Sequential Energy Upgrades
Architects, homeowners, and builders tend to focus on what makes the building look good, not on what makes it work well. Most people living in a typical American house have never experienced an outstanding thermally comfortable indoor environment.
It can be frustrating for a knowledgeable building science contractor to see energy factors cut from budgets in favor of eye candy effects such as stage 4 plaster walls with 8-inch built-up crown molding. In the end, it is the client’s checkbook that drives all decisions.
In the end, for a building contractor, it’s about selling—convincing clients that air sealing and insulation provide more long-term value than Peruvian walnut floors—and finally, making them feel as if the energy upgrade was their idea.
Passive House Fundamentals
If my clients’ goals include energy savings and excellent indoor air quality (IAQ), I steer them toward the Passive House principles of upgrading the envelope. If these goals are not on the plans, I work with the architect on Passive House fundamentals to rework the plans so the building shell performs better. Most states and local jurisdictions require some kind of building energy modeling, but Passive House requirements for energy use are by far more stringent than any existing code in North America.
If clients want to build a full-blown certified Passive House, or need more detailed information than I can provide, I recommend that they go through the Passive House Planning Package (PHPP), a Passive House energy-modeling plan, specific to the building site. There are certified PHPP people all over the country who can help. I like to work with the North American Passive House Network (NAPHN). Though most of my jobs are not on track to be certified Passive Buildings, Passive House guidelines are my target value on every job I get involved in.
Sequential Staging of the Building Envelope
So what is a sensible approach to making an energy-efficient building if the client does not have the money to go all the way? First thing is, the client has to want a good building shell as much as he or she wants the glitz. The next thing is, you have to try to sell a viable long-term strategy that involves sequential upgrades. If this is your client’s goal, and he or she cannot afford the full package, consider doing your next deep energy retrofit in stages.
Building code history shows that insulation requirements are growing more stringent all the time. Most attics and crawl spaces are underinsulated and will get upgraded some day; rodents and other mammals have infested many attics. I tell my clients that ugly or underinsulated attics offer an opportunity to make improvements that will make life noticeably better for the occupants. There is nothing like pictures of a dead rat, or mounds of poop and pools of urine, to convince clients to remove the old insulation. I mention that rodents are not likely to reinfest if borate-treated cellulose is installed. If the existing insulation is decent, it can be a hard sell to convince clients to remove it and do air sealing. After the insulation is gone and the attic floor is vacuum cleaned, electrical upgrades and air sealing can be done. Air sealing an attic is extremely arduous work. There are usually hundreds of linear feet of potential leaky interfaces, so I seal these runs with caulk and liquid sealants.
The pressure boundary of the building envelope is the airtight surface between the outdoor environment on one side and the conditioned occupant space on the other. Light boxes, fans, wiring, and plumbing that comes up to the attic from the walls or drywall all create holes in the pressure boundary. I seal these holes with tape when it’s possible and caulk them when it’s not. I use canned foam as a gap filler, not as an air sealant. I cut off the excess foam fluff and coat over the top of the foam with a high-quality elastomeric caulk or liquid for the air seal.
In a crawl space retro, after I clear out the debris, I sweep the dirt floor clean and lay out a tight vapor barrier on the earth.
For durability, I always use at least 10-mil plastic and a high-quality tape designed to adhere to polyethylene. Do not use tapes designed for other applications. To protect the plastic from being punctured during work or future crawls, I cover it with Ramboard or similar, or large pieces of cardboard or even carpet. However, the covering should be inspected every year tomake sure there are no moisture leaks in the plastic that might wet wood and other surfaces where mold can grow. I am very fussy about breaking the vapor skin. I always leave some material there for future crawls so I can protect my crawl and work area. In areas where foot traffic will occur, I put building wrap (such as Tyvec) under the 10-mil to protect it from being dirt and pebble punctured, and I cover the 10-mil with Thermo-ply.
Lastly, when all the underfloor work is complete, I crawl around with a good light and look for tears and holes that might have occurred during construction.
In concrete floors, I pull up any covering, test for slab moisture, and seal the concrete.
Attic and crawl space work can be done with very little disturbance to occupants. If possible, I encourage clients to make new access portals on the exterior before I start the work. This cuts down on my traffic to the interior of the house and makes access easier in the future.
Many of my clients report that the biggest noticeable changes in their living space result from air sealing and putting down a vapor barrier.
Attic insulation and air sealing.
Crawl space insulation and air sealing and vapor barrier.
Sidewall insulation and air sealing; new siding and trim.
