FAQ's about NUDURA Insulated Concrete Forms
What about cold pour joints at the middle of a tall wall height? Are they permitted?

If you can at all avoid having a cold pour joint in your wall, it's best to try and avoid it - particularly mid-height of a wall (i.e. halfway between lateral supports such as a floor slab, an interconnecting floor or a roof ). The reason why this is - IS because THAT point on a wall height is where the MAXIMUM "bending moment" will occur in the wall when the backfill comes against it (in a below grade application) OR when the wind acts against it (in an above grade application). It's at this point that the wall requires its most strength to resist bending. In fact, the wall acts just like a floor slab does in a suspended floor assembly when load is placed on it.

However, in many cases with taller wall heights (above 10 feet) - it's simply impossible to practically construct WITHOUT having a cold pour joint, particularly when the contractor is also concerned about maximum drop height of concrete in the wall or access for internal vibration. Fortunately, the ACI 318 Concrete Standard (the concrete code) in the US and CAN/CSA A23.3 in Canada both permit walls to be constructed in stages with cold pour joints PROVIDED THAT:
(a)  The VERTICAL reinforcing bars that are installed in the base portion of the wall are cut such that they will extend upward beyond the designated cold pour joint line by at least 40 times the diameter of the reinforcing bar being used. Most reinforcing bars will either be #4 (4/8 or ½" diameter) or #5 (5/8 or 5/8" diameter) bar Therefore, 40x ½" = 20" or 40 x 5/8" = 25". More lap length is obviously better so as long as it exceeds these minimums, the installation will comply with Code. This lap area in the wall is known as the "Lap Splice Length.".

(b)  As an alternate to above, reinforcing stubs cut to TWICE the designated lap splice length could be inserted into the top of the first pour immediately beside the bars of the base pour such that ½ of the bar is buried in the first pour and ½ extends above the top of the concrete pour. If your bar spacing exceeds 2'0" on center, you will need to ensure that sufficient bars are cut to assure that the maximum space between these bars is no greater than 2'-0".

(c)  In addition, the vertical reinforcing bars between subsequent pours must NEVER be spaced more that 1/5th the lap splice length apart from each other nor any greater than 6" apart (so if the lap splice length is 25" the bars should be no father apart than 5"). To attain this, you'll see some ICF installers use a 2 inch deep ring of 3" diameter ABS pipe cut-off dropped around each bar to assist the installer in holding the bar in place. With NUDURA, as long as the steel bars are resting against one side of the web closest to the planned "APPROACH" side of the concrete flow during a pour - this extra step and material is not required- as you'll never be in danger of "floating" the bar out of position and the 2nd tier will always be near the steel placed in the previous pour of concrete.

(d)  Next, the top of the first pour of concrete should be left "rough" in texture between the pours so that the wet concrete of the subsequent pour is able to secure a better "grab" to the previously cured lower layer of concrete below.

(e)  Finally, the second pour of concrete should be adequately vibrated to consolidate the wet layer at the cold pour joint as much as is physically possible to assure there is as little "honeycombing" as possible at this very crucial joint.

All of these steps will help to ensure that a cold pour joint in your wall will conform to the ACI 318 or CNA/CSA A23.3 requirements for wall pours.


How do you fasten the baseboard in a NUDURA house?
The absolute best way is to rip cut plywood to a depth of 2 to 2 1/2" and screw it in place to the webs along all the walls (including the partition walls) before the drywall contractors get there (every third or fourth web works nicely and last web before corners).

Now the drywall contractors can set their drywall on top of it and will cut their top edge or sheets accordingly to suit this height. The result is you have full wood fastening for nails along the complete wall surface and the plywood is guaranteed to be covered by the baseboard.

Air nailers can be used to tack the baseboard into the webs but the holding power (like wood) is limited and it's not as flexible for placement as the plywood idea is- the contractor has to identify the web locations on the floor to get the trim contractor to exactly where to shoot the gun. The air nail magazines also have to be 1/2" longer than they are use to driving.

In the long run, the ripped plywood idea is FAR better.


Using a normal 1104 type box, how do you or what do you use to fasten it to in the walls?
Unlike some of our competitors -, our form thickness which is a consistent nominal 2 5/8" thickness - deep enough to accommodate almost every standard depth electrical box. Deeper boxes are easily accommodated by simply gluing a square of foam on the inside of the form at the location being planned for the box during the pre-pour phase if the installation process.

