

Certified ENERGY STAR, Integrated Design, ZIP System Sheathing Combo Panel

 

The ZIP System wall and roof sheathing, also available in a combo panel (shown here, for both roof and wall) was specified for the exterior sheathing (structural) because it has an integrated water resistive barrier (WRB, in lieu of house wrap). The WRB and the ZIP System tape also provide an air barrier in both directions (inward and outward) to decrease infiltration and exfiltration.

Certified ENERGY STAR, Integrated Design, High Performance Windows

All windows were specified with a maximum U-value of 0.30 and SHGC (solar heat gain coefficient) of 0.25. As you can see, we were able to exceed these specs. In hot and warm climates like the one this house is in (Climate Zone 3), the SHGC has more of an impact on the heating and cooling loads of a home, especially on south, west and east facing walls.

Certified ENERGY STAR, Integrated Design, HVAC Mini-Split, Mitsubishi

The heating and cooling load calculations for this home were very low. For the entire house (2,350 s.f.), the cooling load came out to less than 18,000 btu/h (approx. 1,650 s.f. per ton) and the heating load is 22,500 btu/h. I designed and specified a Mitsubishi Ducted Mini-Split Heat Pump System, with it’s variable refrigerant flow technology, to handle the low loads and dehumidification. There’s one ducted unit (seen below) serving the first floor and one serving the second floor.

Certified ENERGY STAR, Integrated Design, Ducted Mini-Split

The projected energy bills for this home are in the range of $50-$75 per month, depending on occupant behavior and the utility rates at that time. This low usage is due in large part to the low loads, efficiency of HVAC system, the compact fluorescent light bulbs, and the efficient appliances installed in the home.

A couple other features (there are many more) that helped the home perform well and to certify as ENERGY STAR were:

  1. Energy (or Enthalpy) Recovery Ventilator – provides fresh air to the home while recovering some of the heat energy from the return air to pre-condition the fresh air coming in to the home.
  2. Continuous foundation drain at the perimeter of the concrete footing to help prevent water from entering the home through the foundation. The foundation walls were also treated with a dampprofing.

I think you get the idea. Feel free to ask questions in the comments below, if you’d like to know more about how the home was designed or built to high performance.

 

- written by Chris Laumer-Giddens

Enter the text or HTML code here

9 Responses so far.

  1. Sean WIens says:

    I find it interesting that an R13 walls and R20 attic is considered a high level of insulation and an energy efficient house in the USA. What are the code minimums required for your region?

    In the Vancouver region of BC Canada, our walls have to be nominal R20 and our Ceilings R40. This is expected to go to an effective R20 and R40 next year (aprox a 20-30% increase) and a jump again in 2015. I looked and your weather is not unlike our Vancouver weather, it is a bit more extreme on the hot side, but similar on the cold.

    Why do you think insulation level requirements are so low in the USA?

  2. The 2012 IECC is changing our requirements to R-20 (from R-13) in the walls and R-38 (from R-30) in the ceiling. In Georgia, we are permitted to have a minimum R-19 on the roofline through a performance path, which allows us “trade-offs”. Prescriptive path would currently require R-30.

    There is a point of diminishing return with insulation in every climate zone. In ours, I have found it to be around R19-R20 in the walls. Anything beyond that, the R.O.I. is much longer.

    What I recommend in CZ1 – CZ3 (and even CZ4) is to spend the extra money on air sealing. Reducing infiltration goes a lot further, faster, than adding insulation. I’ve found that a 50% reduction in air sealing from 7 ach50 (standard code built home) to 3.5 ach50 has the potential reduce the heating or cooling load by as much as 30-40%. That much of a reduction usually only happens when you go from no insulation to R13 or higher, not from R-13 to R-19, or even R-30. It’s just not cold enough for that here.

  3. John Poole says:

    Beautiful job, Chris! Great integration of architecture and energy efficient design. So is this what one might call a “new old home” (i.e., new structure, but designed along vernacular lines)? Were you involved with a local historic commission in designing this home? Once again, congratulations!

