Ask the Expert: Why does building science matter when you weatherize your home?

June 7, 2023 | 6 min read
Matt Sharpe, senior engineering consultant

A “building science” approach to weatherization recognizes each home is a unique system. This can improve the health, safety, and durability of any weatherization effort. And it identifies the materials and approaches that best meet your weatherization goals.

To learn more about this “home as a system” approach, we turn to Matt Sharpe. He's a senior engineering consultant for Efficiency Vermont working with customers to optimize their buildings and energy use for more than 20 years.

What does treating the home as a system mean?

This approach means understanding how parts of your home work together. And how improvements in one area may affect other parts of your home system.

Windows and doors, attics and basements, insulation, and heating systems all interact. When done correctly, weatherization helps these parts work together. When they work together, they improve your comfort and safety. They can also control moisture and save you money on energy.

Insulation and air sealing help reduce energy waste and lower costs. When you tighten your home, you improve its thermal envelope. But then you also have to pay attention to moisture and adequate ventilation. Moisture in your home is common, but too much can lead to dangerous mold and rot. And different materials will handle air flow, heat, and moisture in various ways. You’ll need to consider all of these when deciding how to insulate and weatherize your home.

Why is addressing moisture so important during weatherization?

The right amount of moisture helps keep your home free from mold, rot, and bacteria. It can also boost comfort by avoiding “too dry” or “too moist” conditions.

Drying out a damp or wet basement can significantly help control moisture in your home. You can install gutters and improve the grading around your foundation. That helps improve water runoff from the ground and from your roof. You may also need to add perimeter drains inside your basement to help channel water to a sump pump.

You can also cover dirt floors in your basement or crawlspace with durable plastic vapor barriers. And you may be eligible for a rebate on a new energy-efficient dehumidifier. This can also help control moisture and improve comfort.

What are other ways to control moisture?

Leaky homes are often thought to be “too dry.” That’s because cold drafts bring in dry winter air that replaces the warm, moist air that leaks out. Insulation and proper air sealing can help keep moisture from leaving your home. That prevents it from reaching cold areas where it can condense and cause problems.

Attics are easy targets to seal and insulate. You can do the same for basements, crawlspaces, and heating ducts. Windows and doors can also be easily sealed. You can use weatherstripping, storm windows, or window inserts. And don't overlook sealing around window trim, baseboards, wood paneling, and wall outlets.

How do you strike a balance between “too dry” and “too wet” in a home?

Leaving a house leaky wastes energy and allows warm, moist air to condense inside. That’s why it’s important to stop the air. Sometimes, installing mechanical ventilation can be the best way to strike this balance. As weatherization experts like to say, “Build tight and ventilate right.”

Efficiency Vermont offers incentives for moisture control through our whole-home weatherization program. This can include moisture management practices like installing vapor barriers over dirt floors. It can also mean installing exhaust ventilation systems. And it checks for proper venting from bathrooms and clothes dryers.

What do folks need to know about control layers?

Control layers in walls or ceilings are poorly understood parts of weatherization. Some assume “insulation” takes care of air, moisture, and heat issues. Sometimes, it does … but other times, insulation can only achieve one or two of those goals.

Talk to your contractor about controlling all three. There are many factors to consider, but here’s a common one: spray foam insulation.

Building codes say closed-cell spray foam can be used on unvented ceilings. That's because it's able to limit air, heat, and moisture flow. But open-cell spray foam does not limit moisture flow on its own. So open-cell spray foam can only be used on unvented ceilings with other control layers that address moisture. Using the wrong combination of insulation and control layers can cause problems for any weatherization. That's because it may fail to address the moisture, air, and thermal needs of your home system. This can all lead to incomplete weatherization or negative impacts on your home.

There's a lot to know about building assembly, so talk to an Efficiency Excellence Network contractor. They'll help you understand your project. And how it will incorporate vapor, air, and thermal barriers.

What does weatherization have to do with health and safety?

The “home as a system” approach also includes health considerations around the materials used during weatherization. Adding one of the four common types of insulation can be a great do-it-yourself project. Rigid foam or fiberglass batting can be installed without special equipment or training. Others, like cellulose, require specialized equipment and are better left to the professionals.

Spray foam insulation has additional health considerations. The chemicals in the foam are activated and cured on-site. So, it should only be installed by a qualified professional. It’s also possible someone in your home, could be sensitive (or become sensitized) to components of the spray foam. That can happen during application or afterwards.

Talk with your contractor about what best meets your weatherization goals. Discuss the project with multiple contractors. Learn about the materials and approaches they'll use. Ask for the specifications of those materials. And ask for the MSDS (Material Safety Data Sheet) for the materials used in your home. And you should discuss what happens if a product is installed incorrectly.

If you choose to use spray foam insulation in your home, you'll have to be out of your home during and after its applied. Talk to your contractor about how long you should be out. That time can range between 24 and 72 hours. Read the EPA's guidance about spray foam insulation. And make sure you understand the health risks and ventilation requirements of the spray foam used in your home.

Efficiency Vermont does not promote or influence what type of insulation contractors use. So long as it meets the minimum program requirements, the area is properly air sealed, and state energy code for R-values are met. Working with Efficiency Vermont and an Efficiency Excellence Network partner can help ensure your contractor follows the manufacturer’s guidelines for installation. 

When should you call an expert?

Any product installed that doesn't account for ventilation, or air and moisture control, can have negative impacts. The same is true if it's installed by someone who isn’t trained. The “home as a system” approach addresses moisture, exhaust, and ventilation, as well as health and safety, in all projects.

Comprehensive weatherization addressing these concerns is eligible for Home Performance with ENERGY STAR program rebates and Home Energy Loan financing. Efficiency Excellence Network members certified through the Building Performance Institute can recognize these potential issues. And they can include remedies in the scope of their weatherization work. 

At the end of the day, each home and each project is unique. It’s important to talk with trained professionals to evaluate your home. That will help you understand your home's specific needs. And then you can choose the available options to achieve your weatherization goals. 

Want to learn more? Contact Efficiency Vermont

Our Energy Advisors can answer your questions, connect you to resources, and provide virtual home energy visits.