How do you pick the right target?

It's really hard to get somewhere when you don't know where you want to end up! When I set out to alter House 5, I didn't have a clear endpoint in mind. It's not a simple choice, at least to someone who has once or twice overthought a problem. In my consulting work I've helped people achieve net zero energy buildings; accomplish Deep Energy Retrofits; head towards Passive House certification; qualify for the Thousand Home Challenge; and even nail LEED Platinum a few times. What should we be aiming for?

From an energy standpoint, achieving Passivehouse certification with an existing house would be the most challenging task. It has the most rigorous requirements. The house is modeled in the Passive House Planning Package, a densely layered Excel spreadsheet that models buildings in great (some would say mind-numbing) detail. The maximum heating load allowed is 4,750 BTU/sf/year, and that's based on a strict German method for accounting for usable sf. For our house, a ballpark allowable heating number is perhaps 7-8 million BTU (MMBTU) annually. Note that this is a load, not a consumption figure. For example, if the allowable heating load were 8 MMBTU/year, since fossil fuel heating equipment isn't 100 percent efficient, the consumption would be greater than 8 MMBTU. If we stuck with the oil boiler, and it operated at 80 percent efficiency, it would consume 10 MMBTU of oil annually, or about 70 gallons/year.

This would be a very tough target. Passive houses in this climate have a higher percentage of their glazing on the south, and don't shade it in the winter. They are 4-5 times tighter than House 5 is now. They are more efficient in terms of exterior surface area to usable floor area. I pretty quickly concluded that, as much as I have been a proponent of many aspects of the PH approach, this house wasn't going to get shoe-horned into the PH fold in any way that could be described as elegant.

Having worked on a number of very successful Deep Energy Retrofits (DER - see both of my keynote addresses and my Client Case Studies on the energysmiths web site) I of course did some modeling around a major envelope retrofit. Components of the existing house are:

Basement walls are uninsulated; there's one inch of foam beneath the basement slab

First floor over the basement is insulated with R-19 fiberglass batts, installed at the bottom of the 2x10 floor joists, which means that there is about four inches of air above the batts, which means that the rim joist area at the perimeter of the house is not insulated.

The above grade walls are 2x6 with cellulose insulation

The sloped roofs are 2x10 with cellulose, and the attic has about fourteen inches of cellulose (the ceiling area is about 50/50 sloped/fat)

The windows are fiberglass Thermotechs, which means that the sash and frame of the window are fiberglass pultrusions filled with molded polystyrene foam, and therefore are more insulating than typical wood windows. The double glazing has a layer of a hard coat low-e called Energy Advantage, which is optimized for solar gain rather than insulating value (Thermotech recognizes that cold climates benefit from solar heating!), and is filled with argon. The overall window R value is perhaps 3.3, which is not really much better than typical wood windows, except that the glazing Solar Heat Gain Coefficient (SHGC) is 0.68, which is much higher than normal windows these days, which may have a glazing SHGC of 0.4.

When we moved into the house, the blower door test was about 900 CFM50 - a very good number for a new house, compared to average new homes. Some targeted air sealing dropped this to 650 CFM50, and I know there's more work to do, especially at the rim joist area in the basement.

The house definitely has winter solar shading, from trees (fewer than when we moved in) and in the depth of winter, the house to the south.

I put all of this into the model, and it reports that the house would use about 300 gallons annually for heating. I think this is pretty close. A previous tenant used 435 gallons per year for heat and DHW. Knowing what I know now about how inefficient the oil boiler was at making DHW in the part of the year when there was no need for heat, it seems possible that they used 300 gallons of oil for heat and the balance for DHW.

I then cranked up the R values in the model - R-40 walls, R-50 roof, R-20 basement walls, windows to R-5 triple glazed, and cut the blower door number to 325 CFM50, half of what it is now. This drops the heating demand by a factor of three, to about 100 gallons of fuel oil annually. It's worth noting that at this point I would still be well above the PH heating load criterion and still close to double the air tightness requirement.

This level of investment would be high. It's adding the equivalent of four inches of polyisocyanurate foam to all surfaces - walls, roofs, basement walls - and doing a major window upgrade (Thermotech windows can be triple glazed, and this could be retrofitted to the windows without replacing the window, a marked advantage over most windows.) Two things would make me consider doing this to a house:

1 - The house is in need of re-cladding - the siding and roofing are in poor condition

2 - The house is fairly simple geometrically and has a good surface-to-floor area ratio.

House 5 fails both these tests. At eleven years old, its surfaces both inside and out are in very good condition. The exterior trim is unpainted cypress, which will never in our lifetimes need replacement. The wall cladding is cedar shingle, another low maintenance, durable material. On the inside, the trim is unpainted cypress, and the walls and ceilings are skim coat plaster, all in good shape. Plus, an interior DER reduces usable space (tough with small rooms, especially bathrooms and kitchens), doesn't fix as many thermal bridges, and is disruptive to the occupants.

On the simplicity front, this house probably set a record for corners, roof planes, and lineal feet of perimeter for a home designed to be affordable. We have sixteen corners, seven roof planes, and 164 feet of perimeter for a house with 1,589 gross sf. Contrast that with a 28 x 36 cape - four corners, two roofs, 128 feet of perimeter. That's a less interesting house, to be sure, but it certainly would be easy to retrofit. I see myself adding insulation to the roof when it comes time to re-roof, but for now, the house exterior is in too good condition to tear into it for a DER, and it's too complicated a job.

The next possible target I evaluated was the Thousand Home Challenge. I'm going to save this, and the rest of the story, for another post. It's 8 pm on Saturday night, I spent the day plumbing, and I hear Sam Adams calling me.

 

 

Comments

[Adam Hirsch]

I'm having a lot of fun reading these, Marc. :)

[Marc Rosenbaum]

Adam, to misquote Emma Goldman, who never actually said, "if I can't dance, I don't want to be in your revolution", if we can't have fun doing what we do, why bother?

Emma apparently did say "if voting changed anything, they'd make it illegal"

[matt]

Just found your blog -- It's one I will follow for sure.

A note on the fridge - I too just went with a GE. Out here in NY, we can still get GE 17's (16.5). They are rated at 300 Kwh per year. I'm attempting to post a link :

http://www.homedepot.com/Energy-Star/Appliances-Kitchen-Appliances-Refrigerators-Top-Freezer-Refrigerators/GE/h_d1/N-5yc1vZbv5jZ1z141o3ZloZ1z141fzZ1z0zo3r/R-202822214/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053