All the ICF veterans out there, what roof and floor systems are the best in terms of cost, thermal bridging, longer span structural strength, avoiding condensation, etc? So far, the most repeated types I've heard of are composite systems (ecospan), ICF systems (insuldeck), or steel SIP. I will be building a narrow rectangular two story ICF home (it's on a narrow lot) - dimensions are going to be approx 24x80ft. I'm essentially going to be GC'ing my build with heavy involvement start to finish from an architecture firm (in the middle of the interviewing firms). The above are the three floor and roof systems I'll be considering. I want a flat roof. I'd prefer that the exterior walls serve as the main structural walls for the house without need for structural interior walls. Then for each type, they have different pros - radiant heating abilities with insuldeck, high structural integrity and quick installation with ecospan (the ICF installer I'm considering does ICF Walls and this, so I'd have both done by one sub)...and steel SIP I don't know much about except that I keep hearing about it for floors and roofs. I'm located in South Louisiana.

24 ft span is nothing....Best for cost, thermal bridging, span, condensation......wood trusses....IMHO

I'm not an ICF pro, but I did my own house with ICF (Nudura) and Insuldeck about 7 years ago. The Insuldeck was fairly straightforward and fits well with the ICF. Overall, I was happy with the construction process and the end results. I had a pretty standard sloped roof, so went with a traditional lumber frame for it. Seems like the Insuldeck engineering and build would be pretty straightforward for the design you are looking for. Sorry, but I can't give you any input on the other 2 systems you are considering.

for information on insuldeck please email peteratinsuldeckdotcom

Looking at the Insuldeck images, they have big gaps between the foam blocks. Anyone know why? It doesn't look like a normal ICF structure, and I'm not sure what those gaps are about. It would erode R-values if they're not filled with insulation.

For steel SIPs, check out ThermaSteel. They have steel studs or joists wrapped around continuous EPS foam. Their "rPanels" are the ones designed for roofs: https://www.thermasteelinc.com/content/revpanel-system

I thought this article at JLC about steel-framed roofs was very interesting: https://www.jlconline.com/how-to/framing/framing-roofs-with-steel_o

Using wood would conflict with some of the rationale for ICF to begin with. I'm a big fan of steel. With ICF or ThermaSteel roofs, there's no bridging, which is the typical objection to steel (ThermaSteel's studs/joists don't go through the foam – they're turned sideways, which is brilliant).

Most of the solutions you're thinking about don't need separate underlying joist/rafter structures, right? They are the load-bearing structure of the roof themselves. For bigger picture structural strategies with steel, I recommend looking at Blue Sky Building and Ecosteel. Blue Sky has a steel bolted moment frame that doesn't need any load-bearing walls at all. The structural support comes from the corner columns and horizontal beams connecting those columns – that's the bolted moment frame. They use "structural steel" for the columns -- hollow structural sections, which is normally seen in commercial, not residential. Applying it here means the exterior walls don't need to do anything structural -- they can just be there for enclosing and insulating the home (ThermaSteel panels would be a great complement to Blue Sky's system -- their structural capability would be redundant, but I like redundancy in construction, and their R-values will be outstanding. Plus you need to be able to attach things like siding, drywall, cabinets, and TVs to the walls, so ThermaSteel's steel studs are handy there.)

You sound like you are trying to sell yourself on what you want.....guessing once you get the cost you will switch to wood like the rest of us.

Attaching roofing, electrical, drywall, to that stuff looks like a major pain. ICF is hard a lot of times but for a horizontal surface it has got to be 10x harder......wow.

You're talking about attaching drywall, roofing, etc. to steel framing? That's easy. It's just screws, often self-tapping screws. Steel studs are extremely common in commercial construction, and attachment is pretty well sorted out. I wouldn't use wood in my build.

Thanks everyone. I stepped away - appreciate the feedback. It seems like ecospan is the least known, and that's a notable trend. Time to do more research!

Posted By BlueFlight on 09 Dec 2020 07:03 PM
Looking at the Insuldeck images, they have big gaps between the foam blocks. Anyone know why? It doesn't look like a normal ICF structure, and I'm not sure what those gaps are about. It would erode R-values if they're not filled with insulation.

For steel SIPs, check out ThermaSteel. They have steel studs or joists wrapped around continuous EPS foam. Their "rPanels" are the ones designed for roofs: https://www.thermasteelinc.com/content/revpanel-system

I thought this article at JLC about steel-framed roofs was very interesting: https://www.jlconline.com/how-to/framing/framing-roofs-with-steel_o

Using wood would conflict with some of the rationale for ICF to begin with. I'm a big fan of steel. With ICF or ThermaSteel roofs, there's no bridging, which is the typical objection to steel (ThermaSteel's studs/joists don't go through the foam – they're turned sideways, which is brilliant).