As you already know, standard depth boxes can be cut and fitted directly into the interior foam panel beside a web by cutting the foam to a 2 ¼" depth (leaving 3/8" foam covering the concrete). Boxes can either be metal or plastic (Nurell® Nylon or other ULC or cUL approved box products). Cuts are made normally using pre-profiled hot knife attachments.

NEC NMD Cable Installation in Shallow Groove


How do you attach Hardiboard (Cement Board) siding to NUDURA & what screw do you recommend for use with Hardlipanel or Hardiplank?
The attached information has come to us from Compass International. They make a screw which you'll see outlined on the attached PDF file which features a coarse thread screw with a flat head that also features scraping blades on the underside of the head to countersink the head into cement board product.

Compass Intl Hardi Plank Fastener

I've also included a copy of the NER Report for James Hardie Products which verifies that the report accepts use of specially manufactured nails for anchorage of Hardipanel and Hardiplank into metal studs with an ultimate holding power of approx. 105 lbs/nail.

NER 405

Attached you will find NUDURA product pull testing of # 6 Drywall screws & # 10 coarse thread Pan Head screws into NUDURA high density polypropylene webs achieve an average ultimate pullout of 222.3 lbs. and 274.7 lbs. respectively (1 kilo Newton = 224.8 lbs of force). The Compass Screw being specified has been tested with other polypropylene web based ICF systems and has been known to achieve an average ultimate pullout performance of approx. 243 lbs. which falls in the anticipated test range shown in the NUDURA test data. This substantially exceeds the results noted for the nail performance into metal stud wall and therefore qualifies it for use for fastening Hardipanel and Plank products with our system. In addition, the attached Compass screw complies with the generic screw description given by the NES report for use with both Hardipanel and Hardiplank.

01-06-M0288-3 Fastener Pullout Evaluation of Fastening Strips

We would suggest that in keeping with Hardiplank's installation instructions that the planks be single screw - blind fastened at the top of the plank at 16" o/c (every other web). As far as requirement for building paper below, I defer to either the Hardiplank supplier AND the local governing codes in conjunction with our Evaluation Report. In some cases (i.e. the new IRC), so long as the siding is designed to shed water, and the substrate is a sheathing product, there are exemptions to the requirement of the paper being required. If both permit and it does not void warranty protection provided by the siding manufacture, our normal position is that an additional building paper is not required.


The plastic inserts in the ICFs are spaced at 8" on center. Where can cuts be made to shorten an 8-ft section to fit at the end of a straight run? It seems that the NUDURA literature indicates that tolerance was ± 1", but I'm uncertain if that answers the question.
The literature is correct that NUDURA's cut tolerance is ±1 ". What this is based on is the cut (or score) lines provided on the outside face of the EPS that are spaced every 2" on center. These lines coordinate precisely with the reversible interlock pattern on the top and bottom of the form units. Whenever cuts are made along these lines, the installer can be sure that the form interlocks will always connect. Using these cut lines as primary guides, the installer can layout the length of wall to a tolerance of ± 1" of the corner pins of the building (this means that some minor adjustment of the wall's position relative to the chalk and pin lines on the footing may be required to meet the interlock spacing). Should the installer be unable to reduce or increase the length of the wall due to property set backs or other elements of construction, then NUDURA recommends the installer start at each corner of the wall and work towards the center of the length of wall to be erected. Once at the center point of the wall, the installer can cut one of the forms to the necessary length required to complete the exact length of wall needed. If this method is used, the installer will not be able to use the interlock to overlap the vertical joints for locking the forms together. This is not a problem as the installer will simply have a vertical seam line - up the entire height of wall being built. NUDURA calls this a vertical stacking seam joint. Simple form support consisting of 1 x 4 cross battens (one per course on either side of the forms) screwed into the webs on either side of this joint will assure it poses no danger of separation during the pour.


How do you finish the detail using EIFS?
Attached please find our typical detail for addressing the 'haunched' slab condition (Detail B6D01 - attached).

