The purpose of this guide is to provide useful examples of high performance retrofit techniques for the building enclosure of wood frame residential construction in a cold and somewhat wet climate. The examples demonstrate effective management of liquid water (rain and ground water), airflow, water vapor flow and heat flow. Retrofit ventilation approaches are reviewed because mechanical ventilation is taken to be a necessary component in high performance buildings. This guide does not address mechanical heating, cooling or water heating systems beyond outlining basic combustion safety measures.
Existing homes present an incredible variety of conditions. The variations of building techniques over time and across different regions combined with the inherent individuality among builders lends to a mind-boggling variety of configurations in existing housing stock. Rather than try to encompass all of the possible solutions responding to each of various existing conditions, this guide details a limited number of options for deep energy retrofit of common configurations found in wood framed New England homes. Through its experience in guiding high performance retrofit projects, BSC has found the solutions in this guide to be applicable to the vast majority of circumstances. Some retrofit projects will require solutions that are not described in this guide.
Introduction to DER
Massachusetts gas and electric utilities are sponsoring a limited Deep Energy Retrofit (DER) program to provide support to customers who wish to incorporate a deep energy retrofit as part of regular maintenance or remodeling activities. This guide is intended to provide the technical framework for this program.
The guide is composed of two parts. Part 1 explains fundamental DER concepts and outlines prerequisite measures for DER projects participating in the DER program. Part 2 provides specific technical guidance for the high performance retrofit of residential building enclosures. This technical guidance is presented in the form of illustrated schematic details accompanied by explanatory text and notes.
What is a Deep Energy Retrofit?
Deep Energy Retrofit (DER) refers to the retrofit of the building enclosure and other building systems in a way that results in a high performance building. A successful DER will result in very low post-retrofit energy use and also provide benefits to building durability, comfort, and indoor air quality (IAQ). DER may also increase the usable space or amenity of a building. For example, retrofitting the thermal enclosure of attic or basement spaces may make it possible to expand finished living area into these spaces where it had not been possible before.
DER achieves performance on par with best-in-class new construction. That is, the performance resulting from DER will exceed new construction code standards and rival the performance of high-performance new construction. In fact, many of the techniques and strategies illustrated in this guide have been adapted from proven high-performance and super-insulation techniques used in exemplary new construction projects.
What levels of thermal performance constitute “high performance”? Years of helping builders, developers and designers to reach high performance goals involving tens of thousands of homes has led BSC to identify a set of performance targets for major building enclosures components. The set of performance targets is often expressed as “1.5-5-10-20-40-60” where 5 refers to the target R-value for windows and doors; 10, the target R-value for slabs; 20, the target R-value for foundation wall assemblies; 40, the target R-value for wall assemblies; 60, the target R-value of the attic/roof assembly; and, 1.5, the target air tightness of the building enclosure system measured in terms of air changes per hour at 50 Pascals (ACH50). These targets provide a framework for identifying high performance enclosures—enclosures that reduce the heating and cooling load of the enclosure system to a practical minimum. When we want to describe the performance goals for a DER enclosure, it suffices to use the expression “1.5-5-10-20-40-60”. These are the levels of thermal performance that are represented in the guidance and illustrations contained in this guide.
While the enclosure measures in a DER are aimed at reducing heating and cooling loads, DER also addresses the mechanical systems that serve those loads. A comprehensive DER will also replace older and standard efficiency heating, cooling and water heating systems with efficient equipment configured to provide efficient performance.
Finally, since the essential purpose of the enclosure system as well as the heating and cooling systems is to allow users of a building to control the indoor environment, we cannot neglect the fundamental importance of air quality in the indoor environment. At the most basic level, we need to think of air quality as it pertains to life safety. It is also important to provide for control of moisture and dilution of contaminants through ventilation. A DER must provide robust combustion safety as well as effective mechanical ventilation (see Prerequisites for High Performance Enclosure Retrofit below).
A DER project need not be a comprehensive building enclosure renovation project. In fact, most DER projects address only one or two major components of the enclosure such as the roof or walls and windows or basement walls and slab. As a matter of health, safety and fundamental performance, the prerequisite for any DER project – even limited DER projects – will be to ensure combustion safety and to provide the means for effective ventilation.
Why Deep Energy Retrofit?
As the name would imply, DER measures are intended to provide deep reductions to energy use. Energy savings are not the only reason to undertake a DER, however. A DER project typically provides many benefits beyond energy savings. A successful DER will bring important improvements to comfort within the home and to durability of components affected by the DER. A DER project may be undertaken in pursuit of passive survivability, to reduce carbon footprint, to eliminate maintenance burdens, or to make strides toward energy independence. DER measures may be incorporated into projects bringing long-sought aesthetic updates (such as installing new siding) or improvements (such as remodeling a basement) to a home. Persons undertaking retrofit projects do so for many different reasons. And DER projects are capable of delivering benefits responding to a variety of different objectives. In considering the investment in DER, it is only logical that the comprehensive costs for the project be evaluated relative to all the benefits. Although there may not be specific quantitative methods to apportion costs among various benefits, the cost should be recognized as shared among various benefits.
