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
How-To

Framing a Crawl-Space Foundation

These time-saving tips make short work of setting sills, posts and girders.

By Larry Haun Issue 77
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Synopsis: This article explains how to frame a crawl-space foundation, a system of wood posts and girders surrounded by a poured-concrete or masonry-block foundation. Author Larry Haun offers tips on placing and marking mudsills and laying out support posts. An accompanying chart lists typical spans for floor girders.

There is no “best” foundation. Depending on what part of the country you live in, the preference might be slab, post and girder or full basement. In many areas, the crawl space is common. A crawl-space foundation consists simply of bearing walls surrounding a system of piers, posts and girders that support the floor. Crawl-space foundations are readily adaptable to a variety of sites, and they’re relatively inexpensive.

The bearing walls are usually built of masonry block or poured concrete set on a concrete footing, and construction follows conventional techniques. It’s the carpentry side of the job—the sills, the posts and the girders—that I’ll cover here.

Checking the foundation

The first task is to check the foundation for square and parallel. A good foundation contractor will leave the foundation square and level, but it never hurts to check before laying down the sill. If the foundation is rectilinear, check it by measuring diagonally from corner to corner; if it measures the same both ways, it is square.

If the foundation has offsets in it—for example, if it is shaped like an “L” or a “T”—there is still an easy way to check the comers for square. This is done using the Pythagorean theorem: a² + b² = c². On the job, this is usually called the 6-8-10 rule. Just measure 6 ft. from the comer along one side of the foundation, 8 ft. along the other side and then check the length of the diagonal. If it is 10 ft., this corner is square. It’s that simple. It doesn’t have to be perfect because you can do some correcting when you lay down the sills. You can use other multiples of 6-8-10, like 3-4-5 or 12-16-20. On a big building with long walls, use as large a multiple as possible to avoid error.

When you’re convinced that the foundation corners are square, find out if the walls of the foundation are parallel. Measure across one end, then move to the other end of the foundation and measure again. If you come up with the same distance, the walls are parallel. Check this distance with the plans. Some error is permissible, depending on the size of the building. Walls that are out of parallel 1/2 in. over 10 ft. are worse than walls that are out of parallel 1/2 in. over 100 ft.

You need to check that the tops of the foundation walls are level. When I first get to the job site, I kneel down next to the foundation and sight across it. If the walls aren’t parallel to each other, I know something’s wrong, and that at least one wall isn’t level. You can use a builder’s level or a water level to determine what’s wrong.

For more photos and details on framing a crawl-space foundation, click the View PDF button below. 

Fine Homebuilding Recommended Products

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

Sledge Hammer

Used to tap walls or sheathing into position, we all this the “persuader” on the job site. This is a demo model, so it can survive the job site and the back of the truck — a true must-have.
Buy at Amazon

Portable Wall Jack

Raise walls safely with the Guardian wall jack — we’ve personally seen small teams raise large walls with these devices, and they work great.
Buy at Amazon

Smart String Line

String lines — sometimes called dry lines — are invaluable for straightening walls and a million other things. The reel makes it easy to stretch and wind the string.
Buy at Amazon

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
View PDF

New Feature

Fine Homebuilding Forums

Ask questions, offer advice, and share your work

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

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Up Next

Video Shorts

Featured Story

Fast, Accurate Wall Framing

A rear addition provides a small-scale example of how to frame efficiently.

Featured Video

How to Install Exterior Window Trim

Learn how to measure, cut, and build window casing made of cellular PVC, solid wood, poly-ash boards, or any common molding material. Plus, get tips for a clean and solid installation.

Related Stories

  • A New Approach to Foundations
  • Mortar for Old Masonry
  • Tall Deck on a Sloped Lot
  • Simple, Site-Made Trusses

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

Video

View All Videos
  • FHB Podcast Segment: Designing and Building an Efficient Slab-On-Grade Home
  • FHB Podcast Segment: Is Foam Against Form Boards a Good Idea for a Garage Slab?
  • FHB Podcast Segment: Lime Wash Recipe for an Old Concrete Basement
  • FHB Podcast Segment: Masonry Chimney Care 101
View All

Site Work and Foundations

View All Site Work and Foundations Articles
  • FHB Podcast Segment: A Permanent Wood Foundation in the Adirondacks
  • Concrete Funnel
  • A Strong Case for Wood Foundations
View All Site Work and Foundations Articles

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 2025
    • 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

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