We are told by the various EIFS manufacturers that the best way to deal with this detail (regardless of whether or not you are installing on a 'haunched' slab) is to first finish the exposed or near grade (6' height) portion of the slab or wall with the finish parge coat. The details you see attached here are insulated with EPS foam sheet (do not use XPS as it results in poor bonding) and then finished with a 2 coat applied finish acrylic parge known as Prep-Coat B-2000 by Durock Alfacing Ltd., which is sold by each of our distributors. This parge coat should also be completed using a heavy nylon mesh reinforcing interlayer to provide impact and tensile strength to the EPS foam panel below. Obviously if you elect to parge directly to the concrete haunch then this step is not necessary.

Detail 2 Haunched Slab with EIF's Finish

As for the transition, from EIFs to parge coat, the EIFS manufacturers recommend the client be counseled on their input and endorsement of inclusion of a surface applied decorative foam trim strip near the base of the wall at this condition, over which the EIFS finish base coat and fiber mesh will be monolithically face applied AND BACK wrapped - then anchored into the face of the NUDURA Webs with screw fasteners or foam adhesive. The trim can consist of a simple 1 to 2" thick x 6" deep EPS foam trim strip that is angled top only or both top and bottom to shed water over the transition joint between the slab and the form and provide a physical break line between the finish acrylic stucco of the EIFS and the acrylic parge coat below. (see Detail 2 - attached). This trim strip would be continuous around the building about 4 to 6" above the finished grade level.

If there is an objection to this sort of detail, let them know that it's either this or a similar type of material breaking detail such as a cut reglet with a metal trim strip or they could be facing ugly cracking at the joint or worse - spalling of the finish coat at the joint after repeated seasons of differential movement between the slab and the form interface.


How does an R22 Wall perform as an R50 Wall?
Both the attached documents are produced in consultations with the PCA and CTL Engineering in Skokie, Illinois.

One is the report which 'theorizes' using computer modeling in accordance with ASHRAE 90.1 that a 10' thick minimum ICF wall (Ours has got this beat by 1 ¼' thickness) will in many cases perform equivalent to a Stick or Frame Built wall insulated to a value of R50.

Study the report tables closely - you'll see this is true for more southerly US regions only - as you come farther north the number goes steadily downward and if we in Canada lived and died by the claims of this report - we would have all stopped selling ICFs years ago, as it suggests we can only credit the ICF for thermal performance of R22 (it's calculated R Value) only slightly better than a frame wall. What this report does NOT take into consideration is the Air Tightness of the building - which Peiter van der Verf"s "ICF Comparison to Wood Frame" does.

The crux of his report is that it was based on actual statistical analysis of a number of different dwellings of similar sizes in both formats and correlated the annual energy expenses for each. Bottom line - it proves with example that you can save an average of 44% on heating and 32% on A/C costs going with ICF construction over frame.

CTL Equiv to R50 Clean Copy Compressed
ICF comparison to Wood Frame


The thermal resistance on a 6" form unit is R22; could you please explain this in detail? Is it just the 6" form without the concrete or with the concrete that makes up the R22 factor? We have been told that it has a R50 rating.
Attached is a copy of our R-Value Calculation which reflects the fact that the R-Value is derived from an aggregate total of values credited for the form insulation along with the concrete core as well as the air films on each side of the assembly as is dictated by the ASHRAE Handbook of Fundamentals 2001 edition.

NUDURA R-Value Calculation

As to the R50 claim, this is a reference to a 1998 report (attached) that was released as the conclusions of a study that was prepared by CTL Engineering of Skokie Illinois that was based on ASHRAE 90.1 climatic zoning. The study examined the comparative results of performance of both wood frame and ICF construction in each of the 38 designated climatic zones of North America using a computer modeling program that was capable of crediting the effects of concrete thermal mass. The modeling study concluded that, depending on geographic location across the USA and Canada, a contractor would have to build a wood framed wall insulated to a level of as much as R50 to equate the thermal mass performance of any typical 5 ½' to 6' thick core ICF wall located in the same region.

CTL equiv to R50 Clean Copy Compressed

An even better illustrative report is an actual comparative study that was completed by Dr. Pieter VanderVerf, an ICF industry building science specialist which proved through actual facility monitoring, that on average, ICF building owners spend 44% less on heating costs and 32% less on air conditioning costs than owners in similarly sized frame constructed buildings (see that attached report as well).

