Methane Zone

LA Methane Zone

The City of Los Angeles conducted a detailed study of methane levels all over the city and created two zones which are:

• the Methane Buffer Zone
• the Methane Zone

 

This study points out that all developments and projects within the specified Methane Buffer Zone must be subjected to a methane level assessment first. If the location of the proposed project is found out to be free from methane, the project may push through without additional methane mitigation plans. On the other hand, if the assessment result states that methane levels are present in the area of the proposed project, a mitigation plan must be designed to keep methane gases from entering the building.

Developments within the specified Methane Zone are more rigorous. All developments within the Methane Zone require the same assessment and testing as the areas in the Buffer Zone but a minimum Mitigation Plan is required regardless of the methane levels discovered in the area. The minimum plan required consists of a below grade passive venting network, complete with risers and an impervious membrane just below the slab, and behind any below grade walls.

What you need to comply?

Once a methane level is determined through the probe assessment, a methane mitigation plan can now be formulated.

 LADBS (Los Angeles Department of Building and Safety) has provided a Methane Standard Plan which provides intricate guidelines in the development of a project’s specific plan. The project site can be categorized as Level I thru Level V. When Methane Levels increase the requirements needed to be complied also increases in order to mitigate the dangers of methane intrusion.

There is a direct relationship between project zoning, test results and the final design.   The relationship is costs.    This is where Ralph Ray Construction, Inc sets itself apart from all other mitigation related companies.    Once the Methane Level is determined the focus becomes the design and exhausting efforts in order to meet all requirements to a budget. 
 
LADBS is very meticulous about construction costs associated with methane mitigation requirements.   To create a competitive market price and keep costs as low as possible, the City has approved the use of eight different membranes. 

The primary component that drives cost to most designs is the impervious membrane. The primary function of this membrane is to block methane gas from rising into the building. All eight membranes, regardless of brand have passed the rigorous testing standards set forth by the City. Each of them are considered to be “Equal” regardless of brand yet there are rare circumstances such as specific jobsite conditions that favor the use of one membrane over the other.

Why Choose Brand A over Brand B membrane?

Simple…Cost! Although six of the eight choices of membranes are spray applied CMA membranes, they differ considerably in cost.  The primary reason for the cost difference is not the quality of the product but the coverage per gallon when applied.   All six spray applied products offer the same ten year product warranty and all are very close in cost per gallon.

However, the coverage of the products per gallon differs considerably.  Certain brands carry a much higher thickness, and are required to be installed much thicker than others.  As a result, the material coverage balloons the cost of the product. Between the two brands, there is a 65% difference in terms of coverage and this extreme difference creates a dramatic impact on cost.
 
The other two membranes are HDPE based sheet products.  Those two membranes are typically reserved for very large projects and/or the highest level gas readings, combined with a high water table, and tar seeps or both.

 
What about Water?

What’s good about the majority of the membranes is that they were originally used as water vapor barriers.   It was later found that the same base product, with a slightly different assembly could also be utilized as a methane gas vapor membrane.  All of the approved gas vapor membranes can serve a dual purpose - water and gas vapor membrane wrapped into one barrier.
 
When a high water table exists in a subterranean portion of a structure or parking garage, it may cause a hydrostatic condition. In order to solve this issue, two basic options are available and that is, one, incorporate a full time active de-watering system in the subterranean drain system and two, develop a “boat” design and leave the water in place.  Two of the eight products can be used successfully in a hydrostatic condition, without additional waterproofing required.