June 8, 2017

Flanged Window Install Guide for High Performance Enclosures

flangepage1Sequencing For Making Flanged Windows Airtight

Flanged windows are ubiquitous in American construction.  As we push toward higher levels of enclosure performance – with increased insulation levels, airtightness and vapor control – window specifications are getting more robust too. And while it can be a relatively straightforward thing to select a better window, it isn’t so readily clear how to match it with a better installation.

Let’s make a high performance installation too. Download the guide here (PDF).

Simple is Better

It needn’t be complicated.

There are a few key concepts that guide us:

  • Absolute control layer continuity: of water, air, insulation, and vapor control – from component to component.
  • Maximize drying potential, to build drying reserves and a safety buffer.  In cold and mixed climates this means vapor open toward exterior and vapor variable toward interior.
  • Durable and cost effective: with quality components, properly installed, the installation should exceed the life of the windows, no call backs and no up-charges.

Armed with these three commandments, we breakdown, tweak, and repackage the familiar steps of installing a flanged window.


The WRB is a high-performance three layer monolithic membrane – SOLITEX Mento 1000: waterproof, airtight and vapor open.  We make connections in a weather-lapped fashion, always starting at the bottom and overlapping materials as we work up, assuring proper drainage. EXTOSEAL Encors, a self-sealing, highly form fitting butyl-acrylic adhesive forms the sill pan.  Face tape with CONTEGA Solido EXO, a vapor open, airtight and waterproof SOLID acrylic adhesive with highly form-fitting fleece backing.  One may also face tape with TESCON Vana, waterproof, airtight and vapor permeable all-around SOLID acrylic tape.


Because the WRB is our outboard airtight layer the connection to the flange and window must be continuous all the way around – this includes at the sill and heads.  We are making a waterproof enclosure so moisture intrusion should be minimal, but in case there is some moisture intrusion, the vapor permeable nature of the flat taping assures drying capability and protection from damages.


If the framing cavity is insulated, there should be an airtight and vapor variable control layer inboard of the insulation.  INTELLO Plus is the most robust smart vapor retarder available and is extremely airtight.   Connecting the membrane to the window becomes essential – for moisture protection, comfort and efficiency.   We make these connections with TESCON Profect or Profil tapes.  With split release paper backing, these tapes are made for making tight inside corner connections.  We show how to premake corners so that these tightest of spots are successfully dealt with.

Download the Guide

We hope you find this step-by-step instruction guide useful. DOWNLOAD HERE (PDF).  Complete your high-performance enclosure with with a high performance flanged window install.

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3 Responses to Flanged Window Install Guide for High Performance Enclosures

  1. Wes Highfill August 5, 2017 at 7:08 am #

    I highly question taping the bottom flange. This goes against everything I’ve ever learned about window installation, which is to leave the bottom flange unsealed to allow water out if it makes its way in.

    • John August 15, 2017 at 11:03 am #

      Hi Wes,
      Glad you bring that up. We do have different details from the norm because we are using materials that are airtight, watertight, and provide moisture control. In our blog post The Pro Clima SOLITEX MENTO Difference we dig in to the mechanics of this. SOLITEX weather resistive barriers are monolithic, rather than relying on pores like other WRBs. This layer provides active vapor transport of water molecules, while preventing bulk water drops from entering. Having these materials to work with allows builders to simplify and truly airseal assemblies while providing an even greater level of protection. Hope that addressing the concern. As always, we’re happy to talk more.

  2. Floris August 15, 2017 at 1:03 pm #

    Additionally, sealing the bottom flange with vapor open tapes (TESCON Profect/CONTEGA SOLIDO EXO, FIDEN EXO) – does allow the gap under the window to dry outward if any unforeseen water gathers in that spot. With the waterproof sill made out of EXTOSEAL ENCORS as additional protection for the wall below the window.

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