Friday, June 18, 2010

You Can't Talk PassiveHouse without Talking Insulation

Time to talk insulation! The Passive House Planning Package energy modeling showed us that ideally we need to get our wall section thermal resistance toward R50 on the existing house, and closer to R60 on the addition (we have more room to play on the addition as we can put insulation on the exterior as opposed to having to eat up floorspace).  We have been playing with a variety of options to see how we can achieve this, without sacrificing too much floor space.  The existing house is just under 20 feet wide, and it is considered “legal non conforming” - meaning that it does not meet the current zoning regulations for set-backs, but it is allowed.   We are not allowed to make the house any wider, and we want to keep the red brick exterior anyway.  Therefore, all our insulation must be added to the interior.

A 20 foot wide house is not that easy to lay out functionally.  Once you put a staircase in, and some circulation space to get past the stairs, throw in a sofa and your rooms are getting pretty narrow. 
Our desire to make very thick walls certainly compounds this problem. Too much insulation and we'll end up with the ecofreako version of Merzbau.  Our desire to use low embodied energy insulation, which have lower R-values per inch as compared to petroleum based foams makes this nearly impossible.  Soooo  - we need to make some compromises.

With the existing balloon framed wall construction, there are only really only 2 options available for insulating the wall without removing all of the interior pine sheathing.  We either blow in a fibrous insulation  - like Cellulose or Fibreglass, or we fill the cavity with foam.  The challenge with anything fibrous is that we can’t guarantee that it won’t get wet from the outside.   With foam, we are not worried about the moisture, and we get the very desirable effect of creating an air barrier at the exterior wall.   Our plan is to use Icynene Pour and Fill formula (see-  - editors note: Hey Icynene, How about a sponsorship?). The blowing agent is not an HCFC, so the global warming potential is much lower than other foams we had considered.

We need much more insulation that we can achieve with foam, so we looked into several options.  The reality is, that we simply do not have sufficient space to get R50 from fibrous insulation alone – we need something with more thermal resistance per inch.   So, we are going to rely on polyiso for the much of our insulation in this project (see .  This is another type of foam that has low global warming potential, but great thermal resistance.  It is far from a perfect solution, but we think it is the best compromise of all our objectives.

The sections below are sketches of two of the wall types we will use.  One is for the new construction addition and one is for the retrofit of the old part of the house.  We need to have several versions of the wall section for the older part of the house because there are places that we simply can’t accommodate a 17” thick wall.  We'll have to keep our contractors on their toes as this is not your standard construction. 



  1. Good Day:

    I would like to point out that while I understand the need and desire to use blown in foam for air and moisture sealing porperties. I think you should reconsider your use of Roxul vs. Cellulose. Cellulose is 85% post consumer recycling that contains approximately 1% the embodied energy of Roxul yet maintains equivalent R value per inch. Cellulose is manufactured locally here in Ottawa and uses far less fuel to transport both raw material and finished product.

    There is another study that I have at work that goes into more detail on the embodied Enery numbers that I will try to find and post later this week.

    I am posting as someone in a similar situation with an 1910ish farm house in Ottawa which scored 20 on the preaudit however my renovation budget is much tighter than yours.

    I am interested to see how you proceed with renovation vs. reconstruction etc. as this project progresses.


  2. Thanks for the comment Mike - there is lots to like about blown cellulose. A couple things steered us towards the Roxul - Roxul is also recycled, also manufactured regionally, and is good from an indoor air quality. It has a couple added advantages for this project - it is very fire resistant (no small issue in the Glebe recently), we like the fact that it could be taken out again when someone else renovates (or heaven forbid tears it down) years from now and can be reused, and finally we won't have to worry about any settling issues or incomplete fills. All to say, could have been done with blown cellulose and we like the low embodied energy, but ultimately leaned towards the Roxul.