Attic Insulation in Renton, WA

Renton does not have one kind of attic, so it cannot have one kind of attic job. A 1920s house below downtown, a post-war plant house off Talbot, and a 1995 two-story on the Highlands are three different problems under three different roofs, and the right answer for one of them is a waste of money in the next. Before you take a quote from anybody, work out which attic you actually have.

The one we want to talk about most on this page is the low-pitch post-war roof, because it is the Renton attic where spray foam stops being an upsell and becomes the only product that fits. In a lot of the rest of this city we will point you at cheaper work and mean it.

Which Renton attic do you have?

Take a light and a tape measure to the hatch. Four things tell you most of what you need to know: how much headroom there is at the ridge, how much there is out where the roof lands on the exterior wall, whether the framing is rafters with a ridge board or factory trusses with webs criss-crossing the space, and how deep the existing material actually sits when you push the tape into it.

Pre-1940: downtown, Renton Hill, Kennydale

Small attics framed in 2x4s, a few inches of whatever was cheap in 1935, and in the story-and-a-half houses a set of knee walls with triangular voids running behind them. Access is a panel in a closet ceiling, or a gable vent off a ladder, or genuinely nothing at all. These attics were not built to be worked in and they have often never been properly looked at.

The honest answer here is usually not foam on the flat parts. It is sealing every hole in the ceiling below, then adding depth on top, with foam on the knee wall faces and the shallow sloped sections where there is no depth to add. The geometry is close to the older Seattle neighbourhoods, written out in detail in the Seattle attic insulation guide.

Post-war and mid-century: the low-pitch roof

A large share of Renton went up fast between the mid 1940s and the early 1960s around the plant and the work that came with it. Compact single-story houses, 2×4 walls, small footprints, and roofs built at a shallow pitch because a shallow roof is cheaper and faster. You cannot stand up anywhere in these attics, and out toward the walls you cannot sit up either.

What is up there now is usually original loose fill that has settled to half the depth it started at, sometimes batts laid in with the facing on backwards, sometimes rodent-damaged material that needs to come out before anything else happens. See insulation replacement for what that part of the job looks like. But the thing that makes this attic different from every other attic in Renton is not what is in it. It is how little room there is to put anything else.

1980s to 2000s: Highlands, Fairwood, Benson Hill truss attics

The biggest group of Renton houses we get called to, and the group most likely to spend money on the wrong thing. Truss-framed, decent blown-in depth through the middle, installed to the code of the day. The attic is not the failure here, and there is a section further down on what these houses actually need.

Newer: The Landing, Southport and recent infill

Built to a much later energy code and generally performing. If your house or townhome is from the mid 2000s onward and the complaint is one room, we look at that assembly and nothing else. Quite often we tell people there is no work here worth doing.

Low-pitch roofs: when R-value per inch stops being a luxury

Here is the arithmetic nobody does at the kitchen table. The commonly cited target for an attic floor in our climate zone is around R-49. Blown fiberglass is typically published around R-2.2 to R-2.7 per inch and blown cellulose around R-3.2 to R-3.8, so reaching that target takes somewhere between roughly fourteen and twenty-two inches of material. In a walkable attic those inches are effectively free. You run the hose a bit longer and the invoice barely notices.

On a shallow post-war roof they are not free, because they do not exist. Over a house around twenty-six feet wide at a pitch in the 3:12 to 4:12 range you have three feet or so at the ridge and it falls away fast in both directions. By the time you reach the exterior wall you are looking at four to six inches of height, and a vent baffle wants an inch and a half of that. That thin band is not a corner case. It runs the entire perimeter of the house, directly above the line where every room meets its outside wall.

That last row is the whole argument. Everywhere else in a house, paying a premium for R-value per inch is buying something you did not need, and we say so on spray foam vs fiberglass batts for attics. In the heel of a low-pitch Renton roof there is no deeper option to compare against. You either put in a product that delivers R-6 to R-7 per inch or you accept a cold ring around your ceiling forever. That is the one place in this city where we will argue hard for closed-cell foam, and it is a small quantity of it.