When is the time for Deep Energy Retrofit
The best time to perform a DER for a major building system is when repairs or renovations are needed for that building system. For example, a re-roofing project (made necessary by the existing roof condition) is likely to represent the best opportunity to provide a super-insulated roof and bring the attic into conditioned space. If homeowners desire to remodel and finish a basement space, DER methods can provide guidance for achieving high levels of performance while avoiding typical finished basement problems. The cost for superinsulation of exterior walls (for an existing home) is typically lowest when siding and trim are being replaced. In fact, even when facing the expense of re-painting an exterior, it is worth considering whether those resources might be directed toward a DER for the exterior wall that will essentially eliminate the need for painting for many years into the future.
One of the early participants in the National Grid Deep Energy Retrofit Pilot program observed that significant expenditures to replace (as in siding or windows) or renovate (such as a basement or attic) a building component essentially prevents that building component from receiving further performance improvement for the life of the component. In other words, once windows are replaced, a roof is re-roofed, or siding is re-moved and reinstalled on an exterior wall, it is very unlikely that these systems will be upgraded for a long time. Certainly, once the renovation or replacement has been implemented, the most cost effective opportunity for high performance retrofit is past.
This is why the DER program is designed to capture opportunities presented by typical home maintenance activities such as re-roofing, re-siding and remodeling or finishing basement and attic spaces. When resources are already allocated for repairs or renovations to a major building system to meet non-energy-related needs, the benefits of DER can be achieved at a relatively small increment.
What does a Deep Energy Retrofit mean for the existing building?
A DER causes a home to leapfrog well beyond the level of performance typical for current building practices. DER extends the useful life of the building or the building component by positioning it to perform, and perform well, for another 50-100 years.
What is important to keep in mind is that significant changes to the building enclosure will have profound effect on the dynamics of water, air, vapor and heat flow within the home. What may have worked before the retrofit – e.g. a leaking window where the water was able to dry through an uninsulated wall – may not work after the retrofit. By virtue of the fact that the building is standing and people are living in it, we can guess that the building is working. But we may not know exactly how it is working. So one must approach DER with a healthy dose of humility. It is important to be aware of ways in which the DER could change the dynamics of the building. Modifications to the building must aim to always reduce known risks.
Plan for the Future—DER and Long-term Goals for the Building
The DER project should be undertaken in the context of a comprehensive plan toward a longer-term vision for the building. Goals may not be defined in terms of energy savings alone. Comfort, usability of space, reduced maintenance, aesthetic improvement or changes, etc. may factor into the goals for the building. This guide is directed to homeowners whose long-term goals include high performance in terms of energy, health and safety and durability.
Like any plans for a major journey, the plan for the long term evolution home should include safe stopping points. Few will have resources to take on a comprehensive DER in a single project. For most, an incremental or phased approach is more feasible. This guide includes many suggestions for detailing measures in a way that allows later measures to pick up where earlier measures left off.
Owners of older homes encounter many reasons to make major repairs or improvements. A leaky roof, wet basement, tired siding, desire for more space or more usability of space, etc. might be the motivation for a major renovation project. Significant improvements, maintenance or changes to the building should be seized as opportunities to make steps toward the larger goals for the building. Otherwise, undirected expediency – addressing the most pressing needs with the least costly, least difficult means – might block opportunities thus making it more difficult, and ultimately more costly to progress toward long-term objectives. If there is a plan in place that charts a path toward long-term objectives, the odds are much better that even immediate problems can be addressed in a way that facilitates the next step toward the long-term goals. In plotting the best route to long-term objectives, the order of changes does matter. For some typical building problems or items on the long-term “to do” list, a DER project can be used as a means to address the issue. Other typical problems or potential problems must be addressed before undertaking a DER project.
Prerequisites for High Performance Enclosure Retrofit
Changes to the building enclosure will have a significant impact on the dynamics of water, air, vapor and heat flow within the home. Upgrades to the mechanical systems will also affect these dynamics Certain measures should be implemented prior to or as part of any DER project to ensure that these changing dynamics do not have negative ramifications for health and safety. These prerequisite measures for DER projects are outlined below. The measures relate to:
- Remediation of existing hazardous conditions,
- Combustion Safety, and
- Indoor air quality.
