Opinions on Pre-Cast Insulated Concrete Walls
Hello,
My wife and I are in the design phase of building our new house. I have probably sketched out fifty different designs so far trying to get what we want in the house.
We initially thought about using SIPs or ICFs to build the house. I like the idea of a well insulated and sealed house, but both of those options would require a lot of interior and exterior work once built.
Started to look at insulated concrete from the other perspective where the insulation was on the inside. There are cast-in-place, tilt-up and precast concrete systems that incorporate the insulation on the inside. I really like this idea as I enjoy the look of bare concrete.
I’m trying to get the wall details hammered out and think I may be over thinking the amount of insulation. I want the house to be a little over build, energy efficient enough so solar makes sense.
Any advice or feedback welcome.
Thanks,
Mick
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Replies
A few questions:
1) What climate zone are you in? The amount of insulation required by code and common sense, and the concerns about ground freezing are both dependent on the climate.
2) There are a lot of different pre-cast concrete designs which have varying degrees of thermal bridging issues. What products and manufacturers are you looking at?
3) What type of insulation are you thinking of for the other parts? I'd recommend EPS for more R-value per dollar and vastly lower climate impact than XPS.
@Charlie Sullivan
1. The house will be built just outside the Boise city limits. Zone 5, Requirements: Ceiling R49, Mass wall R13/17, Slab R10. I think my design idea is well above those.
2. There are many wythe connector manufactures; two I'm most interested in are Thermomass, CarbonCast and HK Ties. All do precast, some do tilt up and cast in place. I would prefer cast in place as I think it would allow the most sealed, thermally broken structure.
3. I'm want to use all EPS for all of the insulation, possibly using Foam-Control MAX. It all depends on what is cost effective.
Mick
Those are all good systems--not the types that I was worried about.
The code allows reduced insulation R-value for a mass wall. But in mid winter, it won't give you much benefit. I'd want more like R40 in the wall, which gets expensive doing it purely with foam. If you can do it with reclaimed foam, super-thick foam becomes more affordable.
Given the climate, you'll either need to follow frost-protected shallow foundation guidelines to prevent frost heaving, or have the foundation deep enough. Without looking them up I'm not sure but I suspect you will need more for that.
Insulation on the top of the roof would be a good idea, to get thick insulation, at low-cost with reclaimed foam, without thermal bridging.
How will you do wiring and plumbing?
@Charlie Sullivan
From the idea I posted the walls were at R30 and I think the roof was R58 for the house. With the insulation on the top of the roof as well it would be a little hard to get a thermal break as I want the roof concrete to tie into the outer wall concrete.
The wiring, plumbing and some of the HVAC would be run before the concrete is ever poured. The forms get put up, all the services get run and then the concrete is poured afterwards. Wiring and plumbing are pulled once the forms are removed. Takes a lot of forward planning.
Mick
Related question, would I need insulation on the top of the roof?
Mick
Maybe Nudura One Series if you like exposed concrete on a budget?
Sam Nudura One Series would still leave insulation that would have to be finished. I think the labor cost and time to build up the blocks would be comparable to cast in place.
Mick
So somebody should invent a double sided ICF system: plywood-cavity for concrete-insulation-cavity for concrete-plywood...
@Sam Bargetz
They do, http://spidertiesystem.com/ , but it seems like a lot of work compared to using traditional forms just placing the insulation inside.
Mick
We're also looking for solution alternatives like the OP (concrete-insulation-concrete).
Have you considered shotcrete/gunite type approaches that sound interesting like:
1) https://tridipanel.com/disaster-resistant-building-materials/ (pictures with Jimmy Carter on habitat for humanity homes got me excited)
2) http://www.gctm2.com/
3) https://www.rsg3d.com/faqs
4).... must be others
If you have and have abandoned those approaches I'd love to know why (or if anyone else has information about them)
5) We're also trying to get information/experience on a product that isn't exactly what you are looking for, but... we've become open to it because it would allow the exterior finish to be applied more easily called:
THERMAEZE (from Certainteed)
https://bartleycorp.com/wp-content/uploads/2014/03/ThermaEZE.pdf
This gives up on the idea of concrete-insulation-concrete and instead moves to exterior insulation (which is better from heating/cooling perspective) but it makes it easier to finish the outside than if we just tried to bolt/glue insulation and siding/stucco mesh to the outside of the concrete.
Like you, we had moved to concrete-insulation-concrete because of the difficulty of applying finish coats, but... (maybe?) Thermaeze makes it easier to reopen that approach? The inside would still be concrete which could be left bare or easily be stuccoed over.
We have considered many different options. When we first decided to build a house I started looking and more energy efficient building forms. Initially I really liked the idea of SIPs, but there are many drawbacks I saw for them such as difficultly sealing and potential rotting issues.
