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Maine Firm Develops a New Type of Insulated Block

The Comfort Block combines concrete block and EPS insulation into a 16-inch thick package

Posted on Jun 2 2017 by Scott Gibson

A Maine-based concrete block manufacturer, Genest Concrete, has developed an insulated block combining concrete and expanded polystyrene. The blocks are designed to be assembled with a thin layer of adhesive rather than conventional mortar.

The product, called Comfort Block, was developed at the manufacturer's Sanford, Maine, plant after co-general manager Chris Genest returned from a trip to Germany in 2006. It's an inside-out version of an insulated concrete form (ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure.), a building component that also combines rigid insulation and concrete but in a way that leaves the insulation exposed on both outside faces of the wall.

Comfort Block uses three 2 1/2-inch-thick pieces of EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest. insulation, protected inside concrete cavities. Like ICFs, Comfort Block is reinforced with steel and grout. It forms a wall 16 inches thick.

Blocks sell for about $7 each, or $10.50 per square foot of wall, not including labor to set the block or the application of plaster and stucco finishes.

German construction methods are far ahead of ours

Genest said he went to a Munich trade show a decade ago to see the high-quality block-making machinery that German manufacturers are known for. But while he was there, Genest couldn't help but notice that many of the buildings in the area were made from extruded clay blocks forming insulated walls up to 20 inches thick.

"At first I thought these guys were crazy," he said. "But the more I looked into it, the more I saw an incredible amount of research and development was going into these products."

When he got back to Maine, Genest started sketching a version of the block that would meet U.S. building codes and would be accepted by builders here. Limitations with the block-making equipment he had, plus a desire to replicate the German model, led to the design. Genest also is working on an 8-inch-thick version of the block.

The block includes an internal chase for wiring, so there's no need for gypsum drywall on the inside or conventional siding on the outside. The elimination of a thick mortar layer between courses is another time-saver. Genest says that mortar is used between courses of conventional CMUs because of their slightly irregular dimensions. Comfort Blocks are sent through a grinding machine after they are cast to bring them to a precise, uniform height.

So blocks need only a very thin layer of mortar or adhesive between courses, Genest says. The mortar can be applied with a hand-held tool (see Image #2, below) that dispenses a layer 1 mm thick (0.04 inches). An alternative is spray adhesive in a can. Both products are imported from Germany, as is the dispenser. The tools are so common there they can be purchased in any hardware store, but are unknown in the U.S.

“It’s really quite embarrassing how far behind the United States is with the advancement of modern masonry construction," he said.

Blocks come in a variety of sizes — wall block, end units, and corner block, for example. Wall blocks, what Genest calls the CB Stretcher, are 8 inches high, 12 inches long and 16 inches wide and weigh 45 pounds each.

The company's website says that the blocks have a "thermal mass performance" of R-30 or more. Genest says that's based on the R-value of the EPS, about R-4 per inch, plus estimates and modeling on both a similar German-made block and an earlier version of the Comfort Block. There has been no third-party testing of whole-wall R-values, so it's not clear how thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through the concrete webs of the block would affect performance. Genest acknowledges that coming up with a precise R-value for an assembled Comfort Block wall has been a challenge.

Making the product worker-friendly

Genest says that the simplicity of the system will make construction approachable for owner-builders. Working with a single trained mason, homeowners should be able to pick up what they need to know in an hour or less.

Genest said that could be a plus in an era when younger workers are failing to take the place of older masons who are hitting retirement age and getting out of the trade. If the product is going to be successful, he said, it can't be complicated and fussy to use.

“You have to get this product to market, and it has to be friendly to the trades," he said. "All the trades around here know lumber, and if you don’t have a solution for them and you don’t make it relatively easy and not scary they’re going to throw it under the bus so quick you won’t have a chance. They’re not going to want to do it. We need to work with them.”

