Just found your site and now I can’t stop reading it. Great
info.

A question: On a previous post you had said that the cost for
ICF up to the roof would have been about the same as stick
frame but now you’ve changed your mind. What happened? What
was the difference in cost?

As for cost, I am not sure that the cost will be any different, as you will have the additional cost and labour of installing the exterior styrofoam and foaming and/or taping the seams to offset the resulting thinner layer of sprayfoam insulation you will require on the inside, but the energy savings are worthwhile.

You could also preserve the racking resistance provided by the 1/2” sheathing shown in your drawings by instead using metal strapping run diagonally across the stud bays, which many builders use. This would reduce your wall thickness by 1/2”.

Also it seems that even with the extra thickness of the exterior styrofoam, the total wall thickness would be very similar to the wall thickness you would have had when you were considering ICF’s for all floors, or am I mistaken? Sprayfoam on the exterior of a house, btw, is also a great alternative to to rigid styrofoam sheets as long as you properly accomodate for fastening the exterior cladding.

As for the sprayfoam on the interior, it is expensive but nothing beats it for completely air sealing and completely insulating the house. This is especially true when you consider that the R-value of a wall is reduced by double-digit percentages due to even the smallest holes dues to improper sealing of the vapour barrier to protrusions in the wall and/or improper installation of conventional (batt) insulation. Actually even if you are really determined (as few installers are) it’s almost impossible to do a good job with protrusions in the wall created by s pipes, cables and electrical boxes using tuck tape, acoustical sealant and poly. This is not the case with sprayfoam insulation.

Regardless, it’s definitely something to consider and I like the idea of reducing the amount of sprayfoam we need as it’s quite expensive.

We built our own home (we were crazy enough to also do about 85% of the subcontract work ourselves, see http://newhome.daxack.ca) and would have loved to go ICF to the roof, but it was beyond our budget as well. As we were going with an acrylic stucco finish, the exterior foam was a given. However, with this finish, there needs to be rainscreen protection, which slightly ventilates the back of the foam and reduces its effective R-value slightly.

On the plus side, because of our ICF foundation, the stucco contractor needed to use 2” foam instead of the usual 1.5” so that it would be even with the ICF. In addition to this, the rainscreen protection came from placing the air barrier completely on the outside of the home. Many homes are built with the air and vapour barrier shared, with wrap around the end of floors to connect the barrier from one floor to the next. Having an entirely separate air barrier on the outside of the framing makes for a better air barrier, in my opinion (and in the opinion of our building inspector, who pointed out that insulation could be installed before the stucco was installed because it made the building air tight).

The best way to avoid this (other than using ICF’s which do not allow thermal bridging) is to also insulate the home from the outside either using 1 to 2” of rigid eps foam insulation boards with the seams filled and taped or spray foam insulation, in addition to insulation in the cavities between the studs. This will reduce the amount of insulation you need to spray on the inside the achieve the R-value you want. Insta-Insulation, often featured on Holmes’ show, is a big proponent of this exterior insulation method. In fact, Canada Mortgage & Housing Corporation, who publishes a wide variety of building construction related documents, recommends that houses be insulated on the exterior of the sheathing. Building Science Corporation (http:/www.buildingscience.com), a great organization that publishes a wealth of construction-related information, much of it free, has a lot information on their website about this. They produce a great book, ‘Builder’s Guide to Cold Climates’ (described as ‘A systems approach to designing and building homes that are safe, healthy, durable, comfortable, energy efficient and environmentally responsible’).

Given you have yet to frame the walls, you are still able to adjust the design to accomodate some external insulation to reduce or eliminate thermal bridging.

I must admit, this project has (at least for now) brought the neighbourhood together. I’ve heard such horror stories about neighbour protests and injunctions, and (knock on wood), we’ve had the complete opposite. It definitely reinforces why we decided to stay and build :)