Your home is an envelope

Back again for another round of the discussion board.  Today I thought I’d add on to what was discussed in the previous blog.  Energy Star ratings of a home are heavily dictated upon the homes envelope.  The term envelope is a pretty relative term which takes on a pretty important meaning when it is used in new homes.  What it is, is the entire sealed compartment within the walls of the home.  The moisture barrier and other products are used to create this.  With the strict energy codes along with even stricter guidelines by my company it must be as tight as possible.  We start creating the envelope of the home as we start the framing process.  As exterior walls start to go up, we apply house wrap which helps keep the elements from entering into the home.  As we start to add interior walls, I make sure all the walls running into the exterior walls have pre-poly.  The reason for this is to have a seam for tying in the rest of the poly once we have past the point of insulation.  Most builders don’t do this vital step and rely on the caulking of the poly to the actual wood members where the inside walls meet the outside framed wall.  Proper install of the windows is also a vital part of this.  80% of all moisture damage in a home comes from windows if not installed correctly.  Once the home is framed, the mechanical systems are assembled and installed.  Many holes are cut inside the home and penetrations are added through the exterior walls.  These are vital areas to be sealed back up prior to the install of the insulation and poly that covers it.  Heat, moisture, and air are all able to flow through these areas unless it is prevented.  Now its time to  be insulated.  Insulation may seem like a pretty simple task, but the way it is put in is one of the most watched over areas in my inspection process.  Much to what people might think, more is better when it comes to insulation.  Small voids in the insulation allow heat to transfer and thus creating possible condensation points in the home.  I plan on touching on the differences between spray foam and fiberglass insulation at a later date.  After insulation and inspecting for the possible voids, we move to the next step.  That’s where the poly comes into play which most consider the true envelope.  If not installed proper, this can lead to major moisture concerns down the road.  Hundreds of gallons of water per year can escape from the smallest of holes in the poly if not repaired.  Many misconceptions have led people to believe that a new home should breath and there should be holes in the poly barrier of the home.  This is the farthest thing from the truth in the way homes are constructed today.  Air flow creates moisture and moisture creates major problems if not controlled.  This has been the leading factor in my decisions to install air to air exchangers where applicable.  If we can’t rely on the walls or windows to bring in fresh air or lose moisture, then we need to do it mechanically.

Properly running air exchanges removes the homes dirty moist air as it builds up and replaces it with cold fresh air from the exterior.  Air exchangers are designed to be run in the winter and off in the summer and should have its filters cleaned as often as the furnace filter.  Spring and fall we typically have windows open which itself acts like a passive air exchanger.  The efficiency of the air exchange unit is my primary reason for installing.  The fact it can pick up heat from the air leaving the home and mix it with the cold air coming in gives it this efficiency.  That is where the exchanger part of the name came from.  One of the major bonuses it also creates is a healthier environment.

A homes envelope is much more complex than this, but I hope I have helped uncover some of the most important aspects of it.  The bottom line is to keep a home that is built in today’s energy conscious environment as tight as you can.

I plan on touching base on all of my homes mechanical systems as this blog progresses.  Feel free to add any ideas you might want to cover as well.  Thanks for reading!