# Presentation: 118326

## Evaluation of Homes Built to the New Minnesota Energy Code

- Bruce D. Nelson, P.E.
- Minnesota Energy Office

## 2000 Minnesota Energy CodeMajor New Features

- Air tightness
- Rim joist air/vapor barrier
- Attached garage air barrier
- Mechanical ventilation
- Air quantity & distribution
- Protection against backdrafting

## Objective of study

- To examine the effectiveness of energy code features in new homes
- To determine occupant understanding and practice of home maintenance
- To compare performance of homes built to 3 different energy codes
- NOT designed to evaluate compliance with the energy code

## Study design

- 43 randomly selected homes in Twin Cities metro area
- 21 “Category 2” homes
- 17 “Category 1” homes
- 5 Chapter 7672 homes

## Performance Indicators Studied 

- Effectiveness of Building Envelope
- Ventilation and Mechanical System Effectiveness
- Indoor air quality
- Energy Use
- Comparison of 3 codes & years built
- 1994 code / Category 1 / Chapter 7672
- 1994 / 1998 / 2000

## Envelope Detail Problems Found

- Cantilevered floors over garages
- “Bump-outs” for entertainment centers and fireplaces
- Rim joist penetrations
- Shower and tub enclosures along exterior walls
- Additional framed cavities adjacent to exterior walls and attic bypasses

## Attached Garages

- Air leakage from floor cavities situated over attached garages
- Simple practices could remedy this situation

## Envelope Bump Outs

- Framed fireplace cavity on an exterior wall

## Rim Joist Areas

- Unsealed rims make for cold floors and may contribute to stained siding

## Shower and tub enclosures

- Cold could lead to surface condensation and mold, as well as accumulation of water in the wall cavities

## Additional Framed Cavities and Attic Bypasses 

- Light fixtures, speakers, etc.
- Interior soffits
- A leading cause of ice dams

## Ventilation System Performance

- Mechanical ventilation systems meet or exceed the minimum airflow requirements of the new energy code.
- Indoor air appears to be adequate
- by measurement of humidity, and
- satisfaction expressed by home owners

## Balanced mechanical ventilation (HRV/ERV) systems (25 homes)

- Adequate airflow through the in most cases - However, several minor installation problems
- Only 22% of these homes had controls to  distribute ventilation air out of the ductwork
- 32% of HRV/ERV systems were not balanced
- 7% of these homes had improperly placed exterior hoods
- 30% had no condensate trap

## Exhaust-Only Ventilation Systems (3 homes)

- All had adequate air flow (one measured 69 cfm for a required 70 cfm flow)
- Each of the systems had controls to distribute fresh air

## Cost of ventilation systems

- Balanced mechanical ventilation systems - $2200 to $2800
- Exhaust-Only - $300 to $500
- Other reports have compared overall cost/benefit of these approaches

## Indoor Air Quality

- Indoor winter relative humidity is being maintained at healthy levels
- Because these homes are tighter, there is less potential for entry of indoor air pollutants
- Potential for backdrafting is much lower for 2000 code homes than 1994 code homes

## Potential for spillage or backdrafting of combustion appliances 

***Potential *****for spillage or backdrafting of combustion appliances**

## Slide 18

## Building practices that needed to change

- Rim Joist
- Space Heating
- Domestic Water Heating
- Combustion air
- Ventilation
- Make-up Air

## Relative Energy Consumption

## Overall Cost to Comply with the New Energy Code

- added $1.00 to $1.15 per square foot (approximately 1% of the total cost of the home)
- Considering current energy cost only, a simple payback of about 9 years
- Additional benefits to occupant health and building durability would shorten this payback period

## Recommendations for Energy Code Writers

- The new features of the Minnesota energy code do work:
- Homes are tighter
- Potential for backdrafting is significantly reduced
- Energy Performance appears to have improved significantly

## Complete report available at www.commerce.state.mn.usEnergy / Specially for Builders page

**Evaluation of Homes Built to the New Minnesota Energy Code**