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Green Basics

Remodel Project: Weatherization

Air sealing, insulation improvements, and equipment upgrades save energy dollars

Tuning up a house’s performance can be quick and relatively inexpensive
Weatherization is an opportunity to improve energy efficiency without extensive modifications to the structure of the house. It should involve a whole-house systems approach that considers energy efficiency, combustion safety, moisture management and building durability.

Test for leaks, make improvements, then test again.
A whole-house systems approach to home performance generally includes a battery of before-and-after tests that check for air leakage and measure the performance of the heating, cooling and ventilation systems. Hiring a home energy auditor is a good first step for evaluating the performance of a house. An auditor will typically use a blower door, Duct Blaster and infrared camera, among other tools, both to quantify and qualify the energy wasting areas of a home. After the testing, the remediation work begins, and when it is finished, the auditor comes back to retest. The results of his second visit tells you how well the improvements are working to save energy. (For more information on blower-door testing, see “Blower Door Basics.”)

Air sealing is the most important
Contrary to what some homeowners might have read or been lead to believe, replacememt windows and more insulation are not the first steps toward a more efficient house. Before any other improvements are made, air leaks must be sealed. Adding insulation to a very leaky house is counterproductive, and it makes it harder to find the leaks in the future with all the new insulation piled on top.

Will it take more than weatherizing to make the house efficient?
Some houses may not be worth energy efficiency improvements until structural problems or serious site or plumbing problems are addressed–problems that may be beyond the expertise of a weatherization contractor. Concerns may include mold in a bathroom that doesn’t have a fan or an operable window or old windows that won’t are stuck or won’t close completely; serious water leaks in the basement; or weakened foundations or structural framing.

Informed homeowners use less energy
Some energy problems aren’t directly related to the building but to the people who live there. If homeowners leave incandescent lights on 24 hours a day, won’t use exhaust fans in bathrooms and the kitchen or leave windows open in winter, homeowner education may be just as important as anything else.A Weatherization case study:



Building envelope

Conduct blower-door tests before and after the project, along with room-to-room pressurization tests. Perform air-sealing work in the basement and attic. Use infrared imaging to find places where insulation is inadequate. If required, weatherstrip doors and windows. If required, add insulation in the attic, using formaldehyde-free insulation.


In houses that have forced-air heating systems, test ducts for air tightness. Check the operation of the combustion equipment for efficiency and combustion safety. Install smoke and carbon monoxide alarms if they’re not already present.


Replace incandescent bulbs with compact fluorescents.


Insulate hot water pipes and, if necessary, the water heater.


Case Study

First evaluate, then remediate

Comfort and high energy costs were the problem

The Manuses’ home suffered from a variety of common problems, including an uneven heating system that left them uncomfortable on cold winter days, and their energy costs were particularly high given the house’s moderate square footage and San Francisco’s temperate climate.

Prior to the renovation, monthly energy bills averaged $350, even with the thermostat below 65°F on cold days. By setting priorities based on an initial comprehensive home-performance evaluation, Sustainable Spaces created a phased plan to maximize the client’s return on investment in dollars as well as in health and comfort. The Manus family now has a comfortable home with clean air and significantly lower energy bills.

Design Notes

TEST IN, TEST OUT. Weatherization experts know the value of using scientific equipment to evaluate a house’s many systems. The beauty of testing is that it is carried out before energy improvements are made and then again after the remediation work is completed. The second round of test verifies the efficacy of the improvements.
Image Credits: Matt Golden/REGREEN

Reduce the heating load, then make other reductions

To address the homeowners’ goals and concerns in a practical, cost-effective manner, Sustainable Spaces started with a detailed performance inspection, including insulation, outdoor air infiltration, duct leakage, heating and cooling load and systems, moisture issues, water heating, lighting, appliances, and general durability, to evaluate the home as a system.

Based on the findings, the team prescribed a list of priorities targeting those issues that resulted in uncomfortable rooms, unhealthy air, and wasted energy. The project started with building fundamentals—envelope-sealing and weatherization, duct-system redesign and replacement, additional attic insulation, and a lighting retrofit.

By first reducing the home’s energy load, the team significantly reduced the size of major system improvements, including a new hydronic air handler and air filtration system, a new high-efficiency hot water heater (now the home’s primary heat source for domestic hot water and space heating), and a demand recirculation pump for convenience and water conservation.

