FHB Logo Facebook LinkedIn Email Pinterest Twitter Instagram Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe

In every issue you'll find...

  • Expert insights on techniques and principles
  • Unbiased tool reviews
  • Step-by-step details to master the job
  • Field-tested advice and know-how
Subscribe Now!
Subscribe
  • How-To
  • Design
  • Tools & Materials
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
  • Join
  • Log In
Subscribe
Renovation Book Excerpts

Mat Slabs: An Inventive Foundation for Difficult Sites

For building sites with tricky soil conditions, mat slabs provide an effective solution.

By Mike Litchfield

When it comes to cutting-edge technology, a mat slab fits the bill in several respects. Though little known 10 years ago, today mat slabs are a standard solution for building sites with difficult soil conditions. Typically reinforced with a double layer of rebar throughout its pad, a mat slab is capable of bearing loads at virtually any point and distributing heavy loads across an expanse of weak subsoil. 

Mat slabs are particularly well suited to sites on moderate slopes, or where you will
 be cutting the building pad into a hillside. In
 the project shown here, mat slabs poured on several levels were a much quicker and more affordable alternative to drilled pier and grade beams because the slab did not require footing excavation and expensive pier drilling. The mat slab only required forms on the outside perimeter, cutting forming costs in half. The engineer determined that a tee footing was not a viable option given the soil conditions and hillside location. 

R5_CH10_GH_0029

  1. After the building pad was excavated, leveled, and compacted, perimeter forms were set and crushed drain rock was spread. The worker is using a tamper to compact 4 in. of crushed drain rock on undisturbed earth. The stone was held back along the perimeter so that the concrete at the edge of the slab would contain the gravel. Above the compacted stone, there will be 12 in. of concrete; around the perimeter, the concrete will be 16 in. thick.

  1. To create a clean step (a retaining wall) in the foundation, the crew drove in steel stakes, ran horizontal pieces of rebar behind the stakes, put in expanded metal lath behind the rebar, and then backfilled with stone. The yellow 16-mil plastic sheeting is a vapor barrier to prevent moisture from migrating up from the soil to the slab. Dobie blocks atop the sheeting will support the lower level of rebar. To facilitate installing rebar in the retaining wall, formboards are not yet in place. 

  1. After rebar was installed in the retaining wall, formboards were set and a double layer of rebar was placed in the slab in the foreground. C-shaped rebar spacers connect upper and lower rebar grids, keep the upper layer from sagging, and stabilize the grid during the pour. 

  1. Because the concrete contains 3⁄4-in. gravel, the mix must be vibrated to be sure there are no air pockets. A boom truck was able to deliver concrete to distant parts of the forms on this 56-yd. monolithic pour. 

  1. Framing commences on the finished mat slab. The concrete wall along the back edge is a step-down retaining wall between foundation levels.

This blog was adapted from Renovation 5th Edition (Taunton, 2019). A hefty 656 pages, R5 is a trove of pro tips and techniques that builders shared with me over four decades, plus roughly 1000 photos taken on job sites across North America. I hope you find it useful. – Mike

Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters
×

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

New Feature

Fine Homebuilding Forums

Ask questions, offer advice, and share your work

View Comments

  1. User avater
    dominicfrost2 | Jan 02, 2020 02:29am | #1

    fantastic

  2. User avater
    reberthill | Jan 20, 2020 05:33am | #2

    Really Great work

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

More Renovation Book Excerpts

View All
  • Planning and Acquiring Building Permits for Renovation Projects: A Simple Chart
  • Soundproofing: A Successful Hybrid Approach
  • Using Metal Studs to Level a Sloping Ceiling
  • How to Level an Exterior Doorsill
View All

Up Next

Video Shorts

Featured Story

Using Liquid Flash at a Wall-to-Foundation Connection

Brian Pontolilo demonstrates how to air-seal where the concrete foundation, mudsill, and ZIP System sheathing all meet.

Featured Video

Video: Build a Fireplace, Brick by Brick

Get an overview of the process of creating a traditional-style fireplace that burns well and meets current building codes from experienced mason Mike Mehaffey.

Related Stories

  • Podcast 480: PRO TALK With Painter-Remodelers Miquel and David McCarley
  • Podcast 477: Members-only Aftershow
  • Podcast 476: PRO TALK With Carpenter Caleb Carpenter
  • Why I Love Carpentry

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Video

View All
  • Podcast 480: PRO TALK With Painter-Remodelers Miquel and David McCarley
  • Podcast 477: Members-only Aftershow
  • Podcast 476: PRO TALK With Carpenter Caleb Carpenter
  • Podcast 474: PRO TALK With Production Manager Morgan Thomas
View All

Remodeling

View All Remodeling Articles
  • Podcast 477: Members-only Aftershow
    Podcast 477: Members-only Aftershow
  • Podcast 476: PRO TALK With Carpenter Caleb Carpenter
    Podcast 476: PRO TALK With Carpenter Caleb Carpenter
  • Kevin Ireton working on a door
    Why I Love Carpentry
  • Beth and her team in front of a Done Construction van
    Beth Pointer: General Contractor, Kitchen and Bath Remodels
View All Remodeling Articles

BOOKS, DVDs, & MERCH

Shop the Store
  • 2021 Fine Homebuilding Archive
    Buy Now
  • Code Check Building 4th Edition
    Buy Now
  • Pretty Good House
    Buy Now
  • Outdoor Projects
    Buy Now
  • Shop the Store

Fine Homebuilding Magazine

  • Issue 309 - Aug/Sept
    • 10 Steps to Install Crown Molding on Cabinets
    • How to Get Sturdy Walls Without OSB
    • Choosing the Right Construction Tape for the Job
  • Issue 308 - July 2022
    • Pretty Good House Book Excerpt: Copper Farmhouse
    • 10 Dos and Don'ts for Electric In-Floor Heat
    • A Sturdy Rail for Outdoor Stairs
  • Issue 307 - June 2022
    • How to Raise a Post-Frame Home
    • Trimming Deck Stairs
    • Evolving an Energy-Efficient Envelope
  • Issue 306 - April/May 2022
    • Framing Stairs to an Out-of-Level Landing
    • Building a Zero-Energy Home for Less
    • Good-Looking and Long-Lasting Traditional Gutters
  • Issue 305 - Feb/March 2022
    • The Steady Surge in Residential Solar
    • The Fine Homebuilding Interview: William B. Rose
    • How Good Is Your Air Barrier?

Fine Homebuilding

Follow

  • twitter
  • facebook
  • instagram
  • pinterest

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences

Taunton Network

  • Green Building Advisor
  • Fine Woodworking
  • Fine Gardening
  • Threads
  • About
  • Contact
  • Advertise
  • Careers
  • Copyright
  • Terms of Use
  • Site Map
  • Do not sell my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2022 The Taunton Press, Inc. All rights reserved.

X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Account

  • Log In
  • Join

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Shop the Store

  • Books
  • DVDs
  • Taunton Workshops

More

  • FHB Ambassadors
  • Reader Projects
  • Podcast
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • twitter
  • facebook
  • instagram
  • pinterest

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 70%

Subscribe

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in