I am building an ICF house (more specifically ICF to the roof with wood trusses roof) and one particular item I will be focused on will be the building envelope air-tightness. For the air infiltration I am targeting to achieve the passive house standard which is 0.6 ACH50 (0.6 air-changes-per-hour at 50 pascals pressure difference) or better.

I was wondering if you could share the following:
1. What was your blower test result of the building?
2. Do you have any advice on how to make the ICF building envelope more air tight (connections to slab, windows, services penetrations, roof  etc.)?

Many thanks in advance!

Consider two air barriers on the roof part of it. And think not just about air tightness, but also about reducing pressure differentials (important since it takes both a hole and a pressure differential to move air).

I will install a Zehnder HRV for the mechanical ventilation system (if that's what you mean by how to reduce pressure differential to move air).
For the roof system, I am planning to have closed cell foam sprayed on the roof deck (not on top of the ceiling) so the attic will be insulated. Also the roof will be covered by a vapor barrier - though I am not sure how much air-sealing is provided by it.

For example, if you run dedicated and balanced supply and return HRV ducts to closed door rooms, you don't upset the pressure balance of that room.

I did one that we tested last year, we got 1 ACH without too much effort, I'm confident had we really put an effort into it and tried we could have reached .5 ACH

5" EPS below slab, on top of the footing
Amvic R30 block to roof
5" Spray foam in roof to underside of sheathing
Fiberglass windows

Major leaks we had during the blower door test

Warped front door
Improper sealed mechanical room window
Navien boiler leaks
Sump pump leaks
ERV pipe leaks
Shower base leak around drain

Posted By M. S. on 15 Mar 2015 08:24 PM

2. Do you have any advice on how to make the ICF building envelope more air tight (connections to slab, windows, services penetrations, roof  etc.)?

Many thanks in advance!

After much research I would use SIGA tapes on all penetrations and transitions. If you go on Green Building Adivsor you will see that the SIGA tape held on the best and it is top notch when it comes to sealing around windows, pipe penetrations, wall to roof transitions, etc.

Long-term studies show that caulks/sealants don't last and over time the bond will break due to drying and house movement. What the tape does is it allows for movement since it is stretchable and it never dries out. It is also vapor permeable so it allows for drying.

Chris and LBear: thank you both for the suggestions and advice: I will surely take them into consideration during the building.

Posted By M. S. on 17 Mar 2015 08:46 PM
Chris and LBear: thank you both for the suggestions and advice: I will surely take them into consideration during the building.

I would also like into UlimateAir for the ERV/mechanical ventilation. They are about 1/2 the cost ($2,300) of a Zehnder ($4,800) and US made.

Posted By M. S. on 15 Mar 2015 10:32 PM
I will install a Zehnder HRV for the mechanical ventilation system (if that's what you mean by how to reduce pressure differential to move air).
For the roof system, I am planning to have closed cell foam sprayed on the roof deck (not on top of the ceiling) so the attic will be insulated. Also the roof will be covered by a vapor barrier - though I am not sure how much air-sealing is provided by it.

I have an Ulitmate Air ERV. Works great. One thing I like about it (don't know if Zehnder offers the same) is an option to run the fan at full speed with the exchange wheel turned off. This works to bring cool air in at night and exhausts the warm air. Helps a little bit with a/c load in the summertime.

I suggest you seriously reconsider the advisability of using a vapor barrier on the roof. You are thinking of putting it on the topside of the sheathing, right? I so you will form an air tight volume between the vapor barrier and the foam on the underside. An air tight volume will never be 100% water vapor tight. What will happen is as the space heats and cools during the day & night the air inside will expand and contract. When it contracts it will suck in air and when it expands it pushes air out. The problem is water vapor will not follow the air so in time the vapor level will increase to the point where it will condense during the cool period. This will cause moisture to accumulate in the sheathing, exactly what you tryng to avoid. A closed volume in an environment of daily warming and cooling essentially becomes a water vapor pump, sucking in but not blowing out. The closed cell insulation on the underside is the ONLY vapor retarder you want in the roof system.

You do not want a vapor barrier in the house walls either. Vapor retarder, yes, vapor barrier, no. And that on only one side like Tyvek on the outside of the wall, which of course applies only with frame walls, not ICF walls.

I worked at the Strategic Petroleum Reserve in Louisiana and Texas. We had pumps and valves stored in the laydown yard that were tightly sealed against the weather. It was surprising how much water vapor built up inside, condensed, and caused rusting. We had to change our storage techniques to get away from tightly enclosed spaces so that air and water vapor would be free to move in and out.

We had to change our storage techniques to get away from tightly enclosed spaces so that air and water vapor would be free to move in and out.

I've seen the same for radios mounted outside in "airtight" boxes. It didn't work unless you also added heat or dehumidification to dry the air.

Posted By Lbear on 17 Mar 2015 09:03 PM

Posted By M. S. on 17 Mar 2015 08:46 PM
Chris and LBear: thank you both for the suggestions and advice: I will surely take them into consideration during the building.

I would also like into UlimateAir for the ERV/mechanical ventilation. They are about 1/2 the cost ($2,300) of a Zehnder ($4,800) and US made.

I don't want to turn this thread in a UltimateAir vs Zehnder HRV/ERV comparison, but to keep the readers informed: the Zehnder ComfoAir 350 (218cfm) and UltimateAir 200DX (200cfm) have similar prices - see the links below I found doing a quick search (you may get different prices, but this is what I quickly found on-line):
 - Zehnder: 2195 USD - http://www.smallplanetworkshopstore...t-215-cfm/
 - UltimateAir: 2299 USD - http://www.hvacquick.com/products/r...Ventilator

Note that the above prices are ONLY for the box itself (it does not include any optional components and duct system). It is true that Zehnder offers its "fancy" duct system which may double the cost of the "package" but that duct system is not mandatory and the same duct system can be used for UltimateAir. The other optional components (remote control, etc.) have more or less similar prices for both manufacturers. From what I have read on different discussions both systems are very good and offer almost the same list of features - in the end it is a personal choice or functionality on which one to get.

In my case, due to the volume of the house ~40,000 cubic ft,  I was told I actually need the ComfoAir 550 which has its max output at 315 cfm (UltimateAir does not have a product with similar output) -  I still need to confirm what I was told.

I need the higher cfm due to:
 a. I will not install dedicated exhaust systems in the bathrooms so it does not affect the balance of the air pressure provided by the HRV.
 b. the local code requires a particular level of cfm for the bathrooms which can not be met with a maximum of 200 cfm (still need to confirm this with the building inspector).