Image Credit: Genest Concrete
Image Credit: Genest Concrete A layer of mortar 1 mm thick is enough to bind courses of the block together. Alternately, a masonry adhesive can be used. The block is also reinforced with steel and grout poured into wall cavities.
More Green Building News
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 (ICF), 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 EPS 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 bridging 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.
Weekly Newsletter
Get building science and energy efficiency advice, plus special offers, in your inbox.
24 Comments
Extruded clay thermo-blocks
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.
Insulation rating
"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!
My question exactly. Here in Zone 7 it is best not to have thermal bridging. I like the exterior rigidity and other benefits; including thermal massing during our summers: Hot days and cool nights reward masonry exteriors. But within that rigid envelope a second thermal envelope is needed. Yes, more expensive. But if designing for multi generations it makes sense.
Am I wrong...
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?
Rebar
Ethan, the caption for image 2 lists steel and grout.
Response to Ethan T
Ethan,
Thomas Stone is correct. Note also this sentence from paragraph 3 of the article: "Like ICFs, Comfort Block is reinforced with steel and grout."
Thermal Insulation Continuity?
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?
Response to Bill Burke
Bill,
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.
I've seen the testing reports
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.
Anyone know if the can be used for basements?
I've had a few conversations with Chris Genest, the owner, over the years about it. Originally he said no, but now he says yes--it just needs to be protected by a heavy-duty waterproofing membrane, as the block is not waterproof.
Looking at their website, no.
THX Malcolm - I decided to email the company directly last night ...
This morning I got a one word reply: "Yes" from one of their employees who used to be a mason & built a complete home in Maine using the "Comfort Block".
Interestingly, when I inquired how much it would cost to ship a "Perfect Block" from manufacturing in AZ to Maine for a 30X40 house, to do the basement
The shipping costs were 50% of the material costs ($12/block) so $6/block !
begreener,
I don't see anything to back that up on their website, which says where each product can be used. No photos, no details, no text. Maybe he is right, but I'd want a more explicit go-ahead before using them that way.
I agree - this is the only (3) reference(s) to foundation walls that I could find:
https://www.genest-concrete.com/how-to-lay-comfort-block/
excerpt(s):
There’s no doubt that concrete block is a hugely versatile building material. With CMU blocks, you can create structures as small as backyard fire pits or as large as home foundations. But we’ll admit, it requires skill (and a lot of patience) to work with. When you search, “how difficult is it to lay concrete block?” you’ll find a lot of forums with curt answers like “difficult.” “just hire a mason…” and “how are your hands?”
What if we told you that building walls, foundations, outdoor fireplaces, and more could be a whole lot easier—for builders, landscapers, and motivated DIYers alike? Inspired by German-style concrete wall systems, Comfort Block introduces precision-ground interlocking concrete block technology to make construction faster, easier, and more precise"
What Can Interlocking Concrete Block Be Used For?
The appropriate application of these interlocking concrete blocks will depend on the Comfort Block system you choose, but here are a few projects where these innovative CMU blocks work well:
Fireplaces
Pizza Ovens
Outdoor Kitchens
Landscape & Retaining Walls
Sheds
Garages
Greenhouses
Pool houses
Home Foundations & Whole Home Construction
Large Scale Commercial Projects
That style of prose reminds me of the chatbots we're plagued with.
begreener,
You had more luck than me.
My main concern is that block foundations - at least around here - have both vertical and horizontal reinforcing. Can you get rebar though them in either direction given the foam and the small gaps between the blocks ?
Malcolm, yes, they have horizontal grooves and vertical chambers for rebar. You do lose the EPS where you have vertical rebar but they still have a high whole-wall R-value for concrete blocks.
If you want higher performance, because the exterior needs to be finished anyway, it also works well with a (properly installed) EIFS foam-and-stucco system on the exterior.
Response to #12: They freely acknowledge that this kind of block is best used within a reasonable distance from where it's made, due to the size and cost of shipping.
Michael,
They sound like a great idea. Hopefully either Genest, or some other manufacturer, starts plants elsewhere.
Responding to #18
Hi Michael!
When I talked to Perfect Block by phone this week, they did say another plant (original in AZ) was on it's way in Michigan (I think)?
I'm an American living in France and just thought I'd chime in on what I see happening here.
There is a clay brick version of the block I see around. It's used mostly in non-seismic areas as a complete wall, or combined with cast concrete for seismic. Since it's conduction, not convection, that is the major culprit with concrete blocks, making the path from exterior to interior as long as possible helps. That can be seen in the image I posted for this clay version.
The most common wall system uses a standard concrete block with INTERIOR insulation. I've attached 2 images for that. One shows a light gauge steel frame inside the wall with fiberglass insulation. The other shows a product that should really be made available in the USA. It's EPS or GPS insulation factory bonded to 4x8 gypsum board sheets. These are simply glued to the inner face of the block wall. Electrical is run in conduit attached to the face of the block. Water supply likewise. The foam panels can easily be routed out for these. Or often they are glued using very thick dabs of a mortar glue that leaves a gap between the back of the insulation and the block wall, as shown in the attached image.
These interior systems have their advantages and disadvantages, as do most systems. They are very fast to put up and they take advantage of the durability of the concrete block at the exterior. The exterior finish is usually just a 1 coat stucco. The main disadvantage is that they are not continuous where upper floors meet exterior walls. And of course they leave the thermal mass outside the conditioned space.
I expect to be building a house in the next few years. I will use AAC blocks, supplemented on the inside with the light gauge steel frame and batt insulation. AAC is not the most common material here but it is readily available. It solves the continuity issue and provides more than 60% of the required insulation. By adding the inner batt system I can also run my plumbing and electrical inside the block instead of having to rout the blocks for them. Since the thinnest structural AAC block does not provide the total insulation required, this approach allows me to use the thinnest block, while achieving the required insulation and avoiding the hassle of running plumbing and electrical in the block walls themselves. A win/win/win.
Hi JollyGreen!
What is the r-value of that clay block & thickness?
I agree about the lack of insulated plasterboard here in the US - there is one made from MgO board....
https://innovapanel.com/mgo-nail-base-retrofit-wall-panel/
I like service cavity concept in the wall too (as well as in floors with an open web truss)
The lack of any information on using Comfort block as just a foundation material tells me that they really want people to be building masonry structures (tougher sell in New England)
Genest also has an interesting photovoltaic flat roof tile (ceramic) that they import from Tejas Borja (BIPV).
https://tejasborja.com/wp-content/uploads/2021/02/Folleto-gama-SOLAR-en.pdf
Porotherm is made by a German company called Wieberberger. It is the most common brand name I see around for the clay blocks. They come in a variety of configurations and thicknesses, including with some kind of fiber insulation in them. I don't have any personal experience with them. But I found this information on one building supply website.
https://www.clayblock.ie/product/porotherm-425-t8-uninsulated/?srsltid=AfmBOoov_EZsnWhpJ3eteXJS_21A0A2XyaD2-mKy4NzxEr8MIIyq6IpG
This is a block that gives a wall 425mm thick, 16.75 inches. It has a metric R-value of 5.55, which converts to R31.5 in our North American units.
Log in or create an account to post a comment.
Sign up Log in