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

Crawl space detail

alfie | Posted in Construction Techniques on June 17, 2008 02:16am

I am interested in comments on the attached PDF of a cross-section detail through a crawl space. I started with a standard detail that showed a basement, and modified it to show a conditioned crawl space with slab (a short basement). Is the termination of the slab at the foundation correct?

SEE NEW ATTACHMENT in later post.


Edited 6/17/2008 11:48 am ET by alfie

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

Replies

  1. Danno | Jun 17, 2008 02:52pm | #1

    When I took drafting class, we were taught to do that detail a little differently--we had the slab edge resting right on the footing with an expansion strip between it and the wall. Maybe things have changed.

    There are a couple of things I didn't see that you may think about (or maybe are included, but just not in your drawing): Re-bar in the bottom third of the footings (2 parallel bars running the length of the footings. (Where to place the re-bar is often argued about, but we were taught to put them near the bottom to help the concrete in tension (since concrete has little strength in tension).) 

    On the outside of the footing there should be drain tile and gravel, separated from the fill with landscape fabric (or perf. pipe contained in a special sleeve of fabric to prevent clogging with silt). We were told to also show drain pipe inside footing, but my feeling was that why provide a path for water to the inside (they were connected to the outside footing drains.) Lastly, I don't remember if your drawing had these things, but there should be in this order, under the slab from the undisturbed soil up--compacted gravel (or pea gravel, which is rounded and from what I've been told doesn't need compaction), rigid insulation, vapor barrier, then slab. Vapor barrier under the slab is very important. We put wire mesh (6x6 welded wire fabric, if I recall correctly) near the bottom of the slab too, to prevent cracking.

    Foundation details are very important--house rests on it (goes without saying) and it is very hard to fix things after it's done!



    Edited 6/17/2008 7:55 am ET by Danno

    1. wane | Jun 17, 2008 03:35pm | #2

      Wall insulation works better on the outside of the foundation ..

    2. alfie | Jun 17, 2008 04:00pm | #3

      Thank you for taking the time to write your thoughtful response. I took a .jpg from the Building Science Corp. web site and tweaked it a little as an illustration of the conditions around my question. For some reason on this particular drawing they didn't mention the vapor barrier. Also, the steel isn't shown, but we can agree that it should be provided consistent with normal practice. Based on what I have read on building science, from the the ground up it should be compacted earth, stone layer (no fines), vapor barrier, rigid insulation and then slab.

      Most people I talk to, and details that I have seen drawn, show the slab resting on the footing, just as you described. However, the premise for my inquiry is that there is a high water table, surrounding areas are wet, and there is an engineered septic system. So the idea is to avoid footing drains, but to have a crawl space. If there were to be footing drains, they would end up at approx. 6' below grade. This would put them lower than the level of the wet areas, and the only way to remove water from those drains would be pumping up. The idea is to keep things simple and build upwards.

      So question to all: What are the implications of building the slab the way I depicted it in my first post in this thread?

      1. JohnFinn | Jun 17, 2008 05:59pm | #4

        Why not do something like this:

         

        1. alfie | Jun 17, 2008 06:04pm | #5

          I could go for something like that. Thanks.

      2. Danno | Jun 18, 2008 05:10am | #10

        I wasn't sure as I wrote my reply whether the vapor barrier should go below or above the rigid insulation. Building Sciences should know, so whatever they say, I'll go with.

        I don't know of any problem with slab edges not resting on footing. Might eventually settle unevenly, but if the gravel is compacted and so on, don't really see that happening.  Seems like I've seen it done your way many times, so it can't be very bad! There's a guy named Brownbagg here that doesn concrete for a living, maybe he'll respond. I'm not sure how a person goes about notifying someone of a thread other than posting directly to them and then the rest of the forum can't see the post.

        Maybe I'll try posting to him and see what happens. --Edit: I tried, he isn't recieving emails from Breaktimers, so....

        Edited 6/17/2008 10:16 pm ET by Danno

        1. alfie | Jun 18, 2008 02:09pm | #12

          Thanks. I am attaching an updated detail. I'll check again but I believe the vapor barrier goes below the rigid insulation, otherwise the insulation would always be wet.

          I appreciate your reaching out to Brownbagg. I am hoping somebody who does concrete will see this and respond.

