ICF Insulated Concrete Forms - The Good * The Bad * AND the Ugly!
This article is neither a criticism or an endorsement of insulated concrete forms (ICF) but the results of many years of experience dealing with foundation flaws and cracking problems with this type of construction usually long after the builder is no longer taking any responsibility for their work.
Insulated concrete forms (ICF) have become popular today for many home builders because concrete professionals or contractors are not needed. Typically, the carpenter, or home builder, or home owner on site can assemble the forms without any outside help.
What is an ICF form? There are many variations but basically it is two polystyrene sheets with plastic snap ties extending from one side of the form to the other. The plastic snap ties provide two purposes, one is to hold the 2 polystyrene sheets apart and two, hold the rebar for reinforcement after the forms are placed.
Advantages of ICF construction:
- Can be assembled without skilled labour.
- Provides ready to go wall insulation on both sides of the foundation.
- Provides internal structure to hold rebar and in most cases more rebar then would be used in a traditional foundation construction.
- The forms can be easily modified to account for changes in the plans such as windows and doors.
- More rebar is used for reinforcement in an ICF built foundation therefore it could be argued it is stronger than standard concrete poured foundations.
There are probably more advantages but for the purpose of this article the above list are the obvious ones.
However, we at NextStar experience many problems with ICF basements and find that most home builders are unaware or in denial of any of these problems.
Disadvantages of ICF construction:
- ICF construction foundation usually cost more to complete versus the standard wood form and pour.
- ICF forms require extra support during setup to ensure the forms remain vertically plumb before and after pumping the concrete into the forms. This extra cost may not be factored into the overall cost.
- More care is needed to select the correct concrete slump as well as the aggregate size to make sure it meets the ICF form manufacturer’s specifications.
- Requires a membrane of some sort on the outside because of the wick effect of the snap ties which will be explained later.
- The thermal mass advantage may be questionable since both sides of the foundation are insulated. Some reports indicate there is higher energy efficiency during colder months, but less energy efficiency during the warmer months. Geographical location is an important factor to consider in determining the true energy efficiency results of an ICF foundation.
- The plastic snap ties result in more penetrations through the concrete resulting in more opportunities for water to penetrate. Also, this higher volume of penetration spots may weaken the concrete wall.
- Diagnosing ICF foundation issues is more difficult for foundation repair professionals.
The first and most important issue is that all ICF forms have some type of plastic or polypropylene snap ties to hold the 2 sides of the form together. The smooth finish of these materials can allow water to wick inside the concrete and seep inside of the foundation. The ICF forms themselves have gaps between the blocks that would allow water direct access to the concrete. When inspecting a problem foundation, the first thing we look to verify if a membrane has been installed.
If a membrane is installed properly there should never be a leak. If there is a leak either the membrane has been damaged, or it was not installed high enough before it was back filled allowing water to get past it at ground level. The reason a membrane is so important is because if you have a foundation that is wicking chances are you don't have one leak you probably have hundreds. The standard crack injection methods are comparable to the whack a mole game, once one leak is injected and fixed guaranteed two more areas will start leaking shortly thereafter.
In most areas of North America, the building code is now dictating that ICF basements have proper membranes installed and in some cases dimple panel as well and directing water to a weeping tile system. However, we continue to see newly built ICF foundations with no membrane or some sort of tar substance instead that is not adequate, in some cases backfilled before it is inspected by a building inspector.
Standard basement wood forms have metal snap ties every 16 inches horizontally and 24 inches vertically. In an ICF foundation every block form may have 4 to 5 times more protrusions through the concrete to the exterior. Metal snap ties in the wood forms bond well to the concrete but the ICF forms have smooth finished off plastic ties that does not bond as well to concrete and will eventually allow water and moisture to penetrate the foundation.
When a crack is identified, the foam must be chiselled off the internal wall in order to expose the crack before standard crack injection methods work. The foam makes it more difficult to identify where the leaks are located which involves more labour time. Usually we find that a crack has originated from a plastic snap tie. It develops when the concrete shrinks during the cure process.
We always warn homeowners that crack injection in an ICF foundation is only repairing a symptom of the real problem and that being the absence of a proper membrane. Some foundations are so bad that it requires excavation and a proper membrane installed along with weeping tile. Cracks or flaws in a standard poured foundation can be successfully repaired with polyurethane or epoxy injection but is not a successful long-term solution for an ICF foundation. Fixing one location only chases the water to the next snap tie or flaw.
If an ICF foundation has been installed properly there should be no issues. But if any issues do occur, the foam hides any flaws and homeowners do not discover the problem until long after the structure is completed.
- Don’t properly support the forms when the concrete is poured, often from being in a rush or to save costs. They avoid using a vibrator or tamping to prevent blowouts in the form leaving many areas of the foundation with honeycombed voids. This is a large problem with many foundations we see and in some cases the voids are so bad the ground water easily runs through.
- Often large voids are left under a window or a door sill plate because wood is used to form around the openings, but they don’t leave out the bottom sill plate for concrete to be pumped into thus leaving large voids in these areas. The only effective way to repair this is to remove the foam then make up an epoxy sand-gravel grout to structurally bond and fill the void area.
- Many builders use the wrong recommended aggregate size and slump by the manufacturer of the ICF forms which contributes to many problems.
Should you decide to build with insulated concrete forms hire experienced installers that have installed standard wood forms for concrete construction as well. Ensure the forms are well supported, plumb and the concrete is vibrated. Even if it costs more it will pay for itself in the quality of the foundation.
If one of your considerations was for thermal mass to heat or to cool you may want to consider a standard foundation and only foam insulating the exterior instead. This will allow the temperature of the foundation to match the interior temperature of the structure.
With ICF, always install an external membrane that can be secured above grade and install a secondary dimple panel membrane with weeping tile if possible. If you do this correctly you should never need help from a foundation repair contractor. Pay and do it right the first time or pay dearly later.
Credits ©2019 NextStar Technologies
Authors C Groner , N Wathen , L Frey