I had heard about ICFs a few years ago also and started reading up on them and even talked to a few reps from Amvic and BuildBlocks, then with a few builders who used them. All assured me that the house we wanted could be built with them for the amount we are looking to spend. But wanting to pay for as little labor as possible, ICFs still have to be finished the same as stick built houses. Also there are condos being built a few blocks from my work that are using ICFs and it is taking them a very long time to erect the walls. From the way ICF manufacturers talk they should go up a lot faster. In comparison there are other stick build apartments also going up that the shell is almost complete with windows. Both started about the same time.
I had looked at a lot of the shotcrete styles of building. One of my favorites was https://www.gigacrete.com/. But it still requires a lot of labor and expertise. I wasn't able to find anyone local who was familiar with it.
Thermaeze is similar to the sandwich. Seems off that their pictures show most of it gets installed to the inside.
This idea of building a house has become a rollercoaster. There are so many different ways to accomplish the same thing. The thing I came up against time and time again is knowledge locally of the building techniques. Many of the new ideas are very regionalized or overseas.
What has set my mind toward the concrete/insulation/concrete sandwich is that there are many concrete contractors local. Just on the road to our house there are three concrete plants and two big contractors. The architect we found initially for SIPs development also has worked with the Thermomass system are the nearby Air Force base. There they used precast panels. We like the look of bare concrete accented with wood and metal. Once the shell is done I can do most of the work myself or with the help of friends and family in the business who know finish carpentry and electrical. I like the idea of having a concrete roof that we can have an upper patio on and that we don't have to work about it rotting out.
I'm pretty sold on it. I just want to make sure that it is designed so that it is as comfortable and efficient as possible. It should last a few lifetimes if we do it right.
Mick
We seem to be on a similar path with no happy ending so far. We can do the finishing with a complete shell as well.
(1) We looked at spidertie, too -- it seems like a lot of work if you want to do more than 2" of insulation (which we do).
(2) We built a SIP house -- it went up shockingly quickly and easily (my wife and I did it ourselves, with moderate building experience but no experience with SIPS). My frustration with SIPS is the lack of STC (sound) rating. We can hear deer walking outside like they are in the bedroom with us. I wouldn't build with this system again anywhere near a road... or deer... or birds....
(3) Since posting I tracked down more information on Thermaeze... it appears to be discontinued, so... even if you had liked it, it isn't possible
Maybe I'm coming back around to Thermomass' cast in place system...
@Flying Beet
Our land is about a quarter mile from some rural train tracks. I love trains, just not at three in the morning. I think the plans we have will mitigate any of those sound issues.
There are a lot of different cast in place systems like Thermomass' system. I'm looking into HK Ties because they are located in Utah not too far away. They like Thermomass have several different tie designs for different types of building. Several of the foam manufacturers are also located here in Idaho so I have a range of choices. A couple of the precast plants that use these systems are in the region as well.
Seems to be a never ending search for products, vendors, contractors, resources and knowledge. Just waiting on finalized first plans before deciding final direction.
Mick
What is wrong with wood, a well planned double wall may well be the most cost effective and energy efficient wall you can build. Concrete has very high embodied energy, please consider Mother Earth in your calculations.
@Doug McEvers
There is nothing wrong with wood if that is what is your preference. Personally for me I prefer concrete, not saying there won't be decretive wood in our house.
Everything is from your own personal outlook. I should face the house differently, but I want to wake up in the morning, have my coffee and look at the mountains to the East. I the evenings I want to sit up on the patio and watch the sunset to the West. Having the house face those directions isn't the ideal, but it is my preference to make the house our house.
Many of the ideas that have gone into our plans are based on where products are produced and if they are viable for our solution. It's all a balance between desires, needs and costs.
Mick
@Mick and Flying Beet
Did either of you ever come to a solution. I am investigating a cast in place center insulated concrete foundation wall on which a double stud light frame wood structure will stand.
I have obtained pricing on composite center insulation wythe ties (HK and EZ-Bar) and fiberglass form ties (Fibre-Tie and Steel-Dog) are am having second thoughts on the approach.
Curious where your recent paths ended.
Thanks,
https://www.nudura.com/products/nudura-plus-series/nudura-xr35/
Nudura now makes a R-35 ICF panel with a 6" and 4" concrete cores and 4" of EPS on each side, for a total of 8" of rigid foam.
THE INNOVATION CONTINUES WITH OUR NEW XR35 PLUS SERIES FORM.
The XR35 has been created with a higher R-Value due to its 4” (102mm) EPS panels on each side of the concrete core. It is available with a 6” (150mm) and 8” (203mm) core as a standard form and a 90° corner form.
The fastening strips remain 5/8” (16mm) below the surface of the EPS and are located at 8” (203mm) in the center. The fastening strip is marked with a diamond pattern making fastening the interior or exterior finishes quick and easily on-site.