The two honest ways to do it

The hybrid, which is what most of these houses get. A couple of inches of closed-cell in the heel and anywhere else the depth runs out, a wind dam so the loose material holds its depth at the edge, baffles keeping the vent path open above, then blown-in deep through the middle where inches cost almost nothing. It is a modest amount of foam doing a disproportionate amount of work, and it is far cheaper than the alternative.

The roof deck, which is a bigger commitment. Closed-cell on the underside of the sheathing, vents closed off, attic brought inside the heated house. In a low-pitch Renton attic this makes sense mainly when the ducts live up there, or when the space is so tight that nobody can realistically work the floor properly. It costs considerably more and it changes the building, so we talk about it before we quote it.

What we will say before we spray a roof deck

• The roof comes first. Foam bonded to sheathing means a future leak will not show up as a stain on your ceiling. If the roof is near the end of its life, do that first or do neither.
• You cannot do half of it. A partly foamed deck with the vents still open is worse than either option done properly.
• Sometimes the honest answer is to wait. If a re-roof is coming in the next few years, the sensible moment to fix a shallow attic is when the sheathing is off and everything is reachable from above.
• Access is the price. A crew on their belly under a 3:12 roof works a fraction as fast as a crew standing up, and that is hours, not materials.

If you are on the Highlands, in Fairwood or on Benson Hill, you probably do not need foam

We will say this plainly because it costs us work. If your truss attic already has blown-in at a reasonable depth and it is dry and clean, adding foam on top of it is a poor buy, and adding more blown-in through the middle is not much better. The heat is not leaving through the insulation. It is riding on air through the holes underneath it.

What that money should do instead, roughly in order: seal the ceiling plane (see air sealing), deal with the flex duct running through a cold attic, top up the eaves where the depth tapers off and add wind dams so it stays put, and then treat the bonus room over the garage as its own project. The bonus room is the one place in these houses where foam genuinely belongs, because the knee walls, the sloped ceiling and the floor over an unheated garage are all shallow assemblies with nowhere to add depth. It is the same argument as the low-pitch roof, in a smaller box.

Getting into a Renton attic

Access decides more of the price here than anywhere else we work. In the newer subdivisions there is a pull-down stair in the hallway and it is fine. In a post-war rambler it is a small square in a bedroom closet, and once you are through it you are lying down. In the pre-1940 stock it can be a gable vent, a panel behind a bolted-down dresser, or a hatch we cut and trim out because there is not one. We go up and look before we quote, and if a hatch has to be cut, you hear it before the day rather than on it.

Three things that stop a job. Rodent damage is normal in this housing stock, not rare, and soiled material comes out rather than gets covered. Loose grey pellets that look like tiny popcorn may be vermiculite, which gets tested and not vacuumed. And in the oldest houses, live knob and tube has to be cleared by an electrician before anything is buried, which is a separate trade and a separate bill.

What a Renton attic job costs

Our rates are the same across the service area. Spray 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 sits lower at roughly $0.50 to $0.70. As a whole-project figure, 1,000 square feet at three inches often works out somewhere around $2,200 to $5,400. Trade labour in this area runs roughly $95 to $175 per hour, and in a low attic the hours are the number that moves.

What specifically changes a Renton attic total: whether a person can stand up or has to crawl, how much of the ceiling plane needs sealing, whether failed material comes out first, whether an electrician has to go ahead of us, and whether a bonus room is part of the scope. A hybrid job that foams only the heel and blows the rest is at the cheap end. A foamed roof deck on a house with ducts up there is a different order of number. Nobody can price any of that from the kerb, and we will not pretend to. The wider picture for this city is on spray foam insulation in Renton, and the general method is on our attic insulation page.

How we handle a Renton attic

Renton attic questions

Related services and reading

• Spray Foam Insulation in Renton
• Attic Insulation
• Air Sealing
• Closed-Cell Spray Foam
• Spray foam vs fiberglass batts
• Insulation Replacement