frequently asked questions
1) What type of insulation is best for homes in St. Louis?
It depends on the part of the house and what problem you’re solving.
Attics: Loose-fill fiberglass or cellulose can work well when depth is adequate and air leaks are sealed first. Spray foam is sometimes used at rooflines, but it changes how the attic behaves (it becomes part of the conditioned envelope).
Walls: Dense-pack cellulose or fiberglass in cavities is common; exterior continuous insulation is ideal during major remodels because it reduces thermal bridging.
Basement/crawlspace walls: Rigid foam board or closed-cell spray foam is often used because these areas see more moisture exposure than above-grade walls.
The “best” insulation is the one that matches the assembly, includes air sealing where needed, and won’t create moisture issues in your specific space.
2) How much insulation should I have in my attic in Missouri?
Most St. Louis homes benefit from a deeper attic insulation layer than they currently have, but the more important point is this: air sealing usually matters before adding more insulation.
If warm, moist indoor air is leaking into the attic in winter, adding insulation alone won’t fix the root problem. Common leakage points include attic hatches, recessed lights, plumbing stacks, bath fan housings, and top plates.
A good approach is:
air seal major penetrations
confirm ventilation strategy is appropriate (for vented attics)
add insulation to the target depth
3) What’s the difference between air sealing and insulating?
Insulation slows heat transfer. Air sealing stops air movement. They solve different problems.
If your home feels drafty, has hot/cold spots, or pulls odors from the attic/crawlspace, that’s usually air leakage.
If temperatures swing mainly with weather and the HVAC runs constantly, that’s often insulation level and continuity.
In St. Louis, air sealing is a big deal because humid summer air can move into cavities and condense on cooler surfaces.
4) Will insulation lower my energy bills?
Often, yes, but not always in the way people expect.
Insulation tends to help most when:
the home has low attic insulation, missing insulation, or severe gaps
the home has major air leaks (stack effect is strong in winter)
ducts run through unconditioned areas (attics/crawlspaces)
If your bills are high due to an oversized/undersized HVAC system, leaky ducts, poor humidity control, or bad windows, insulation helps—but it may not be the main lever.
5) Why do my floors feel cold in winter even when the heat is on?
Cold floors are usually caused by one (or a mix) of these:
uninsulated or underinsulated floor system above a crawlspace
air leakage from the crawlspace rim joist or floor penetrations
duct leakage or poor airflow balancing
crawlspace conditions: cold air moving under the floor, especially in vented crawlspaces
The fix depends on whether the crawlspace is treated as outside (vented) or brought into the building envelope (sealed/conditioned approach).
6) Does insulating a crawlspace help with humidity and musty smells?
It can, but insulation alone isn’t the moisture solution.
Musty smells often come from:
exposed soil and ground vapor
standing water or chronic dampness
humid outdoor air cycling through a vented crawlspace
mold growth on wood or insulation facing
If you insulate without controlling ground moisture and air movement, insulation can get damp and fail. In mixed-humid climates like St. Louis, crawlspace work usually starts with moisture management (ground cover/vapor control, drainage, air sealing), then insulation in the right location.
7) Is a vented crawlspace a problem in St. Louis?
It’s not automatically “wrong,” but it often performs poorly in humid summers.
Vented crawlspaces can pull in warm, humid air. That air hits cooler surfaces (ducts, framing, subfloor) and can lead to condensation. That’s why some homes do better with a crawlspace strategy that reduces humid air exchange and controls ground vapor.
The right approach depends on:
whether you have ducts down there
how wet the site is
how the crawlspace is currently built and behaving
8) Should I insulate crawlspace walls or the floor above?
Both can work, but they create two different crawlspaces.
Floor insulation (between joists):
keeps the crawlspace “outside” the thermal envelope
relies heavily on good installation (no gaps, supported batts, air sealing at rim joist)
can struggle if the crawlspace is humid
Wall insulation (crawlspace becomes semi-conditioned):
brings the crawlspace into the thermal envelope
often improves comfort and protects ducts/plumbing
usually requires better air sealing and moisture control details
The wrong choice for your existing conditions can create condensation and durability issues.
9) What are signs my insulation is failing or no longer doing much?
