Dramatic Second-Story Addition: Another Tough Compliance Problem Solved

Dramatic Second-Story Addition: Another Tough Compliance Problem Solved

Posted on 06. Feb, 2012 by in Case Studies

In early October, I got a call from Steven House of House+House Architects. They were doing a remodel in Marin and needed our Title 24 energy services. House+House is an award-winning firm whose focus is mainly single-family custom home design. Their work  is characterized by a daring contemporary sensibility, and they have a large body of work both within California and also in Mexico.

So what do daring designs have to do with Title 24 energy compliance? Well, they need a lot of special attention because they often feature expansive windows to celebrate the crisp and brilliant California sunshine, and in the North Bay area, they let in gorgeous views as well. Vaulted ceilings, also a common design feature, can require special attention to the roof assembly to ensure that there’s enough space to fit the necessary amount of insulation.

A Dramatic Second-Story Addition

The stats: 4,000 SF total, including their proposed 768-SF addition, a master suite. This was a ranch house north of San Francisco, built 1962. House + House had remodeled it 18 years ago, for a previous owner. The place was recently sold, and the new owner approached House + House for a second expansion.

The additional conditioned space consisted of an expansion outwards on the second, over the first. This new interior space was all contiguous – which could help the energy model. Thankfully, the local jurisdiction had no “beyond code” green ordinances that would apply to Additions. So we just had to make compliance, not beat it by 15% or more.

First floor plan of a custom home remodel by San Francisco architects Steven and Cathi House of House+House Architects. House+House had actually remodeled the same house for a former owner 18 years previously. Although the wraparound porch was not included in the energy model, it is a key design feature in this remodeling project.

Can We Keep the Existing Heating System?

The owners wanted to keep the existing furnace and water heater, which meant we might have to assume legacy numbers (bad for compliance). There was no cooling system. The drawings I received showed two mechanical areas, both inside conditioned space (good for compliance). Vaulted ceilings on the second floor portion of the addition meant that the duct chase up there could also be claimed as being within conditioned space for additional credit.

The project had a very tight budget. We needed to weigh the cost of additional measures carefully. The fact that there was no cooling system meant that the house probably didn’t need one due to shade trees – but, in Title 24 you can’t count those shade trees. This can result in artificially high cooling loads (bad for compliance).

The majority of the addition was on the second floor, and involved adding new floor space and raising the ceilings on much of the existing space. Design by Steven and Cathi House of House+House Architects.

The Need to Avoid a Whole-House Model

We were concerned that if we had to run it as a Whole House, that we would have to take into account the original conditions from 1962 and 1993 respectively. With any existing home built more than 10 years ago, if the windows are not known, we generally have to assume the worst: aluminum single glazed. If we can claim the windows as wood framed that’s a little better, but it’s still probably not low-e insulating glass. Insulation levels in existing walls would have to be a lookup based on the dates built. So we had a strong mandate to make it work as Addition Alone – but ultimately, the goal was to keep construction costs down.

The first step was to see if by some chance it qualified for prescriptive compliance, which would get us out of a lot of extra steps. If the overall glazing is under 20% of total conditioned floor area for whole house or for the addition alone – that would be the path of least resistance. No dice.

Let the Trade-Offs Begin

The preliminary drawings included many beautiful renderings that were very helpful in getting a good holistic sense of the space. The architects were still refining the elevations and window schedule with exact window dimensions, so we began the energy modeling without them. One unusual design feature was the angled wings, and hidden alcoves. This usually means that we need separate elevations for each wall, and the architects were still refining those drawings.

The angled walls added a new challenge as well, in that it can be difficult to approximate the window widths when working from a foreshortened elevation angle. Usually I can take an educated guess at the openings, but for difficult projects, there’s always the chance that a plan checker could call the energy report into question, so I wanted every assumption to be well-documented and defensible. One of those assumptions was to locate the heating ducts within conditioned space (big compliance credit).

There was also an indication on those drawings that the owner **might** be adding a second furnace in the garage to feed the new addition space. I advised House+House to find a way of enclosing that furnace within conditioned space so we could keep that duct credit either way. They were planning to use Milgard vinyl framed windows, which was good news; Milgard offers many options for varying grades of efficiency.

