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

Preventing patio slab from heaving

Maclf2922 | Posted in General Discussion on March 7, 2009 01:12am

My wife and I moved into a 6 year old ranch home in the north eastern Ohio area last May. The basement is a 13 course block with a walkout onto a cement pad. The pad was cracked when we moved in. The interesting thing about the cracks were that the patio was flat in the middle but each side was broken down at the ends much like an upside down U. I had the slab removed and replaced in the summer. The old slab was 6 inches thick and poured directly on the soil without a gravel base yet it still cracked. The new slab is 4 inches thick and poured on a gravel base. It has expansion Celotex joints at all points near the house and wrapped around the deck posts. Once it got very cold (below 10 degrees) you would hear occasional loud popping (similar to a handgun firing) coming from the deck walkout on the first floor. I discovered that the slab had risen by the walkout door and pushed up the side trim framing the door. The concrete slab rose 3/4 inches and I assume this pushed up the trim. The slab also has a hairline crack running across the width of the slab. I am not sure what caused the popping sound.

My question is: Did the slab rise due to moisture freezing under the slab? If this is the cause, can I reduce the moisture in the ground by putting drainage pipe 16″ underground and at the end of the slab to drain moisture to a lower level of the yard?

Maclf

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

Replies

  1. Bing187 | Mar 07, 2009 01:42am | #1

    I'm sure some folks with more knowledge than I in regards to soil mechanics will chime in here, but......

    I try to do slabs like this one over a decent (8" or better) of 1-1/2" stone. I find that in addition to the value it gives in regard to drainage, it has some voids that (I think) give a little expansion room for when the frost heaves the slab, as it looks like yours has.

    Drainage around the slab might help, but my opinion is that it will be minimal. Most slabs DO move up and down a little (1/2"+-) seasonally......at least in my neck of the woods.

    As a builder, I'd be a lot more concerned with the fact that the slab was poured flush with the bottom of the door...big no-no in my opinion. Primarily for the reason that it's begging for water infiltration at the door, and all along that sill area, but secondarily (is that a word?) for the problem that you're having; if the slab comes up, it wreaks havoc with trim, and can push up on the threshold to the point of the door binding.

    Someone will undoubtably be along with an idea to reduce movement....Sorry to say that I'd be inclined to re-do if the job were dropped in my lap.

    Bing

  2. MikeRyan | Mar 07, 2009 03:50am | #2

    From the way the slab looks discolored, I would speculate that the water is draining off the raised grade to the right and has no where to go BUT onto the slab.  Putting a drain 16" down will not correct it unless you have a place for it to drain to.

    I also agree that the slab being on the same grade as the basement slab will just create problems in the future.

    Solution:

    Jack this slab up, put down a DEEP gravel base that will act as a sump ror the runoff and repour....or just live with the cracking/shifting and accept the fact that you will never be able to put a pool table there!

  3. jimAKAblue | Mar 07, 2009 06:18pm | #3

    The slabs aren't being pushedup because of a little water under them. They are heaving because the entire earth surrounding your house is expanding!

    Typically, the heat of the house will keep the immediate surrounding area of the house from freezing but once you get past a foot or two, everything is frozen solid and expanding. The slab would raise up and be cantilevered over that soft zone next to the house.

    You should have provided at least 1" clearance for the slab to raise up near any trim. I would have opted for a bit more but 1" will usually be sufficient for most winters. You might consider cutting the concrete back or cutting the trim up to provide relief.

    One other option would be to cover the slab inside that cove to keep it from freezing. You wouldn't need much cover to prevent it from heaving. Snow is actually a good insulator but the heat escaping from the house melts it fast on the patio.

  4. LIVEONSAWDUST | Mar 07, 2009 10:55pm | #4

    You have a lot of water feeding those downspouts that go through the slab, I would wonder where they are leading or if there are leaks in the line. also appears the surrounding landscaping is too high.

    In my experience, seems like you can only have frostheave if you have enough moisture to freeze, if it was drained properly you wont retain enough moisture.

