California’s New Requirements for Designing and Building Attics and Walls

Notes from SCE course : Understanding California’s High Performance Attics and Wall Requirements.

October 30, 2017–note that these notes are still helpful in 2020 but current Title 24 codes are more stringent when it comes to residential in terms of solar and tighter better insulated homes.

Steve Easly- instructor

Notes by Guy Van Meulebrouck PE (attendee)

  1. In a house-attic ductwork makes up 40% of the house’s total surface area. So, keeping heat from transferring from an attic to a duct is one of the most significant improvements an architect can make to a house. By creating spaces for ductwork inbetween the attic and ceiling energy bills can drop by as much as 40% for a house. Likewise, commercial wood buildings with ductwork in attics benefit greatly from the architect creating a space between the ceiling and attic for ductwork, conduits, and piping etc. . This can be achieved somewhat economically by using scissor type trusses instead of trusses with horizontal bottom chords (one adds drywall to the bottom of the raised bottom chords and saves money that would otherwise be spent sealing each and every penetration of pipe, conduit etc into the attic. Energy bills and comfort benefit from this too. Note that Code enforcement on this has been more relaxed in the past but less and less so each year until Zero Net Energy buildings are a reality

  2. Attics have to be sealed airtight where ALL ductwork, air outlets, electrical conduits, smoke detectors, security systems, sound and IT systems, and pipes pass through it. This is important enough to warrant being called out in specs, shown on plans, and inspected during construction.

  3. California Codes are advancing steadily towards the goal of Zero Net Energy (ZNE) by the year 2020 for residences and 2030 for commercial buildings. The goal is for buildings to create as much energy as they use-all without costing too much more than previous buildings. Surprisingly, substantial steps towards ZNE involve collective education and agreement throughout the building industry to not do stupid things.

  4. If architects use the same specs and details in 2017 as they did prior to 2016-their buildings will not fall within the current legally accepted “standard of care” of design. Steve recommends a free resource book called “Guideline for Designing Energy Efficient Building Enclosures” as a source for up-to-date details and specifications. Below is an example of one of the details available.

attic detail 1

wall detail 1

One can get ahold of this PDF book in several ways:


  2. Steve Easly’s website

  3. contact me at or by my website

  1. California has it’s share of moisture related lawsuits for buildings, reportedly even more than Texas and Florida. One reason Steve cited is that eventhough California is less humid that Florida and Texas-the fact that somewhat humid air cools off so much at night causes relative humidity in attics spike every night, often to the point of reaching 70% relative humidity (RH). 70% relative humidity is a magic number for mold to growing. Likewise, air leaking from inside the building to outside hits the 70% RH mark inside of leaky walls on cold days. Raw outside air leaking into an air conditioned building can also reach 70% RH as it cools down while leaking through walls, attics, and roofs.

  2. Steve introduced Cross Laminated Timber (CLT) as an effective new tool for combining exterior wall systems with structural systems.

  3. Keeping attics properly vented even after insulation is installed is complicated and often overlooked. Improperly vented and improperly insulated attics area easier to mold. They waste energy, create comfort issues in spaces below, and introduce dusty hot and somewhat toxic attic air into the inside. Raised heel trusses is one of many improvements attics should have. “Raised heel” means making sure the attic truss meets the exterior wall in such as way as to allow extra height for insulation (see detail below-also from “Guideline for Designing Energy Efficient Building Enclosures” )

my own note: Ridge vents outperform any other attic ventilation scheme I have seen. It is permissable to use more attic ventilation openings than code minimum, especially in climates where winters are not too severe.

  1. Air leakage in buildings will continue to be an area for code concern in the design, construction, and inspection phases.

  2. Low E windows were discussed and compared with tinted windows. Window tints add color to glass to filter sunlight. Low E windows spray a very thin coat of silver onto one surface of glass. Low E adds about $1.50/SF of cost to windows but to properly assess true cost, one considers sizing of HVAC systems (first cost) plus energy bills (and comfort).

    The advantage of low E is that it can reflect energy in such a way as to keep heat from escaping the inside yet diminish solar heat which enters the building. Tinted glass only serves to reduce solar load. It is difficult to tell that a window is low_E coated by looking through it (as opposed to heavily tinted windows). Architects have a choice of how many low E coatings a window gets. Oddly enough, extra coatings does hardly anything for heating loads but matters greatly for air conditioning loads. Conclusion: for buildings up in the mountians- one coating of low_E is OK. For buildings with lots of east/west glass, the extra coatings are worthwhile. Overhangs are recommended for south glass. (My own personal note here: Windows should be specified early on in the design so that the air conditioning and heating systems can be accurately sized. Any changes to insulation and/or glass must be brought to HVAC designer’s attention immediately, since the building may not work when the HVAC systems are not matched to the glass types, and actual insulation values).

  3. Advanced Framing was discussed as a way to save money on building costs plus make more room for insulation at the same time. Advanced Framing works like this: say a conventionally wood framed building has a framing factor of 25% (meaning 25% of the wall is taken up by wood studs, headers and lintels). It is possible to build sturdy buildings with framing factors as low as 13%. This is achieved in part by aligning studs from floor to floor and not using traditional excessive safety factors. There are additional techniques of single top plates and innovative lintels. The American Panel Association (APA) has published free guidelines for safely eliminating excess wood framing ( My own note here: the HVAC and Electrical engineering practices have been forced by code to reduce their traditional safety factors and this has resulted in more comfortable indoor spaces and some reductions in first costs. Now it’s structural’s turn to do the same.

Below are examples of the free CAD details that are available on the APA website;

wall detail 2

wall detail 3

  1. Compressed batt insulation: What makes insulation effective is trapped dead air. The uncompressed batt insulation thickness must precisely match the wall cavity size or the wall will experience up to a 28% decrease in effectiveness due to compression. This includes the way the contractors install the batt insulation. It is common for installers to push the edges of the insulation in order to position the batt inside the cavity. Pushing in even 1/2” causes enough compression to show up in Infra Red photography as a hot spot/cold spot. A reminder that these types of insulation breeches combined with leaky edges and openings in drywall (around electrical receptacle outlets for example) promote dust and air infiltrating into cold spots and causing mold. Electrical wires and plumbing pipes are another source of compressed insulation. Steve presented an ingenious solution for electrical wiring: One notches the bottom of wood studs with a dado blade (1/2” deep). Now, the electrician routes the wires down the side of the receptacle studs and across the bottom of the studs through the notches. Labor wise, the notch method is quicker than drilling holes in every stud (if dado’d while the studs are still in a pile).

  2. Overhangs, eaves, soffits, and floor plates are common sources of heat and air leaking and current (and future) codes actually prohibit these leaks and breaches. Careful attention to details is required during design, construction, and inspection. See the above mentioned websites for possible details of solutions.

  3. Contractors shrinking down HVAC ducts to fit into structure is a common source of air constriction. This results in heating and cooling problems as well as energy waste. (my own note: Allow engineers to size ductwork as independents. The cost of engineering fees are often less than the buried costs of the contractor designing the HVAC system (“free” but sometimes hidden in the contractor overhead). Engineered drawings allow for meaningful competitive bids). In either case, the architect should make certain there is room for ductwork. If ductwork is between trusses, lateral bracing has to be considered. If dropped ceilings and soffits are used, clearances for can lights and duct insulation (3 to 4” additional to duct’s actual size).

  4. The exact R value of wall and roof insulation varies with the construction details. In order to get the lowest required R values one puts the insulation on the outside of the walls and on the top of the roof. This approach also makes for less infiltration and less mold potential.

End of notes.

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