CS – PH Retrofit (EnerPHit) – sliders or not? Other considerations regarding the envelope.

I often get questions from clients regarding the choices I have made for my EnerPHit of my cabin. This space is dedicated to sharing some of the valuable learning from my Living Lab situation.

Question: “Did you install a sliding glass door as part of the passive-grade windows on your house?”

The simple answer is no. But this is how I got there.


Whether to go with a sliding wood or sliding glass door for a PH retrofit is a good question. I went through a process of discovery that involved Hajo, my PH architect, and me doing my own online research and by living in situ. In doing so I started to better understand how my decisions surrounding my renovation would impact me and my home. Living in it provided me with insights about what would best fit my situation and allowed for “live” changes in the design.

Fenstur Windows made a beautiful wood sliding door, but glass sliders weren’t an option at that time because they wouldn’t meet the PH criteria. Since then things have changed and they offer a lift and roll door that is PH certified (that may have changed since time of publication). Fenstur did however build all-glass French door option that achieved PH certification and were a gorgeous product which. I had drawn into the plans.

After spending another winter in the cabin, which has a SE exposure and is exposed to the winter elements (sun exposure, strong winds and driving rain) I decided to install a PH certified single glass patio door (to spec).  Living in the space and observing the elements provided me the opportunity to adapt the design to best suit the environment.

Challenges & Issues:

  • Winter – ESE exposure, strong winds, and driving rain;
  • Cost of going with PH doors and windows; 
  • Cost of hardware and locking mechanisms for doors over 21/2″ thick; and
  • Adding cork layer take them to 4″.

Solution: PH Certified single glass patio door.

Question: “We are repairing the front of our house and are wondering about the cost of the Fenstur windows and any special installation needed?”

The installation will depend on your current home situation and the design. I recommend considering the bigger picture and whether or not you consider other envelope upgrades at the time of installation? Are there any improvements to the envelope that have been done or being considered, such as new air barrier (AB) and/or WBS, additional insulation or consideration on that wall your upgrading?

For example, my situation:

  • The preparation for the door window involved:
  • Pulling siding and adding an AB (air barrier). This same process can be used for windows
  • Installing outriggers (TJI beams on edge) to allow for the addition of 9/1/2″s of insulation to exterior walls; and
  • Framing the door (or window) to meet the specs provided by the designer and manufacturer (Siga) of AB/WBS (Weather barrier system) and rainscreen.

All of this adds to the cost but installing PH doors and windows are an investment in crucial upgrades to the envelope of your home, which are then offset by reduced energy needed to heat your home, and can be amortized over 30+ years making the actual investment even less.

Challenges & Issues:

  • Expensive, but from my perspective an investment worth the price;  
  • Having doors and windows built to spec make them more costly; and
  • Include the cork layer adds more $;


  • Save some cost by going with a PH certifiable door or window, but to a PH architect will run modelling to come up with the specs to fit your home’s design and optimize performance.
  • You can also order a door or window that meets the PH certification (triple glazed, +++, but not tuned per the PH design; and
  • Reduce size and number of windows based on the conventions of PH technology and concepts.

Successful outcomes:

My goals with my PH renovation evolved as I learned more about what I was hoping to achieve: 

  • A question I asked was “Did I want or need to obtain PH EnerPHit cert or not?”
    • The realities of my cabin’s performance characteristics in the PH certification process. This applies in general small space homes <750-1000sf. According to my PH architect it related to – area to volume are skewed in the modelling software used for the designing/certification;
    • Balancing costs –was installing unrealistic amounts of insulation in my roof to meet the PH cert criteria the best choice -or would slightly less insulation achieve my overarching goals of net-zero energy (10 months of the year) and ability to live off-grid for 10-14 days post-storm events?
    • The advice I received to consider what my goal was – PH EnerPHit certification or to increase my resiliency Self-sufficient?
  • Resiliency is the goal then it is a highly efficient little unit the latter won out.
  • Using the PHPP tool to design the renovation;
    • Understanding and acknowledging the small space and disproportion of the small cabin volume.
  • The cost of French door vs. single patio all-glass door is less expensive and perform better than the French doors; The doors and windows are simply a beautiful product;
  • They seal, warmth and management of light into the home is unlike any window or door I have lived within; and
  • I have some, but limited carpentry skills and with the help of my Architect did all of my work myself. I have made mistakes, but all fixable and have enjoyed working with these windows and doors.

Lesson learned:

  • Investing in a good PH architect or PH Certified Designer was the best investment in this project. It’s not so much about achieving the certification, but the paradigm they bring to the conversation, and how to resolve issues as they come up; and
  • All glass with wood frame = best U values of the options available (all wood, or mixed); and
  • It is all about the envelope, and the management of the air inside your home windows and doors has been the weakness in every house I have lived in and only learned this in my late 50s when I started this project on Thetis.

Author: Doug Fenton – EP/Sole proprietor