          File format
  2. dovetail97128 | Jun 17, 2008 06:25pm | #6

    A qualified "Yes" to your question about the slab termination detail.

    If the frost proof depth of the footing lies below that elevation of a 30" crawl space then the drawing is accurate. Live where frost depth is 48" then with a 30" crawl you are going to have 18" difference between the bottom of the footing and the slab.
    All depends on location.

    They can't get your Goat if you don't tell them where it is hidden.
    1. alfie | Jun 17, 2008 06:52pm | #7

      Thanks. Please see updated detail, now showing frost depth of 42". Note, the top of slab is 18" below grade, rather than 30".

      1. dovetail97128 | Jun 17, 2008 06:59pm | #8

        In the real world you are going to have compacted fill down to the footing level inside the foundation at least around the perimeter. Tough to form and pour the footing without having room to build it. So the picture should really show either a sloped fill line starting at the bottom of the footer and sloping up to the level of the gravel beneath the slab or a gravel filled cut inside the foundation wall. Minor detail though.
        They can't get your Goat if you don't tell them where it is hidden.

        1. alfie | Jun 17, 2008 07:10pm | #9

          Thanks, that's a helpful point.

          1. User avater
            BillHartmann | Jun 18, 2008 06:31am | #11

            Have you thought about doing a frost protected shallow foundation system.Basically that uses foam insultion under the ground on the exterior to increase the frost depth so that the footings can be shallower..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          2. alfie | Jun 18, 2008 02:12pm | #13

            Hadn't thought about it but I will now. First place to check will be the building code. If it does not say you can do that, I'll have quite a time getting an OK from the BI. Thanks.

          3. Snort | Jun 18, 2008 02:31pm | #14

            Why is the slab recommended if it's only a 30" crawl? I've been under some houses with "rat slabs"... maybe 2" of concrete, pretty roughly detailed, and it was a pain in the knees, or whatever other part of the body was crawling on it.Unless it's a stand up crawl, we use 10 mil plastic material with taped seams. Some builders run the plastic after the walls are built, then form the piers on top. It eliminates the sketchy detailing of wrapping and taping the piers. Problem with that is the wear it can take during construction.Consider having your rim joists foamed, much better sealing than fiberglass... foam companies will also do the vapor barrior and spray the walls.Conditioned crawls are a good way to go.
            If dogs run free, then what must be,

            Must be, and that is all.

            True love can make a blade of grass

            Stand up straight and tall.

            In harmony with the cosmic sea,

            True love needs no company,

            It can cure the soul, it can make it whole,

            If dogs run free.

          4. alfie | Jun 18, 2008 02:35pm | #15

            Thanks. I'll think about that.

          5. User avater
            BillHartmann | Jun 19, 2008 02:50am | #16

            "U.S.Code AcceptanceProvisions for FPSF are included in the 2000 and 2003 edition of the International Residential Code (IRC).The American Society of Civil Engineers developed a standard, "Design and Construction of Frost-Protected Shallow Foundations", ASCE/SEI 32-01. This standard is referenced by the 2000 (by amendment) and 2003 International Residential Code (IRC). ASCE/SEI 32-01 is also adopted by the 2003 International Building Code (IBC) which allows FPSF to be used on multifamily buildings, houses four stories and above, very large houses, malls, schools, and offices.In areas of heavy termite infestation, local codes may restrict the use of rigid foam insulation on the outside of the foundation, or may require termite resistant insulation."http://tinyurl.com/6a9fr9
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          6. alfie | Jun 19, 2008 02:58am | #17

            Thank you - I'll investigate this further.

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

Picture-Perfect Pergola

Built from locally sawn hemlock, this functional outdoor feature uses structural screws and metal connectors for fast, sturdy construction.

Featured Video

Micro-Adjust Deck-Baluster Spacing for an Eye-Deceiving Layout

No math, no measuring—just a simple jig made from an elastic band is all you need to lay out a good-looking deck railing.

Related Stories

  • Podcast Episode 692: Introduction to Trade Work, Embodied Carbon, and Envelope Improvements
  • FHB Podcast Segment: Embodied Greenhouse Gas Emissions and the Building Codes
  • Old Boots Learn New Tricks
  • Install Denim Insulation Like a Pro

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 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

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