15 January

One size doesn't fit all for AVBs

Since starting this blog, I have been asked not only about air barriers and how they work on a building, but also, how they interact with the rest of the building envelope, particularly as it relates to below grade/blind-side waterproofing and roofing.  As the cliché says, the devil is in the details. 

To borrow another cliché, one size doesn’t fit all when it comes to construction details.   Does an Egyptian pyramid look like the Sistine Chapel?  Of course not, and they’re not built the same either.  I raise this point because as construction professionals we sometimes try to fit all details into the same category.  But think about it. A fenestration is not always the same in every building.  On one building it may have an opening with steel studs, gypsum sheathing and a flanged window. On another, the fenestration may have steel studs, gypsum sheathing and a curtain wall assembly. 

The same is true when it comes to air and vapor barriers. For example, choosing a fluid or sheet applied air vapor barrier depends largely on the building details.  A cluster of pipe penetrations can be detailed more easily with a fluid applied membrane than with a sheet applied membrane. Conversely, on large expansive walls, a sheet applied membrane might be a good fit.

Tie-ins are crucial details to consider when deciding on the best option for keeping air and vapor out of a building.  Most system failures occur at tie-ins so you have to get it right when tying into a roof or foundation.  The only sure way to know if systems will work as intended is to specify a single source manufacturer. This is the route I recommend, because the manufacturer can show you how their systems interact and will warranty the entire system. Companies that manufacture entire building envelopes can give you all the necessary details about how building features from penetrations, to tie-ins, to issues like chemical compatibility will work with other products like sealants, masonry anchors, and roofing materials.  As they say, forewarned is forearmed (and that’s the last cliché for the day!)

For more information on total building envelope details, click here: http://www.carlislenvelop.com

Keep those questions coming in! Here is one I received recently. See if you can guess the answer to this reader's question. The first person who replies with the right answer wins a branded CCW polo shirt!

How many sides of a building comprise the complete building envelope?

  1. Four
  2. Eight
  3. Six

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