Design Tips

 

Design Suggestions for the 2016 Standards

 

 

Use these links to jump to the topic of your choice.

 

Compliance Equalizers

Siting

High Performance Attics

Above-Deck Roof Insulation

Attic Radiant Barriers

High Performance Vaulted_Cathedral Rafter/Ceiling Joist

High Performance Walls

Quality Insulation Installation

Thermal Mass Floors and Walls

Glazing with a lower U-factor and SHGC

Skylights

Single Glazing

Glazing Area

Cool Roofs

Whole-House Fans

R-8 duct insulation

All HVAC and ducting in conditioned space

Ductless Mini-Split

High Efficiency Furnace

High Efficiency Air Conditioning

Tankless Water Heating

Point-of-Use and Compact Distribution Design

Solar Domestic Water Heating

Photovoltaic (PV) Solar-Electric System

 

 

 Major Compliance Equalizers

  1. Photovoltaic. Available as a compliance credit everywhere except Climate Zones 6 & 7.
  2. Solar-thermal water heating. Available as a compliance credit in all climate zones. Costs about $10,000.
  3. Entire HVAC system in conditioned space. Ducts and air handler are installed below the ceiling, inside the thermal and air barrier of the envelope. Available as compliance credit in all climate zones. Costs more for the extra 2′ of wall studs for a 10′ ceiling in order to furr down for 18” diameter ducts.

 

Siting

Site the house on an East-West axis.

Minimize glazing on East and West sides of house.

Glazing on South and North sides of the house. You can control the heat gain with overhangs. Consider 3′ roof overhangs with an 8′ plate, 4′ roof overhangs with higher plates. Overhangs won’t help much on East-West glazing, but still worth considering.

Side Fins–Also consider  1′ deep side-fins at both sides of each glazed opening, maximum 1′ away from the opening.

Porches–Consider extending the roof overhang even further by creating continuous porches along East, South and West faces of the building.

Avoid gable end roofs if possible or add individual 3′-4′ deep overhangs at windows on gable ends. Side fins can mess with your design, but 4′ or more overhangs will benefit compliance. This is not so critical in Climate Zones 6 & 7, but worth considering, even there. I realize that you’re dealing with small lots and sideyard setbacks, so these are just suggestions.

 

The computer performance approach is based on the Prescriptive approach. It measures YOUR building against the prescriptive requirements. Most of the following are based on the prescriptive requirements—knowing those, you’ll have a sense of where your building deviates and is likely to be assigned a credit or a penalty.

 

High Performance Attics

High performance ventilated attic consisting of: 2×6 top chord trusses @ 24” o.c. with raised heel, R-38 batt ceiling insulation and R-18 batt insulation below the roof deck. With R-18, a radiant barrier is not required, as the insulation is in contact with the underside of the roof sheathing.  Raised-heel trusses can add 9″-12″ to the wall height to accommodate the 12″ R-38 insulation (it is available in 10.5″ high-density batts).  There’s a cost increase (I’ve seen a reference to 12-15%) for raised-heel trusses, but I have no hard numbers.  

Credit: Harry Whitver

 

Another option to avoid compressing the R-38 might be to cantilever the truss beyond the wall line, making the bottom chord part of an exterior soffit.  I don’t know what the cost differential would be compared to a standard truss, but you’d be designing-in some nice overhangs (as mentioned under ‘siting’). 

TRUSS WITH SOFFITED EAVE

 

 

Above-Deck Roof Insulation

You can use above-deck roof insulation instead of below-roof deck insulation. R-8 continuous rigid insulation and Radiant Barrier required except in CZ 1 & 16. This is very beneficial in bringing down attic temperatures if ducts are in attic. You’ll need to sort-out who installs it—the roofer or the insulation contractor? Also, R-8 is about 2” thick. You may wish to add another layer of roof sheathing as a nailing surface for the roofing. For additional information, see NEWSLETTER #3.0 PART 1.

