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Whether to Build with ICF or traditional framing?

WHekqJvTbX | Posted in General Questions on

I am in the planning stage for building a cottage. An existing cottage will be torn down and a new one built to replace it. The basement will be made using ICF (currently no basement or reliable foundation on existing cottage). The decision that I need to make is whether to continue with the ICF for the upper two floors to the roof or to build the upper two floors with traditional wood framing.

I have read lots of articles promoting ICF as a building material, but written mostly by the manufacturers. I would like to get some “real world” feedback from builders or home owners that live in (or build) foundation to roof ICF homes.

Taking labor into account the claim by the manufacturers is that building costs for ICF are only about 5% more expensive than traditional wood framing. Reading some of the feedback on this site some people claim 3x to 5x more expensive for ICF. I am still waiting for a quote on ICF installation so I don’t know what to think about this difference in expense.

I am building a cottage in Zone 5 (Ontario). The cottage is adjacent to a lake with a lot of tree coverage. The exterior wood on the existing cottage (built in 1963) suffers from a lot of mold/mildew/moisture damage, so I would guess that the area is dark and damp.

On the plus side for ICF I like the idea of a quick installation (by a qualified professional). Given the choice I would like to have this structure built quickly.

The other thing that I really like is the solidness of the concrete walls. We have endless problems with small rodents tunneling through the 2×4 walls. They chew up the insulation and leave it in clumps for nests. In some cases the mice/chipmunks completely remove chunks of insulation. The insulating capabilities of my existing walls must be almost non-existent by this point in time.

Heating will be a combination of wood stove and forced air propane furnace. The area is isolated from any gas line service so propane will have to be trucked in and stored in tanks. I am restricted to using the EXACT same foot print as the existing cottage so there are some limitations as to what can be done regarding passive solar heating and my architect is addressing that.

The expected usage model will be continuous occupation during the Summer and Fall months and then only on weekends every two or three weeks during the Winter, so the cottage will remain empty for a stretch of 2 to 3 weeks at a time over the Winter. I expect to never completely close down the cottage. When we are not present I will maintain the furnace at 7 Celsius during the Winter just to ensure that the pipes don’t freeze and the place doesn’t become an ice-cube when we are away. At some point in time in the future I expect to live there year round.

For the moment lets assume that the differences in building costs are not significant and not address those yet. My 2 biggest concerns are;

1) What would be the relative difference in cost of heating the ICF during the Winter versus wood frame construction (ie 2×6 with Styrofoam sheathing outside or double stud 2×4 walls)


2) Given that the concrete has a high thermal mass, if we are away for 3 weeks (with temp left at 7 Celsius) how long would it take to warm the cottage back up to a comfortable level?

Keeping in mind that future rodent damage is almost a given. This may not happen immediately but it is sure to happen.

Whats the level of comfort living in a “concrete block”? Is it comfortable? Are you always cool and damp? Is it toasty warm?

What do you recommend and why? ICF or wood? Are there any ICF home owners out there that can comment. Was it a mistake? Do you like it? Was it the best thing you ever did?


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  1. user-966377 | | #1

    Hi There,

    I am currently working on an ICF house in Toronto, Ontario.
    The basement and ground and second floor walls are Durisol Block (, and even the floors are concrete as well.
    You mention thermal mass in your question. Traditional poly- based ICFs place equal amounts of insulation on both sides (interior and exterior) of the concrete core, thereby negating any effects of the thermal mass. Durisol places all insulation on the outboard side of the concrete, and the entire wall can act as a thermal mass, storing heat during the day and releasing it at night when you are there, and storing heat in the walls while you are not there, possibly decreasing the amount of work by the furnace.

    The project we are working on has an extremely low heat loss due to the high insulation in the walls and the thermal mass in the concrete itself. Your system, with a wood stove and forced air gas furnace, should be able to start up relatively quickly when you get there, upping the air temperature inside from the 7 degrees Celsius. The walls will take some time to gather heat from the inside, but the air temperature should be fine.
    Any increased cost of installing the ICF could be offset by a smaller furnace running less frequently due to higher insulation than the 2x4 wall assembly you described above. Plus, with a wood stove as well, and plenty of trees and firewood around in northern Ontario, the furnace load can be reduced even further.

  2. GBA Editor
  3. GBA Editor
    Martin Holladay | | #3

    Here's an article by a homeowner who built an ICF home:
    Foam Forms Create an Energy-Efficient Concrete House

    Here's a video tour of her house:
    Green Home Tour: DIY ICF House With Energy Star Rating

  4. WHekqJvTbX | | #4

    Yes, I saw the article, but it didn't really go into enough detail to answer my questions. It still left a lot of questions unanswered. I also read all of the responses and most of them got side-tracked with windows :(

    Who I would really like to hear from is other homeowners that have already built and lived in a foundation to roof ICF home. Even feedback from some of the contractors that have built ICF would help.

