The Building Envelope

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Over eighteen years of work experience in the forensic investigation, design, analysis, consulting and inspections of residential, commercial and retail building envelope components. 

Saturday, December 19, 2009

Windows & Doors

Miami-Dade and Broward County are located in what is referred to as the "High Velocity Hurrricane Zone" in the Florida Building Code.

This means that these two Counties have stricter design requirements then the rest of the state.

The minimum (hurricane) wind speed that one must design for is 146 mph in Miami-Dade and 140 mph in Broward. This wind speed is the same for all buildings and not to be confused with the design wind pressure which varies from building to building.

In order for a manufacturer of windows and doors to be able to sell their product to the public it must comply with the above Code requirements, be tested and receive a product approval or Notice of Acceptance (NOA) from Miami-Dade county.

Just because a product has an NOA does not mean that it can be used everywhere. The product comes rated at a certain wind pressure that must be equal or greater than what the architect or engineer has determined is the design wind pressure for your home.

The tip here is: MAKE SURE THAT, BEFORE YOU BUY WINDOWS OR DOORS, YOU ASK TO SEE A COPY OF THE NOA AND CHECK THAT THE RATED WIND PRESSURE FOR THE WINDOW IS SUFFICIENT TO MEET THE DESIGN WIND PRESSURE FOR YOUR HOME.

Forensic Investigation of Glazing

The steps in determining what went wrong is to:

1. Determine the design criteria (applicable code).
2. Identify the specifications for the project provided by Architect or Engineer.
3. Confirm project design wind loads.
4. Review shop drawings & calc's for compliance w/ code & project specs.
5. Review product NOA's or State approval documents.
6. Perform inspection to confirm product and installation.

Things to look for:

Design:

1. Proper wind load factors and tributary areas.
2. Adherence to limitations of product NOA's or State approvals.
3. Allowable stresses of steel and aluminum.
4. Allowable load of anchors including (edge, spacing & cantilever reductions)

Installation:

1. Check product for compliance with NOA's or State approvals.
2. Check glass type & interlayer.
3. Check anchor types and shimming including substrate conditions.

Thursday, December 10, 2009

Glass Types for Building Envelope Products

There are typically four different glass types used in glazing products: From weakest to strongest they are: Annealed, Heat Strengthened, Tempered and Laminated.

1. Annealed glass is your basic non-impact glass type. It is used in applications where the required wind load is not so high and safety requirements are not a concern. When annealed glass breaks, it breaks in sharp chards.

2. Heat Strengthened glass is also a non-impact glass. It undergoes a "heat treatment" that increases it's strength to twice that of annealed glass. It is used in similar applications to annealed glass but where the required wind loads are much higher. When heat strengthened glass breaks, it also breaks in chards.

3. Tempered glass is your basic impact glass. It undergoes a more aggressive "treatment" that increases it's strength to four times that of annealed glass. It is used in "small missile" impact applications typically installed 30 feet or higher above ground and in safeguard applications. When tempered glass breaks, it breaks into very small cubes.

4. Laminated glass is your typical impact glass. It is a combination of two (usually) of the three previously mentioned glass types that are "laminated" together with an interlayer between them. It is typically used in "large missile" impact applications installed up to 30 feet above ground. When laminated glass breaks, it breaks based on it's glass type make-up but is held in place by the interlayer...similar to a car's windshield.

Designing in Florida

Issues to consider when designing a project in Florida.

1. What County is it in? The Florida Building code, 2007 edition identifies Miami-Dade & Broward Counties as being in the High Velocity Hurricane Zone therefore subject to stricter code compliance.

2. Is the County in the Wind Borne debris region? This encompasses all areas where the design wind speed is 120 mph or greater OR 110 mph if the design area is within 1 mile of the coast. The wind borne debris region requires impact protection or impact resistant products.

3. The glazing product most have either a State of Florida OR a Miami-Dade County product approval.

4. Local ordinances: Some municipalities require compliance above and beyond the Florida Building Code requirements. Check with the local building department prior to design. Example Coral Gables (Miami-Dade County) does not allow light gage framing as exterior walls. Some coastal municipalities require turtle friendly glass specs to be used to prevent disorientation of turtle hatchlings.

5. Inspections: Some municipalities require a special inspector form to be provided prior to issuing a permit.

These are just a few of the unique requirements of designing a project in Florida.

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