Description

Key Features

Moment Resistance

The overlapping sleeve design helps resist post rotation at the base. That matters when lateral loads hit the top of the post and you want a more stable connection without jumping to a custom-fabricated base.

Built-In 1 Inch Standoff

Tabs inside the Simpson Strong-Tie MPB88Z Moment Post Base hold the post 1 inch above the concrete. That gap helps reduce rot risk from standing water and ground moisture in outdoor builds.

Faster Layout

Stamped embedment indicators, template attachment holes, and the one-piece body simplify placement before the pour. Less layout guesswork means a cleaner install and fewer jobsite delays.

Overview

The Simpson Strong-Tie MPB88Z Moment Post Base is a cast-in-place post base for nominal 8×8 wood posts used in post-to-footing connections. This is a moment post base designed for anchoring wood columns and posts to concrete footings while helping resist rotation at the base. Model Number: MPB88Z. If you are building decks, fences, carports, or other outdoor structures where post stability and long-term durability matter, this connector is built for that job.

What separates the MPB88Z from a basic post base is its sleeve-style body. Simpson designed this patent-pending connector to encapsulate the post and provide moment resistance when lateral loads are applied at the top of the column or post. In plain terms, it gives designers and contractors a stronger starting point when they want to reduce bracing or open up sightlines without stepping into a custom base solution.

The built-in 1 inch standoff tabs are not just a code detail. They keep the bottom of the wood post lifted above the concrete so water is less likely to sit against the end grain. That is a real-world durability feature, especially on exterior projects using treated lumber. Simpson also added weep holes so standing water can drain out and so you have a quick visual check point at the embedment line.

Installation is set up to be straightforward. The one-piece design avoids the extra parts and assembly that slow down layout. Internal top-of-concrete tabs, stamped embedment indicators, and form board attachment holes help you place the base before concrete is poured. Once the concrete work is right, setting the post and fastening it is more predictable.

This model is made from 12-gauge steel with a ZMAX coating. That combination gives you the stiffness expected from a structural connector plus corrosion resistance suited for many exterior and treated-wood applications. For contractors working on decks and exposed structures, that finish matters because the connector is doing its job outdoors, not hidden inside a dry wall cavity.

The MPB88Z includes the specified Simpson Strong-Drive heavy-duty connector screws: 1/4 inch x 3 inch SDS screws. Simpson is clear that those screws are part of the designed connection and that lag screws will not achieve the same load. That is worth paying attention to because it removes guesswork and keeps the installed connection aligned with the product’s tested intent.

In use, this connector is aimed at builders who need a heavy-duty 8×8 post base for concrete footings and who care about both structural performance and clean installation. It makes the most sense for deck builders, fencing crews, general contractors, and remodelers building outdoor living structures where post movement, moisture exposure, and install efficiency all matter. If you need a standard post base just to hold a post off the slab, this may be more connector than you need. If you need a purpose-built 8×8 moment post base with integrated standoff, drainage, and embedment guidance, this is the right kind of hardware.

Designed for Cleaner Layout and Drainage

This connector is built to make placement easier before the pour and to help the finished base manage moisture better after the job is done. Those two details save headaches later, especially on exterior posts that see weather year-round.

• Stamped indicators and internal tabs identify the required concrete embedment depth
• Weep holes at the embedment line allow water to exit and provide a visual inspection point
• Template attachment holes simplify setup during form work

What’s in the Box

• (1) Simpson Strong-Tie MPB88Z Moment Post Base for 8×8 posts
• 1/4 in. x 3 in. Simpson Strong-Tie Strong-Drive SDS Heavy-Duty Connector screws

Key Specifications

Post Size	8×8
Material	12-gauge steel
Finish	ZMAX coating
Width (W1)	7 9/16 in.
Width (W2)	7 9/16 in.
Height (H)	7 1/4 in.
Depth (D)	7 1/4 in.
Included Fasteners	1/4 in. x 3 in. Strong-Drive SDS Heavy-Duty Connector screws

Compatibility

Post Fit

Designed for nominal 8×8 wood columns and posts.

Application

Built for post-to-footing installations in concrete for decks and other outdoor structures.

Fastener System

Uses Simpson Strong-Drive SDS Heavy-Duty Connector screws. Simpson notes that lag screws will not achieve the same load.

Built For

Deck Building Fences Carports Outdoor Structures Post-to-Footing Connections General Contracting Remodeling Exterior Treated Lumber Work

Pro Tip

When you set the MPB88Z in concrete, keep the concrete level inside the connector no more than 1/4 inch above the embedment line. That preserves the drainage path, which is one of the reasons this base holds up better outdoors.

At a Glance

8×8

Post Size

12 Ga.

Steel Thickness

1 in.

Post Standoff

7 9/16 in.

Body Width

Tool Nut’s Take

Tool Nut’s Take

Simpson Strong-Tie MPB88Z Moment Post Base Means Business

This is the kind of connector you buy when a basic post base is not enough and you want a cleaner, more thought-out solution for an exterior 8×8 post on concrete.

• Who it’s for: Contractors, deck builders, and serious DIYers building outdoor structures with nominal 8×8 posts and concrete footings.
• Why it stands out: The sleeve design adds moment resistance, the 1 inch standoff helps fight moisture damage, and the built-in placement details make install more predictable.
• Worth knowing: This is a cast-in-place connector, so you need to plan it before the pour. Also, use the specified SDS connector screws, because Simpson explicitly says lag screws will not deliver the same load.

Common Questions

• What size post does this base fit? It is designed for nominal 8×8 wood posts.
• Is this a standard post base or a moment post base? It is a moment post base designed to help resist rotation at the base of a wood column or post.
• Can it be used outdoors? Yes. It has a ZMAX coating for exterior and treated-wood applications, and it includes a 1 inch standoff plus drainage features to help manage moisture.
• When is it installed? The MPB88Z is installed before concrete is placed as a cast-in-place connector.