Window & Door Mullions

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Available from these manufacturers

MG-150

S-14000

Equal-leg mullion, 700-08 mullion

Tube mullion

clipped aluminum tube mullion

PGT clipped aluminum tube mullion

Clipped aluminum tube mullion, 3 in., 4 in. and 5-1/2 in. aluminum tube mullions

Made for the way you live

The connection makes the difference.

Mullions connect adjacent openings into a coordinated assembly. Clipped and unclipped approaches need a plan for the surrounding structure. True Impact plans this connection for your measured opening, then handles the approval, permit and installation across Broward, Palm Beach and Miami-Dade.

Operation: Structural connection between openings
Where it fits: Combined window and door layouts
Details to plan: Span, load path, anchorage and connection type

A fixed window and a single-hung window joined by a full-height vertical mullion

Choose with confidence

The right fit starts with the details.

Select the connection for the complete assembly. Mullions are structural components, not decorative trim or interchangeable accessories.

Your project, considered as a whole.

Opening dimensions and the surrounding structure
Glass, frame finish and operating hardware
Product approvals for the selected configuration
Access, installation, permits and finish repairs

Understand approvals & permits

Look closer

Product resources.

Approvals, drawings and installation documents from each manufacturer that makes this product. Ratings and installation details apply to the exact assembly described in each document.

Mr. Glass

Authorized dealer

MG-150Unclipped mullions
Product approval (LMI)Installation manual Specifications
MG-150Clipped mullions
Product approval (LMI)Specifications

Compare Mr. Glass series All Mr. Glass approvals Mr. Glass catalog Mr. Glass warranty

Check an approval’s current status in the Florida Product Approval search or the Miami-Dade product approvals (NOA). Page updated October 3, 2026.

Your next step

Let’s find the right fit for your home.

Tell us about your project. We’ll help you explore the opening, the options and the details that shape your estimate.

Serving Broward, Palm Beach and Miami-Dade.

Let’s get in touch

Before you get started

Questions homeowners ask first.

Costs, timing, approvals, and the details worth asking about.

All your questions, answered

What should I consider when choosing this product?

Select the connection for the complete assembly. Mullions are structural components, not decorative trim or interchangeable accessories.

How much will my project cost?

Opening sizes, glass, finish, access, installation and permits shape the price. Request a written estimate for your actual property rather than relying on a generic per-opening number.

How do I know which product approval applies?

The exact manufacturer, assembly, glass, size, anchors and installation conditions must match the selected approval. We start with your opening and property requirements, then compare suitable options.

design pressurepsfDesign pressure (psf)The wind load a window or door is approved to resist, in pounds per square foot (psf). A rating like +80/−140 psf gives the inward push (+) and the outward suction (−).Each opening on your home has a required pressure based on wind speed, height and location. The product must meet or exceed it, so a higher rating covers more openings.

LMIlarge missilelarge-missileLarge missile impact (LMI)A test in which a 9 lb piece of 2x4 lumber is fired at the glass and frame, followed by thousands of wind-pressure cycles. The unit must stay closed and in one piece.The Florida Building Code requires large-missile protection for openings up to 30 ft above ground in the windborne-debris areas that include South Florida.

SMIsmall missilesmall-missileSmall missile impact (SMI)A test with small steel balls that simulate roof gravel, followed by wind-pressure cycles.Openings more than 30 ft above ground, such as high-rise condos, need small-missile protection. Some products are approved for both.

HVHZHigh-Velocity Hurricane ZoneHigh-Velocity Hurricane Zone (HVHZ)Miami-Dade and Broward counties, where the Florida Building Code applies its strictest testing and approval rules.A product used in the HVHZ must be approved for it. Some products are approved only for outside the HVHZ, so they cannot be used in Broward or Miami-Dade.

NOANOAsNotice of Acceptance (NOA)A product approval issued by Miami-Dade County after independent testing. It lists the approved sizes, glass, pressures and installation details, and it has an expiration date.Your permit needs a current approval for the exact product. An NOA is the standard proof in the HVHZ.

Florida Product ApprovalFlorida Product ApprovalsFlorida Product Approval (FL number)A statewide product approval from the Florida Building Commission, shown as a number like FL42522. Its installation drawings set the approved sizes, glass and anchors.Every window and door installed under a Florida permit needs an approval, either a Florida approval or a Miami-Dade NOA.

laminated glassLaminated glassTwo layers of glass bonded to a plastic interlayer. If the glass breaks, the pieces stay attached to the interlayer and the opening stays closed.Laminated glass is what makes an impact window impact-resistant. It also blocks most UV and reduces outside noise.

insulated laminatedinsulated glassInsulated laminated glassA laminated glass layer paired with a second pane, separated by a sealed space often filled with argon gas.It keeps heat out and the air conditioning in far better than laminated glass alone, and it is quieter. It costs more and makes the unit heavier.