ICF Comparison to Wood Frame

Both of these studies point to the benefits that "Thermal Mass" brings to the energy story when considering ICFs. Thermal Mass is - in essence, the ability of a higher mass wall (solid concrete being among the very best examples of this type of wall) to "slow down" the flow of temperature effect from one side of the wall to the other - in essence either absorbing the energy or minimizing the effect of a temperature transition from one side of the wall to the other.


What does RSI means in terms of foam insulation being required? Can you direct me to a site that explains what RSI is?
Our NUDURA EPS foam insulation provides an R-Value of R4 per inch of thickness (our foam is 1.35 lbs/cubic foot density) (Our form provides R22.4 Total R Value or RSI 3.94)

To understand RSI or Resistance (Systeme Internationale), we have to better understand its Imperial Counterpart - (R-Value).

Though R-Value has no "layman" assigned units of measure (since the units are too complex for saying in simple English), "R" is understood to be the measure of a material's resistance to heat flow or "thermal resistance" for a given thickness of insulation material. The actual scientific units are as follows:

R1 = 1 hr.ft2.°F/BTU or 1 hour-square foot-degree Fahrenheit per BTU or British Thermal Unit.

To understand what this means - it's better to look at the "inverse" of Thermal Resistance which is Thermal Conductance or "U-Value Coefficient" which is 1/R. This means that the U-Value Coefficient of a material having an R-Value of 1 will be equal to:

1 BTU/hr.ft2.°F or 1 BTU per hour-square foot-degree Fahrenheit

In laymen's terms, it means that in a one hour period, a one square foot section of insulation material having a thermal resistance of R1 will allow 1 British Thermal Unit of heat energy to escape through it for every Fahrenheit degree transition that exists between one side of the material and the other. It stands to reason therefore that as the R-Value for the material goes up, the U-Value coefficient becomes more efficient and the rate of heat transfer goes down.

Now - relate THAT to the Metric or "SI" Equivalent:

The Metric U-Value Coefficient is similar in how it is calculated, except that the time element is assumed within the expression of "power" being that a "Watt" is equal to a consumption of 1 joule per second:

1 RSI = 1m2.K /Watt (The "K" for "Kelvin" is equal to our more common "Celsius" degree system)

Again, in layman's terms:

A 1 meter x 1 meter square of material having an RSI of 1 will also have a U-Value Coefficient of 1 W/m2.K and therefore will lose at energy at the rate of 1 Joule per second for every Celsius degree of temperature differential that exists between 1 side of the material and the other.

To convert R-Value to RSI us the following equation (I extracted this directly from factors given in the Ontario Ministry Housing's "Code and Construction Guide for Housing"):

R1 = .176 RSI . Therefore, to convert R Value to RSI, simply divide the R-Value by the inverse (5.685)


R 12 = 2.11
R 20 = 3.52
R 22 = 3.87

Our NUDURA EPS foam insulation provides an R-Value of R4 per inch of thickness (our foam is 1.35 lbs/cubic foot density) (Our form provides R22.4 Total R Value or RSI 3.94)

The following website contains some more supplemental data but I believe the conversion factor is probably of the most value to you.

Insulating Your House


To put siding on normally one would use roofing nails, but with NUDURA, screws are a must. What type of screw, and size?
A standard No. 6 x 1 ½" to 1 ¾" coarse thread "bugle" style or "flute" head (¼" dia. head) zinc coated or otherwise non-corrosive screw will do nicely (NOTE: as inexpensive as they are, drywall screws with the black sulphur coating will eventually corrode). However, the head profile of a drywall screw is an ideal screw to use as reference as it is a good model of the head shape and diameter that's required. Equally as useful are standard bright (chrome like) finish No. 6 or No. 8 dia. x 1 12" pan head coarse thread self-tapping screws. These have the added bonus of being able to be used for a multitude of anchorage purposes besides siding fastening and do not corrode as easily as drywall screws. USE SCREWS - NOT NAILS. They will make for the most secure method of anchorage of your siding system into the polypropylene webs. Why? Pull testing of fasteners into polypropylene has determined that by far the most assured fastening for resisting required loading as noted in local building codes are screws - a #6 self tapping screw into NUDURA fastening strips can provide an ultimate pullout holding capability of approx. 222 lbs of force. In addition, use a power driver to speed installation with the torque set to the lowest possible setting - as with nailing, your objective is to stop driving the siding BEFORE it begins to simple into the foam- you want the siding to slide loose so that it can expand and contract in the sun. Remember, it hangs from the screws rather than being anchored firmly by them to the surface of the NUDURA foam.


