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

AG-rated pressure treated lumber in below-grade concrete; and 1/4″ rot-resistant material

strawmyers | Posted in General Discussion on April 1, 2014 08:43am

Going to be building a 15×10 attached screened-in porch off the back of my house this year.  Been working with an engineer I know regarding the structural details.  For tie-in to resist rotational forces at the joint purposes, the corner posts are spec’d as 3 pressure-treated 2×4’s with a 1/4″ spacer between each one (to bring the outer ones out to the same thickness as the spec’d 1.75″ wide LVL’s) instead of a 4×6 deck post.  The posts will be 36″ underground and sit on an 8″ deep 20″ wide footer that is 42″ underground, then have concrete poured around them the entire 20″ width of the hole to 6″ above grade with a tapered top to direct water flow away.  The bottom of the posts will actually sit on 2″ tall composite spacers to get them above the height of the joint between the footer and the pier in case water penetrates that joint.  One goal of the project was to minimize support posts to minimize visual breaks.  This porch is being built off of the dining room where I put in the 6′ glass patio door last year, for those of you who saw that project.  Great view of the woods.  Burying the posts versus attaching them to the top of the piers with brackets adds substially greater resistance to lateral and rotational forces… which is important when asking 2 structural supports to do the job that at least 4 would usually be doing.  So two questions I’d like your input on:

1. Any issues with using “above grade” -rated PT lumber in this application instead of “ground contact and fresh water immersion”-grade?  The engineer doesn’t think so since the lumber will be encased in 20″ of concrete and spaced above the footer/pier joint on the composite material… but also encouraged me to do more research on the matter.  I intend to e-mail the lumber supplier; but I’m expecting they’ll say “no good” simply for liability purposes since the product is stated as above-grade use.  There will be no direct contact with the soil; but I know that water readily passes through concrete as it’s poreous.  Anyone of you pros successfully doing this?

2. Looking for suggestions for the rot-resistant 1/4″ thick material to use as spacers between the PT 2×4’s.  Thinnest PT plywood I can find is 1/2″ (too wide); and engineer says no deal substituting with 1/4″ untreated plywood.  Needs to be at least 3.5″ wide.  Total length needed will be ~48′ (~12′ apiece); but does not have to be a continuous 12′ section.  Thought about the 1/4″ fan-fold XPS; but had concerns.  Namely, I’d like something more rigid (like wood or composite material), there would be a lot of unused leftover wasted, and XPS really holds onto water once it gets wet (accelerating rate of breakdown of the wood its smashed between???) 

 

Here’s the view I’m trying to interupt as little as possible (the various construction materials are cleaned up, now, by the way… this was taken right after I finished the project):

 

View Image

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

Replies

  1. DanH | Apr 01, 2014 09:01pm | #1

    In general, embedding wood in concrete is worse than embedding it in dirt.

    Also, 20" is an awfully large hole.  Certainly the footings don't need to be that large, do they?

  2. DanH | Apr 01, 2014 11:49pm | #2

    I was wondering because we built a pretty big enclosed deck and the footers were a max of 12".  But we probably had more supports per square foot.

  3. MYBuilder | Apr 02, 2014 08:34am | #3

    Whenever my engineer and I disagree, I always ask him what type of train he drives because a "structural engineer" would not have said that. Low blow in this case because I have no details. No offense meant. However, wood in concrete that can not be waterproofed is not permanent. Above ground contact treated lumber means above ground, 8". No rotting leaves stuck against it no snow standing around it. ABOVE GROUND, able to dry out.

    Then there is the matter of the vault footings with the toothpick posts. If an engineer doesn't specify what material to space it with and how to fasten it toegther to get the strengh needed, how can one know the outcome of the forces.

    View or no view, if you are spending the money and taking the time, search for permanence. I would consider a footer to +8" and a steel column bolted to it. It can then be trimmed out to flush with the trim you will be using for the LVL. You were going to cover the LVL on all six sides, right(waterpfoof)?

  4. sapwood | Apr 02, 2014 10:55am | #4

    This is one of the nuttiest ideas I've read about here, in a long time. And you want to make it worse by using materials that are only suitable for above ground use. Good grief. 

    Get another engineer. Tell him to design a steel moment frame that sits on concrete footers with above ground connections. Enclose the steel with any suitable material of your choice if you don't like the appearance of steel. 