 

Attic Radiant Barriers

  • Radiant barriers must also be installed on gable ends.
  • With R-18 batt insulation below the roof deck a radiant barrier is not required, since the insulation comes in contact with it.
  • If you’re using above-deck continuous rigid insulation, a radiant barrier IS required, except in Climate Zones 1 & 16.
  • For additional information, see NEWSLETTER #3.0 PART 1 and NEWSLETTER #3.3.

 

High Performance Vaulted Rafter/Ceiling Joists

  • 2×14 R/CJ @ 24” o.c. with R-38 Batts will work prescriptively in Climate Zones 1-3 & 5-7, although in Climate Zones 1 & 2 you’ll need to add R-4 continuous rigid above-roof deck insulation.
  • Add R-14 above-deck continuous rigid insulation for Climate Zones 4 & 8-16.
  • This assembly’s insulation requirements are affected by whether the HVAC and ducting are entirely within conditioned space as well as the compliance approach selected; the above assemblies are suggested as a general starting point.

 

High Performance Walls

  • If you plan to build with 2×4 studs, expect to use 2” (R-8) continuous rigid insulation in all climate zones except 6 & 7. Using 2×6 studs for all your projects costs a bit more, but you save if you go to 24” o.c.
  • 2×6 studs @ 24” o.c. with R-25 batt insulation are recommended. This meets the prescriptive requirements for new construction in climate zones 6 & 7.
  • All other climate zones, add R-4 minimum continuous rigid insulation to the 2×6 assembly.
  • How do you attach your exterior wall finish through continuous insulation? Plywood or OSB non-structural sheathing over the continuous rigid insulation to form the base for 3-coat stucco. Note that the City of Irvine, for one, will not accept 3-coat stucco directly over rigid insulation]. Check with your building department before you add the non-structural sheathing, as it may not be necessary.
  • See NEWSLETTER #3.0 PART 2R.

 

Quality Insulation Installation for Ceilings and Walls

  • NEWSLETTER #3.2 (Holey Insulation) details the effect on your buildings’ efficiency when insulation is poorly installed.
  • HERS raters I’ve spoken with tell me that without Qii (Quality Insulation Installation), insulation is always poorly intstalled. 
  • Qii is an excellent compliance credit.
  • Downside: Qii is more expensive. Few insulation contractors actually install Qii correctly.  Calling for Qii triggers a HERS inspection during construction and it’s likely that the HERS rater will have to return multiple times to make certain the contractor installed it correctly, during which time the walls (including tubs & showers) cannot be closed up.
  • Whether it’s cheaper to specify Qii instead of Solar-Thermal water heating or a Photovoltaic offset is something that is worth evaluating.

 

Thermal Mass Floors and Walls

  • Slab floors, either on-grade or above-grade can be used as thermal mass.
  • Slab floors with a carpet covering are not considered thermal mass as the carpet is the equivalent of R-2 insulation between the concrete surface and the air in the conditioned space.
  • Smooth concrete floor surfaces including colored and polished concrete, sheet vinyl and vinyl tile are not considered thermal mass, as the floor may, at a later time, be covered with carpet.
  • Textured concrete floor surfaces are considered thermal mass, as carpet and padding are unlikely to be installed in the future.
  • Textured concrete that is considered thermal mass would be: Stamped, Bomanite, Tile, Terrazzo, Exposed Aggregate.
  • Thermal mass exterior walls must be insulated to the equivalent of an R-13 wood-framed wall. 2X4 furring with R-13 will be fine.
  • If exterior mass walls are insulated on the outside face of the wall, the thermal mass is now inside the ‘thermos bottle,’ and can offer compliance credits.
  • There’s a compliance penalty for the R-13 exterior furred wall; if you want the Masswall compliance credit, using 2×6’s with R-25 batt insulation is recommended, with continuous rigid in all Climate Zones except 6 & 7.
  • Thermal mass works best if there’s no insulation between the inside face of the wall and the air in the conditioned space. Furring the inside face of the wall with 2x2s and gyp board will give you a surface to hang pictures, but will create the same condition as if you had carpeted the face of the wall.
  • Straw-Bale walls act as both thermal mass and wall insulation (R-30) and do not require additional furring and R-13 batt insulation.

