Wall Insulation

Spray foam in walls is a straightforward, excellent job when the studs are open, and a much more limited one when they are closed. That single distinction decides almost everything about your wall insulation project: what we can install, what it will cost, how well it will perform, and whether we will tell you to do it at all right now.

This is the thing homeowners get confused about most often, and it is the thing a salesperson is most tempted to blur. So we are going to be blunt about it on this page before we talk about anything else.

Open studs: this is when wall foam is genuinely great

When the cavity is open to the room, we can see every bay, spray to a controlled depth in controlled passes, trim it flush, and walk it with you before the drywall goes on. Nothing is hidden. Coverage is verifiable. The foam bonds to the sheathing, the studs, and the plates all at once, which is what turns a wall from a pile of insulation into an air-sealed assembly.

These are the five moments in a Seattle house when the studs are already open, and they are the moments worth planning around:

• A remodel that takes the drywall off. A kitchen, a bathroom, a whole floor. If the rock is coming down anyway, the incremental cost of doing the walls right is the smallest it will ever be.
• An addition or a bump-out. New framing, no demolition, clean access. This is the easiest wall job there is.
• A gut of an older house. Very common in Ballard, Wallingford, and Beacon Hill Craftsmans that are getting their first serious update in eighty years.
• New construction. Framed, wired, plumbed, inspected, then insulated. Straightforward.
• A re-side. This one gets missed constantly. When the old siding and sheathing come off, the wall is open from the outside, which is a legitimate moment to insulate and a good moment to fix the assembly from the weather side. If you are getting bids for new siding, call us during that process, not after.

Why closed-cell usually wins in a Seattle 2×4 wall

Most of the older stock around here is framed with 2×4 walls, which gives you a cavity about three and a half inches deep. Craftsman bungalows, mid-century ramblers, split-levels: same limitation. You cannot add depth without furring the wall out and losing interior space, so the only lever you have is R-value per inch. That is exactly the situation where closed-cell spray foam earns its higher price.

Those cavity figures are the foam itself, not the whole-wall number. Studs, plates, and headers conduct heat around the insulation, so the assembly always performs below the cavity rating. Anyone quoting you a single clean wall R-value is simplifying. If you want the full picture for our climate, read the R-value guide for Seattle, climate zone 4C marine, and if you are still deciding between products, open-cell vs closed-cell covers the tradeoff in detail.

In a 2×6 wall, which shows up in newer Bellevue, Renton, and Kent construction, you have more room and open-cell becomes a reasonable option again. Depth changes the math.

Closed walls: injection foam and drill-and-fill, honestly

If your drywall is staying up and your siding is staying on, spray foam is off the table. What is on the table is injection foam: holes drilled in a grid, usually from the outside between siding courses or from the inside in a discreet line, with a slower-rising foam pumped into each bay and the holes plugged afterwards.

It is a real product and it does real work. An uninsulated pre-1960 wall filled with injection foam will be noticeably better than it was. But here is the honest list of limits, and every one of them is the reason we put open studs first on this page.

• You cannot see the result. We fill by volume and by feel, and we can check with a thermal scan afterwards, but nobody is looking at a finished bay. In an open wall, coverage is visible. In a closed wall, it is inferred.
• Obstructions block the fill. Fire blocking, let-in bracing, wiring runs, old pipes, and previous batt insulation all interrupt a bay. Each obstruction means another drill point, or a section that simply does not get filled.
• It is not the same product as sprayed closed-cell. Injection foams are lower density and lower R-value per inch than closed-cell. You are not getting R-6 per inch through a drill hole, and any quote implying otherwise deserves a hard question.
• Air sealing is partial at best. It fills the cavity. It does not seal the top plate penetrations, the wiring holes into the attic, or the gaps at the rim. Those are the leaks that actually move air through your house, and they are air sealing work, not wall filling work.
• The patching is visible on some siding. Cedar shingles and lap siding usually recover well. Stucco, brick veneer, and painted clapboard in good condition can end up with a visible grid of plugs.