    1. DanH | Apr 02, 2014 12:17pm | #5

      There's nothing wrong with using wood, so long as it's a truly rot-resitant product.  But (in addition to using foundation rated wood) use solid lumber rather than 3 sticks lashed together, and don't jacket it in concrete.

      1. florida | Apr 02, 2014 04:34pm | #6

        "truly rot-resitant

        "truly rot-resitant product"

        That has to be the funniest thing you've ever said!

  5. strawmyers | Apr 02, 2014 08:54pm | #7

    I appreciate the insights and opinions (of varying levels of bluntness): that's why I come here.  There are a couple of different views here; so I'm going to get further thoughts from both sides.

    For those against the use of any type of wood underground, have you ever used and how to do you feel about these "Pro-Anchors"?

    http://www.menards.com/main/building-materials/post-frame-materials/accessories/6-laminated-column-pro-anchor-3-ply/p-1807211.htm

    I will ask the engineer about the steel moment frame.  Images I found online look like they'd be a lot of overkill for such a small project; and possibly cost-prohibitive.  I am certainly interested in learning as much as I can about all viable options, though.

    For those in the "foundation/GC wood is fine underground" camp: I understand that encasing the posts in concrete is universally hated by both groups, what would you use as fill, instead?  Compacted stone, pea gravel, sand, just the original dirt taken out of the hole, or something else?  Still need to use a footer pad with the post secured to it with some kind of bracket, right?

    1. strawmyers | Apr 02, 2014 09:01pm | #8

      Any experiences one way or another with the various plastic footer forms designed to be used in conjunction with sonotubes?

      http://www.bigfootsystems.com/

      http://www.soundfootings.com/Index.php

      http://www.homedepot.com/p/Sound-Footings-Plastic-Concrete-Footing-Form-TB22/202532049#specifications

    2. DanH | Apr 02, 2014 10:09pm | #9

      One approach is to embed a piece of rebar in the end of the post and then set the post ON TOP of the wet concrete footing (so there's no depression to collect water around the end of the post).  Back fill with non-peaty soil or medium/fine crushed rock -- not pea gravel as it provides no lateral stability.

      Note that structurally a post buried in the ground provides stiffness against tilting that a post sitting on a concrete pillar does not.  If posts are placed on concrete pillars then additional diagonal bracing is needed to keep the posts from racking.

      1. strawmyers | Apr 03, 2014 08:10pm | #10

        lateral forces

        DanH wrote:

        Note that structurally a post buried in the ground provides stiffness against tilting that a post sitting on a concrete pillar does not.  If posts are placed on concrete pillars then additional diagonal bracing is needed to keep the posts from racking.

        That is what dictated the original design: need to withstand those lateral and rotational forces without having to use bulky diagonal cross-bracing.  Looks like the steel moment frame would accomplish this as well... I'll have to see what the estimated cost comes back as for that. 

        Do you see any benefit or detriment to wrapping the post in some drain wrap style house wrap before placing in the ground?  Thought it might help by providing a slight air space between the post and compacted stone/soil... but then worried it might lower uplift resistance for that same reason.

        1. florida | Apr 05, 2014 06:30am | #11

          This seems way overcomplicated to me but maybe I'm missing something. Why not use treated 6" X 6"  posts dug down below your frost line, sitting on a 12" bed of compacted gravel and continuing up to the floor assembly? That's the way we build 99% of our decks and some of them are 10' off the ground.

          1. DanH | Apr 05, 2014 07:54am | #12

            Yeah, for once Florida and I agree.  (Or, rather, Florida agrees with me.)

          2. AndyEngel | Apr 29, 2014 02:30pm | #13

            Really? Just a compacted gravel footing? That would never fly up here, but I guess I'm not sure why not.

          3. florida | Apr 29, 2014 08:42pm | #14

            I guess because we're building on very compacted sand. I've built dozens of piling houses with nothing under the piles at all. Certainly when we drive piles for houses nothing goes under them.  Actually I've only started putting gravel under my posts in the last couple of years. I was spanked by a BI last year for not pouring "a bag," his words, of Sakrete around the posts of a beach front porch. Still not sure what a 60 pound bag of Sakrete will do but we did it anyway.

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

Rescuing Old Hardware

Whether it’s already in your house or picked up at a flea market, vintage hardware almost always needs help.

Featured Video

SawStop's Portable Tablesaw is Bigger and Better Than Before

The 10-in. Jobsite Saw PRO has a wider table, a new dust-control port, and a more versatile fence, along with the same reliable safety mechanism included in all SawStop tablesaws.

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