How can one construct to prevent termite infestation?

Here are 3 important factors related to this issue:
(a)  Although termites can potentially chew through foam, it is a proven fact that they do not ingest EPS foam for any nutrient value, hence the risk of them foraging into foam in the same manner as they do wood is greatly reduced.

(b)  The most basic concern is that the termites will attempt to access the foam below grade since the vast majority of termites are subterranean - so the most logical defense against attack is to protect the EPS foam below grade.

(c)  It's also a proven fact that termites will seek means of protecting themselves from exposure to the exterior daylight. Therefore, if means are provided to eject the termites to grade condition around the building, then the termites are forced out to the surface and will then construct mud shelter tubes up the foundation or building face above grade, thus indicating their potential locations of strike at any building site.

Some EPS manufacturers impregnate their foam products with borate additives to deter termites from chewing into the foam. However, the borate additive is a highly toxic chemical which cannot be introduced selectively in the form. Because of the nature of the ICF manufacturing process, this toxin must be throughout the form and thus is constantly present immediately under the drywall finish of the inside of the home or building, which in itself poses a health risk to those occupants who may be hypo-allergenic to the borate substance. The borate additive can also potentially "weaken" the foams internal chemical bond strength which could reduce it's effectiveness as a structural form on site during concrete pouring if the borate is not evenly and properly dispersed throughout the EPS foam being injected into the form during manufacturing. For these reasons, NUDURA has elected NOT to employ this method for our form manufacturing.

There are fortunately some excellent alternative options to resolve the termite intrusion problem while not having to succumb to introducing a new toxin into your living environment.

As a healthier alternative, NUDURA recommends the following system of detailing for use with its form system:
(a)  First, per Code requirement, use an SBCCI or ICC-ES approved termite barrier to apply to the exterior walls for all foam plastic areas below grade. There are a select group of products available meeting this requirement, though among them, NUDURA has found the approved peel and stick waterproofing membrane/ termite barriers to be the most cost effective.

The "XT" Membrane System by Polyguard is among the most well known and can be obtained through their distribution by contacting:

Polyguard Products, Inc.
PO Box 755
Ennis, TX 75120
PH: 800-541-4994

More detailed information is contained in the attachments. This membrane consists of a combination of 2 products - (i) a steel mesh impregnated trim strip use to flex around corners and footing junctions and then to complete the system (ii) a triple thickness heavy flat membrane too thick for termites to penetrate that is used to cover all the flat wall areas.

Cover Letter for Termite info General Rev 04/16/04

Polyguard brochure HTML file original

(b)  Additionally, NUDURA can provide detailing to your NUDURA Trained Installer to enable treatment of the grade level of the form system with a feature called an "inspection strip" - a specially cut horizontal band that reveals the concrete in the cavity directly to the outside, preventing any termite from being able to access the foam at grade or get to it without first being ejected to grade at the outside. In this manner, any potential strikes at a residence are easily identified by the local pest control operator via the evidence or presence of mud shelter tubes.

(c)  The above noted measures are more assured to guarantee success of combating termites when used in conjunction with an effective ground spray or other Pest Control Operator recommended method of termite treatment such as "bait and trap" systems like "Sentricon" or other newer methods. This is a system of selective strike baiting and poisoning that is a more "surgical strike" method of poison deployment which works by first "baiting" termites with food in stations deployed around a building then subsequently replacing the food with poison which the termites coat themselves with, then deliver directly into the colony. It's best to contact the local Pest Control professional to find out what can work best for your area and what systems have a proven track record for success.

Sentricon Contact info

Sentricon process

(d) For areas where excessive termite pressure exists, consideration of any above grade finish which bonds tightly to the EPS as a hard coating can often minimize even further the potential for rarer forms of airborne termites from being able to penetrate the finish to the foam. This risk is (to our best information sources) minimal, as you will note that the new International Codes recognize that subterranean strikes are the real concern for termite penetration.


