Exterior of home with Marvin Essential Direct Glaze windows and Polygon Windows
Product Design Options

Mulling Options for Windows and Doors

Bring Ambitious Projects to Life with Mulling Solutions

One of the unique features of Marvin products is the ability to mull window and door configurations while maintaining high performance and durability. Expansive window sizes and larger certified assemblies bring more of the outside in, creating striking window and door assemblies that meet design trends.

Mulling Methods

Marvin offers different mull types and can be either factory applied or field applied, dependent on the mull type. The standard mull uses a mull pin that connects the frames, providing strength to the system. Standard mulls are certified and ideal for single family residential, multi-family, and light commercial projects.

The reinforced mull uses a full-depth reinforcement mull pin that adds to the strength of the mullion system to meet stringent project performance requirements. It is also certified factory mulled and a great solution for single family residential, multi-family, and commercial projects.

The method used will vary depending on the product, project type, and required performance ratings. For field mulling of non-certified assemblies, field mull kits are available and include all the components necessary to mull units together.

Push the Limits of Possible with Certified Assemblies

Certified assemblies are important for projects with designated performance requirements and significant environmental exposure. Marvin helps you deliver with three factory assembly types:

Marvin offers a Prep for Field Mull option to simplify both the ordering process and final field assembly at the job site. Large assemblies are split into sub-assemblies with all the components and preparation for field mulling done at the factory.

Refer to the Architectural Detail Manuals (ADM) found in the Technical Specifications to see mulling guidelines for Ultimate, Modern, Elevate®, and Essential windows and doors.

Product size will be a factor in mulling capability, and other product limitations may apply. Please contact your local dealer for specific product sizing and mulling capabilities.

Get The Details

Mulling Faqs

  • What is mulling?

    Window and door mulling is a process in which two or more units are joined together by their frames.

  • What is the difference between factory mulled windows and field mulled windows?

    Factory mulled windows are joined by the manufacturer and shipped assembled. Field mulled windows require onsite assembly.

  • What are the types of mulling available from Marvin?

    Standard Mull is one in which the frames are joined tightly together with no reinforcement or space between.

    Mull Reinforcement or MRF are vertical or horizontal mulls that have aluminum reinforcement members attached to them and are clipped and fastened together making the mull 3/8" wide.

    Space Mulls are vertical or horizontal mulls with wood blocking between them to a specified width. They are sealed at each end and covered at the exterior with a metal space mull cover. Space mulls come in 3/8", 1", 2", 3", 4" and 6" size widths.

    Stud Pocket Mulls are similar to space mulls except the wood blocking is removed just prior to the window being installed.

    LVL Mulls are used for structural applications and come from Marvin in 1" and 2" widths (other widths may be available from other sources). Similar to space mulls and MRFs, they are sealed at the ends and covered to the exterior with a metal mull cover.

  • What are the different mulling assembly configurations available?
  • Which Marvin collections can be mulled?

    Ultimate, Modern, Elevate®, and Essential windows and doors can be mulled. Product size may limit mulling options. Other product limitations may apply. Contact your dealer for product sizing and mulling capabilities.

  • What are the performance considerations with mulled windows?

    Improperly assembled window and door mulls can result in product failure, air infiltration, and water penetration. Window and door mulling should be performed by a qualified window and door expert with a high level of user competency and confidence using power and hand tools. Manufacturer instructions should be strictly followed.