Cellulose Insulation for Double-Studded Walls
A double-studded wall assembly is an increasingly popular way to frame homes as their design allows for a continuous layer of insulation free of thermal bridging. But what is the best way to insulate a double-studded wall? In this article, you will learn your options for insulation materials, how to install your insulation, and how much it will cost.
Table of Contents
- Why choose a double-studded wall?
- What’s the best insulation for a double-studded wall?
- Is cellulose a good insulator?
- Is cellulose insulation fire-resistant?
- Do bugs damage cellulose insulation?
- Is cellulose insulation a sustainable material?
- How is blown-in insulation installed in a double-studded wall?
- How do I keep the blown-in cellulose from settling and leaving a gap at the top of the wall cavity?
- Do I need straps to hold the cellulose in place?
- How much does it cost to insulate a wall with dense-packed cellulose?
Why choose a double-studded wall?
A double-studded wall has two stud-framed walls allowing for an extra thick wall cavity that can be filled with insulation. The main advantage of this design is that the exterior and interior frames are separated by a continuous layer of insulation, eliminating unnecessary thermal bridging or heat transfer. This design is a favorable option for a high-performance, comfortable, and energy-efficient home.
What’s the best insulation for a double-studded wall?
The best insulation for a double-studded wall is blown-in insulation, either fiberglass or cellulose. Cellulose is a better insulator and is more sustainable.
Double studded wall assemblies are, on average, nine and a half inches thick, with a large cavity between the stud walls. Batt insulation fits nicely between studs in a traditional wall, but the cavity in a double-studded wall should be filled with dense-packed insulation material to create a continuous layer of insulation with no thermal bridging.
Is cellulose a good insulator?
Yes. Dense-packed cellulose has an r-value of about 3.6 per inch, about 30% better than fibreglass. You get more performance in a thinner wall, which is good news for renovations where you’re short on interior floor space.
Is cellulose insulation fire-resistant?
Cellulose insulation is treated with the flame retardant borate and is as resistant to flame as fiberglass and mineral wool insulation.
Do bugs damage cellulose insulation?
No. Cellulose insulation is treated with borate, which is a flame retardant and pest repellant.
Is cellulose insulation a sustainable material?
Yes. Cellulose is made of 80% or more recycled material like newspaper. It stores carbon and requires less energy to manufacture than both fiberglass and mineral wool.
How is blown-in insulation installed in a double-studded wall?
The inner stud wall is lined with a large sheet of fabric (or other material) that is attached to the studs with staples. This creates a large empty cavity that can be filled with insulation. Bags of insulation material are fed into an insulation blower that is typically located on a truck or rig and is equipped with a very long hose. The installer makes small holes in the fabric sheet through which the insulation is blown. The walls are filled until they are very full and pushing between the studs.
How do I keep the blown-in cellulose from settling and leaving a gap at the top of the wall cavity?
Cellulose installed in wall cavities is packed very densely, so it will not settle to create gaps. It’s a common misconception that blown-in cellulose will settle when used in walls because the cellulose used for attics is loose and is known to settle.
Do I need straps to hold the cellulose in place?
The insulated wall cavity is packed so tightly, that the fabric sheet will push between the inside studs, making it a challenge to install drywall or another type of sheathing. There are a few approaches to solving this problem, but for most installations, ¾ inch-wood strapping is an effective and space-efficient option.
In some cases, a belly rollercan be used to massage the overfilled cavity until the material is distributed and flat enough for a drywaller to install sheathing. This approach doesn’t always work, especially if the cavity is very full.
How much does it cost to insulate a wall with dense-packed cellulose?
Expect to pay about $3 to $5 per square foot to have dense-packed cellulose properly installed in an average 9.5 inch double studded wall cavity.
By choosing a double-studded wall, your home is well-equipped for the installation of high-performance blown-in insulation. Cellulose is arguably the best material for the job in terms of performance and sustainability.
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