Advertisement

Renovation & Design

Stud wall inside ICF foundation a good call

Question: I’m in the process of preparing to finish an ICF basement and was going to frame the basement with 2x4 finger-jointed lumber. The rationale is that I plan on being in this house for several decades and I want to have the flexibility to change things down the road. Who knows what technology will bring in 20 or 30 years, and what appliances or devices you will want to mount, and what power requirements might be? I want the flexibility to be able to run cables inside the walls, if required. I plan on using the finger-jointed material because they are much truer and straighter than traditional spruce studs.

So, I was going to frame the exterior walls over the inside of the ICF. I also plan to run all of the wiring cables within the framing and put in additional insulation before drywalling.

I’d appreciate your comments on what I’m proposing.

Thanks, Marc A.

Answer: Planning ahead and installing a complete 2x4 wall inside you ICF foundation should have no negative repercussions, but one issue may provide some questions. If and where to install a polyethylene air/vapour barrier may be a difficult decision and there may be debate about the necessity, even among building professionals.

Insulated concrete form (ICF) foundations are a modern method of using rigid polystyrene for insulating a concrete foundation wall, by providing that material as the forms for pouring the wet concrete into. Instead of removing the forms once the concrete cures, like traditional forms, it is left in place to form an insulated surface inside and outside of the foundation wall. That finished product, with embedded plastic ties and nailing flanges, may be covered on the inside with wall sheathing without any further framing or air/vapour barrier. Due to the unique design, with foam on both the exterior and interior surface, the concrete will be warmer in winter than a typical concrete wall. That property, and the polystyrene inside layer, will eliminate the possibility of condensation inside the foundation, and negate the need for installation of standard 6MIL polyethylene on the studs, before the wall covering.

While it is not a requirement, there is no reason not to frame an entire stud wall inside an ICF foundation, except for the loss of the few inches of extra space inside the perimeter of your basement. The benefits are well laid out in your question. That extra few inches of wall cavity make it much easier for installation of electrical wires and components, as well as many other parts of typical systems. The one main drawback of using ICF for a proposed finished basement is the need to cut out the foam for installation of electrical wires, light and receptacle boxes, and any other components desired inside the finished perimeter basement walls.

By installing a traditional 2x4 stud wall inside the foam-covered foundation, you will create an excellent space for running not only any electrical components, but low voltage cables for some alarm, sound system, and other home components. Also, if you are planning to add a basement bathroom, wet bar, laundry sink, or other components requiring plumbing, you will make that job much easier, as well. It will be possible to run water supply piping inside an exterior wall without the risk of frozen pipes. While this may have also been possible by gouging out channels in the ICF foam, that would have required added damage protection. Metal protective plates, or similar items, would have been required over water pipes and wires that would have been subject to damage from wall fasteners, due to the proximity to the front face of the wall covering. With a full stud wall, there will be plenty of depth to drill holes and mount any of those components out of the reach of screws or nails used for attaching the drywall.

Insulating the new walls will also not be necessary, but will be a good idea to provide maximum thermal protection and keep heating bills to a minimum. I suspect that you are planning on using friction fit fibreglass or mineral fibre batts, for that purpose. While those provide very limited air/vapour intrusion protection, the inclusion of a thin layer of plastic sheathing inside the studs should not be necessary to prevent warm air intrusion from the home. While warm air may penetrate this wall cavity, the chances of excessive cooling and condensation are minimal, because of the double layer of integral foam sheathing in the ICF. Having foam on both sides of the foundation will prevent loss of heat from that rigid wall to the exterior, keeping the concrete relatively warm, even in the dead of winter. The design, with the foam directly connected to the inside of the concrete, will also prevent a significant amount of warm air from penetrating the finished foundation wall. Both of those properties combined are the reason why 6MIL poly is not normally required by the manufacturer, prior to installation of wall coverings.

There may be some contractors or building officials who disagree with this omission, in some jurisdictions, so be prepared to defend this position. A case may be made by following the ICF manufacturer’s specs, as they should have tested their product according to various Standards for air permeability and other criteria. Regardless, there may always be some debate when newer building products are introduced to professionals used to building in a certain way.

Your decision to build a complete stud wall inside your ICF foundation does have merit in allowing additional insulation and a better cavity for installation of electrical, plumbing, and other components. While a 6MIL poly air/vapour barrier should not be necessary for inclusion in the wall assembly, opinions from some in the building industry may be contrary.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

Advertisement

Browse Homes

Browse by Building Type