When it comes to spray foam, there isn’t a single "best" type for the entire house. Instead, experienced installers often recommend a hybrid approach. They typically use closed-cell spray foam in areas like basements and rim joists where moisture resistance and structural support are needed. For attics and walls, open-cell foam is frequently the better choice due to its ability to expand, fill irregular spaces, and offer excellent sound reduction at a lower cost.

This guide breaks down why this tailored strategy works so well for the unique climate of southeastern South Dakota. Drawing on insights from professionals in the field, we’ll look at the specific properties of each foam type, where to apply them in your home for the best results, and what factors you need to consider before investing in an insulation upgrade.

The Two Types of Spray Foam Explained

At a basic level, all spray foam insulation is created by mixing two chemical compounds that react and expand. The difference between open-cell and closed-cell lies in the structure of the bubbles, or "cells," formed during this reaction.

• Open-Cell Spray Foam: The cells in this foam are not completely encapsulated. Think of it like a sponge. This structure makes the foam softer, more flexible, and allows it to expand significantly upon application, filling every crack and crevice. It’s a fantastic air barrier but not a water vapor barrier.
• Closed-Cell Spray Foam: Here, the cells are completely sealed and packed tightly together. This makes the foam rigid, dense, and impermeable to both air and water. It offers a higher R-value per inch and can even add structural integrity to walls and roofs.

Here’s a direct comparison of their key characteristics:

Why the Sioux Falls Climate Demands a Specific Strategy

The weather in Sioux Falls isn't gentle. With winter temperatures often dropping below zero and summer humidity creating a sticky environment, a home’s insulation has to perform double duty. It must keep warm air in during the winter and hot, moist air out during the summer. Studies show that proper professional air sealing and insulation can reduce heating and cooling costs by an average of 15%.

In a cold climate like South Dakota's, preventing heat loss is the top priority. The high R-value of closed-cell foam makes it an obvious choice. However, moisture management is also a big deal. As warm, moist indoor air moves towards the cold exterior sheathing in a wall cavity, it can condense, leading to potential mold and rot. Closed-cell foam's low permeability stops this vapor drive in its tracks, making it ideal for certain applications. Open-cell foam, on the other hand, allows any moisture that gets into the wall cavity to dry out, which can be beneficial in other areas of the house.

A Room-by-Room Guide for Your Home

Applying the right foam in the right place is how you get the most out of your investment. Here’s how professionals often map out a Sioux Falls home.

Attics and Roof Decks

For most attics, open-cell spray foam is the preferred material. Its high expansion rate is perfect for sealing the complex angles and gaps around trusses and rafters. It creates a complete air seal, stopping the "stack effect" where warm air rises and escapes through the roof. This is a primary source of energy loss in many homes, accounting for up to 25% of a home's heat loss.

When creating an unvented or "hot roof" assembly, it's important to ensure the foam is applied directly to the underside of the roof deck. This approach brings the attic space into the conditioned envelope of the home, which can help stabilize temperatures and protect any HVAC equipment located there.

Basements, Foundations, and Crawl Spaces

This is where closed-cell spray foam truly shines. Basements in our region are prone to moisture from the surrounding soil. Closed-cell foam is not only waterproof but it's also recognized by FEMA as a flood-resistant insulation material. Applying it to foundation walls and rim joists seals off the main entry points for cold air and dampness. Its rigidity can also add a bit of strength to the structure.

Exterior Walls

The choice for exterior walls depends on the construction and your goals.

• For New Construction or Gut Renovations: Closed-cell foam provides the highest possible R-value in a standard 2x4 or 2x6 wall cavity. This maximizes thermal performance without needing to build thicker walls.
• For Budget-Conscious Projects: Open-cell foam is a great option. While its R-value is lower, it still provides a superior air seal compared to traditional insulation like fiberglass batts. It effectively stops drafts and provides excellent soundproofing between rooms and from outside noise.

Things to Consider Before Making a Decision

Choosing  spray foam isn't just about picking a type. You need to look at the bigger picture of your home and your budget.

• Your Budget: Closed-cell foam can cost significantly more than open-cell. A professional evaluation can help determine where to use the premium product for maximum impact and where the more affordable option will suffice.
• Your Home's Age and Condition: Older homes often have irregular framing and more air leaks. The expansive nature of open-cell foam might be perfect for sealing these old-construction quirks. But if a basement wall has moisture problems, the water-blocking power of closed-cell is non-negotiable.
• Ventilation Needs: Spray foam creates a very airtight home. This is great for energy efficiency, but it also means you may need to address mechanical ventilation, such as an air exchanger (HRV or ERV), to maintain healthy indoor air quality.
• Long-Term Goals: Are you planning to stay in the home for 30 years or sell it in five? The higher upfront cost of closed-cell foam delivers greater long-term energy savings, but the payback period is longer.

Questions People Ask About Spray Foam

Can I install spray foam insulation myself?

This is strongly discouraged. Spray foam insulation involves a chemical reaction that requires precise temperatures, pressures, and mixing ratios. Professionals use specialized equipment and wear extensive personal protective equipment (PPE). A DIY job can result in poor performance, off-gassing, and even safety hazards.

How long does spray foam last?

When installed correctly, spray foam insulation should last for the life of the home. Unlike some other insulation types, it doesn’t sag, settle, or degrade over time. It’s a permanent solution that becomes part of the building’s structure.

Is spray foam safe after it's installed?

Yes. Once the foam has fully cured, which typically takes about 24 hours, it becomes an inert plastic. During this curing period, the home should be well-ventilated, and homeowners should not be present. A professional installer will ensure the site is safe before, during, and after application.

Does spray foam help with pests?

Because spray foam creates a complete air seal and is a rigid, dense material (especially closed-cell), it makes it much harder for insects and rodents to enter a home. It's not a food source for them, and they can't easily burrow through it.

What happens if there is a roof leak?

This is a valid concern. With open-cell foam, its sponge-like nature means water will likely pass through it, making a leak visible on the ceiling below. Closed-cell foam, being waterproof, will block the water. This can sometimes make a leak harder to detect, which is why it's important to have a well-maintained roof regardless of your insulation choice.

The Best Plan Is a Custom Plan

Ultimately, the most effective insulation strategy for a Sioux Falls home is not a one-size-fits-all solution. It involves a hybrid approach, using both open-cell and closed-cell spray foam where they make the most sense for moisture control, thermal resistance, and cost. By creating a custom plan, homeowners can balance performance and budget to achieve long-term energy savings and a more comfortable living space.

Getting a Professional Assessment

The only way to determine the ideal insulation strategy for your specific home is through a professional evaluation. Experienced installers can perform an energy assessment and recommend a tailored solution that fits your property's unique needs and your budget. For homeowners in the Sioux Falls area looking for this kind of expert advice, the team at FOAMWORX Spray Foam Insulation provides detailed evaluations and can be reached by phone at (507) 407-0678 or via email at [email protected] to schedule a consultation.

Reviewer: Jacob Wright has 6 years of experience in spray foam insulation. He reviewed this content and made sure it focused on the real decisions homeowners deal with every day.