Our contractor used your material for our basement walls. It looks great and now I'm interested in finishing the interior. We do not have fastening strips installed. I wasn't aware that I should have asked for them. Are the fastening strips able to be put on after the wall is complete? Should I strip the wall with 2"x2" for nailing/screwing strips for the sheetrock? I'm guessing it's pretty hard to hit the plastic cross ties being they are staggered. What is the most recommended?

The first question I have in response to your Email, is could you advise us the name of your contractor and whether or not you know if your contractor was able to attend one of our training courses and whether or not he is a qualified NUDURA™ Trained Installer? If he is, he would already know and should have passed on to you that Gypsum Board or drywall does NOT require a sub-grid of wood or metal strapping to be applied to our forms. Rather, the gypsum board or drywall can be screwed DIRECTLY into the form system into the 3/16" thick high density polypropylene FASTENING STRIPS that are embedded every 8 inches on center approx. ½" below the face of the foam on each side of the form.

He would also know that the technique we teach in our courses is to ensure that when placing the forms, is to always "establish an effective layout pattern". This means that he strives to ensure that wherever possible, units are to be placed in such a manner that:
(a)  With the exception of any wall segments requiring custom cuts lengths - all corner units and standards are to be placed assuring that the cross tying web fastening strips are in vertical alignment with each other. (These are indicated by NUDURA's trade mark "squiggle" pattern that is molded on the outside face of the form wherever the fastening strip is embedded).

This ensures that NUDURA's patented vertical interlock teeth on the bottom and top of each fastening strip/web solidly lock together with each other - which in turn prevents form float up or settlement during concrete placement and eliminates having to install additional form support as well.

(b)  At custom cut wall segments, we teach that if striving to make cuts specific to the Interlock Guidelines, it's best to ISOLATE any web misalignment in a straight wall length to a single area and limit it to assure that the webs ONLY misalign by a maximum of 2 inches (1 interlock), so that ONLY in that 1 specific area does the dry-wall contractor EVER have to concentrate on screw placement to be specific to the fastening strip pattern. AND if deciding to cut off the guidelines, we teach utilizing a vertical stack joint method where-by NONE of the webs misalign AND that only at this one joint will the webs EVER be less than 8 inches on center. BY using these techniques all the drywall contractor needs to do is mark the floor and ceiling area with a pencil where the (squiggle) indications are and he can be assured his screws will engage into our fastening strips any where in alignment with those marks.

I suspect by your question that he has NOT followed these rules of placement and has created a problem for the gypsum board contractor by NOT doing so. It's certainly NOT the end of the world but without knowing just how badly this misplacement is, it's hard to suggest a remedy to the situation. Photos of the condition (whereby the "squiggle" pattern is visible) would help.

My gut feel is to fasten DIRECTLY into these webs as much as possible. The value here is to have the thermal barrier protection provided (as required by code) by the gypsum board as tight to the foam plastic insulation as possible. However, if the alignment pattern is so overwhelmingly inconsistent, a horizontal grid of 1" x 2" wood strapping placed at 12" o/c is probably your only out. Screw these strips into the squiggle areas of our forms using 2" long drywall screws and screw in place at 24" o/c maximum.


I've been looking for an ICF system that uses extruded foam insulation board, rather than expanded ICF. Although more expensive, extruded foam board is known for have better R-value, better R-value retention over the long term and has better moisture resistant properties.
Yes- you are correct - Expanded Polystyrene foam is less expensive, but THAT is not the major deciding factor for most ICF companies using Expanded Foam over Extruded.

We cannot argue with your first claim - i.e. Higher R-Value - as our best source for foam plastic insulation data (BASF Corporation) confirms (as do most Canadian and American Building Codes confirm) that Extruded Polystyrene Boards in North America do perform initially at marginally higher R-Values than Expanded Polystyrene foam does - classifying it as a type III or IV foam having densities of between 1.5 to 2.0 lbs/cubic foot density. Expanded Polystyrene foams are normally classified as Type I and II foams having densities between 1 and 1.5 lb/cubic foot density. Most ICFS (NUDURA included) have foam densities in the type II range. According to Statistical Data provided under Section of the Ontario Building Code R Value of EXPANDED Polystyrene range between R3.8 to R4.4 per inch (NUDURA is R4 per inch) whereas EXTRUDED Polystyrene is classified as having an R-Value of R5 per inch.