Most of the solutions you're thinking about don't need separate underlying joist/rafter structures, right? They are the load-bearing structure of the roof themselves. For bigger picture structural strategies with steel, I recommend looking at Blue Sky Building and Ecosteel. Blue Sky has a steel bolted moment frame that doesn't need any load-bearing walls at all. The structural support comes from the corner columns and horizontal beams connecting those columns – that's the bolted moment frame. They use "structural steel" for the columns -- hollow structural sections, which is normally seen in commercial, not residential. Applying it here means the exterior walls don't need to do anything structural -- they can just be there for enclosing and insulating the home (ThermaSteel panels would be a great complement to Blue Sky's system -- their structural capability would be redundant, but I like redundancy in construction, and their R-values will be outstanding. Plus you need to be able to attach things like siding, drywall, cabinets, and TVs to the walls, so ThermaSteel's steel studs are handy there.)

How I love new information! Thanks so much for these new suggestions. I'll research these. I know my architect in general is looking to incorporate commercial building techniques and materials in the home design to take advantage of material and structural engineering advantages they may bring. Even if they end up being pricier compared to another roof or floor, there maybe other savings not considered (same argument for ICF when compared 1:1 to the cost of wood studs). Thanks!

Posted By newbostonconst on 07 Dec 2020 12:31 PM
24 ft span is nothing....Best for cost, thermal bridging, span, condensation......wood trusses....IMHO

Good to know 24 ft span is manageable - we have an open floor plan, and that is the max span we'll be dealing w/ due to the lot size. Because of where we are, I'm trying to avoid wood as much as possible. I'm in S. Louisiana, and I'm trying to cut down on food for mold and termites. The air is constantly damp here.

Have you considered Structural Concrete Insulated Panels (SCIPs) for the floor, exterior walls and roof? If interested, contact Gulf Concrete Technology in Long Beach, Mississippi. www.gctm2.com My projects have used this system with great success.

I think you need to separate roof systems from floor systems in the discussion.
For subfloors, we have used precast concrete, Lite-Deck, I-joists, Floor trusses, iSpan, bar joists, all with concrete poured over them. As well as the wood systems with no concrete.
For flat roofs we have used Lite-Deck and parallel chord trusses.
We have thought through and implemented a lot of details, done a lot wrong, and a few things right. We still have a lot of room to learn.

Subfloors: We have been using iSpan for our subfloors, which is a composite. It takes some more detailing, and does cost more than wood. The problem with Insulspan, iSpan, or precast is that you interrupt a layer of the ICF foam in order to install. This leaves a cold floor edge (in Michigan). Thus we now hang the iSpan from an interior brickledge (again increasing the cost). We use iSpan because it is a very stiff floor, and most of our clients want polished concrete. If they don't, we will use wood framing every time. The trades like it better, it is faster and less expensive, with no condensation potential or cold edge.

Flat roofs: Insulspan has varying thicknesses of the foam, and at its thin point does not have enough insulation to be effective (in my opinion). In order to perform well and not condensate, you should add additional insulation underneath, which then makes fastening the drywall a bit more difficult. Secondly, the thermal mass doesn't help when it is outboard of the insulation. Third, in order to waterproof it you need to build a roof above it, or detail it like a commercial roof with rolled roofing. This is an expensive option, with little benefit. Wood framed roofs are unlikely to condensate because the structural members above insulation are the same temp as the air. Using parallel chord trusses for flat roofs gives plenty of space for trades to run their services in. Unless you have a compelling reason, I don't think the effort is worth reinventing the wheel.

Posted By rvalue on 05 Jan 2021 01:09 PM

Subfloors: We have been using iSpan for our subfloors, which is a composite. It takes some more detailing, and does cost more than wood. The problem with Insulspan, iSpan, or precast is that you interrupt a layer of the ICF foam in order to install. This leaves a cold floor edge (in Michigan). Thus we now hang the iSpan from an interior brickledge (again increasing the cost). We use iSpan because it is a very stiff floor, and most of our clients want polished concrete. If they don't, we will use wood framing every time. The trades like it better, it is faster and less expensive, with no condensation potential or cold edge.

Does the iSpan system integrate as well as InsulDeck into an ICF wall?