Using energy modeling software to determine the amount and balance of airflow to each room and to design ductwork to ensure that the system is properly balanced, the team took the guesswork out of making the home comfortable and efficient. Finally, after completing remediation, every step was tested and commissioned to ensure that the home performed as designed.


LEAKY DUCTS CAN ACCOUNT FOR 1/3 OF THE HEATING BILL. Insulated ductwork that is properly sealed with mastic goes a long way toward sealing leaks. Replacing the ducts in this California house with insulated ones helped decrease the heating load by 25%.
Image Credits: Mark Piepkorn/REGREEN

Key systems

General Design and Construction

*Home engineered for balanced, comfortable heating

*Air quality improved through duct and envelope sealing

*Airborne pollutants extracted with high-efficiency filtration

*Energy consumption reduced through heating and electrical load reduction

Building Envelope

*Blower-door test to identify amount of air leakage; building envelope sealing to achieve compliance with ASHRAE 62.2 requirement for hourly fresh-air exchange

*Noninsulation contact-rated can lights replaced insulated models

*12″ of blown-in cellulose installed in attic to achieve R-38 or greater insulation


*Duct-blaster test to identify amount of duct leakage (before, 360 CFM25; after, 76 CFM25; leakage reduction of 79%)

*Total heating load reduced from 50,600 btu to 38,200 btu, a decrease of 25%

*Ducts replaced with properly designed and installed R-6 wireflex ductwork

*System engineered based on ACCA Manual J load calculations, Manual D (ducts), and Manual S (sizing of equipment)

*System commissioned to ensure airtight ducts, proper static pressure, and proper room-by-room airflow

*Existing furnace replaced with properly sized hydronic air handler

*Energy Star programmable thermostat

*High-efficiency air filtration system

*New high-efficiency, fast-recovery water heater with side taps for hydronic heating

*Insulated hot-water pipes

*Demand recirculation pump to conserve water and energy and reduce time for hot water delivery


*Homeowners instructed on proper usage of new equipment

*Programmed thermostat to balance comfort and efficiency


AFTER SEALING AND INSULATING, SMALLER HVAC SYSTEMS ARE POSSIBLE. Weatherization can substantially reduce a house’s heating and cooling loads. After completing remediation work on this California home, the weatherization contractor determined that a domestic water heater could supply enough heat for the whole house.
Image Credits: Peter Yost/REGREEN

A solution for heat and hot water

The homeowners originally wanted a tankless hot water heater, but their home-performance inspector recognized that large gas bills and lack of comfort and indoor air quality were their underlying concerns. Although tankless water heaters can be a good fit in some situations, a systems-based approach revealed that a high-efficiency, power-vented storage water heater was more economical and appropriate for the new combined domestic hot water and space-conditioning system.


Teams and processes

Sustainable Spaces takes a holistic approach, evaluating a home’s performance as a dynamic, interdependent system in order to identify specific steps to improve indoor air quality, comfort, and energy efficiency while always keeping the homeowners’ objectives in mind. A licensed general and solar contractor specializing in home testing and building performance remediation for existing homes, Sustainable Spaces sought first to understand the owners concerns and behaviors. Combined with quantitative data about the home’s performance, this allowed Sustainable Spaces to tailor solutions to their goals, budgets, and priorities while creating an efficient, comfortable, and healthy green home.

Location: Castro Valley, California

Homeowners: Kathy and Mike Manus

General Contractor: Sustainable Spaces Inc.

Area affected: 1,800 ft2


Sustainable Spaces created a roadmap for this project based on multiple phases, focusing first on those items with the biggest impact but within the framework of the client‘s long-term goals. A phased approach fitted the Manuses’ budget while achieving measurable results. By focusing improvements on air quality, comfort and environmental impact in addition to energy savings, Sustainable Spaces was able to get buy-in from the client for more integrated solutions.

Bird’s-Eye View


Remodeling Details



green points

LEED for Homes Weatherization, as part of a gut rehab project, may make a project eligible to earn LEED for Homes certification. Two key elements required are a quality insulation installation and good air sealing.

NGBS-Remodel Refer to the ANSI standard and follow the appropriate path based on conditioned floor area involved in the remodeling or addition project and the year in which the original home was built. NGBS

One Comment

  1. Dave Tool | | #1

    Power Tools
    Absolutely make sure you seal those air leaks first and foremost. For some reason homeowners I work with tend to discount the amount of heat lost through tiny cracks and crevices without realizing these miniature leaks can completely undo all the combined weatherizing efforts you've put in to the rest of the house!

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