Genest's market area is New England. Because block is heavy and expensive to ship, Comfort Block will remain a regional offering unless the company can find block producers elsewhere who are willing to become licensed partners.

Genest Concrete was founded in 1927 by Chris Genest's great-grandfather, who emigrated to Maine from Canada and opened a sand and gravel pit in Sanford. His grandfather, then his father and uncle, took over and expanded the business. The company, which employs 80 people, produces architectural masonry, landscape paving stones, stones for retaining walls, and pavers and slabs for roof decks and plazas.

Note: An earlier version of this post incorrectly gave the price as $10.50 per block, not $10.50 per square foot of block.

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Image Credits:

  1. Genest Concrete

Jun 2, 2017 8:39 AM ET

Extruded clay thermo-blocks
by davor radman

Extruded clay thermo-blocks over here have R value 15-30, but.. The really big and expensive ones are rarely used, from what I see, and either way, >=4 in of external insulation is required either way.

But thinner blocks are more cost effective. R15 block + R15 rigid is noticeably more cost effective than R30 block, because external insulation is done at the same time as stucco, so most of the expense you gotta pay anyway.

Jun 4, 2017 11:19 AM ET

Insulation rating
by Nathan Spriegel

"The company's website says that the blocks have a "thermal mass performance" of R-30 or more. Genest says that's based on the R-value of the EPS, about R-4 per inch, plus estimates and modeling on both a similar German-made block and an earlier version of the Comfort Block. "

"Comfort Block uses three 2 1/2-inch-thick pieces of EPS insulation, protected inside concrete cavities."

In other words R-30 AT BEST. With all that concrete bridging I understand why they have yet to perform "whole wall" testing!

Jun 5, 2017 10:51 AM ET

Edited Jun 5, 2017 10:51 AM ET.

Am I wrong...
by Ethan T ; Climate Zone 5A ; ~6000HDD

in thinking that the actual structure in CMU construction comes from rebar and grout poured in the cavity? How can these adhered blocks pass muster from a structural perspective?

Jun 5, 2017 11:19 AM ET

by Thomas Stone

Ethan, the caption for image 2 lists steel and grout.

Jun 5, 2017 11:38 AM ET

Response to Ethan T
by Martin Holladay

Thomas Stone is correct. Note also this sentence from paragraph 3 of the article: "Like ICFs, Comfort Block is reinforced with steel and grout."

Jun 7, 2017 9:02 PM ET

Thermal Insulation Continuity?
by Bill Burke

To reiterate what Nathan Spriegel has already pointed out, these blocks don't provide continuity of the thermal barrier. It may be an 'inside-out' version of an ICF, but the ICF DOES provide continuity of the thermal barrier. You would need to install a water resistant barrier on the outside and then add a layer of continuous insulation to get decent performance. These blocks work like metal studs with cavity insulation. Is there something about this product I've completely missed that indicates otherwise?

Jun 8, 2017 7:25 AM ET

Response to Bill Burke
by Martin Holladay

I agree with your analysis. For many decades, CMU manufacturers have been developing a variety of new blocks with foam inserts. All of these products share the same flaw: there is no continuous insulation layer, so thermal bridging reduces the thermal performance of the wall.

Jan 30, 2018 6:24 PM ET

Edited Jan 30, 2018 6:24 PM ET.

I've seen the testing reports
by Michael Maines

I've seen the testing reports for Comfort Block, performed by Building Science Corp--this is the rare situation where "thermal mass performance" really does have an effect. The concrete has a higher R-value than that in regular blocks, most of the webs don't extend through the product and they are offset, so while there is still thermal bridging, it's not like a regular CMU. On their own they exceed code-minimum R-value standards in Zone 6, even without taking the thermal mass effect into account--pretty amazing for a CMU. Installation is very fast, with a rolled-out adhesive instead of conventional mortar.

With the addition of exterior insulation they would be very high performing, though if you're going to that trouble it might be more cost effective to use thicker insulation and regular CMUs.

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