QU: What are the environmental benefits of ICF (Insulated Concrete Forms)

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I would just like to add a comment on ICF's or insulated concrete forms. I think there are a couple of pro's and con's to ICF construction overall. The basic fact that we are dealing with in an ICF is Mass wall - thermal mass to be exact. Thermal mass has been used for centuries in buildings and is having a residential resurgence here in parts of North America - but one must remember how and when it is used and its desired effects. High thermal mass buildings have been used generally in warm clients - such as Adobe style buildings and this is great - and ICF home is almost that - a high tech adobe home - but not quite. The key factor that you want in the mass is to store energy - but remember storage and "resistance to heat loss" is not the same thing.

A high R value of an insulated wall is different from the overall mass effect of a building - and so marketing claims of high insulation values need to be carefully reviewed. Thermal mass storage in regions such as Vancouver, Winnipeg and Arizona – work VERY differently. To use mass effectively in an environment in Canada - you want to essentially incorporate the mass into your home and heat that mass with passive solar heating - in house heating. Ideally, the best way to do heat the mass is through passive solar applications; however, the heating of mass is the beneficial part. Effectively implemented the mass releases its energy back into the house at night as the house cools and thermostats are set back. Think of it this way - a cast iron skillet that is heated - then turn the heat off - the cast iron "stores/holds" the heat long after and will release the heat back to the environment after the burner is turned off. Twenty or so minutes after the burner has been turned off the cast iron skillet will still be warm and the area close to it will still be warm. This is essentially what you want to do with your house. To be completely effective - you want to keep as much of the mass exposed to the interior of your house - and insulate this mass on the outside. If you don't, the heat will go straight through. If you have ever felt a concrete warehouse on a shady cool day - you will note that the wall feels virtually the same inside as out - there is no "resistance" or warm air pockets - it is a solid substance. For a material to be an insulator – it needs to have air pockets that contain warm air and that have a tough time leaving the building envelope.

Mass has very few air pockets. This can be a difficult concept. Water is a fantastic mass – i.e. ocean or lake effect of mass. It can absorb a lot of heat – and then slowly release it. But it is also a conductor – bath tubs and electricity don’t get along. It is important to understand mass effect – it is a tricky subject and too often it is confused as an insulator – it is not. So how does this relate to ICF’s? ICF’s are a great building system – BUT I always joke that once a home is built with styrene ICF’s that the homeowner should go get an ice scrapper and take off the interior insulation. This is because the way “most” ICF’s are built is with two inches of styrene (a resistance value of R 10) then six inches of concrete core, this is the “storage;” then another two inches of styrene insulation – ideally there should be no insulation on the inside of the wall that will trap or resist the stored energy from coming back into the house. Overall this ICF wall has almost the same R value as a standard 2x6” wall with batt insulation - R 20. The difference is the mass – but if you take a house with a high mass wall and you – try to visualize this – stick energy into the wall – it passes through the R10 styrene and sits in the middle of the mass. At night when the outside temperature is -10 degrees Celsius –inside the thermostats are set back to +22 degrees Celsius – the energy inside the wall has to make a decision – where will it go? Because the mass is warmer (energy coming from the house) – and heat flows toward the cold, the energy will move towards the outside – towards the -10C – because the resistance to go back into the house is the same as going out – there is no incentive for the energy to back towards the house. Is there a better answer? Yes, look for forms that add more insulation to the outside surface – the outside surface should have a thicker styrene on the outside than on the inside or other type of insulation that essentially provides less resistance for the energy to move back towards the inside of the house.

ICF’s are easy, fast and air tight – but my concern is the marketing of the energy efficiency of these systems. R values can be misleading. This wall will work very well in climates such as Nevada where they have a diurnal or flywheel climate effect of hot and cold fluctuations day and night. So by the time the heat starts to leave the wall late night early morning the outside climate starts to warm up again and it is now cooler inside the house than outside – so the energy in the mass which was starting to leave towards the outside is now realizing that is cooler in the inside of the house and will reverse direction and move towards the interior of the house. As the day goes along – night falls and it is cooler outside than inside – the energy then again changes direction and moves toward the colder surface – this “tug of war” continues and hence the mass has the desired effect. When this happens – you get a mass that is maintaining its storage capacity. Where as in Canada we may see -10 C or colder for more for a week – in which case energy is passing practically straight through and the question of having an R20 fiberglass wall system built to an R 2000 air tightness standard would be just as worthwhile. One should also keep in mind the environmental effects of the concrete –1) concrete is a very high embodied energy product and 2) the process of making the styrene blocks themselves. There are other alternatives to the styrene systems as is on display at the Sustainable Building Centre.

Also there are ICF companies doing it well – and secondly if you want a mass wall – good old form systems with exterior applied insulation do the same thing. Essentially wrapping a concrete house with a really warm blanket will have the same effect. Troy Glasner troyg@ekosbuild.com EKOS Building Solutions Simplifying Sustainable Living