Common red flags:
insulation is sagging, missing, compressed, or falling out
insulation looks dirty or wind-washed (air is moving through it)
wet insulation or staining (roof leak, plumbing leak, crawlspace moisture)
uneven temperatures and drafts that persist after HVAC servicing
pest contamination in attic or crawlspace
If insulation is wet or contaminated, it’s often a removal-and-replace situation, not a “just add more” situation.
10) Spray foam vs fiberglass: which is better for St. Louis homes?
They do different jobs.
Fiberglass insulates well when it’s installed perfectly and air isn’t moving through it. It’s cost-effective for attics and walls, but it doesn’t air seal.
Spray foam (especially closed-cell) can insulate and air seal in one step, and it can handle some moisture exposure better than fibrous insulation. But it’s more expensive and can make future access/repairs harder depending on where it’s applied.
A lot of St. Louis comfort problems are air leakage problems, which is why spray foam is attractive in certain areas. Still, it needs to be used where it makes building-science sense, not as a default.
11) What’s the difference between open-cell and closed-cell spray foam?
Open-cell: lower density, more vapor-permeable, expands a lot, typically used for interior applications where drying potential matters.
Closed-cell: higher density, more rigid, higher R-value per inch, more resistant to moisture vapor, can add structural stiffness.
Closed-cell is often chosen where space is tight or where moisture exposure is a concern. Open-cell can be useful where you want the assembly to dry more readily. The right choice depends on location (roofline, rim joist, crawlspace walls) and the moisture profile of that assembly.
12) Can insulation help with summer humidity inside my home?
Indirectly, yes.
Insulation reduces heat flow, but humidity control is mostly about air movement and HVAC performance. In St. Louis summers, humid outdoor air sneaking in through leaks can overwhelm your system.
Insulation helps most when it’s paired with:
air sealing (attic plane, rim joists, penetrations)
duct sealing (especially if ducts are in attic/crawlspace)
correct HVAC sizing and runtime for dehumidification
13) Should I insulate my basement walls in St. Louis?
Often, yes—especially if the basement is used or semi-finished.
Basement wall insulation can:
reduce cold-wall discomfort in winter
reduce condensation risk on interior surfaces
make the basement easier to keep at a stable temperature
But basements are moisture-prone. The insulation strategy should consider:
bulk water control (drainage, grading, gutters)
vapor behavior (avoid trapping moisture in the wrong layers)
whether you’re finishing the space
14) Why do some attics have mold even with insulation?
Mold in attics often comes from moist air + cold surfaces, not from “bad insulation.”
Common drivers:
bathroom fans dumping into the attic
attic air leaks from the house below (stack effect)
inadequate or imbalanced attic ventilation (in vented attic designs)
roof leaks
Adding insulation without air sealing can sometimes make attic surfaces colder in winter, which can increase condensation risk if air leaks remain.
15) Is it worth insulating ductwork in the attic?
If ducts are in a hot attic, insulating them helps, but sealing ducts often matters even more.
Leaky ducts in an attic can:
dump conditioned air into the attic
pull hot, humid air into the system
cause rooms to run hot/cold
A good duct strategy is usually:
seal major leaks
ensure ducts are properly supported (no kinks/crushed flex)
confirm insulation is continuous and intact
16) What’s “R-value,” and why does it matter?
R-value measures resistance to heat flow. Higher R-value generally means better insulation performance.
But real-world performance also depends on:
installation quality (gaps, compression, missing areas)
air movement through/around insulation
moisture (wet insulation performs worse)
thermal bridging through framing
So R-value is necessary, but not sufficient. A lower R-value installed correctly can outperform a higher R-value installed poorly.
17) Is blown-in insulation better than batts?
Blown-in insulation can be better in certain situations because it:
fills irregular cavities more consistently
reduces the chance of gaps from poor cutting/fitting
can top off attics quickly and evenly
Batts can work well, but only when installed without compression, voids, or misalignment. In older St. Louis homes with uneven framing or lots of penetrations, blown-in often does a better job of coverage.
18) What should I check before adding more insulation to my attic?
Before adding insulation, it’s smart to check:
any roof leaks or staining
bath fans venting properly to the exterior
obvious attic air leaks from below (sealed?)
recessed lights and wiring safety considerations
whether attic ventilation is designed to work as intended (for vented attics)
existing insulation condition (dry, not contaminated, not wind-washed)
Adding insulation over unresolved moisture or air leakage problems can lock in the wrong conditions.