Wall insulation
If the studs are exposed, spray foam is usually the best thing you can put in them. If the drywall is up, the honest answer is often a different material entirely. Serving New Jersey and Pennsylvania.
Attics and crawl spaces are accessible. Walls are not. Once drywall is up, the cavity behind it is sealed, and spray foam has no way in that doesn’t involve taking something apart.
So before anything else: are your walls open? New construction, an addition, a gut renovation, a room stripped to the studs — that’s the moment when foam does its best work and costs the least, because access is free.
If your walls are closed and staying closed, be careful of anyone who quotes spray foam anyway. It isn’t a product you can inject into a finished wall, and a contractor who implies otherwise is describing a different material.
New builds, additions, gut renovations, and any room already stripped back to framing.
This is where foam wins. Best performance, lowest cost, no demolition.
An existing finished house where the drywall stays up.
We’ll say it plainly: spray foam isn’t the answer here, and for most houses the attic gives a bigger return anyway.
Replacing siding in the next few years? That’s the one moment an existing wall opens up from the outside. Doing insulation then costs a fraction of doing it as its own project, and it’s worth sequencing the two together.
Cavity depth sets the ceiling on performance. Here’s what each option gets you.
| Assembly | 2×4 wall (3.5″) | 2×6 wall (5.5″) | Air barrier |
|---|---|---|---|
| Closed-cell, full fill | ~R-23 | ~R-36 | Yes |
| Open-cell, full fill | ~R-13 | ~R-20 | Yes |
| Flash & batt hybrid | ~R-15–R-20 | ~R-23–R-28 | Yes |
| Fiberglass batts alone | ~R-13–R-15 | ~R-19–R-21 | No |
Flash and batt is worth knowing about, because it’s often the sensible middle. A thin layer of closed-cell foam goes on first to seal the cavity and control condensation, then fiberglass or mineral wool fills the rest. You get the air seal from foam and the depth from cheap material. The catch is that the foam layer has to be thick enough for the climate zone, or you’ve built a wall that collects moisture inside itself — which is exactly the calculation people skip when they do this on their own.
Wall targets in New Jersey and Pennsylvania depend on which edition of the energy code your jurisdiction enforces, and on whether the assembly uses continuous exterior insulation. We confirm the requirement for your township at the estimate rather than quoting a number from memory.
The room above an unheated space has cold on multiple sides. It’s the single most common comfort complaint we’re called about, and the floor band matters as much as the wall.
The short walls in a converted attic or bonus room. The back of them faces open attic, so insulation sitting there without an air barrier is doing very little.
Newer construction attached to older, often with a poorly detailed junction where the two meet. That seam leaks more than either wall does.
The wall that takes the winter wind loses more than the sheltered side. Worth prioritising when a full-house job isn’t in the budget.
Interior walls are a different job with a different goal — sound rather than heat. Open-cell foam is the material for that, and we cover it on the soundproofing page.
What moves the number: cavity depth, foam type, how much masking the site needs, whether we’re working around plumbing and electrical that’s already roughed in, and whether a thermal barrier is required before the space is occupied.
Small single-room jobs carry a minimum, because mobilising a rig for one room costs nearly what it costs for a floor. If you’re opening more than one room, doing them in the same visit is meaningfully cheaper. Other pricing is on the main pricing section.
Get a written priceWalls are the one job with a narrow window. Miss it and it gets expensive.
Roof on, windows and doors in, the building dried in. Foam needs a dry substrate and a stable temperature to cure correctly.
Electrical, plumbing and HVAC in place and signed off. Spraying before the rough-in inspection means cutting foam back out.
Usually one day for a house. Masking, application, trimming flush to the studs, and cleanup. Re-entry timing given in writing before we start.
We provide thickness, R-value, coverage and product documentation for the inspector, so the drywall crew isn’t waiting on paperwork.
Which in an occupied space also serves as the thermal barrier over the foam required under IRC R316.4.
No, and we’d rather say that than take the job. Spray foam expands many times its liquid volume and has to be applied to an open surface. What can go into a closed cavity is dense-pack cellulose or injection foam, both installed through small holes and both different products with different properties. If someone offers to spray foam your finished walls, ask them exactly which material they mean.
In a 2×4 cavity the depth is your constraint, so closed-cell usually earns its higher price — it’s the only way to reach a decent number in three and a half inches. In a 2×6 you have room to work with, and open-cell at full fill often hits target for less money while giving better sound performance. Exterior walls exposed to driving rain or wind-washing are a case for closed-cell either way.
A hybrid. One to two inches of closed-cell foam goes against the sheathing to seal the cavity and keep the sheathing warm enough to avoid condensation, then batts fill the remaining depth. You get the air seal from the expensive material and the depth from the cheap one. It works well, but only if the foam layer is thick enough for the climate zone — too thin and you’ve created a wall that collects moisture where you can’t see it.
For the air seal, no — a couple of inches of closed-cell already stops air. For R-value, yes, because you only get the rating for the inches you install. With open-cell we fill the bay and trim flush to the studs. With closed-cell, full fill in a 2×6 often overshoots what code requires, so partial fill can be the better value. That’s a specification decision, not a corner to cut quietly, and it should be written into your quote either way.
It’s a real trade-off and worth knowing before you decide. Fishing a new wire through a foam-filled cavity isn’t practical, so future work usually means opening drywall and cutting foam back locally. Open-cell is considerably easier to cut and patch than closed-cell. If you know you’ll want flexibility — a home that’s mid-renovation, a shop, a space you’ll rewire — get the conduit and boxes in now, while the walls are open and it’s nearly free.
Yes, and it’s the best opportunity an existing house ever gets. With sheathing exposed, the assembly can be sealed and insulated properly from outside without disturbing a single room. It needs coordinating with your siding contractor and it’s weather-dependent, so plan it rather than decide on the day the siding comes off.
If the walls are already open, insulate them — you will never have cheaper access. If they’re closed and you’re choosing where to put a limited budget, the attic almost always returns more per dollar in this climate, and it’s where we’d send you first. Walls become the priority when they’re genuinely empty, when a specific room is unusable, or when you’re opening them anyway for other reasons.
Tell us which part of the building is the problem. We’ll come out, measure, and give you a written fixed price. No obligation to proceed.
