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

2 foundations, 1 building

davidmeiland | Posted in Construction Techniques on October 9, 2006 04:27am

Got a set of house plans here. For reasons I won’t go into, the foundation detail calls for a slab-on grade under about 40% of the house, and a perimeter foundation under another 40%. These two sections are separated by about 10 feet, and floor joists ‘bridge’ from the slab to the stemwall. The slab has enough height at the edge facing the stemwall for the joists to be hung from the side. See pic attached.

Of course it occurs to me that the two halves of this foundation could move differently and affect the floor (or other parts) of the building. It’s definitely unusual. The slab area is mostly over bedrock, and the perimeter foundation is over soil. The designer does not want the entire thing elevated over a single perimeter foundation, hence the slab area.

Comments?

Whoops… attached the same pic twice.

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

Replies

  1. DanH | Oct 09, 2006 05:12am | #1

    Make sure an engineer signs off on it.

    If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
    1. davidmeiland | Oct 09, 2006 06:05am | #2

      Definitely. They won't get a permit without it.

      What concerns me is the degree to which my agreeing to build it constitutes an agreement that the design is serviceable. I have thought in the past about trying to draft a contract clause that deflects this kind of liability but I've never talked to my attorney about it. It seems reasonable that design professionals should be responsible for whether or not their designs work, but I have heard of many cases where the builder got caught for building something as drawn.

      1. stevent1 | Oct 09, 2006 06:11am | #3

        DM, Is the footing stepped?Chuck Slive, work, build, ...better with wood

        1. davidmeiland | Oct 09, 2006 06:14am | #5

          Do you mean the slab area? It may be, I have not really checked out the elevations closely, just walked around in the brush out there. There aren't detailed plans yet, although I expect them this week. The slab as drawn in my pic looks like a major use of concrete.

          1. brownbagg | Oct 09, 2006 06:37am | #6

            if the slab on bedrock not much you can do anyway and if you had column, fill and slab on other end it woulld still move different. sometime you just got to accept a little movement,and the idea of column with floor joint will acept this. the question is "How would you do it different"Beside a house really dont weight that much.

  2. User avater
    rjw | Oct 09, 2006 06:14am | #4

    >>Of course it occurs to me that the two halves of this foundation could move differently and affect the floor (or other parts) of the building.

    You're right

    Doesn't strike me as a great idea - depending on details, plan on patching a lot of slight settlement cracks over the years.


    Youth and Enthusiasm Are No Match

    For Age and Treachery

  3. IronHelix | Oct 09, 2006 01:33pm | #7

    Looks like the intersect of the center floor to the slab and the crawlspace foundation deserves the use of expansion joint assemblies.

    Placement of wall partitions might effect some considerations for "crack/fracture control" in the wall lay out, and placement of expansion seams in the ceiling drywall system will be essential.

    Could be a cool set up....reminds me of the a colonial log cabin sequence of paired log houses with a a covered porch between in which that open area was often the summer kitchen/porch.

    Can you post floor plans? Might be an insight for more thoughts!

    ..............Iron Helix

     

  4. User avater
    SamT | Oct 09, 2006 03:33pm | #8

    I wouldn't use stucco as sheathing.

    And I would try to avoid OSB or ply in the bridge zone.

    They're gonna move seperately, try to keep walls crossing the bridge flexible, relatively.

    Keeping the above in mind, should work fine.

    SamT
  5. User avater
    Gene_Davis | Oct 09, 2006 05:06pm | #9

    Other than wanting to have a detail that can permit some movement where the joists hang to the "slab," I don't see much of an issue with the concept.

    I am pretty sure it was FH, a few years back, that did a piece on a house that was done as a "bridge" concept, with two independent foundations, and an above-ground section linking the two, everything heated, finished, one single roof atop.

    Sounds like a nice little challenge.

  6. Catskinner | Oct 09, 2006 05:11pm | #10

    I think all of your intuitions on this are correct.

    You might consider widening the strip footing or overexcavate and replace under it or both to minimize the difference.

    1. davidmeiland | Oct 09, 2006 05:53pm | #11

      Thank you all for the comments. It seems like the slab area will not move at all. It's substantially on rock and in fact will probably require some scribing. I don't like the fact that I will need to fill under part of the slab, but it's unavoidable. I suppose I could just pour a few extra loads of mud in there instead of bringing in rock or sand.

      I'm wondering about the possible wisdom of getting some piers under perimeter foundation. The rock is under there also, just not as close to the surface. We only have to go 12" below grade here with a footing. A few more feet and I could probably hit rock there too.

      Anyone have experience with the designer's liability issue? This will definitely come to me as an engineered plan, and my contract will definitely refer to those plans. However, I'm pretty sure that some will stick to me if any hits the fan. I would imagine that hitting of the fan would be some ways down the road, not during construction or shortly thereafter.... maybe during a really rainy winter.

      1. User avater
        SamT | Oct 09, 2006 07:02pm | #12

        Include the cost of repairing DW cracks twice in the next five years.

        If the movement lasts longer than 5 years, there are other problems.SamT

      2. Catskinner | Oct 10, 2006 05:19am | #13

        On the subject of "a few loads of mud", don't rule out CLSM (controlled low strength material) a.k.a. lean fill.It's fairly inexpensive and would most likely even out your bearing conditions.If the rock isn't that far down you could trench down to it, dump the CLSM in, rake it out, and form footings on it. It's going to cost about twice what an overex and replace will cost, but you can do it in a day and it is everything-proof.As for liability, it would not be a bad idea at all to get a geotechnical investigation, report, and opinion. Shouldn't cost much over $2,300, which is far less than some alternatives I can think of.

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

FHB Summit 2025 — Design, Build, Business

Join some of the most experienced and recognized building professionals for two days of presentations, panel discussions, networking, and more.

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

  • Fight House Fires Through Design
  • Making the Move to Multifamily
  • Custom Built-ins With Job-Site Tools
  • 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 332 - July 2025
    • Custom Built-ins With Job-Site Tools
    • Fight House Fires Through Design
    • Making the Move to Multifamily
  • 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

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 70%

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