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

machining composite decking

john7g | Posted in General Discussion on July 11, 2006 06:36am

Been wanting to ask this group about this for a while & Zahs post got me moving on it.

Has anyone done anything not prescribed by the mfg of the composite decks like making lap joints?  When I replaced the front porch deck I didn’t want gaps.  Here in the SE pine needles get caught in them & it gets to be a real pain trying to keep it looking clean.  I’ve read & reread (not saying I didn’t miss something) at the mfg web sites regarding installation & also where they brag about how stable the material is.  But in every installation they call for a gap between deck boards.  Why mandate a gap if it’s so stable?  Finally found one little statement regarding the movement of the joists that the deck was attached to.   Hmmm… not much movement lengthwise even in PT joists in my opinion.  And widthwise… the movement will only be affecting one screw through each board in most cases.  So I ran an experiment and rabbetted the edges of the boards (alternately) and installed them kind of like T&G but with rabbets instead.  Each board got one screw at each joist near the edge holding down the adjacent rabbetted board (except for the starter row).   The size of the of the deck is 7’ x 4’ (with the boards 7’ long running perpendicular to the joists) so kind of limited but in the year since I began the experiment I’ve not seen any issues and am happy enough to now go forward on the larger (& more expensive) back deck with the same process.  The temp range it’s seen ranges from 15f to 100f with little protection from the rain.  It also is about 2’ above grade so it gets decent venting.  Also there’s been no mold/fungus growth so far that is common on PT around here.  <!—-><!—-><!—->

<!—-><!—->

I know that this voids any type of warranty the mfg may offer but I usually don’t keep enough of the paperwork to maintain the warrantees anyway such as original receipts and the tags on the boards so I’m not worried about that

 <!—-><!—->

Has anyone else done anything like this?  <!—-> <!—->

 <!—-><!—->

John

 

BTW, other than it being very heavy the comp decking is fun to work with.

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

Replies

  1. User avater
    AaronRosenthal | Jul 11, 2006 06:44pm | #1

    Very interesting experiment.
    In the Trex use I have done, I always gapped to spec, because, when I consulted with the manufacturer, they always told me the "growth" of the material was not dependant on annular rings, like wood, but that the plastic composite grew evenly throughout the piece.

    Quality repairs for your home.

    AaronR Construction
    Vancouver, Canada

     

  2. woodway | Jul 11, 2006 07:27pm | #2

    I've interpreted the gap suggestion by the manufacture as cautionary sage advice and not related to their statement about the product stability. Regardless of the material used in it's construction, when that deck is exposed to direct sun, the temp of the material (dependent somewhat upon color) is going to rise significantly. One hundred forty degrees would not be out of the question. With that temp rise, your going to get expansion and if there is no way to relieve that stress, some buckling has got to take place. In your first deck, that's only four feet in width, that expansion may not be significant enough to cause problems but it's still occurring. If you then assume that you can do the same thing on a deck that's much wider, say 12 feet or more , you had better make some allowances for that expansion or your going to experience some additional costs for repair down the road. Not to mention the labor and frustration involved. It's not the one screw per board that's the problem, it's physics and it still applies regardless of how you lap the boards. If it expands and it will, you need some space for that expansion to take place. The deck, or the wall next to it, is going to move or the deck will develop a wavy surface.

    When they installed the sidewalk in front of the houses on my block, they didn't install any expansion joints that I can see. For the last six years, the sidewalk in front of my neighbor's house lifts as much as eight inches on hot summer days. Two sections, that probably weigh a couple thousand pounds each, will lift completly off the ground. The city, who installed the walk now wants my neighbor to fix the trip hazard that's developed and do it at his expense.

    1. john7g | Jul 12, 2006 04:56am | #3

      Thanks Aaron & Woodway,<!----><!----><!---->

      This is exactly what I was looking for, somebody to knock the blinders off my tunnel vision. 

       

      Not sure why I overlooked this ‘til now but today I took a scrap of the decking I had left that was sitting in the sun and probably around 100f (outside temp was 90f and I think the material may have been actually hotter than 100f) and took a measurement then froze it in the deep freeze with a thermometer I know to be reliable to a temp of 0f (This was after a 9 hour cold soak  After only 4 hours it had already shrunk 0.040”.) and re-measured to find a 0.048” difference in width (about 3/64”)(measured with a vernier caliper so it’s pretty accurate).  Cumulative effect over the length of the next deck is over 1.5” of expansion and guaranteeing problems… if I install when it was the coldest/narrowest.  Looking back at the 4x7 and the time of year I installed I got lucky since it was installed last August in the heat of the summer (I’d rather be lucky than good) and at max expansion. 

       <!----><!---->

      I’m still going to go ahead on the larger deck but won’t be trying to get it done as early in the day as possible and will wait ‘til it’s good and warm before attaching.  <!----><!---->

       <!----><!---->

      I don’t think I’d ever do this for a customer due to the warranty issues and the additional complications of the temp of the install but I do like the look of the front deck as well as the feel of the composite on bare feet.<!----><!---->

       <!----><!---->

      Cheers<!----><!---->John

      1. User avater
        BruceT999 | Jul 12, 2006 05:29am | #4

        John, another reason that the manufacturers require spacing is for air circulation. Without enough air movement, water that gets through the cracks will sit on top of joists and eventually rot them and/or cause mold problems.BruceT

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

Builder’s Advocate: An Interview With Viewrail

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

Related Stories

  • Design and Build a Pergola
  • Podcast Episode 689: Basement Garages, Compact ERVs, and Safer Paint Stripper
  • FHB Podcast Segment: Are Single-Room ERVs the Answer?
  • Fire-Resistant Landscaping and Home Design Details

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