Hi All,

I've heard whispers that 'Civil Engineers don't like straight runs of ICF', which suggests that box-shaped plans are less structurally sound than ones with a few jogs in them.

Are there any 'rules of thumb' on how long a straight wall of ICF can be before it's recommended to have a curve, bumpout, or such thing?

Any advise is welcome - we had issues with our home designer being unable to line up exterior walls on different floors, so it looks like I'm now the designer...

Thanks in advance!

Posted By Geergirl on 26 Jun 2014 06:25 PM
Hi All,

I've heard whispers that 'Civil Engineers don't like straight runs of ICF', which suggests that box-shaped plans are less structurally sound than ones with a few jogs in them.

Are there any 'rules of thumb' on how long a straight wall of ICF can be before it's recommended to have a curve, bumpout, or such thing?

Any advise is welcome - we had issues with our home designer being unable to line up exterior walls on different floors, so it looks like I'm now the designer...

Thanks in advance!

I think you meant "structural engineers" as civil engineers tend to focus on roads, bridges, etc.

Why would you want a home to look like a shoebox anyways? Aesthetically, changes in the wall plane add dimension and depth to the home. Rectangles are great for 1st grade and for storage containers but make for lack luster looking homes.

What is usually more important is wall height. There are a lot of variables at play like wall height, wind loads, terrain, wind exposure, etc.

There are plenty of rectangular ICF storage warehouses out there and they are structurally sound. Aesthetics are not as vital in a warehouse as it is in a home.

Lbear - are you an Engineer? Generally speaking, Structural Engineering can often be considered a specialized type of Civil Engineer, same as a Geotechnical Engineer. I might end up consulting with both on this project, but that comes along-with designing the house plan.

I'm disappointed in your post as it doesn't answer my question, but rather plays with rhetoric.
I can design a house with a million gables, fancy details, etc - but if it's not buildable, or more expensive than my budget allows, it's worthless. I'm not fond of shoeboxes either, so I'm aiming for a compromise between the two.

Varying height can be fun - but cathedral ceilings are harder to insulate, the light bulbs are harder to change, and they waste both space and heating/cooling energy. It can also make it challenging for the roofers. I'd rather stick with a 9' or 10' ceiling, and decorate it with say, vaults, coffers and other such fun things.


So please try again?
Thanks!

PS - my terrain is DEAD FLAT - were talking less than a foot over MILES.
I've already oriented the house to take advantage of heating/cooling, daylight etc.

Search for and download the Prescriptive Method for ICF houses. It's a HUD, I think, document. As I recall it gives a limit of 60 feet for a straight line wall, but it may depend on the design wind load for your area. It's a very good document and provides all sorts of specifications for ICF construction. Build to it and you shouldn't have any problems with building inspectors.

dmaceld, THANK YOU, I hadn't come across that document previously, so I will give it a good read!

A licensed structural engineer is typically a licensed civil or structural engineer who has specialized structural engineering knowledge and experience, and who has passed an additional structural engineering exam so as to a receive a structural engineering endorsement to their license. The prescriptive method is commonly used for ICF homes provided you don’t have to address anything that takes you outside the prescriptive method limits like larger roof overhangs, taller walls, higher wind loads, stricter seismic requirements, etc. Flat terrain doesn’t limit ICF construction. If you use pilasters as required, there really isn’t any maximum straight run of ICF wall. We like rectangular, single story, ranch style homes for all the reasons you indicated and several more.

Posted By Geergirl on 26 Jun 2014 08:20 PM


I'm not fond of shoeboxes either, so I'm aiming for a compromise between the two.

I didn't mean to come across as being brash. There was some sarcastic humor in my post but I guess it fell on deaf ears. That's the problem with emails/posts is that the tone of the message can be misconstrued.

As far as your questions go:

I just ran across this situation myself. Some counties will NOT accept a civil engineer stamp on a residential structural drawing. All the time and money spent would be wasted as the plans would be rejected by the building department. One would figure there wouldn't be a problem but I would contact your local building department before you proceed because each county will have it's own quirky rules. A structural engineer that is licensed and in good standing for that state will not have any issues. A civil engineer stamp might not pass the building department for a residential structural drawing.

The point of my response was that ICF can be designed to whatever you want the house to appear like. Once again, local codes, HOA's and the like will dictate what kind of parameters you are allowed within your home design. Some areas forbid certain types of aesthetics and it would be a shame to spend thousands designing and engineering a home that would only later get rejected by the city/county/HOA Architectural Review Board, etc. Out of 6 communities I was looking at, only 1 allowed the type of home I wanted to design and build. The other 5 would not have allowed my design and it would have been wasted $$$ if I bought any of those lots.

