If you’re researching how demising walls are built, you’re probably a developer or owner of a multifamily residential building. And, you probably already know that demising walls are crucial to privacy and comfort — the 2 things your tenants want most out of their building.
This post will analyze how demising walls built with Element ICF contribute to occupant comfort and compare their performance to the traditional, wood-framed assemblies.
Standard Demising Wall Code Requirements
Demising walls can be either load-bearing or non-loadbearing — there’s no specific code requirement for this. Whether or not these walls support the live and dead loads of the structure above is strictly a design and constructability matter.
That said, building codes demand 2 things from demising walls — that they resist fire and noise transmission.
Fire Rating
Element ICF walls’ 3-hour fire rating easily surpasses the standard code requirements mandating a 1-hour separation. Of course, drywall is still required on either side of the wall to meet the ignition requirements.
Reduced Noise Transmission
Element ICF demising walls make it simple to exceed code-mandated Sound Transmission Class (STC) ratings — the standard, 6.25-inch core offers STC-56. This rating not only meets most locales’ codes but means that most sounds — apart from those produced by heavy wood-working equipment — are faint or not heard at all.
When developer Nigel Furgus launched a website for his 30 University Crescent (30 U.C.) multifamily midrise development in Winnipeg, Manitoba, he made a curious observation. The most visited page on his development’s website was the “Soundproof Construction” page. This statistic is a good indicator of what today’s tenants are looking for — a private, noise-free home.
Airtightness
Opting for Element ICF demising walls guarantees another critical feature that wood-framed walls struggle with: airtightness. Just like blocking noise, stopping airflow between residential units is crucial for occupants’ comfort — no one needs to smell their neighbor’s dinner, delicious as it may be. What’s more, airtight walls prevent drafts and boost energy efficiency by blocking heat loss through convection.
While the airtightness mechanisms of ICF walls haven’t been studied thoroughly just yet, we do have solid proof that these walls are far more airtight than their wood-frame peers. In a study of 49 ICF homes, the RDH Building Laboratories found that, on average, ICF buildings have an airtightness of 1.26 ACH50 (Air Changes per Hour at 50 Pascales — a standard airtightness measurement).
In contrast, most Canadian wood-frame homes allow roughly 4 ACH50, whereas their U.S. counterparts measure even higher, at 5 ACH50. This means that ICF walls are about 4-5 times more airtight than those built with the conventional wood frame.
The difference in performance stems from the walls’ construction. ICF walls have a monolithic concrete core and 2 layers of continuous insulation, while wood-frame walls rely on loose-laid house wrap to cover all of the crevices in the wall assembly. Unfortunately, using house wrap leaves lots of room for flaws, especially where its edges are taped. Worse, the building paper used to achieve airtightness can be expected to deteriorate far faster than a solid concrete core.
Don't miss a thing
Sign up to receive the latest info on new Element ICF products, special offers and more.
Demising Wall Comparison — Element ICF vs. Conventional Wood Frame
Now, let’s dive a bit deeper to review and compare the key components of Element ICF and wood-framed demising walls.
Wood-Frame Demising Wall Construction — 9¼-Inch Thick Wall, 1-Hour Fire Rating, STC 57
- Structure: 2 rows of 2 x 4 wood studs spaced 16 inches on center, resting on individual sill plates. These sill plates and the studs they support are separated by a 1-inch gap — this facilitates “decoupling,” a process where 2 sides of the same wall are separated so that soundwaves are isolated to one side of the wall.
- Insulation: 4-inch batt insulated stuffed into the stud bays on each side.
- Finish: ⅝-inch gypsum wall board on each side of the assembly.
- Best practice for airtightness: cover one side of the assembly with a vapor barrier, then wrap the other with Tyvek. This way, you’re creating an effective air barrier but preventing the detrimental double-vapor barrier effect.
Element ICF Demising Wall — 15¼-Inch Thick Wall, 3-Hour Fire Rating, STC 56
- Structure: 25-inch concrete core
- Insulation: 2 x 2¾ EPS foam panels, one on each side of the concrete core
- Finish: on one side — 2 layers of ⅝-inch gypsum wall board hung on 2 x 2 wood strips. The strips are attached to the wall at 24 inches on center. On the other side — a layer of ½-inch gypsum wall board.
- No other elements are needed to achieve airtightness, as the wall’s monolithic nature is inherently airtight.
Wrapping It Up
Blocking noise transmission and curbing airflow between residential units are 2 essential priorities for ensuring your tenants’ comfort. With Element ICF demising walls, both are easily achieved without additional elements, like housewrap or vapor barrier, and with no extra steps, like decoupling a stud assembly. What’s more, Element ICF walls enhance the units’ energy efficiency and take less time and effort to erect.