The claims with respect to moisture resistance (at least when first installed) are also true. The vapor permeance of EXPANDED is known to be an average of 200 ng/Pa.s.m2/25mm thickness or about 3.1 perm-in. whereas EXTRUDED foam is initially known to have an average vapor permeance of about 50 to 60 ng/Pa.sm2 /25mm or about 1.1 perm-in.

That, however (according to BASF Corporation) is where your claim accuracy ends as over the long term.

EXTRUDED Polystyrene in long term studies has been confirmed to lose it's R-Value over time. This is mainly due to the result of greater long term shrinkage. The panels over time will not only incrementally decrease in thickness but more dramatically in overall size and as the panels shrink back from each other, the joints between the panels open up revealing gaps that can be as much as ½" wide over time when installed in a 2 x 8 configuration over a wall surface behind typical retrofit brick veneer installations. As this happens, the claims with respect to R-Value and vapor permeance tend to diminish over time. Expanded Foam R-Value, however, remains stable over the life of the product (As do most reputable ICFs, NUDURA guarantees it's R-Value for 30 years).

Q:  I've heard that water can actually permeate expanded foam board and break it down over time. This does not happen (at least not to the same extent as) with extruded foam board.

A:  This is a False Statement with respect to type II foam which is what most ICFs are composed of (including NUDURA). As the attached physical property review of EPS Type II foam states, Type II foams are unable to absorb anymore than .5% of their own volume with water - even under full immersion. The break down over time claim is also not factual - at least for type II EPS foam designated for construction.

Q:  Is there a reason why you manufacture ICF systems with expanded foam rather than extruded XPS, other than the fact that it is cheaper?

A:  The answer here is YES....there are two very important reasons why we do NOT use Extruded Foam in our processes. The first is OFF-GASSING. North American extruded foams currently use Blowing Agents of either Carbonated Fluro-carbon (CFCs) or Hydro-Carbonated Fluro-carbons (HCFCs) both during and after manufacturing which as I'm sure you know can significantly effect degradation of the earth's ozone layer.

The other reason is much more important to the execution of the manufacturing process as well as the FUNCTION of the completed form and that is that EXPANDED foam can be SHAPE molded whereas EXTRUDED foam CANNOT. This is first of all significant from the stand-point that its THIS factor that enables EPS foam to be molded integrally with the cross tie members that enable an ICF to be formed into pre-molded blocks or (as in NUDURA's case) foldable form units - that just would not be possible with sheet stock material. This factor is HUGE when it comes to a comparison of labor savings on site. The Extruded Panel Systems have to be painstakingly assembled piece by piece either in-shop or in field even before the blocks can be stacked to form the wall.

In addition, there is no actual chemical bond of the ties to the sheets of foam the way that an expanded foam system features - hence the expanded blocks are sturdier. The vertical interlocks between panels are also better augmented by virtue of shape molding since all EXPANDED foam ICF products usually feature an interlocking tooth pattern that will not permit the form units to "rack" longitudinally the way extruded panels tend to do in field. NUDURA additionally features a patented TIE or FASTENING STRIP interlock as well it's interlock tooth pattern that physically "clips" the courses together. This tie interlock would NOT be possible in an extruded foam system.

Finally, the expanded foam's capability is further utilized within forms like NUDURA's to create a vertical repetitive dovetail or dado cut pattern in the interior surfaces of the form so that the foam panels will intimately and permanently be bonded or cast tightly with the concrete. This effectively eliminates any risk of the EPS foam delaminating from the concrete, thus removing any possibility of an un-flashed air cavity condition from forming between the EPS and the concrete.

So... despite the apparent advantages of Extruded Foam - its disadvantages to forming ICFs are far outweighed by the advantages that Expanded Foam is able to bring to the table from a functional standpoint.


