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©2016 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 58, no. 11, November 2016

Joseph W. Lstiburek, Ph.D., P.Eng., Fellow ASHRAE

About the Author
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in Westford, Mass. Visit www.buildingscience.com.

Sometimes I don’t get it. Why would anyone deliberately recommend a thermal bridge when it is completely unnecessary? The window industry must hate the foam sheathing industry, and as a result the foam sheathing industry hates the window industry. Yup, we have a vice versa. That is the only way I can explain it. Read on.

Anyone ever heard of a “ROESE”? Get used to it. It is a “rough opening extension support element” that is “a projection [“bump-out”] or extension to the structural wall framing at the rough opening perimeter” according to the American Architectural Manufacturer’s Association (AAMA) and the Window and Door Manufacturers Association (WDMA), respectively. According to AAMA and WDMA, a ROESE is necessary when a flanged window is installed with walls sheathed with exterior continuous insulation—insulating sheathing—most typically foam plastic insulating sheathing.

A ROESE is not a ROSE is not a ROSE by any other name. It is a thermal bridge.

Let’s take a look at a ROESE in action.

Photo 1 shows a wall sheathed with oriented strand board (OSB). The window openings are “picture framed” with a wood “bump out.” The thickness of the wood bump out is intended to match the thickness of the continuous insulation to be installed later.

Photo 2 shows the bump outs being waterproofed with peel and stick flashing membranes. Note the primer being installed prior to the installation of the peel and stick flashing membranes. All good. All very good.

Photo 3 shows the windows being installed in the openings and a fully adhered water control layer being installed. The fully adhered water control layer is being integrated with the flashing membranes at the bump out openings. This is all good. Excellent, in fact. No water control issues. None at all. And no air control issues. So what is my problem? It is just that the wood bump out is a thermal bridge. What is the point of continuous insulation if we run a thermal bridge through it at every punched opening?

According to AAMA and WDMA, the function of the bump out is to support the weight of the window and to “allow direct structural attachment of the window in order to transfer wind loads to the structure” when you install exterior continuous insulation. Seems reasonable. Except why now? Never needed this before. The building industry has only about 35 years of historical experience showing that this is not necessary. Installing flanged windows over foam sheathing goes back to Deep Purple and “Smoke on the Water.”

We have hung things off foam sheathing to figure out long-term creep performance. We have hung things off foam sheathing to figure out deflection and moments. We have sucked on windows installed over continuous insulation to understand wind loading. We have blown on windows installed over continuous insulation to understand wind loading. Others have done this. Lots of others have done this. Even the foam industry has done this.

Testing and field experience show that bump outs are not necessary. Did the window industry just “wake up”? What problem are we solving? Besides having to learn origami and apply the knowledge at window-to-wall interfaces and door-to-wall interfaces?

 

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Comments

  • 14 Nov 2016 | Gregory Brown
  • Hello - I like the article! Its seems there is another industry standard applied to openings in multi-story buildings? I did not read the entire article however I will, and so the comment I'm making hear might not be completely on target. But, the idea of the wood frame extension with ROESE greatly increases the labor units for starters, not to mention the decrease in a buildings ability to maintain an efficient thermal barrier as you mentioned. The structural consideration of a single 8d ringed shank nail has .40 N/cm dry and .70 N/cm wet pull strength resistance. Because the spacing is 6"OC at the fin perimeter of the window frame when nailed over the foam board you end up easily meeting the most severe exposure and zone conditions with the ROESE. I think it would be applicable as a provision for canted walls of a multi-story building, but then the construction type would probably prevent this from even happening. Nice point your making though. Thankyou
  • Reply
  • 04 Nov 2016 | Matthew J Matlak CSI,CCPR,FMPC
  • send Pictures - Please
  • Reply

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