Improve Comfort and Energy Efficiency From the Ground Up
Your concrete slab may look solid and permanent, but without proper insulation underneath or around it, heat can escape through the floor and cold ground temperatures can make interior spaces uncomfortable.
Under-slab insulation helps create a thermal barrier between your concrete slab and the ground. Spray foam insulation can help reduce heat transfer, limit air movement, and create a more comfortable, energy-efficient space.
We provide professional spray foam insulation solutions for homeowners and builders throughout New Hampshire, Southern Maine, and Northern Massachusetts.
Ready to improve your home's insulation? Contact Weathertight Spray Foam for a free consultation and estimate.
What Is Under-Slab Insulation?
Under-slab insulation is insulation installed beneath a concrete floor or along the edges of a slab to reduce heat transfer between the building and the ground.
It is commonly used during new construction, additions, garages, workshops, and other projects where a concrete slab is being installed.
In colder climates like New England, properly insulating a slab can be especially important. New Hampshire's energy code includes specific requirements for slab insulation and slab-edge insulation.
Why Insulate Under a Concrete Slab?
A concrete slab is in direct contact with the ground, which can make the floor a significant pathway for heat transfer.
Proper insulation can help:
- Reduce heat loss through the floor
- Keep floors more comfortable
- Improve overall energy efficiency
- Reduce unwanted air movement
- Create a more consistent indoor temperature
- Help protect conditioned spaces from cold ground temperatures
- Complement other insulation and air-sealing measures
For heated slabs, additional insulation may be required depending on the construction and applicable building code.
Spray Foam Under-Slab Insulation
Spray foam can be used as part of an under-slab insulation system to create a continuous insulating layer beneath or around a concrete slab.
Because spray foam expands as it is applied, it can conform to the surface and help minimize gaps and areas where air can move around traditional insulation materials.
The appropriate insulation type, thickness, placement, and installation method depend on the building design, slab construction, climate zone, and applicable code requirements.
Under-Slab Insulation for New Construction
Under-slab insulation is easiest to install when it is incorporated into a project before the concrete is poured.
It can be considered for:
- New homes
- Home additions
- Garages
- Workshops
- Finished or conditioned slab spaces
- Heated floors
- Commercial and light-industrial spaces
Planning insulation before the concrete is poured allows the insulation contractor and builder to coordinate the entire floor assembly.
Slab Edge Insulation Matters Too
Insulation isn't only about what goes directly underneath the concrete.
Heat can also escape through the edges of a slab, which is why slab-edge insulation is an important part of an energy-efficient slab assembly.
New Hampshire's residential energy-code materials specify slab-edge insulation requirements based on climate zone and provide several approved configurations for extending insulation down and/or beneath the slab.
Our team can help determine the appropriate insulation approach for your project.
Under-Slab Insulation for New England Homes
New England homes experience significant temperature changes throughout the year. Cold winters can expose poorly insulated slabs to cold ground temperatures, while air leakage and inadequate insulation can make conditioned spaces harder to keep comfortable.
For projects in New Hampshire, Southern Maine, and Northern Massachusetts, proper insulation should be considered as part of the overall building envelope.
New Hampshire's current state building code was updated effective July 1, 2026, and building projects must comply with the applicable code requirements.
Who Can Benefit From Under-Slab Insulation?
Under-slab insulation may be appropriate for:
- New home construction
- Slab-on-grade homes
- Home additions
- Garages and workshops
- Heated concrete floors
- New foundations
- Conditioned outbuildings
- Renovation and remodeling projects where the slab is being replaced
The best insulation approach depends on the specific project. We can evaluate your plans and help determine what makes sense for your application.
Why Choose Weathertight Spray Foam?
At Weathertight Spray Foam, we understand the challenges that New England homeowners face when it comes to insulation and energy efficiency.
We provide spray foam insulation services throughout:
- All of New Hampshire
- Southern Maine
- Northern Massachusetts
Our goal is simple: help homeowners create more comfortable, energy-efficient spaces with professionally installed insulation.
Get an Under-Slab Insulation Estimate
Planning a new home, addition, garage, or other concrete slab project?
Talk with Weathertight Spray Foam before the concrete is poured. We can discuss your project, insulation options, and the appropriate installation approach.
Contact us today for a free consultation and estimate.
Frequently Asked Questions
What is the purpose of under-slab insulation?
Under-slab insulation helps reduce heat transfer between a concrete slab and the ground. It can improve floor comfort and contribute to the overall energy efficiency of a building.
Can spray foam be installed under a concrete slab?
Yes. Spray foam can be used as part of an under-slab insulation system when the product and installation method are appropriate for the specific application. The insulation system should be designed and installed according to applicable building codes and manufacturer requirements.
Is under-slab insulation required in New Hampshire?
Specific insulation requirements depend on the type of construction, slab design, climate zone, and applicable building code. New Hampshire's residential energy-code materials include requirements for slab-edge insulation and additional insulation for certain heated slabs.
Should a slab have insulation around the edges?
Slab-edge insulation is an important component of many slab insulation assemblies because heat can escape through the perimeter of the slab. The required configuration depends on the project and applicable code.
Can you insulate an existing concrete slab?
Under-slab insulation generally needs to be installed before the concrete slab is poured. For an existing slab, other insulation strategies may be possible depending on the structure and project goals.
Does under-slab insulation help keep floors warmer?
It can help reduce heat transfer between the ground and the building, which may contribute to more comfortable floor temperatures, particularly in conditioned spaces.
Where does Weathertight Spray Foam provide under-slab insulation?
We serve homeowners and construction projects throughout New Hampshire, Southern Maine, and Northern Massachusetts.