 

Glazing with a Lower U-Factor and SHGC

  • The prescriptive baseline for residential glazing is 0.32 U-factor/0.25 Solar Heat Gain Coefficient (SHGC).
  • Consider going even lower than the baseline: Jeld-Wen V-4500 has a 0.22 U-factor/ 0.19 SHGC, but reduced Visible Light Transmittance.
  • The best way to help compliance in Southern and Central California is to limit heat gain with a lower SHGC.
  • If you don’t use glazing with a National Fenestration Rating Council sticker, we’ll have to use the default tables. As an example, a dual glazed, lo-e vinyl DEFAULT window has a 0.58 U-factor and a 0.53 SHGC. This will radically hurt compliance. 

 

Skylights

  • Velux makes a 0.29 U-factor skylight with 0.13 to 0.22 SHGC with the roller shade closed (CPD# VEL-N-19-00031-00002). Fixed Pan-Flashed skylight. Check NFRC website before specifying.

 

Single Glazing

Single glazing can still be used, but the U-factor must have a weighted average of 0.55. To achieve this, you need 2.5 s.f. of dual glazing for every 1 s.f. of single glazing, and your project will suffer a major compliance penalty because the 0.55 U-factor is nearly two times worse than the baseline U-factor of 0.32. Review the list of ‘counterbalance’ components under Glazing Area below.

Glazing Area

If you use more than the 20% prescriptive baseline glazing with more than 5% west-facing glass, there’s a compliance penalty. 30% or more glazing is possible, but consider your climate zone, and whether you want the following components in order to balance the glazing-related inefficiency:

  • HVAC entirely in conditioned space;
  • Heat pump water heater;
  • 17-18 SEER cooling (even if you don’t need cooling, we may need the compliance credit);
  • Qii;
  • Solar-thermal water heating;
  • Photovoltaic offset.You could need some—or all—of the above depending on how much glass and how badly your client wants that west-facing view. Oddly enough, I’ve been told that using less than 20% glazing doesn’t result in a compliance credit any more.

 

Cool Roofs

  • Cool roofs have high reflectance, so they reflect heat back into the sky.
  • Cool roofs have high emittance, so they radiate back out what heat gets past the high reflectance.
  • Not required in Climate Zones 1-9.
  • Required on low-sloped roofs (<2:12) in Climate Zones 13 & 15.
  • Required on steep-sloped roofs (>2:12) in climate zones 10-15.
  • For minimum reflectance and emittance values, see NEWSLETTER #3.3.

 

Whole House Fans

Whole house fans incorporate a fan (typically located in the attic) to pull cooler outdoor air through open windows and up into the attic, exhausting the air to the outside through attic vents. By pulling cooler outdoor air throughout the house, indoor air temperatures and the temperature of building mass are reduced, offsetting next day cooling loads. Whole house fans are prescriptively required in climate zones 8-14.

 

R-8 Duct Insulation

  • R-8 duct insulation is required for ducts in attics in all climate zones except 3 and 5-7.
  • R-6 duct insulation is required for ducts in attics in climate zones 3 and 5-7. Upgrading to R-8 in those climate zones helps compliance.
  • R-4.2 duct insulation is required on ducts in conditioned spaces. For more on ducts in conditioned spaces, please see below.
  • Duct leakage is now a maximum of 5%. All of the above ducts must meet this requirement.

 