Windows can be an easy but expensive way to bump up the score. Sometimes the better window packages are a lot more expensive, so any time we run a project with better than standard windows, we have to ask the architects to ascertain the additional cost, wait for them to get a new quote from the manufacturer, discuss it with their client, and that can take a certain amount of time. If we’re trying all sorts of other options at the same time, it can take a lot of extra time.

The master suite in this second-story addition by House+House Architects features expansive windows and vaulted ceilings.

The Baseline Wasn’t Bad, But…

To my surprise, the baseline trial (assuming the worst for anything not known) didn’t quite make it but it wasn’t off by that much: -7.1%, with more of the shortfall on the heating side. Since they wanted to keep the furnace, the first thing we tried was upping the insulation in the walls from the minimum required R13 to R15. That brought us to -4.2%.

The roof cavity was small and we maxed that out at R30, even with spray foam. So we couldn’t go up on the roof insulation. Next, we tried an 95% efficient furnace instead of the legacy 80% one. It’s easier to swap out a furnace than it is to upgrade every window or do HERS tests. That brought us to +4.5% over.

Well, it turned out that replacing the furnace was not an option, at least not right then. At least I had the actual make and model number, a Carrier furnace. I called Carrier to see if by chance that was one of their more efficient models – but they eventually got back to me several days later to confirm that no, it was a baseline 80% efficient model. Foiled again!

A Lot of Discussion With the Architect

As I’m reviewing my modeling notes, one thing that stands out is that there was a lot more back and forth with the architect than there were actual modeling trials. There were several different measures which, combined in various ways, could have yielded a passing score: replacing the furnace, ducts in conditioned space, R15 walls, the low-leakage duct test (if ducts couldn’t be in conditioned space), and more efficient windows.

It turned out that the ducts could only be claimed as “combination space”, meaning portions of them were within the conditioned building envelope, but not all of them. That still yielded a compliance credit, but a smaller one. We might have to resort to a HERS duct blaster test – which now, in addition to having another thing to ensure during construction, also requires online registry with CalCERTS.

The architects didn’t yet know how the ductwork for the new addition would be configured. They were expecting, not unreasonably, that this would be worked out in the field by the contractor. But, we needed the energy report now, in order to get the building permit, and we didn’t want to commit to anything that would turn out to be impossible later on. We didn’t even know if the new space would run off the same system or not, and since no work was planned on the existing ductwork, that introduced the risk of failing the HERS duct test – and we’d have to start all over again on the energy compliance. Not good.

What Finally Worked for Everyone

Eventually I think we got it to work with the following combination of options:

  • Furnace efficiency dialed back to .80 AFUE (existing furnace)
  • Ducts remain in conditioned space
  • Exterior walls in addition insulation at R15
  • Windows are now .30 U value (Milgard 3DMax package)
  • NO duct test, but one visual duct inspection

CalCERTS: The Final Hoop, We Hope

And then it turned out we needed the CalCERTS registry after all, and I found out a new knotty twist. For a remodel, the energy consultant has to get the homeowner to self-register (with a driver’s license and signed form) before he or she can even create the project online, much less upload the energy report and get the watermark! Fortunately, the owner was on the ball and responded quickly. If he’d been offline or on vacation in Tahiti, the project could easily have stalled.

The CalCERTS folks had designed their system to handle a more typical workflow which is quite different from these one-off, custom projects. So it expected to see all kinds of data like a builder name, HVAC installer name, and permit date, which we typically never have prior to submittal. Fortunately, the CalCERTS folks are always very nice and helpful over the phone, and have always helped out. It’s a new process for them, too.

Although it's not factored for energy modeling purposes, because it shades an existing area of the house that was not included in the model, the wraparound porch is a unifying design element that ties together all the fragmented pieces of the house that were added on over the years. The curved outset wall on the right can also be seen on the first floor elevation.


2 Responses to “Dramatic Second-Story Addition: Another Tough Compliance Problem Solved”

  1. Eric Hubscher

    31. May, 2012

    Wonderful story. Read like a moving story board.
    Great for me…an inspiring back to school wishful architect student

    Love your website too.
    Thousand Oaks, CA

  2. Glass Wool Insulation India

    05. Jul, 2014

    Amazing blog, I like it and well written by you. This blog is useful to the owners who are planning to renovate their house. And we have to discuss with architect to remodel. I appreciate your blog and thanks for sharing it. Keep sharing such a useful posts.

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