NUDURA Insulated Concrete Forms come in five different core sizes. Standard thickness are 4-inch, 6-inch, 8-inch, 10-inch, and 12-inch, with NUDURA reporting that as of 2019 the two most commonly used ICF sizes are the six-inch and eight-inch core. These two will serve as the subject of our comparison to provide you with some additional insight before breaking ground on your next residential project in Alberta.
A Practical Comparison of the Two Most Popular Core Sizes of NUDURA Insulated Concrete Forms
When considering the strength of NUDURA 6-inch and 8-inch cores it feels like we’re comparing apples to apples as both provide unmatched strength when compared to traditional building methods. But it does make a difference when it comes to building height. A standard six-inch core is typically employed for load bearing walls as high as five stories, including this multi-story multi-family residence in Granby Quebec which constructed exterior load-bearing walls with NUDURA 6” Forms and a combination of brick and stucco finish. A standard eight-inch core wall is more commonly used for buildings as high as 10 stories. However, both sizes are often used in conjunction with one another where the thicket 8-inch core is often used below grade and the 6-inch core utilized above grade. A good example is the West Village building in Hamilton, Ontario, a project which utilized a combination of NUDURA 6” and 8” forms for exterior walls. Huntsville Condos (Ontario) also used a combination of 6” and 8” NUDURA Forms in the construction of the 36 unit on 5 floor development.
When it comes to an ability to withstand extreme weather, both the 6-inch and 8-inch core have been manufactured to withstand 250 miles per hour winds, although this level is logically achieved with greater ease via the latter. A prototypical 3,500 psi concrete 6-inch core delivers 252,000 lbs (over 114,300 kg) per linear foot compressive strength while the 8-inch core is 336,000 lbs (over 152,400 kg) per linear foot compressive strength. Both are bulletproof (literally) and explosion proof (50 lbs of TNT with a 6-foot blast radius) which makes them popular for panic room construction, although the thicker the better for projects where security is of significant concern, as per this municipal safe room in Kentucky which used NUDURA 12-inch core walls.
Both the 6-inch core and 8-inch core rebar schedule may be modified to include additional rebar and strength.
Conclusive studies have found that NUDURA ICF systems reach a four-hour fire resistance rating with a 6-inch core wall. However, it’s important to note that the 6-inch core wall just makes the cut in attaining a four-hour rating, whereas an 8-inch core wall achieves the same rating with greater ease. So, while both are superior to both traditional and ICF industry alternatives, the 8-inch core may be preferred if fire rating is the absolute priority. View more on why residential builders are using NUDURA insulated concrete forms for building fire resistant homes in at-risk communities.
The Sound Transmission Class (or STC) for the 6-inch core is STC 50, and the 8-inch core is rated at STC 55 which are both leaps and bounds above the soundproofing provided by conventional construction. Since STC is not a linear measurement there is a significant audible difference in the 5-point differential but when it comes to residential projects it’s negligible at best. It’s only when soundproofing is one of the primary requirements that a builder may consider an 8-inch over a 6-inch core, as with a movie theatre. For example The Ridge Theatre in Florida constructed exterior load bearing walls using NUDURA 8” forms above and below grade. Such measures would not be necessary for a residential client unless they wanted a custom state-of-the-art home theatre extension for a house located near an international airport.
NUDURA 6-inch and 8-inch cores have nearly indistinguishable R-values of approximately R-24 (continuous). However, the 8-inch core has considerably greater thermal mass and will outperform the six-inch core. While the difference is quantifiable, occupant comfort levels are far superior to traditional wood frame construction and even their 4-inch ICF sibling. 6-inch cores remain to be a popular choice for single family home constriction across Canada, Alberta included. For example, this 2,750 sq. ft. waterfront home in Peterborough Ontario is exposed to extreme seasonal temperatures yet the 6-inch NUDURA forms are more than adequate to maintain comfort levels all year long.
The cost for each core (from NUDURA) is negligible. So why would one choose 6-inch over the thicker alternative if one was to decide on price alone? It comes down to the costs to fill concrete. For instance, one cubic yard of concrete filled into a 6-inch core will fill approximately 30% for than concrete poured into an 8-inch core, and thus the concrete costs are proportionately higher for the 8-inch core wall.
There are other cost considerations, but these will be highly contingent upon the unique needs of your custom home construction project. Nine times out of ten a 6-inch core will be all you need, but of course the only way to be sure is to get in touch with Total ICF for your next Central Alberta residential project. We can help you determine the needs of your development and can provide further eduction on NUDURA insulated concrete form construction. Contact us at 403-887-2214 today.