  4. Thanks, John!
    The integration was really what kept us from having any change orders as a result of conflicts in the design. In fact the only conflict happened when someone did NOT follow the drawings. Got past that pretty quickly, though.
    Yes, we also refer to it as “New Traditional”. We worked very closely with the Urban Design Commission and the Historic Grant Park neighborhood to design something that fit within the context of the neighborhood. We pretty much nailed it on the first round, and got through the public hearing with zero comments! We were pretty pleased to make it through so quickly. They can be pretty tough.

  5. Nice work, Chris. In our Philly suburbs I often find myself designing in a contextual/traditional vein as well, which is my preference anyway. Can you comment on why you chose open vs closed cell foam, and how mini-splits work out for you in a multi-roomed (traditional) plan vs ducted? Is the ERV ducted or a central return? I do a lot of rowhouses where new ducting is problematic. Thanks!

  6. Thanks, Don!

    Sound like some interesting work. I like townhome projects…especially in cities like Philly, Boston, NY…
    The open vs closed cell question comes up on every project, and it’s important to note that EVERY project is different. There is no single solution for every home. I find that closed cell is most appropriate in climate zones 5 or higher, but can also work in many situations in other zones. In climate zones 1-3, there is more moisture in the air, so the closed cell makes it difficult for assemblies to “breath”. Climate zone 4 is on the cusp, and it depends what else is going on. I typically only specify closed cell in basements, crawlspaces and roof-lines (CZ4 and higher), but never rule it out as a possible solution. In general, open-cell in the walls is best for most climate zones because it allows any moisture in the walls to get out. In the case of this project, the open cell worked best for the entire envelope because of the location, cost and feasibility.

    Ductless units have the advantage of no ductwork, but that’s also a drawback unless you have an unlimited budget and can put one in every room. They’re also not appropriate for rooms with very small loads, because despite their ability to “dial down” to very low capacities, there is a bottom limit. In the case of Mitsubishi, it’s 3,800 btu/h.
    I typically specify an air share fan to pull air from the conditioned rooms, and push it in to the adjacent spaces. http://www.tjernlund.com/Tjernlund%20_AS1_AS1P_AireShare_Spec_Sheet_8513030.pdf
    There are other similar options, but if the loads are small enough, some rooms don’t really need any direct conditioning. Adjacency to conditioned spaces can be enough.

    The ERV in this house was connected to the central return of the downstairs fan coil. All the bathrooms exhaust through the ERV to allow for more energy recovery, which also eliminates the need for separate bath fans.
    Connecting it to the returns is not be the best design for all situations. Having the fresh air just dump directly in to living space is a very feasible option, and it eliminates some ductwork. The temperature of the air is close to the room temperature by the time it reaches the interior spaces, and I usually locate the supply near the return grille to have it cycle through the system for conditioning and additional filtering.

    There are a lot of different solutions out there.
    One thing to note about townhomes is that the loads tend to be lower in the middle units because of shared (adiabatic) walls, than the units on the end. So, a system that is sized for one may not necessarily work for the other. This is where load calculations and design become critical.

    Thanks, again, Don.
    Chris.

  7. James says:

    Great looking place. I wonder if you have some more photos of the ducted mini splits. I found your magician post on making the head units disappear, and it’s looks like that is what you did here. I’m having trouble finding good during and after construction pics of ducted mini splits anywhere, though.

  8. Thanks, James! I do have a lot of pics of installed ducted units. I will have to email them to you (I have your address), because wordpress does not give me an option to post them in a comment…

    You can also go to an earlier post for the Proud Green Home. We have a few photos of the fan coils with and without ductwork. That equipment is from LG Electronics. The house in this post has Mitsubishi equipment.

    Proud Green Home:http://lgsquaredinc.com/2013/03/26/serenbe-modern-proud-green-home-update-heating-ventilation-air-conditioning-syste/

  9. [...] by Mitsubishi Electric as it was being prepared to be installed in the encapsulated attic of a home in Grant Park, Atlanta, GA. As you can see by the person’s foot and leg next to it, it’s not very big. The [...]