IEQc8.1 - Daylighting

If your windows are not connected to exterior space, as other previous discussions, you can't use prescriptive approach.

Mike, If I am not mistaken, it looks like you have 2 spaces behind the windows but there is no separation wall/glass between two spaces. you can combine those two spaces in one calculation and you can use the exterior window. Additionally, you may need to put a note why you do that.

What Eddy is saying is true as long as there are no walls, soffits, ceilings, etc. that create a smaller opening into the exterior ROS. In other words, you must be able to draw an unobstructed line from every point on the floor to the exterior window. Also, if your space farthest from the exterior window is more narrow than your space next to the window, you will want to draw a line perpendicular to the window from each wall perpendicular to the window to define the width of each "bay".

You need to determine the depth of your daylighting zones. From what i think your layout is, you have one regularly occupied area along the window wall, then what would be considered a walkway and then another occupied area in the center of the building. Your zones for the center space would come from the windows where you have a direct line of site. So establish your depth of your zone, either 2H or the 63 degree angle. If the area of the space in the center of the building lands within the zone, then it can help. Either way it has to be included.

Jill correct me on this if I'm mistaking because I believe you found documentation that allowed you to extend the zone as long as it was within the WFR ratio. Mike, technically yes, because the prescriptive method kind of follows the old rule of thumb with daylight penetration. That rule is a daylit zone or area the depth of 1 1/2 to 2 times the window head height. After that, the illuminance values would be below what may be considered adequate for the task. The higher the head height, the deeper the daylight penetration.

I interpret the 2H in the credit language differently that you do, Todd. I think the 2H (and the 63 degrees which always corresponds to 2H) is shown only to help users determine the effective window head height and not the floor area depth. I think you can us whatever depth you want to calculate your zone as long as every point on the floor has a clear view of the head height of your window. If your results are above 0.180, and you do not have automated shades, the area does not comply (because your area is overlit.) If it is between 0.150 and 0.180 the area complies. And from the May 9th Addendum pg 557 about mid-way down... If the result is between 0.000 and 0.150, a portion of the space is compliant. Calculate the compliant floor area as follows: • Divide the calculated result by 0.150 and multiply by the floor area of the space. This fractional result represents the floor area to be counted as qualifying daylighted area. One question I had when re-reading the original question. Mike, you say your space "looks out over another regularly occupied space." Does this mean that there is an atrium or a space taller that a single floor that is next to the exterior windows?

Jill, I agree with your intepretation that the current Reference Guide language refers to 2H and 63 degrees only for use in determining window head height. I am just curious if you have submitted projects using this approach and if any comments came up. Do the reviewers notice if regularly occupied floor areas are equal to daylight floor areas, for example.

I can't think of a project that I have submitted this way. Mostly because the projects I work on have very few areas that can use the prescriptive method. I'm not sure why you are asking if reviewers notice that ROS is equal to daylight floor area...if they are unequal the qualifying percentage needs to be 75% or more to get the credit. I'm probably missing the question. You can't change your ROS due to how your calculations come out, it is what it is. You can change the depth of your qualifying area. Did that answer it?

Thanks Jill. I was referring to changing the depth of the qualifying area. We are dealing with over daylighting, but I think the designer is too narrowly defining the daylit area. In many of the ROS I believe the whole area should count. We'll give it a try. Appreciate the help.

There is no math or area adjustment for over-daylighting. If your prescriptive calc number is over 0.180, your space is overlit and you must go back to the design and change either the window size, window Tvis or add automated shading devices. The math determines the daylit area, not the designer. When I said "you can change the depth of your qualifying area" I meant this can be done by dividing the calculated result by 0.150 and multiplying that number by the floor area of the space. This gives you a percentage. Multiply this percentage by the room's ROS and this is the qualifying area (aka daylit area). The depth would then be this area divided by the width. Does that make sense?

Yes, I follow your comment. The situation is similar to Eddy's. We have some rooms deeper than 2H but there are no walls, soffits, ceilings obstructing the daylight. We can draw an unobstructed line from every point on the floor to the exterior window. I'm saying we will count the square footage of the whole room. Do you agree?

I probably should have said to the head of the window. And, I wouldn't say I would count the whole room. I would use the whole room in the prescriptive calculation and then use the method above if your number comes between 0 and 0.150 to find the portion that is counted.

You had mentioned head height and that view is unobstructed too. I think we are on the same page on the approach now. Thanks so much for all your feedback. LEED User is really a great tool. Do you have recommendation on simulation tools - or these a thread on that you can reference me too? Only a few of our projects have used simulation.

Hello Elizabeth, Sorry for the delay in responding. This one must have slipped through my email and I just found it here perusing a different question. I didn't really mean "view" in the sense of a qualifying LEED view. You can get the daylighting credit without the view credit if, for example, your view is obstructed by translucent glazing (but you can't get it with the prescriptive method). The point was more what you were saying, that you can draw an unobstructed line from all of the areas that you are considering to the head height of the window. Hopefully, you have already seen the posts on this page from Todd and Eddy regarding simulation tools. The post subject is "Daylight Modeling Programs sanctioned (approved) by LEED GBCI." I will also point you to another discussion on LEED user about cautions when using these tools. http://www.leeduser.com/credit/NC-2009/IEQc8.1?page=5&ip_login_no_cache=38aade8fce6beb9d8c35470b63021844 Since these links don't always last, you can also search for "Glare Control and Partitions" as that is the title of the post. Please keep in mind that LEED is intended as an instrument for market transformation. This credit pushes people to become more educated about daylighting issues and in the process about daylighting calculations and simulation. In the long run, we will all be better off if we are educated about why we are doing daylighting calculations, what they mean and what our daylighting goals are. This is not directed to only you. There are a great number of architects who could benefit from this, as evidenced by the large number of questions and discussion on this topic in LEEDuser. Thank you for the chance to get on top of my soap box which I am probably all too eager to do! ;) Best wishes to you and your project. Come back if you have more questions.