    I agree, though, the slab is too high, I like it at least several inches below the door.

    Best fix in my opinion would be to remove slab, dig up and check downspout drainage, then regrade to provide better slope away from the foundation.

    1. Maclf2922 | Mar 08, 2009 01:04am | #5

      I also have wondered if there are problems with downspout drain leaks under ground which might add more water than the normal drainage. The main house roof above the deck above has two valleys on each side that will direct water over the gutter in a heavy downpour. The water falls through the deck and into each corner area of the slab next to the house. In this last winter there was an ice dam in each valley which during periods of winter warmups would steadily drip water onto the deck which then dropped down to the slab. This makes another source of extra moisture. This is one reason I was considering a deck drainage system to prevent the water from ending up on the concrete slab. I will cut the trim up so that it is not near the slab and I will look at getting the concrete contractor to cut the slab near the house to relieve some of that movement during winter and reevaluate the slab.Maclf

      1. LIVEONSAWDUST | Mar 08, 2009 06:29pm | #6

        On a new house, you shouldn't have to accept ice dam problems, you should investigate that issue first.

        If the downspouts/gutters regularly overflow, they are undersized. That does look like a lot of roof for two downspouts.

        Where do the downspouts drain to?

  5. Catskinner | Mar 08, 2009 08:49pm | #7

    Rumor has it that I'm still an excavation contractor. Back when there was enough left of the economy to actually go to work and get paid, a lot of what I did was fix structural problems as they relate to geo-technical and drainage conditions.

    First, there are three things required for a frost heave; moisture, freezing temperatures, and suitable soil (soil that will retain moisture and behave in a plastic manner). Remove any one and the ground will remain stable.

    The trick for you in this case is that you could put anything you want under the slab including crushed stone, and with the amount of water you appear to have under there you could still have a problem. At that point, we're not talking about frozen soil, we're talking about solid ice.

    So as most of the previous posters have pointed out, any water that does make it to the vicinity of that slab needs to be drained away. The least expensive fix is always to divert it before it hits the ground. After that, a sub-grade drain to a run of infiltrators is probably next best.

    I can't really tell from the photos, but it looks like the posts for the deck are sitting on that slab. If this is indeed the case, it would be best to address this sooner than later. If that deck starts moving with the slab you could find yourself with a whole new set of problems.

    If you can't find a way to divert the water and you need to put in a drain system, post back here and I'll give you some ideas.

    1. Maclf2922 | Mar 08, 2009 10:36pm | #8

      In my area there is a lot of clay and I assume that is what was used as backfill around the house. I honestly didn't pay close attention to the soil type when the pad was repoured other than they did use about 4" of stone before pouring. The posts are anchored into the soil and not attached to the pad. The posts are wrapped in celotex and the concrete was poured up to it.

      The downspouts are the typical size (4"?) but not anything larger than that. As I mentioned before there can be a waterfall of water down the valleys that jumps over the gutter and onto the deck. There is a sheet of aluminum attached the gutter at the bottom of the valley to block the water but it is not wide enough because the water goes past it and onto the deck. I am thinking of hiring a plumber with a camera who can snake the downspouts and the drainage pipe to see if there are any breaks in it that may be adding to the water problem. We currently are receiving quite a bit of sustained rain and I can see that the area of lawn at the end of the pad does have water standing. It would be helpful to have some drainage pipe put in just to reduce that situation.

      Maclf

  6. User avater
    Jeff_Clarke | Mar 09, 2009 04:23am | #9

    My question is: Did the slab rise due to moisture freezing under the slab?

    This is a problem of slab-jacking due to the column footings and slab being monolithic.   I've seen it before.

    Typically, the column footings are poured in sonotube (in virgin soil) which creates the perfect piston which, when freeze/thaw cycles begin, simply goes up and down with groundwater freezing.

    Yes, you need a drainage plane under the slab, but also this is a perfect case where column footings and surrounding slab need to be decoupled (not connected).