I don’t think it matters in what order you do stages 1, 2, and 3. It just matters that you complete each stage so that it’s as close to 100% perfect as you can make it. You wouldn’t build a kitchen that was 85% finished, so try not to settle for 85% of the air sealing on any one stage.
HVAC. These systems are likely to need a complete rethinking. As R-values and airtightness improve, the 100,000 Btu air handler or the 4-ton air-conditioning unit will be way oversized to keep the house comfortable. These units cannot be stepped down, and running them in short blasts would be uncomfortable, noisy, and costly. The ductwork for these units will be taken out as well, so a removal plan and a replacement plan should both be in place. I like a heat pump with a high coefficient of performance (COP) for space heating coupled with a heat recovery ventilator (HRV). There are many choices for HVAC systems, but whatever you choose, make sure it will dovetail in later, or that you won’t have to do too much demo to get it in.
Interior work. I know this is crazy, but most people would rather spend their last $3,000 on countertops than on dense-pack insulation. So it’s your job to show them the logic: They can upgrade their kitchen in five years when they get that promotion, but no way are they going to move out for a month, tear off the Sheetrock, pull the old fiberglass batts, air seal, and blow in cellulose.
Thermal bridging. Ninety percent of the thermal bridges get buried in the assembly. Thermal bridging should be considered in every detail of assembling a new shell or reassembling an old one.
Few people are going to tear off decent 40-year-old siding and trim to upgrade air sealing or insulation. When I am doing sequential upgrades, I suggest that my clients wait until the siding needs major work or replacement and upgrade then.
Here are some general guidelines you can follow when working with a client on a sequential upgrade:
- Chart out the entire energy upgrade, what will go where and in what order.
- Ninety percent of air sealing gets buried in the assembly and may not be accessed again for decades. Do not skimp on the focus and quality of the air sealing.
- When air sealing, choose the best material with the greatest adhesion and the most flexibility. Canned liquid foam does not fall into this category.
- Unless your pressure boundary is at the roof rafter plane and/or the ground level, you must remove all of the insulation in an attic or crawl space to gain access to the leaks. If you do not, your building shell will leak large amounts of air in perpetuity.
- Use a blower door test before you start any work to get a baseline air leakage, and test your work after each phase of air sealing to track your progress.
- Fifty percent or more of the insulation gets buried in the assembly and also may not be accessed again for a long time. Do not go for the low bid. Hire an insulator who cares about his or her work as much as you care about your work.
- Avoid any procedures that you will have to take out later for the next upgrade.
- Thermal bridges and cold bridges are stopped or slowed down with the proper R-value on the cold side. Make sure that highly conductive materials do not share the outdoor environment on one side and the heated space on the other. Thermal control can be as simple as making sure the glazing you order comes with Super Spacers, which conduct less heat than stainless steel or aluminum. Most building designs are riddled with thermal bridges that can be stopped, often with a simple redesign.
- In a retrofit, old superfluous framing members should be taken out in favor of more insulation.
- Ask the engineer if he or she can approve insulated headers in some locations.
- Unconditioned spaces such as porches or garden sheds should have a thermal break as well as an unbroken moisture and vapor barrier (sheet foam, cork, Foamglass, Agepan) where they connect to the conditioned space. This could get costly, but if the opportunity and the money happen to coalesce, go for it.
- Therm software, free from Lawrence Berkeley Lab, can help you locate potential thermal breaks in the shell. Or find someone in your area who is schooled in Therm to review the plans.
- As the envelope gets tighter, materials with high volatile organic compound (VOC) content become more dangerous. That includes carpets, furniture, and stuff from big-box stores.
Any time you do anything to a client’s home, you should look for opportunities to increase its efficiency and comfort, and add to your work scope. Here are some examples:
- Air sealing is about access. If you are lucky enough to expose the pressure boundary of the building shell, go all the way to shut down the leaks.
- Building needs a new roof covering. Access holes can be cut through the roof deck into the attic. The old insulation can be removed easily without greatly disturbing the occupants. Air sealing can be done in half the time with half the pain, and you can easily get to places you couldn’t reach by crawling around. If possible, make new attic access doors on the exterior of the shell. Outside access to the attic eliminates big interior holes in the interior that are complex to seal and insulate. Outside access will provide future service without disturbing the occupants.