PVBPVB interlayerPolyvinyl butyral, the standard flexible plastic layer inside laminated glass.PVB meets most residential needs at a lower cost. Higher pressures or larger sizes may call for SentryGlas.

SentryGlasSGPSentryGlas (SGP)A stiff, strong ionoplast interlayer made by Kuraray, used in place of PVB in laminated glass.It is much stiffer than PVB, so it often allows higher pressure ratings and larger sizes, and it stays clear at exposed edges. It usually costs more.

heat-strengthenedHeat-strengthened (HS) glassGlass heated and cooled under control to be about twice as strong as ordinary glass. It breaks into larger pieces than tempered glass.Approval drawings often call for HS glass inside laminated units to reach their pressure ratings.

temperedTempered glassGlass treated with heat to be about four times stronger than ordinary glass. When it breaks, it crumbles into small, blunt pieces.It is used as the outer pane of many insulated units and wherever safety glass is required.

Low-Elow-ELow-E coatingA microscopically thin metal coating on the glass that reflects heat while letting light through.In South Florida it cuts the sun’s heat coming in, lowering cooling costs and protecting floors and furniture from fading.

U-factorU-factorsU-valueU-valuesU-factorHow much heat passes through the whole window. Lower numbers mean better insulation.A lower U-factor keeps cooled air in, which matters most with insulated glass.

SHGCSolar Heat Gain Coefficient (SHGC)The share of the sun’s heat that passes through the window, from 0 to 1. Lower numbers let in less heat.In Florida’s climate, SHGC is often the energy number that matters most for comfort and cooling costs.

VLTVisible light transmittance (VLT)The share of visible daylight that passes through the glass. Higher numbers mean brighter rooms.It shows the trade-off between a darker, cooler tint and natural light.

NFRCNFRCThe National Fenestration Rating Council, an independent organization that certifies window energy ratings such as U-factor and SHGC.NFRC-certified numbers are tested the same way for every brand, so they can be compared fairly.

thermally brokenthermal breakthermal breaksThermally broken frameAn aluminum frame split by an insulating strip so heat cannot travel straight through the metal.Aluminum conducts heat well. A thermal break keeps the inside of the frame cooler and improves energy performance.

KynarKynar (PVDF) finishA high-performance fluoropolymer paint based on Kynar 500 PVDF resin. It is the classic finish that meets AAMA 2605.It resists fading, chalking and salt air best, which is why manufacturers recommend it near the coast.

AAMA 2605AAMA 2605The highest industry standard for painted aluminum, tested for 10 years of South Florida sun exposure.It is the best choice for strong sun and coastal homes, and some warranties require it near salt water.

AAMA 2604AAMA 2604A mid-level industry standard for painted aluminum, tested for 5 years of South Florida exposure. It is the standard powder coat on many impact windows.It performs well inland. Near the coast, a 2605 finish lasts longer.

anodizedanodizeAnodized finishA finish that hardens and colors the surface of the aluminum itself instead of painting it.It shows the metal’s natural look. Its warranty is often shorter than that of paint finishes.

mullionmullionsMullionA structural bar that joins two or more windows or doors into one larger opening.Mullions carry wind load too, so they need their own approval and anchoring.

egressEgressA window opening large enough for a person to escape through in an emergency.Building codes require an egress window in bedrooms, so the style and size you choose matter there.

sidelitesidelitesSideliteA narrow fixed glass panel beside a door.It adds light to an entry and must be approved together with the door.

transomtransomsTransomA fixed glass panel above a door or window.It adds height and light, and it must be approved as part of the assembly.

frame depthFrame depthHow thick the frame is from inside to outside, in inches.Deeper frames are usually stronger and reach larger sizes or higher ratings. They must also fit your wall opening.

argonArgon gasA safe, invisible gas sealed between the panes of insulated glass.It slows heat transfer better than air, improving insulation.

XOXXO/OXXO, OX and XOXCodes for sliding layouts seen from outside: X is a panel that slides and O is a fixed panel.The layout decides which side opens, which helps you plan furniture and walkways.

Tap again for the full glossary.