When we will tell you to wait

If your walls are closed, your siding is in decent shape, and there is no remodel on the horizon, we will usually tell you not to do this yet. That is not us being modest about the product. It is arithmetic. In most Seattle houses the attic and the crawl space are leaking far more energy than the walls are, and they are cheap and open to work in by comparison. Doing attic insulation and air sealing first gets you more comfort per dollar, almost every time.

So the recommendation is often this: fix the attic now, put the walls on the list, and do the walls the day something else opens them. If you are already planning a re-side in two years, that is your moment, and it is worth waiting for.

The Seattle wall situations we see most

Uninsulated pre-1960 walls

Plenty of houses in this city were built with nothing in the walls. Sheathing, building paper, siding, and air. You can often tell from inside on a cold morning: the exterior walls are cold to the hand while the interior partitions are not. These walls have the most to gain and they are also the ones where a partial injection fill still leaves you better off than you started.

Balloon framing in the older stock

In many pre-1930 houses the studs run continuously from the foundation to the attic with no fire blocking between floors. That means a wall cavity is also a chimney, pulling cold air up from the crawl space and dumping warm air into the attic all winter. Blocking and sealing those cavities at the top and bottom often does more for comfort than filling them does, and it needs to happen either way. We check for this on every older house before we quote anything.

Knee walls and bonus rooms

The short wall between a finished attic room and the triangular space behind it is one of the worst performing assemblies in a Seattle home, and it is the reason so many bonus rooms over garages are unusable in January. The wall is often insulated on the room side with nothing behind it, so the batts sit in open attic air and do almost nothing. The good news: the back side is usually accessible, which makes it an open-cavity job even though the house is closed. Closed-cell on the back of a knee wall, plus sealing the floor cavity underneath it, is one of the highest value jobs we do.

Vapor control, and why the assembly matters here

This is where a marine climate deserves more care than a generic insulation page gives it. A wall needs to be able to dry. If it gets wet, from a leak, from wind driven rain, or from indoor humidity, it has to release that moisture in at least one direction. Insulating a wall changes how it dries, so the decision is never just about R-value.

Closed-cell at sufficient thickness acts as a vapor retarder on the inside face of the cavity, which limits inward drying but also keeps indoor moisture out of the sheathing. Open-cell stays vapor open, which allows drying but also lets moisture move. Which is appropriate depends on what is on the outside of your wall, whether there is a drainage plane behind the siding, whether there is old kraft facing or poly already in there, and what condition the sheathing is in. Two poly layers in one wall is how you trap water, and we have opened up walls that had exactly that.

We will not quote you a code section on this page, because requirements change and we are not going to claim something we have not verified for your specific project and jurisdiction. What we will do is look at your actual wall, tell you what is already in it, and design an assembly that can dry. If your project is permitted, the inspector is the authority on the requirement, and we will build it to satisfy them.

What wall insulation costs around here

Sprayed foam is priced per board foot, which is one square foot at one inch thick. Closed-cell commonly lands around $1.00 to $2.00 per board foot installed in this market and open-cell around $0.50 to $0.70. As a rough whole project figure, 1,000 square feet at three inches often lands somewhere around $2,200 to $5,400. Trade labour in Seattle generally runs about $95 to $175 per hour, which is why access and prep move a wall number so much.

Injection work in closed walls is priced differently, usually by wall area and drill point count rather than board foot, because the variable is bays and obstructions rather than depth. What moves either number: how many exterior walls are in scope, whether furniture and finishes need protecting, whether old material has to come out, how the siding takes a patch, and how much blocking and sealing the house needs first. Full ranges are on the spray foam insulation cost in Seattle page. A firm price needs someone to look at the house, and we are not going to guess at one over the phone.

How we handle a wall job

Common questions about wall insulation

Related services and reading

• Closed-Cell Spray Foam Insulation
• Air Sealing
• Attic Insulation
• Insulation Replacement
• Open-cell vs closed-cell
• R-value guide for zone 4C