- Building needs new siding. The exterior skin is the easiest envelope plane to air seal. This is also an opportunity to install continuous insulation and possibly a rain screen. If you are doing only three walls, insulate them and leave the others for a future project. If the building is old and there is no building paper behind the siding, you cannot insulate the wall cavities. The siding must come off (Big Opportunity!). Air sealing and new wrapping are needed to prevent moisture from wetting the insulation. This is also a time to pay close attention to vapor drive and condensation traps in the entire wall assembly.
- Building needs new windows. There are more high-performance windows coming into the market every year. Keep up on the innovations and don’t necessarily use the windows you used on your last job. If you wish to learn more about high-performance windows, or have any other high-performance building queries, check out the NAPHN.
- Crawl space. Most clients have no idea how funky or scary their attic and crawl space are. Take pictures and show them what they are living with. Explain how air and moisture from the crawl space enters their living space, and how you can stop that from happening.
- Combustion appliances. Explain to clients how the combustion appliances can affect their health and IAQ. Order an envelope combustion safety test.
- The biggest opportunity to go deep is if the client is looking for good IAQ and a thermally comfortable environment. For the designer or builder, this is an open door for your sales pitch.
Heat Recovery Ventilator or Mechanical
If the client’s goal is to make the building super airtight over time, you have to think about the makeup air system. Mechanical ventilation (exhaust fan only) is simple and cheap, but it requires your building to pull in outdoor air at ambient temperatures and moisture, while expelling expensive heated or cooled air. I like the controlled and balanced indoor pressure of an HRV or an energy recovery ventilator (ERV). If the client cannot afford the $10,000 for a whole-house HRV in stage 1 or 2 of a retrofit, make sure to provide space to install it at some later date. I plan the duct route and make sure there are no obstacles to a future install. Keep in mind that all the traditional appliances that extract air from the envelope, including the clothes dryer, will be become obsolete. This needs to be part of the sequential planning. There are more and more choices for HRVs and ERVs coming out of Europe that are versatile for retrofit work, so you have to do a lot of homework to prepare for a future HRV or ERV system.
Upgrading your client’s hot-water system can be done sequentially as well. You can design and build a hot-water production plant on-site over time.
In terms of energy use, I favor making hot water on-site with solar thermal and coupling it with some kind of heat exchanger or heat pump. This will not be enough for a net zero energy home, so you will have to outsource the remaining energy demand using gas, electricity, or fuel oil.
I am currently installing a combination 4.5-ton heat pump for a four-unit apartment to supply domestic hot water only. While this would not comply with maximum Passive House energy demands, the plan is to greatly reduce the electrical load or to zero out the electrical load later with PV and solar thermal added to the roof. I gave the client a solar-thermal option, but he chose the heat pump. One year ago, the apartment needed a new roof. After taking off the old tar and gravel, I air sealed the entire roof and staggered 2-inch extended polystyrene sheets under 4-inch structural insulated panels, above the R-19 fiberglass cavities. The sidewall is near the end of its life. The sidewall is slated to get new windows, air sealing, and continuous insulation. The crawl space is in line for upgrade at some date as well. In the end, if all the phases are implemented, the heating and cooling loads on all four units will be very low.
Whichever system you use, make sure it will synchronize or change out easily with your tight building shell of the future.
Combustion appliances do not mix well with high-performance shells.
As the building gets more airtight over time, you must consider moving the combustion appliances out of the building envelope, or using sealed-combustion appliances, or getting rid of them altogether, or some combination thereof. The logistics of how this can be done and what the new system will be over time must be built into a long-term strategy. If you do it right, your new high-performance house, depending on its size and on the occupants’ lifestyle, could eventually require one-quarter of its present heating-and-cooling load as the case may be, and that 100,000 Btu furnace would go the way of the modem and the vacuum tube.
Find out more about the American Passive House Network.
For information about THERM software, e-mail THERMHelp@lbl.gov.
Contact the author at firstname.lastname@example.org.
The Last Word for Now
Here are some tips:
- Put new high-performance windows on with screws and tape so they can be reused later when the house gets new siding.
- You may not be the person who does the next phase. Make sure you leave a manual behind with the client that explains everything you have done and what you intended to accomplish in the future.
- You have to work with tradespeople, architects, and engineers who are enthusiastic about high-performance buildings and understand the basic principles of building science.
- If the people you work with are not willing to be part of the change, find people who are. Time for sustainable building is running out.
- Completing any of these long-term, cost-effective, and one-time energy upgrades with the best materials and a qualified and inspired team of contractors will yield a better building. Completing them all will reward the client with extremely low heating and cooling loads. But the biggest, and most appreciated, benefit will be superb thermal comfort and IAQ.
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