Building insulation
Building insulation slows heat flow through walls, roofs, floors, and foundations, helping buildings stay more comfortable while reducing heating and cooling demand.
What building insulation is
Building insulation is material placed in or around the building envelope to slow heat transfer. It is used in attics, roofs, walls, floors, basements, crawl spaces, slab edges, ducts, pipes, and other assemblies where unwanted heat gain or heat loss affects comfort, energy use, or durability.
How insulation slows heat
Heat moves by conduction, convection, and radiation. Most common insulation materials work mainly by trapping still air or gas in fibers, cells, or pores, which reduces conduction and convection through the assembly. Radiant barriers work differently: they reflect radiant heat and depend strongly on air spaces and installation conditions.
R-value and whole assemblies
R-value describes resistance to conductive heat flow. The R-value of a wall or roof is not always the same as the R-value printed on the insulation package, because framing, fasteners, gaps, compressed areas, windows, moisture, aging, and thermal bridges can all reduce whole-assembly performance.
Where insulation goes
Attics and rooflines are often high-impact locations because warm air and heat flow can move strongly through the top of a building. Walls, floors over unconditioned spaces, rim joists, foundation walls, and slab edges can also matter. The best location depends on climate, building type, moisture risk, and whether the project is new construction or a retrofit.
Common material types
Insulation can be sold as batts, rolls, loose fill, dense-pack fiber, rigid boards, spray foam, structural insulated panels, insulated concrete forms, or reflective systems. Common materials include fiberglass, mineral wool, cellulose, wood fiber, expanded or extruded polystyrene, polyisocyanurate, polyurethane foam, and aerogel products for specialized cases.
Air sealing and moisture
Insulation is not a substitute for an air barrier. Air leaks can carry heat and moisture through assemblies, so air sealing often needs to happen before or alongside insulation work. Moisture strategy matters too: rain control, vapor control, drying paths, ventilation, and climate-specific detailing help prevent mold, rot, corrosion, and damaged insulation.
Retrofits and tradeoffs
Adding insulation to an existing building can improve comfort and lower energy use, but retrofits need diagnosis. Blown attic insulation may be straightforward; wall, roof, basement, and exterior insulation projects can affect wiring, ventilation, fire safety, moisture behavior, cladding, windows, and indoor air quality.
Why it matters
Good insulation reduces the load on heating and cooling systems, makes indoor temperatures steadier, improves comfort near walls and ceilings, and can help buildings remain livable longer during outages or extreme weather. It works best as part of a complete envelope strategy that includes airtightness, thermal-bridge control, windows, shading, and moisture management.