I am a homeowner in the process of building an ICF home using Nudura.  We have the walls poured up to the roof line and so far everything has gone quite well.  I have been in discussions with the building and siding installer and would appreciate some advice / feedback regarding the preferred approach for the application of flat hardipanel siding on the exterior.

It has been suggested to me (and the idea seems intuitive) to create a rain screen with furring strips to which the siding would then be attached using cor a vent or similar material.  I am not a builder or an engineer, but the air circulation seems like it would definitely help to preseve the siding (and paint on the siding) and an additional assumed benefit would be that the airspace would be more 'forgiving' to any surface imperfections (bulges, etc) in the exterior walls, especially given that the panels will be installed with exposed seams.

In discussions with the siding contractor, he feels that this is a waste of time and money, considering the cement fiber siding is (mostly) impervious to moisture, and that introducing a faster deteriorating material (if the furring strips are wood) would introduce a point of failure between the foam and the hardipanel.

Is there a standard here?  I believe that Nudura suggests applying directly to the foam, but I can't seem to resolve in my mind where the water will go if it does get behind the siding.  I've been told by the siding contractor that there is no way it will go through several inches of foam and concrete, but I'm not entirely confident of his assessment.  Is the best approach to use a non-wood material for the furring strips?

I have seen some indications in earlier posts (http://www.greenbuildingtalk.com/Forums/tabid/53/view/topic/forumid/4/postid/161/Default.aspx) that seem to suggest some type of air space is preferred but wanted to hear some more thoughts.

I have been lurking for a while and appreciate all the great information and discussion, thanks in advance for your time.

I have watched several of my neighbors build ICF houses, two used hardi plank siding that was attached directly to the foam, the other one, wire mesh was applied directly to the foam and then stucco was applied. 

I have built 2 homes in the maryland area using Nudura & Hardi Plank siding. The 1st problem we encountered was that Hardi didn't want to guarrantee the siding unless attachments we're specifically adhered toper ther manufacturers installation manual. As Nudura web attachments are 8" apart , Hardi wanted us to make sure we attached the ends of the planks 2" from the end of the board. Well as we know ICF layout sometimes doesn't work out perfect and some seems we're farther apart and to avoid a heck of a lot of waste that wasn't practical. I approach the install contactor and he added his guarrantee of the product. 3Years latter and not one problem with either home and we have had some hard wind storms and driving rain.

   Just make sure the contractor uses either screws or ring shank nails for the attachment.they did us a vent at the first course of siding to allow any if at all moisture to escape/drain off.