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dalepres 04-20-2011 10:04 PM

How to calculate total glazing allowed in a wall?
Talk about confusing... I am trying to figure out how much window is allowed for a home with a basement. This is the calculation from IECC Chapter 4. As far as I can tell, A is 18% with some restrictions on whether the windows face the south in summer or north in winter. etc. But basically 18%. The rest of that makes about zero sense to me. Can someone translate it to English?

Also, how do garage walls figure in? If the garage is not conditioned is the thermal boundary at the interior wall and none of the garage walls count in the formula?



b. For residences with conditioned basements, R-2 and R-4 residences and townhouses, the following formula shall be used to determine glazing area:
AF = A, X FA X F


AF = Total glazing area.

A, = Standard reference design total glazing area.

FA = (Above-grade thermal boundary gross wall area)/( above-grade boundary wall area + 0.5 x below-grade boundary wall area).

F = (Above-grade thermal boundary wall area)/( above-grade thermal boundary wall area + common wall area) or 0.56, whichever is greater

and where:

Thermal boundary wall is any wall that separates conditioned space from unconditioned space or ambient conditions.

Above-grade thermal boundary wall is any thermal boundary wall component not in contact with soil.

Below-grade boundary wall is any thermal boundary wall in soil contact.

Common wall area is the area of walls shared with an adjoining dwelling unit.

dalepres 04-20-2011 10:16 PM

Well,based on my plan with about 2/3 ratio for below grade to above grade, (or 3/2 for the formula), I end up with about 12% of floor space that I can glaze if I build a basement. I guess we don't get full credit for the basement floor space.

But what I am still not sure of is about wall space in an attic with knee walls and dormers? How much "wall" does a roof represent? Just the vertical wall of the dormer face?

Oh, and does wall include the space around the floor that is covered in siding? Basically the area of the rim joists?

Ron6519 04-21-2011 07:39 AM

Why don't you hire an architect for this? You'll need one to have signed plans to pull any permit.

dalepres 04-22-2011 12:28 AM

I live in the country. No permit is required or available. In the spirit of DIY, I'd like to avoid paying an architect for something as simple as this.

Still hoping for someone who has knowledge in the topic to answer. Otherwise, I just do my best anyway, since there's no enforcement. Mostly I am trying to follow code in the interests of fire safety and personal safety. This issue just seems like it could potentially get in the way of selling later so I am trying to follow the code here as well, even though there's no one to force it.

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