Thursday, June 24, 2010

Death of the Buffer Zone

A much earlier post discussed the benefits of a Dynamic Buffer Zone (DBZ).  We became very attached to the concept, and for a long time worked to ensure our plans could include it.  Sadly it is not going to work in this project.  The energy modeling we did indicates that the DBZ does not have strong effect on the energy performance of the house.  It has advantages with respect to thermal comfort at the front of the house, but overall is not a game changer.  It is however a budget-breaker. We priced several options to have 2 sets of doors at the front of the house to create the DBZ and still have flexibility of how we use the floor space.  We thought people looking to emulate our design may benefit from our research.

Our cheapest option, that was still reasonable in energy performance were very large sliding fiberglass doors – 4 panels, each panel about 4’ wide.  The centre panels would open and give us almost 8’ of clear opening.  However, the air leakage performance on these is not very good over time because they ride on the seal.  Each set of doors would be in the $7-10k range depending on the details and which manufacturer we chose, plus installation (for example -

Next up was to look at fiberglass tilt-and-turn doors to give us the long term air sealing, but the swing on the doors takes up way too much floor space inside.  The cost was closer to $12k per set of doors.
Then we started looking at some of the “lift and slide” options on the market.  These doors slide open like the door on a mini-van – they pop out and then run parallel to the sill, so they are not riding on the seal.  The come in very interesting configurations including the ability to put them into a pocket, or have 3 panels stack on top of the 4th to allow a full 12’ clear opening.  The price ranged from about $14k to almost $18k per set of doors.  The air sealing was very good on these units relative to the two cheaper options.

Finally we looked at folding doors.  The most commonly marketed version out there is called NanaWall – and they have great animations on their website (  These doors fold out of the way to create a large clear opening.  The challenge for us was that most manufacturers gear this product to the coastal climate.  They are not too worried about air leakage, and have very little understanding of solar gain glass (these are on the south side of the house and we want them to let in as much heat as possible during the winter).  After lots of searching, I sorted out that this is all German technology, and there really are only a few parent companies who are all doing the bulk of the manufacturing in Germany.  There is one Canadian manufacturer who builds folding door systems in Canada - (  These doors also range in price from around $14k to about $18k depending on the manufacturer and options for a clear opening of over 13’.

So – we were faced with a pretty tough decision.  We love the idea of the DBZ, and think it would add to our thermal comfort, but it is not getting us closer to Passive House, complicates our interior layout, and costs a fortune.   In the end we decided that we need the money for other energy saving concepts more than we need a DBZ.

However – our search did yield a pretty amazing set of folding doors to allow us to open up the front of the second floor fully to the balcony.  This was always our hope – and these doors are going to make it happen.  The people at Meyers Windows – located in Vancouver, but manufactured in Germany, understood our need for air sealing, solar gain glass (Solar Heat Gain Coefficient of 0.6), sound isolation, and thermal performance (R5.26 which is spectacular for glass doors).  They had experience working on passive house projects in Europe and pretty much understood everything I needed. They were even able to provide the door frames in FSC certified wood. (see

Here is an elevation drawing of the doors.  The right hand panel is a swing door, hinged on the right.  The 4 left panels fold together and stack to the left.


  1. Hey Scott, do the front windows still have a section facing south, despite the dbx being history?

  2. We've definitely stayed with the passive solar design with ample glazing on the south side. See for example the glass sliding doors above which are facing south and open up to the balcony. All part of the passive solar strategy for the house.