The adopted wind speed map places this lot in a wind-borne debris region. The builder installed ordinary insulated glazing with no shutters, tracks, panels or anchors of any kind, and states that the windows carry a design pressure rating higher than the wind pressure calculated for the site. What is the finding?
- AThe design pressure rating satisfies the requirement, because the glazing is then rated for the wind the site will actually see
Pressure rating and impact resistance are two different tests. A window can carry a high design pressure and still be ordinary annealed or tempered glass with no debris resistance at all.
- BProtection is required on the windward elevations alone, so the units on the leeward walls may be left as they were installed
Wind direction is not fixed and a storm's approach angle is unknown when the house is built. The provision reaches glazed openings in the building rather than a chosen set of elevations.
- CProtection is required above the first story alone, since debris near grade is stopped by fencing and by landscaping
Debris at grade level is exactly the hazard, since gravel, roof material and fence sections are all launched low. Nothing in the provision exempts the first story.
- Glazed openings in a wind-borne debris region have to be protected by impact-resistant glazing or approved coverings
Why D is correct
The requirement is impact protection, met by impact-resistant glazing or by an approved covering tested to the referenced standards. A design pressure rating addresses wind load on the assembly rather than the debris strike that the provision exists to resist.
What this question is testing
Whether the candidate distinguishes wind pressure resistance from windborne debris resistance, and knows what forms of protection the code accepts for glazed openings.
On the job
Coastal work is where this is enforced hardest, and it is also where a substitution is most tempting because impact glazing costs several times what ordinary insulated glass does. Panels and tracks count as an approved covering, but they only count if they are actually delivered and if the anchors are installed, so the field check is for anchors in the wall and hardware on the site, not for a bundle of plywood in the garage. Local adoption may add requirements.
Memory technique
Rated for the wind is not rated for what the wind throws.
Exam tip
Pressure rating is not impact rating. Different test, different label.
Where to look it up
IRC Chapter 3, building planning, wind design, protection of openings, with its tables.