These questions and answers are referenced from the ARXX website (

Q: Do I need an engineer to review my building plans?

A: If the design criteria follows the Arxx Prescriptive Design Requirements and does not exceed the applicability limits in that manual, then an engineers review is not required, unless in the opinion of the building official engineering is required.

Q: Does it matter what side is up when installing the ARXX forms?

A: Arxx forms should be installed so that the diamonds are facing up and the sockets are directed down.

Q: Does expanded polystyrene (EPS) present a serious fire hazard?

A: Expanded polystyrene (the material ARXX blocks are made from) will burn if exposed to a large enough heat source, much like many things in the home. The EPS in Arxx forms has a flame retardant additive incorporated during the manufacturing. EPS will melt when exposed to temperatures of 300 F to 500 F. If additional heat is applied and an ignition source persists, the molten styrene may ignite at temperatures over 600 F. (Note the flash ignition point for plywood products is approx. 500 F).

Q: Is burning EPS toxic.

A: Test reports conducted by the National Research Council state: “The maximum toxicity index obtained from the combustion of polystyrene was of the same order as that of wood.”

Q: Does EPS ‘off gas’.

A: EPS in the Arxx forms does not and never has contained any CFC nor HCFC products. The forms are made by a steam process that utilizes ‘pentene gas’ as a blowing agent. The type pentene dissipates from the product within 48 hours of manufacturing. By the time the product is used in construction there would only be trace amounts left in the EPS.

Q: Can I leave Arxx forms exposed to ultraviolet rays for extended periods of time (1 to 3 months)?

A: Yes, but you will notice a light dusting on the surface and a discoloration of the forms. This does not indicate any detrimental effects to the wall forms. We do recommend that if the exterior finish will not be installed within a 3 month period the forms be protected from UV rays by installing a temporary building wrap type material.

Q: Can you vibrate or consolidate the concrete in ICFs?

A: Arxx recommends consolidation with a pencil vibrator, quickly in and quickly out.

Q: Do ICFs promote mold growth?

A: EPS is an inert, organic material. It provides no nutritive value to plants, animals or micro-organisms. It will not rot and is highly resistant to mildew.

Q: Do I have to finish my basement walls with drywall?

A: All building codes in Canada and the US state that plastic insulation (EPS) must be covered by a thermal barrier equivalent to 15 minutes. This is achieved with ½” gypsum board (sheetrock) or an equivalent. Yes, all interior walls in habital space must be covered with a minimum of ½” drywall.

Q: Why is the concrete limited to be poured in 3 foot (1m) lifts?

A: To alleviate the hydrostatic pressure from the concrete, the first 3’ of concrete is allowed to set for approximately 1 hour before the next 3’ is installed. This is achieved by installing the concrete for 3’ all around the perimeter of the project, then go around again, on top of the previous pour, for another 3’ and so on until you reach to desired wall height. (see following question about blow-outs)

Q: Is there a problem when placing concrete, dropping concrete from the top of the wall which may be over 9’ ?

A: No. The specification in the America Concrete Institute (ACI) do not limit the maximum distance concrete can free fall. Engineering studies and reports have shown that free fall from up to 35’ doesn’t reduce concrete quality and there is no evidence of segregation or weakened concrete.

Q: Can you build your Wallsystem in cold weather?

A: Yes, the forms actually insulate the concrete and enhance the curing process. The top of the forms need to be covered so exposed concrete does not freeze.

Q: When can I backfill the foundation wall?

A: The concrete must cure for a minimum of 7 days and the foundation wall must be laterally supported, meaning the first floor is installed. All below grade waterproofing/dampproofing must be installed.

Q: What are ‘blow-outs’ ?

A: A ‘blow-out’ is a break in the form, generally due to the pressure from the concrete during the pour. A pre- pour review of the wall system, installing additional strapping and support will prevent blow-outs. In an Arxx form, generally the size of a blow-out may be 6” wide by 16.75” high. If a blow-out occurs, the concrete pour moves to another area on the wall, the hole is patched and the pour resumes.

Q: How do you control voids in the wall?

A: The concrete mix is a high slump that means the concrete flows easily. The person in charge of the pour should watch the concrete flow evenly throughout the whole wall to ensure there are not void pockets. Arxx also recommends vibrating or consolidation that will enhance the concrete flow.

Q: Can I install a 16’ garage door and/or large windows in a concrete wall?

A: Yes, the Arxx prescriptive code has detailed lintel designs for large openings up to 16’-4”. Larger openings would require an engineered design.

Q: What do termites do to the foam?

A: EPS is an inorganic material and is not a food source for termites. If left exposed, termites will burrow into the foam. Arxx has a detailed section in the Installation Guide on the Treatment and Prevention of Termites. We recommend the application of an SBCCI code approved peel and stick termite barrier/dampproofing membrane by PolyGuard. Please refer to Appendix D in the Arxx Installation Guide

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