    View Image  < Column footing (sonotube likely) jacking slab here

     

    Jeff



    Edited 3/8/2009 9:26 pm ET by Jeff_Clarke

    1. Catskinner | Mar 09, 2009 07:27am | #10

      Jeff, I'm thinking the same thing, see my post #8.Even if the pier is not the culprit, you are still right, the post needs to be decoupled from the surrounding slab.

    2. User avater
      Matt | Mar 09, 2009 03:16pm | #13

      >> Typically, the column footings are poured in sonotube (in virgin soil) which creates the perfect piston which, when freeze/thaw cycles begin, simply goes up and down with groundwater freezing. <<

      Would the post footings be moving up and down assuming they were dug down below the frost line?

      >> but also this is a perfect case where column footings and surrounding slab need to be decoupled (not connected). <<

      In the OP's first post he said: >> The new slab is 4 inches thick and poured on a gravel base. It has expansion Celotex joints at all points near the house and wrapped around the deck posts. << So they are at least somewhat decoupled.  OTOH, you are right that the top of the post footings could be pushing on the bottom of the slab if these post footings are indeed moving.

      OP: So, I guess another question is the deck experiencing seasonal movement? (up and down)?  And...  Were the expansion joint around the posts nailed to the posts?  If so, what is the position of the top edge of the expansion joint relative to the top surface of the slab? 

  7. jigs_n_fixtures@icloud.com | Mar 09, 2009 08:15am | #11

    It looks like a combination of things.  Most of which have been discussed.

    The one that hasn't is thermal shrinkage cracking;  if the slab is 4-inches of 3500-psi concrete, on 4-inches of gravel.  The cracks you are seeing in the slabs are most likely from thermal shrinkage stress.  The control joints on a 4-inch slab need to be no more than 5-feet apart.  If your temperature differential is high then they need to drop down to about 4-ft.

    The gravel needs to be considerably deeper than 4-inches. 

    The water needs to be kept away, or moved away.  If it gets under the slab and freezes it will push it up into the door and trim.  I would also recommend at least 3/8-inch to the foot of fall in the slab away from the house.

     

  8. Pelipeth | Mar 09, 2009 01:53pm | #12

    Nothing to do with your post, but if I was in the circular stair business, I'd give you a call.

    1. Piffin | Mar 09, 2009 07:47pm | #14

      Think he isn't going round and round over this already?;) 

       

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

      1. Pelipeth | Mar 09, 2009 11:48pm | #15

        You would think.......

        1. Maclf2922 | Mar 11, 2009 05:40am | #16

          My thanks for the suggestions and observations about this slab issue. I will try to address as many as I can within my budget restrictions.

          Regarding the stairs on the deck - I hate it! It is ugly and anything would be an improvement.

          Larry 

          1. Pelipeth | Mar 11, 2009 01:17pm | #17

            You didn't design/build the staircase, so your not GUILTY. Tight budget, a firemans' pole would work for starters and an improvement.

          2. User avater
            Matt | Mar 11, 2009 02:31pm | #18

            Do you think the wooden deck is raising during the winter freeze?  A level layed on the deck boards might tell a lot....

  9. Roger6 | Mar 11, 2009 09:32pm | #19

    There have been lots of good suggestions with regards to vertical clearances and control of drainage water. I would only add the suggestion that if you end up digging the existing slab out in addtion to drainage improvments you also add a layer of 2"  polystyrene installation under the slab and extend it out at least two feet beyond the perimeter of the slab. I would also recomend that at the perimeter you angle the insulation downward to minimize drying out the grass along the edge. Roger  

    1. Maclf2922 | Mar 11, 2009 10:46pm | #20

      As far as the stairs, I opened a nice cut on the top of my thinly hair-covered head when I went up the stairs with my head down and one of the crankout Anderson windows was open. As you might guess, I caught the point of the aluminum clad window. Bled very well!Larry

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

Builder’s Advocate: An Interview With Viewrail

Learn more about affordable, modern floating stairs, from design to manufacturing to installation.

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