I have a potential client who is very sensitive to environmental issues as well as personal health issues. She wants to know exactly what gases and chemical compounds will be released into her living environment directly from NUDURA foam blocks. If she does not get the answers to these questions, she will not use the product in her home.
Your client's request is more common than you might imagine and we honestly believe that the data contained in this email should quell many of your client's concerns. First, let's address the composition of the form itself, starting with the polypropylene webs. These webs are composed of high-density polypropylene made from 100% post-consumer recycled plastic. The source material is primarily composed from the plastic that is used in 2 liter and 600 ml pop bottle caps. The plastic is totally inert and does not emit ANY substances whatsoever. Copies of the MSDS sheets for the virgin version of this material are enclosed for your client's reference. However, the majority of focus of most consumers surrounds concerns around the foam plastic insulation. Your client should first of all be made aware of the fact that there is a very distinct difference between high density EXTRUDED (XPS) foam sheet plastic insulation versus lower density EXPANDED Polystyrene (EPS) foam shape molded insulation which is what NUDURA is composed of. For starters, the EXTRUDED foam sheets (Type III and IV higher density foam plastic boards - usually blue or pink are common manufactured colors) are formulated using CFC or HCFC blowing agents that are known to be ozone depleting and potentially dangerous to the environment. These agents stay resident in this type of foam after manufacture and emit slowly over time to the interior or exterior environment. However, NUDURA Foam products are SHAPE formed using a "Pentane" (non-ozone depleting) blowing agent. 100% of this agent flashes or evaporates to the air within 24 hours of fabrication. Further, the forms are oven cured for 48 hours to assure the blowing agent is fully extracted from the EPS foam and assure better dimensional stability of the product. Copies of the MSDS Sheets for the raw bead used in our forms are attached for reference. All Styrene used in our EPS foam manufacture is virgin material only. As you will see, the primary chemical used in the manufacture of the forms is Pre-expanded Poly-Styrene Bead. The only secondary chemical besides the pentane blowing agent is a bromine additive that is actually "polymerized" chemically into each individual bead. The purpose of the bromine is to provide the foam its flame retardancy so that in the unlikely event of fire, the EPS foam is self extinguishing. This is a mandatory requirement of the manufacturing standard (CAN/ULC S-701) for sheet and shape molded foam plastic insulation products used for Building construction in Canada. Most clients express concerns for the volume of "Styrene" and have concerns regarding potential "Offgassing" of the styrene into the living space. However, to address these concerns, please have your client read the attached report which was commissioned by BASF Corporation (our largest bead supplier and the world's foremost authority on EPS Foam manufacture) which is file titled "Long Term Styrene Emissions Report". The report was based on long term and laboratory studies of in-situ testing of foam samples which had been installed in actual residential applications. Carbon tube absorption test apparatus were installed to capture long term emissions in each subject residence. These absorption tube detection devices are capable of detecting particle emissions as small as 8 parts per million per hour. After long term exposure for all cases, the report reveals that not one absorption device used in the tests was able to detect emissions above or equal to this rate nor did any of the clients living in the homes report ANY concerns of health issues or complaints as a result of living in the foam insulated environment where the tests were conducted. On the basis of this testing, we are very confident that your client can be assured of being provided a very safe, healthy and stable environment inside a NUDURA Home. However, rather than take our word for it, may we make the following recommendation? Your local NUDURA distributor (Bird Stairs Limited, Dartmouth) I am certain, would be more than happy to provide a form unit sample for your client to take home and test within her own environment. We suggest placing it in an exposed area of the bedroom as close to her bed as possible and monitor how her own immune systems reacts to the presence of the form unit both awake and asleep for a minimum period of 2 weeks. This will give her ample opportunity to test how she will react with the product WITHOUT financial risk to either her or you. Based on my 10 year history within the ICF industry, talking to numerous clients like yours, I can honestly tell you that neither I nor any distributor I have serviced have ever had one client return a form unit complaining of allergic reaction to the above exercise nor any reaction to subsequent occupancy in their new ICF environment. This however is a decision which should be made by the client solely on the basis of her reactions to the above experiment for as long a period as they feel necessary to establish a comfort with the product. I'm also attaching Fungi testing commissioned by the Expanded Polystyrene Manufacturers Association (EPSMA) which clearly establishes Zero Fungal Growth on any foam specimens tested in accordance with ASTM C1338-00. I hope this data will meet with your client's approval. However, should you or she have any other questions that we might be able to assist with, please do not hesitate to contact your local distributor or NUDURA directly.

E-mail your questions to: cameron.ware@futurestone.com


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E-mail your questions to: cameron.ware@futurestone.com