have 44" to 68" perimeter glazing at a library

Here is what i am working on for a response as to exactly why i believe the 42" line should not be the make or break dimension.

The requirement to establish what some define as the direct line of site at 42” is contradictory to the credit language and to the referenced study by Hechong and Mahone in establishing exemplary performance. It seems that many in the LEED world only think that credit compliance is only determined from this 42” horizontal line. It is even unclear as how GBCI even states in the LEED interpretation 1646 that the view requirement must be met from a seated height of 42”. Again, this is contradictory to the language in the Reference Guide. I make the following case that views in the library for the_____________ are valid based upon the following.

The definition of, or meaning of direct line of site does include anything about having to be parallel, it clearly states that it is uninterrupted path between the eye and the object. The calculations section of the credit language states that a direct line of site must established to the perimeter glazing, nothing about 42”. In the implementation section of the credit, it states that 42” is assumed, and can be adjusted for students or non-typical functions. That statement alone nullifies the 42” requirement.

Figure one in the Reference Guide shows a cone, it is assumed that the bottom line is 42” and the top line runs to 90” on the perimeter. The dashed line is the line of site, again, it is not parallel. It is very vague as to why 42” is so regarded when the credit language references vision glazing between 30 and 90 inches. Based on having vision glazing between 30 and 90 inches clearly implies that I can have a view to the exterior anywhere between 30 and 90 inches. Nothing references that a project team must establish a determined height that is parallel to the floor. If that were the case then project teams would be allowed to have parallel line from the occupants to exterior anywhere between 30 and 90 inches. Again if 42” is a standard why is 30 and 90 inches used in the language?

The credit language states in determining the horizontal view, draw a line at 42”( typical seated height). This whole section references the example of an office space. In the same section it states that the line is used to determine if there are any obstructions at 42” IT DOES NOT STATE that this line is the direct line of site to be used to determine if the occupant has a view, you just can not have any obstructions that high. The next line in the same section states that you are draw 1 or more representative lines of site to the perimeter glazing, refer to figure 1. This line, the line of site is the dashed line. Dashed lines in this situation throughout the industry is the indication of someone vision line. This is not parallel nor is at 42”. It does fall in between what is assume to be 30 and 90”. I want to reiterate, that the 42” line is to determine obstructions, not the line of site.

The final piece to considere as to why 42” is not the standard to determine if there is a view to the perimeter comes from the Heschong and Mahone study, “Windows and the Office”. This document is used to establish exemplary performance requirements. Page 47 establishes the parameters. First off it talks about the cone of vision that is 90 degrees, the cone of vision is shown on page 49 and it is both horizontal and vertical. Refer to page 48 which categorizes the 5 classes of views. Class three is used to establish exemplary performance, but the study also states that class one and 2 are views, they are just not the most desired. Now refer to page 50 and figure 25. It references that the minimum and maximum degrees that one should use to classify a view is 11 and 40. So no less then 11 and no more than 40. Please refer to the section uploaded labeled view compliance. It shows that an occupant sitting at a table will have a vision cone of ______ and ____________.

The point that i'm trying to establish is that we have a cone of vision, both horizontal and vertical so as long as we have certain percentage within that cone, it is acceptable.

This is a work in progress that i'm working on.

I would apply common sense. If the position is a standing one, the height of the vision line should be for standing. If sitting then sitting. The cone idea is good but too complex (expensive) to apply to a LEED credit. Think about the intent of the credit. Do you fullfill the intent? The wording of the credit will never be perfect.