    A lot of stuff presented on the web is theoretical. I don't really care about mathematical models and simulations because as we all know, numbers can say anything that we want them to say. What I need is more practical, real world responses

  5. kevin_in_denver | | #5

    You may be able to get some ICF homeowners to comment if you post at this forum:

    There are also definitely some ICF evangelists over there, whereas they are pretty rare on this site.

  6. user-1012653 | | #6

    Based on studies published by ORNL and Building Science, ICF walls in your zone 5 will give you marginal advantages over stick built, tight homes with similar r value as the EPS foam. I too researched for endless hours, reading everything I could and talking to a few ICF owners in this area to come to my conclusion that a thick foam wall on sticks or double stud will perform much better then the ICF wall. The thermal mass gets you very little unless your duranial temps are working for you. In your zone, they certainly do not. So if thermal efficiency is your goal with ICF, I would look at a different high r, tight wall assembly. However if strength, fire resistances, life of the home, quietness, etc are all requirements, then ICF might be a good option for you. I did talk to someone who wanted all of the above, so they actually furred out the inside of the walls with 2x4s and insulated that as well with blown cellulose. This was also nice for plumbers and electricians so they could install everything in the stud space and avoid the ICF forms and concrete. Obviously it cost even more yet, but they have an efficient and strong home with the ease of a wood framed interior.
    On the flip side, there is someone near me I visited. They are in the design phase of a new home and will avoid ICF at all costs. They were promised big savings and reduced equipment, but the equipment was reduced, but the savings weren't there. The small sized equipment couldn't keep up with the heat loss of the house it is was only performing as an r-24 and not the r-40 the ICF guy pushed on the hvac installer. Plus they did not like the simple things, such as attaching things to the walls. Its either foam or plastic strips.

  7. user-659915 | | #7

    Kelly, I see you're primarily asking for input from owners of ICF homes, which I am not, but I offer the following comments without apology. I suspect that human nature being what it is, most ICF owners will be enthusiastic in their praise of their investment, a few will be grumpy and hypercritical, and you will learn little of value from either camp.

    "Given that the concrete has a high thermal mass, if we are away for 3 weeks (with temp left at 7 Celsius) how long would it take to warm the cottage back up to a comfortable level?"

    As the thermal mass in an ICF wall is thermally isolated form the interior it will have little effect on interior comfort one way of the other. Your cottage will warm up relatively quickly on your winter visits, but it won't offer the thermal flywheel advantage either. And as Jesse L points out, thermal flywheel effects are in any case of little use in regions without large diurnal temperature variations more or less balanced on each side of the human comfort zone (say 95° days and 50° nights).

    "Keeping in mind that future rodent damage is almost a given. This may not happen immediately but it is sure to happen."

    I may be missing something here but surely the exterior insulation layer of the ICF system is as vulnerable to rodent damage as a stick frame wall. For sure the concrete core will keep the critters from gnawing right through to the interior but you are still liable to lose half your insulation without proper exterior protection, the same as you would need for a framed wall. Cement board siding? Brick? Stucco?

    "Whats the level of comfort living in a "concrete block"? Is it comfortable? Are you always cool and damp? Is it toasty warm?"

    You can make almost any home comfortable and toasty warm if you pump enough energy into it. But for what it's worth, buildings made predominantly of wood are by far the most common traditional housing form in extreme cold climates, at least outside of the dense urban areas where fire was a concern. The folks who made these homes had no propane tanks - I'm inclined to think they knew something about how to to stay cosy on a low energy budget.

  8. user-651098 | | #8

    You mentioned that, in the winter, you would only use the cottage every third week-end. You may have to research this idea to see if it is practical or possible. Install a programmable thermostat which would allow you to maintain a set temperature for 18 to 20 days and increase the temperature several hours before you projected arrival. If you have a phone line at the cottage, you may be able to turn the furnace up remotely.
    There may be cheaper rodent solution than concrete. Find a supplier of wide rolls of 1/4 inch mesh (hardware cloth). Install the mesh under the siding so the cottage is enveloped in this barrier. If you buy several rolls for the job, you may find a very good bulk buy price.
    Flash the top of the foundation so the critters can't climb easily.
    If you have a lightning rod ground wire, wrap some flatstock around a lower section of it (or run the cable through a metal pipe). This will prevent the mice from climbing the cable.
    Trim the trees and limbs back from the building. I have seen situations where the squirrels and chipmunks jumped from trees onto the roof to gain access. If branches are too close to the cottage, raccoons can also gain access.
    You mentioned mildew and mould on the wooden siding. Trees excrete moisture and sap which is laden with natural sugars. This is food for moulds. If the limbs overhang the roof and/or the building is shaded from the sun, this moisture will not evaporate as quickly. If the forest is too dense, the breezes won't dry the walls out.
    Falling leaves and pine needles will also affect the roof and clog the eavestrough. The solution is to open up the canopy and the underbrush to allow the sun and the wind to dry the siding and roof.
    You mentioned that the cottage is near a lake. What is the orientation of the cottage relative to the lake? Where is Solar South?
    If you use wood framing instead of ICF, the money saved on ICF foam and concrete can be diverted to increased framing and insulation.

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