Unless one is building in the middle of nowhere that has virtually no rules or regulations, you have a free design pallette but those types of places are rare and most people build within populated areas that are governed by city, county and HOA ordinances. Case-in-point, a friend was looking to buy some land to build an energy efficient home but found out that the HOA forbids PV solar and certain designs. So he passed on the lot but if he didn't do his due-diligence, you would have ended up spending $100k on a lot that he couldn't build on.

Lastly, designing a home is not an easy task. There is a field of study involved and architects must know all the intricate aspects of a house design, flow and aesthetics. If you are attempting a DIY design and this is your first home, I would highly advise on hiring at least a consultant who has experience.

which suggests that box-shaped plans are less structurally sound than ones with a few jogs in them

That's correct, depending on the distances involved.

Are there any 'rules of thumb' on how long a straight wall of ICF can be before it's recommended to have a curve, bumpout, or such thing?

Bumpouts are always a good idea for keeping strength up and mass down, but the answer to your question is 60 feet.
PS - I'm not a licensed structural engineer.

I really luck out with our lot.
Got it for an amazing price too, as a builder had a stroke and needed to sell off the lots as-is (with final grading and power to the lot line, too!)
Semi-rural (10 min from a small town, 30 min commute to work), 2 acres to play with, and the only requirements/strestrictions are no move-on homes, and min 1100 sq ft.
So it's basically m ine to do whatever i like with!

Also, I really love the look of french country homes, which basically are a hipped box with a few gables and things for visual interest.

Some where in the 60' range sticks in my mind also.

You guys are forgetting that the prescriptive guidelines are only guidelines. It is not unusual to see a 150 foot straight ICF wall. The fact that it's stronger with corners is another matter. A long wall will require a stamp of the engineer of record for that job in that state (USA anyway). If engineers actually held stuck to the guidelines they'd be out work and we would get to build much .

The guidelines have lots of pre-engineered wall heights and etc. which can be exceeded by leaps and bounds via engineering. For example, I think there's a 10' unsupported example or two in the document.

This is very similar to a designer thinking he can only go 20' span for an ICF lintel (that's as high as the NUDURA pre-engineered tables contemplate) when you can easily go 40' (WITH ENGINEERING).

Another common one is that windows have to be so far away from the corners. I don't recall if that's in the document or not but many manufactures derive some of their data from the prescriptive method. We and others have done ICF corners that are all glass -- zero concrete. Again, with engineering. If I recall the prescriptive data also has a limit on number of floors etc. Regards.

Precisely TexasICF. The prescriptive method is the “prescriptive” method... I can’t remember the last time that we were able to use the prescriptive method, but we are licensed engineers and fortunately not limited by the prescriptive method either.

You guys are forgetting that the prescriptive guidelines are only guidelines.

If you look carefully, the OP was asking about "rules of thumb", not what could or couldn't be done.

Valid point ICF. Our point was that you don’t need to change/limit an existing/new building plan when using ICF (e.g., change or limit the length of ICF straight walls to 60 feet). In this case, you just need to know about pilasters and use them when required. There are many builders who treat the prescriptive method like a religious person might treat the bible. They will often modify a building plan when using ICF to stay within the limitations of the prescriptive method without realizing that a simple engineering design change will often address the issue without any need to change the building plan.

If the floors and the roof is concrete then
this topic is obsolete.

Thanks all!
The prescriptive document is useful for me as I'd like to limit the 'special engineering' to areas of the house plan that are 'highlights' of the plan, if you will.
We really want a circular tower attached to the house, which is likely gonna cost a small fortune due to all the block-cutting (tho foxblocks now has a radius wall!), so keeping in mind the 'basics' is a good way to ensure we don't go overboard on the 'custom engineering'.

Cheers!

Nudura has custom-made radius forms available. These are made to any radius shown on your plans. I have personally built with standard forms cut into a radius and with Nudura's custom made radius forms - the extra couple bucks for the radius forms pay for themselves multiple time over in labour savings and provide a clean finished product.

For a radius cut the straight form between the webs on the outside of the radius and do 2 1" deep cuts between each web on the inside Buy some cans of foam from the Homarama at $4 per can and fill in the gaps on the outside. This came from my former Fox Block rep. I used it on a 23'6" radius 2 years ago and it worked out fine , with no extra parts to buy. We did cut strips of some 1/4" osb for strapping. No problemo.

As an ICF dealer I love customers doing what you are doing. Your local ICF rep should be able to guide you thru this process. Are some designs stronger than others ? Yes, of course, but , I tell my customers, "If you are the one living in this home, you should have it just the way you want it". Pick a good block, pick a good dealer and GC and keep them close on the front end during the design process. You will be fine.