All HVAC and Ducting in Conditioned Space

  • HVAC and ducting in Conditioned Space is a very good compliance credit. Getting the ducts out of the attic, even with above-deck roof insulation, is beneficial. You’ll need to be sure that you’ve left room to run the ducts (18”diameter, plus another 4” of R-4.2 insulation). You might need a higher plate line to accomplish this. If you’re thinking of a ductless system to save space, see DUCTLESS MINI-SPLITS below.
  • Raising the plate height increases framing, interior and exterior finish costs.  Another option is to incorporate a duct space above the bottom chord of your roof truss.  Run your ceiling insulation along the bottom chord, up over the duct chase, back down and across the rest of the bottom chord.  The insulation must be in direct contact with the air barrier (the gyp board at the top and sides of the chase).
  • The trusses and the gyp board installation may cost more; the HVAC system may be downsized due to the ducts being in conditioned space.  Confirming the second item with an HVAC contractor you’ve worked with in the past would be a good start.
  • Ducts in conditioned space must be insulated with R-4.2 and must be HERS tested for 5% leakage maximum.
  • If the plan checker requires it, you may also have to provide a duct layout—but not duct sizing. The intent is to prove to the plan checker that all the equipment and duct runs really ARE in conditioned space.
  • The HERS rater will also check for this in the field. If it’s been changed, we lose the compliance credit, the calcs must be re-run and there’s no way to be sure that we’ll be able to compensate for the loss of that credit at that time. You want the plans to be clear on this and the HVAC contractor to understand it as well.
  • Putting in two return air ducts can give you better airflow while downsizing the duct diameter. Useful for ducts in conditioned space. See NEWSLETTER #4.2 for layout examples.
  • Avoid specifying a Ductless Mini-Split. While it ought to be more efficient, the Computer Performance Approach will model it as a minimum efficiency split system with ducts in the attic.  This will actually hurt compliance.  It’s an internal function of the computer program and can’t be changed. The computer should accept ducted mini-splits.

 

 

High Efficiency Furnace (94%+)

  • It’s been said that California is a cooling climate. I’m not sure that people in Northern California would agree, but the focus is on saving electricity, so the Performance Approach is biased towards improvements in cooling efficiency rather than heating. Bottom line: Increasing heating efficiency may not get you much.
  • Standard design is still based on 0.80 AFUE, so going to a 0.94 AFUE would boost efficiency by 17%. That’s more than boosting your cooling from a 14.00 SEER to a 16.00 SEER, so it’s worth considering.

 

High Efficiency Air Conditioner (15 SEER+)

  • Standard cooling is 14.00 SEER. Going to 16.00 or 18.00 SEER is beneficial to compliance, but check the increased equipment costs first.

 

Tankless Water Heater

  • Tankless water heaters are now the ‘yardstick’ by which water heating is measured within the Performance Approach. When you install a tankless water heater there is no compliance credit. The yardstick is a 0.83 Energy Factor. Anything less is a compliance penalty.
  • You can increase water heating compliance by installing a 0.92-0.95 Energy Factor tankless water heater.
  • You can also increase water heating compliance by installing a heat-pump tank-type water heater. The greater efficiency of a Heat Pump water heater is penalized by the Standby losses incurred by it’s storage tank, but there should be a compliance credit benefit beyond that of a tankless water heater.
  • For a Heat Pump water heater, try for an Energy Factor greater than 3.0.
  • With a 0.83 Energy Factor tankless water heater, the water heating tips shown below offer some ways to boost compliance.
  • See NEWSLETTER #5.1R for more information.

 

Point-of-Use and Compact Hot Water Distribution Design

  • These offer good compliance credits, but they DO affect your building layout and your cost for water heating equipment, as tankless gas water heaters are about $1500 each and you need to upsize your gas mains by 200,000 BTU for each water heater.
  • See NEWSLETTERS #5.2 and #5.3 for layout examples.

 

Solar Domestic Hot Water System

  • Expect to pay about $10,000.
  • Solar DHW saves 40% on the water heating energy costs—that’s a conservative value, used for compliance calculations. Hard to say how much that works out to on a yearly basis.
  • It’s an excellent compliance credit if the owner isn’t looking to flip the home quickly.
  • See NEWSLETTER #5.2 for more information

 

Photovoltaic (PV) Solar-Electric System

  • If your client is looking to install a PV system it can be used as a compliance credit except in zones 6 & 7. PV credits apply where the cooling loads are more extreme and are intended to offset increased electrical consumption from having to run the A/C more.
  • To the best of my knowledge, this is not intended to allow you to power a heat pump water heater.
  • See NEWSLETTER #7.2 for more information.