I wonder what experience anyone has had with installing rigid insulation under continuous strip footings supporting a standard concrete foundation wall.
Building Science Corp has done the homework for you! http://www.buildingscience.com/doctypes/enclosures-that-work/etw-high-r-value-enclosure-assemblie
Posted: 03:17 pm on March 26th 2013
Thanks Martin. When ever I have an important question about building the first place I look is at the archives for your blog! I believe that you have written (well) about anything that matters! I have a client that is doubtful about installing insulation under a concrete strip footing. Interestingly, my client quoted the bible story about building on sand just like Super Structure Builder did after your blog! My client's regular engineer will not consider insulation under the footing at all. We can find an engineer that will work with us, but resistance has set the stage. Most of the discussion for the "Foam Under Footings" article has to do with a monolithic or raft foundation. We will be pouring a traditional footing ~ 9" below grade for the proposed project. I am fishing for examples and recent experiences that deal specifically with wrapping a deep below grade footing.
Posted: 11:32 pm on March 26th 2013
Wow! looks like an Escher drawing! Thanks!
Posted: 11:59 pm on March 26th 2013
The engineer is concerned with the potential for EPS to absorb water and harbour mould. I did not speak to the engineer so this is 3rd hand information... I believe that the concern is the potential for degradation of rigid insulation over time.
Posted: 12:05 pm on March 27th 2013
Thank you for taking the time to write Ron. I especially appreciate your thoughts about "creep". The point about footings spanning sewer lines is a good one! (one that I have had anxiety about in the past!) I have read and heard a few times in the past month or so that there is evidence that XPS degrades over time. The information has been generated by EPS proponents, but the claim is that XPS looses 52% of it's original stated R value. Apparently XPS is more prone to water absorption over time than EPS. After seeing the photo that Mike Ellison has offered with the copious use of EPS for some serious concrete construction, it seems that EPS has gained significant credentials with engineers. I wonder about the merits of using XPS at all.
Posted: 02:07 pm on March 27th 2013
Carissa Farkus has sent a link to videos that demonstrate techniques for installing EPS under strip footings. http://hammerandhand.com/_blog/Field_Notes/post/Passive_House_construction_time-lapse_a_mountain_of_foam,_delivered/#.UVhanqtASWs There are 6 videos showing the progress for the pour for this project. The techniques used for the preparation for the insulation under footings for the Karuna house are the same as the details that we use for classic PWF wood footings. (This is a GOOD thing!) The advantages to this type of subsoil work and careful consideration of drainage will ensure that the foundation stays dry and any unknowns about moisture issues are not issues since there is no standing water to worry about. This is the type of (visual) information that I was looking for! If the work is done as shown in these videos, the insulation under the footings does not look like a risky proposition to me, but I am not a structural engineer. I have specified under footing insulation for monolithic pours (Raft foundations) many times but have not specified under strip footing insulation.(It's easy to guess that the project that wants under footing insulation is a Passive House proposal!) My understanding is that protecting the footing from frost with an insulating skirt is especially important when the foundation is isolated from the surrounding soil. If the foundation is not contributing to the modification of the temperature of the backfill and the frost is driven deeper than the underside of the footing, the skirt will prevent frost penetration next to the building. I know that it seems crazy, but around here, the frost can be as deep as 8' some years. The experience that I have had in the past with sewer and water lines is that they have been literally "shoved" under footings without proper sub preparation or support around the sewer pipe or under the footing. The footing might span 18" of ABS and uncompacted gravel in the after the fact excavation.
Posted: 07:12 pm on March 31st 2013
1.8 lbs density and netting Dana's question is a good one! JM literature states 2.2 pcf. Would have been great to have a "test section" on site to see what kind of densities the on site crew was actually blowing.
Posted: 10:59 am on July 27th 2013
Booster fans / Commisioning We have recognized for a long time that (E) HRV's are clumsy in the exhaust department. Boosting whole house ventilation for one person showering seems like a funny thing to do. The inability of (E)HRV's to spot exhaust is a shortcoming. We have experimented with the installation of inline (in the duct) fans dedicated to each exhaust duct (very near the recovery unit). We started with 150 cfm fans connected to a timer for each exhaust location (bathrooms, laundry and kitchen) The results were: - initially there was cross duct exhaust, some of the fans redistributed the exhaust through the interconnected ductwork to another room! inline Butterfly dampers fixed this problem by preventing back flow. - The kitchen needed more umph so the inline fan was switched out to a 350 cfm with better results. - The laundry room exhaust is never used, would not install a booster fan from this location in the future. Seems to be a decent and not terribly expensive solution without energy or envelope penalties. The issues mentioned above (different habits for different people) affect the effectiveness of this or any exhaust system. The booster fan solution does the job that a dedicated exhaust for each room would do. We had this system commissioned, which is not normal procedure for a residence. For $250 the system was balanced and the performance perceptibly improved. When investing thousands into a mechanical system it is a no brainer to have proper commissioning done so that the system actually does what it is supposed to do!
Posted: 01:59 pm on April 26th 2014
Electricity Costs Malcolm Taylor asked about the electricity costs because his household costs seem to be similar for a house that does not perform as well as this one does. I wonder if it is possible to discover the amount of energy that the house used during the colder months (kwh) and how that compares to warmer months. Electricity costs vary from location to location so a dollar amount may be misleading. This would make the energy consumption for supplemental heating question a bit clearer. Great house! Great house dwellers!
Posted: 04:43 pm on June 7th 2014
Is there any updated news about PV laminates? They appear to be available both in Canada and the US.
Posted: 10:01 am on March 15th 2016