FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube 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
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

Cust. wants garage on floating slab

happyframer | Posted in Construction Techniques on March 15, 2007 07:16am

Customer wants a 24×36 16 o.c. garage.

To minimize costs, he wants a floating slab. I’m trying to convince him to get a full 4′ foundation.

he insists it can be done so movement and cracking is minimized.

I know builders sometimes put huge pier footings in the middle of garages. Perhaps 3 of those under a 24×36 slab would work. How would that slab look?

Thanks for consideration.

BTW medium clay soil 25 mi. W of Minneapolis

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. User avater
    SamT | Mar 15, 2007 07:58am | #1

    What does the AHJ say about floating slabs? If they don't allow them, there's your out.

    There are methods to frost heave proof floating slabs. Involves underground insulation. Called . . . . . . . . frost protected shallow foundation?

    Well heck, a severe case of CRS just hit.

    Other wise tell him "I sorry sir, but I refuse to build a mistake." and reccommend Shlock Builders, Inc, to him (|:>)

     

    SamT

    Anyone who doesn't take truth seriously in small matters cannot be trusted in large ones either. [Einstein] Tks, BossHogg.

    1. Piffin | Mar 16, 2007 01:28am | #7

      Second method - use drains and hard compacted mineral fill to eliminate the water that freezes and cuases heaving. 

       

      Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

  2. woodguy99 | Mar 15, 2007 03:39pm | #2

    SamT got it, do a search for frost protected shallow foundation.  Proven and accepted way to build.  You can also just do a floating slab without the extra step of "frost protection", but if you're in a northern climate you should expect some movement.  4' frost wall is always a safe bet.

    "This is a process, not an event."--Sphere
  3. User avater
    artacoma | Mar 15, 2007 04:40pm | #3

    I have done a couple. Vancouver island BC

    Well draining base material and compaction is critical.

    I have used a 5" slab thickness and 10" x 16" primeter footing with 5m rebar on a 16" grid with fiber.Keep it out of the sun too.

    Engineer inspected and approved.

    Cheers Rik

    1. karp | Mar 21, 2007 07:59pm | #12

      Same,

      called it a "thickened edge slab"

      1. rasher | Mar 22, 2007 02:10am | #13

        The local garage contractor built my garage last year. Kansas City MO area. I always thought you had to have a 3'-0" stem wall foundation down to below frost here, but apparently not.He used a thicked edge slab with 6 or 8 3'-0" deep piers. (Our slab was 22'x36', so he had to have the piers). Passed city inspection. I know that doesn't mean anything, but this guy builds A LOT of garages around here.He was half the price of my other 2 bidders, and we're happy so far. Like I said, one year old and no problems yet.

        1. Trentgw24 | May 17, 2017 06:36pm | #16

          Garage in KCMO

          Hi Rasher - I know you wrote this original comment almost 10years ago, but I was wondering if your garage is holding up well still? 

          We're located in KCMO as well, and we are looking at demolishing and rebuilidng our detached garage at our home. 

          Right now some of the bids are pretty high for the concrete foundation, and wanted to know if you would recommend this peir method? 

          also - if you remember the garage contractor you used, I would be interested in giving them a call for a bid. 

          Any help would be much appreciated. Thanks! 

  4. Stuart | Mar 15, 2007 04:52pm | #4

    I have a 24x40 garage in Minneapolis that was built on a floating slab.  It's about 15 years old now, I have it loaded to the gills with cars and motorcycles (plus a four post lift) and the slab is holding up just fine.

  5. JoeArchitect | Mar 15, 2007 10:59pm | #5

    In the midwest we use foundations down to frost line if the esterior is masonry. If it's frame with siding, then typically we do a slab with a thickened edge.

  6. Piffin | Mar 16, 2007 01:26am | #6

    36' implies three bay garage.

    You would have cracking so use control joints.

    Structurally no problem.

    What you do is remove organic top and lay drains in stone, then minimum 18" if compacted mineral fill, then form and build

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
    Excellence is its own reward!

  7. MSA1 | Mar 16, 2007 02:42am | #8

    In Michigan if you go over 20x20 you have to have footings/foundation. Unless you can build the whole thing over the weekend when city hall is closed.:>)

    Even under 20x20 you have to at least have a rat wall.

    1. happyframer | Mar 17, 2007 04:04am | #9

      I've never heard the term.What's a rat wall?

      1. MSA1 | Mar 17, 2007 04:49am | #10

        Its like a baby foundation. Its a wall of cement that goes about 18" into the ground. Its designed to keep critters from tunneling under the slab.

        1. woodguy99 | Mar 17, 2007 06:21pm | #11

          Funny, I've never heard that term either, but we do call a thin sloppy slab a "rat slab" for similar reasons. 

           

          "This is a process, not an event."--Sphere

          And I'm a legitimate certifiable Tool Whore.--Dieselpig

  8. Nivek | Mar 22, 2007 05:28am | #14

    built a 30x45 2 storey garage 15 years ago on a floating slab and a couple of years latter made an appartment out of the top storey. gyproc on walls and jointed. no joint cracks as yet! the key was to have good drainage under the slab so that the water that causes the heaving is not present. all we have is about 2 feet of packed stone under the slab and it seems to be working.

  9. user-158769 | Mar 22, 2007 09:11am | #15

     Floating slabs are a great way to go when building single story structures.

    My garage is 36 X24 on a floating slab. My slab is thickened on the edges ( about 10 inches) and the remaining slab is 8 inches thick. I have 1/2 inch dia rebar placed in a mat formation; 12 inches OC.  I had a compacted gravel base ( after first removing grass /topsoil) of about 16 inches before I poured. Garage is 12 years old, and no cracks.

    As an industrial ( steel mill) carpenter in Pittsburgh, PA region, we built loads of floating slabs for small utility type buildings and for  even larger storage buildings...all buildings are in great shape.

    Trick to stopping frost heave is to give water a place to drain, instead of a place to  saturate. You can and should place drain lines underneath compacted fill and "lead" drains so to carry water away from site. Rebar mat will give plenty of strength and you can add chopped fiberglass in the mix for good measure...it helps but no substitute for rebar.

     Don't be afraid of the "unknown" and actually, floating slab technology is well known...been in use for many, many years. Infact, according to history books  I have  read about Frank Loyld Wright, many of his midwestern homes were placed on floating slabs of his  own design.

    Davo



    Edited 3/22/2007 2:12 am ET by Davo 304

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

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

Up Next

Video Shorts

Featured Story

Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring

Listeners write in about fireplaces and ask questions about whole-house ventilation, traditional porch flooring, and gutter sealants.

Featured Video

How to Install Cable Rail Around Wood-Post Corners

Use these tips to keep cables tight and straight for a professional-looking deck-railing job.

Related Stories

  • Podcast Episode 684: Masonry Heaters, Whole-House Ventilation, and Porch Flooring
  • FHB Podcast Segment: Repairing an Old Home While Maintaining Its Integrity
  • Tools and Gear for the Moms Who Get it Done
  • An Easier Method for Mitered Head Casings

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

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, 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

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
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
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

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

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • 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

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

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 81%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

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

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data