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Installing backing in an ICF system or steel framing

QuestionYour book, Build Smarter with Alternative Materials, has given me lots of ideas for doing exactly what the title promises. I am in the process of having a custom home designed that we will contract for construction in the foothills east of Sacramento, California, and your book has convinced me to step away from some of the materials that I have used in the past.

The home will have lots of wood moldings, including crown, chair rail, maybe casing around the windows, wainscoting, etc. What is the most efficient and economical way with steel framing, either before or at the drywall stage, to provide backing for such moldings? I have looked at the possibility of using USG Fiberock panels rather than standard drywall on the theory that a more solid mass will provide backing, but those panels are four to five times more expensive than regular drywall, and I'm not sure that they will work well for that purpose.

AnswerI'm with you—backing is a concern when you don't have something solid to which you can securely attach finish trim. It is very difficult to fasten to the lath-and-plaster interior walls of my own 1932 home.

If your new home is built using an ICF (insulating concrete form) system, you've got a few options, e.g., cutting in chases for backing, electrical wire, and/or electrical boxes. Make cuts with a utility knife or router, or draw a thermal hot knife through the foam for fast accurate cuts. I suggest you consult the ICF (expanded polystyrene [EPS], extruded polystyrene [XPS]) manufacturers before attempting to cut into any of the insulation currently on the market. Ask specifically for the material safety data sheet (MSDS) so you can learn about the material's flash point and toxicity. There are some concerns about toxicity, and the product does give off an odor that some individuals may find offensive—it goes without saying (but I'll say it anyway) that you would want to work with these products in well-ventilated areas..

If you opt to use a router, be prepared for the mess. In polystyrene it resembles a bean-bag chair falling off the back of a pickup at 55 mph! A hot knife makes the job simpler and cleaner. Additionally, the foam cut-out from the chase is in one continuous piece that can be glued back into the chase for insulation before you attach wallboard.

There's no limit to what you can cut with the right accessory blade. To cut or shave high spots, a thermal skinner is just the ticket. This hand-held tool works on the same principle as a hot wire machine, allowing you to cut in chases for steel or wood studs that could be used for backing for your finish trims.

When installing steel or wood backing into the chases, be sure to select an adhesive that is compatible with the polystyrene. Consider using a polyurethane foam both as an insulating sealant and for its adhesion qualities.

You could also use a product called Grappler, an anchor plate that's pushed into the face of an ICF system at attachment points prior to wallboard installation. The galvanized expanded metal plate measures 4"x8" and accepts both screws and ring-shank nails.

With steel framing you have a few options—like using winged Tek screws. Their slimmer body and ribbed head make them smaller than conventional screws with a Robinson head, and they have a drilling tip. The wing tip allows for a solid application from wood to steel. Senco manufactures hardened 15-gauge galvanized finish nails for steel stud and trim application for use in their pneumatic angled-finish 15-gauge nailer. I haven't tested it so am unable to tell you how well it works.

You could also cut and notch a steel stud so it fits between the vertical studs and attaches to the face of each stud. I personally prefer to secure wood blocking between the steel studs in areas where I know I will need to attach fasteners (nails and/or screws). For cabinets, shelving, etc., I would install a layer of 1/2" plywood to the face of the steel studs, covering the entire wall prior to wallboard installation. In the case of cabinets, install the plywood 2" in from the planned outline of the cabinet—just out of sight. The wallboard would then butt up against the plywood.

For windows and doors, I would install wooden bucks. Composite bucks are available on the market if you prefer to not use wood, and fully adjustable plastic bucking systems are available for installing door and window openings in ICF systems.

Good luck with your project!

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Question answered by Leon A. Frechette.

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