The measures described to address indoor air quality include mechanical ventilation and soil gas control. These are, by no means, the only means to ensure good indoor air quality. However, effective mechanical ventilation and soil gas control are essential aspects of the building (as contrasted to furnishings, equipment, materials, etc. that people might bring into a building) that provide the occupants a means to control contaminants and respond to indoor air conditions.
Remediate hazardous conditions
Prior to embarking on a DER project, it is important to remediate any hazardous conditions that will be affected (e.g. exposed or aggravated) by the planned DER work. Also, it is wise to ensure that there are not more serious problems lurking. A DER project – however worthy the goals may be – should not divert resources from where they are more urgently needed. Before embarking on a DER project, inspect and assess the building for:
- Structural integrity of frame and foundation,
- Safety and serviceability of the electrical system,
- Presence of hazardous materials (e.g. lead, radon, asbestos),
- Roof or plumbing water leaks,
- Rot or decay in framing, and
- Insect/pest damage/activity.
The structural system must be structurally sound before high performance retrofit work can begin. Similarly, the electrical system must provide basic electrical safety. Ideally, the electrical system would be brought up to date with current code and brought into alignment with current and projected building needs. The presence of knob-and-tube wiring will preclude retrofit of the enclosure. Hazardous materials that will be affected by the DER work or that may impact the indoor air quality must be remediated and/or removed. Any water leaks, either weather-related leaks or plumbing system leaks should be repaired prior to the DER work unless the DER work will remove the source of the water leak (e.g. if the roof surface or leaking section of plumbing is to be replaced as part of the project). Any framing that shows signs of rot or decay should be replaced. This frequently applies to the framing sill in older buildings. Also, any framing that exhibits pre-conditions for rot or decay – i.e. damp wood – will require remediation. Past insect/pest damage must be evaluated for impact on the building. Current insect/pest activity must be remediated before DER work can proceed.
Follow applicable laws and industry procedures for mitigation of hazardous materials. Engage the services of a qualified professional when needed.
Combustion Safety
Atmospherically vented (or naturally aspirated) combustion appliances are not appropriate for high-performance homes. With the exception of gas stoves and cooktops, combustion appliances in a DER home must be sealed combustion, induced draft, or power-vented. The best approach is to replace existing natural draft appliances with sealed combustion, induced draft, or power-vented equipment. These types of appliances are significantly more energy efficient than natural draft appliances. If replacing equipment is not feasible, draft inducer retrofit kits can provide fail-safe forced-draft performance for some types of combustion appliances. While this can address the combustion safety, adding forced-draft operation alone is unlikely to have a significant impact on energy performance.
Gas stoves and cook tops must be equipped with a range hood that is ducted to the outside.
Solid fuel-burning stoves (e.g. wood stoves and pellet stoves) if not equipped with a fail-safe draft inducer, must have a tight fitting loading door (and no permanent openings or leaks into the firebox or flue) and outdoor combustion air ducted to the firebox.
Solid fuel-burning hearth fireplaces require special treatment to be acceptable in a DER home. The following minimum measures are recommended for fireplaces:
- Flue liner in good condition (flue liner may need to be repaired or a flue liner may need to be installed in older chimneys).
- Air tight hearth doors.
- Outdoor combustion air ducted to firebox.
- Operable flue damper.
If the house has combustion appliances of any kind, carbon monoxide alarms complying with UL 2034 are required in close proximity to the combustion appliances and outside each separate sleeping area in the immediate vicinity of the bedrooms.1
Ventilation
Mechanical ventilation is an essential feature of high performance homes. Ventilation is needed for source control at the location of contaminant sources (e.g. kitchens, bathrooms, craft areas) as well as for distribution of fresh air and dilution of general contaminants. The distribution of fresh air and dilution of general contaminant is referred to as “background” or “wholehouse” ventilation.
The 2012 International Residential Code (2012 IRC) provides code minimum requirements for ventilation systems including the ventilation rate capacity for both background/whole house ventilation and source control ventilation. This guide aims to provide additional guidance toward meeting the high performance objectives of DER projects.
Source Control Ventilation
Controlling contaminants at the source is the most effective means to control contaminants in a home. Source control ventilation systems are exhaust systems that are located near a fixed contaminant source (or fixed contaminant source location) and vented directly to the outdoors. There can be a number of different areas in a home that represent a need for source control ventilation. This guide addresses those areas requiring source control that are common to all homes: kitchens and bath/toilet rooms. . .
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Footnotes:
- The combustion safety measures related to carbon monoxide alarms presented in this guide extend beyond the 2012 IRC by indicating alarms not just outside each separate sleeping area in the immediate vicinity of the bedrooms but also in the vicinity of the combustion appliance. The IRC also references “fuel-fired appliances” whereas this guide indicates carbon monoxide alarm requirements relative to any combustion appliance.