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

Metal Shed Construction (Condensation)

hammagic9 | Posted in Construction Techniques on February 19, 2012 01:01am

I have to build a 30 x 60 metal building for a customer (uninsulated).  Building it with 6 x 6 post and horizontal purlins for my metal walls.  Concrete floor.  Roof will be 4/12 pitch with trusses on 2′ center.  Will have purlins on roof on 2′ centers for metal roof.  This building will basically be holding maintenance equipment for a golf course.  My concern is with an uninsulated building and being fully enclosed is the condensation forming on the roof panels.  I was thinking about installing a titanium vapor barrier over the trusses and then installing purlins over titanium then the metal roof.  This way  i will have ventaltion between the vapor barrier and metal roof panel, drawing air from the soffits to ridge vent. Leave opening at top of titanium venting the interior warm air out the ridge vent.  Do you think this would fix any condenstion problems??  I just want to do this project right from the beginning.  I know people build this type building without this vapor barrier all the time.  Just don’t want to take any chances on them thinking they have a leaky roof.  I have never had a whole lot of experience with this type of construction.  Just wanted to get some thoughts from more experienced contractors on this subject.  Thanks for any help.

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

Replies

  1. DanH | Feb 19, 2012 03:01pm | #1

    What's the source of moisture that you're worried about?

    1. hammagic9 | Feb 19, 2012 04:13pm | #2

      I am sure at times in the winter, when they have to do maintenance in this building on their golf carts.  They will probably run some type of heater.  The lighting could put off some heat.  The concrete could be putting off amounts of moisture, especially during the curing process.  The building itself during the days where it just heats up on warm days and then at nights the temp. out side drops.

      1. DanH | Feb 19, 2012 05:48pm | #3

        But no cooking, no bathing, only a few humans exhaling in a poorly-sealed building.

        Heating alone is not a problem -- it will actually reduce the possibility of condensation.

        1. hammagic9 | Feb 19, 2012 06:32pm | #4

          So your anwser would be no need for any vapor barrier?  Metal walls on purlins and metal roof on purlins? 

      2. User avater
        xxPaulCPxx | Feb 19, 2012 10:52pm | #5

        Some types of heaters can introduce water vapor - like the torpedo propane heaters for instance.  Otherwise vapor from combustion is vented out.

        The concrete should be well drained from underneith, no water there.

        If the air is humid outside, then it cools down - the outside will have condensation.

  2. User avater
    woodandiron | Feb 20, 2012 10:39am | #6

    Here in the Pasific Northwest humidity in the air condences on the inside of metal buildings.  The aluminum canopy on my pick-up rains  inside.  Weather reports include the "Dew Point".  That's where temps and humidity reach the point of causing condesation.  In a dry climate, it's not a problem most of the time.  I would add a vapor barrier.   Jim

    1. DanH | Feb 20, 2012 07:31pm | #7

      How will a vapor barrier do any good?

      1. davidmeiland | Feb 21, 2012 06:27am | #8

        It may not

        do a whole lot of good, but the problem is definitely real. Condensation forms on the underside of metal roofs up here, and drips down on whatever's underneath. Worst cases I have seen are very low slope with metal installed directly over purlins. Building can be enclosed or open (happens in carports). I think closed is more likely to be a problem due to ground and/or slab moisture. A lot of metal buildings have "bag and sag" insulation, wide fiberglass with a plastic vapor barrier under it, rolled out over the purlins, with the metal laid directly over, and moisture finds its way up through seams in the plastic, condenses on the metal, and then forms ponds on top of the plastic. My guess is that rigid foam insulation might be enough to solve it, but maybe not. Here's a shot showing a pond on top of the plastic in an airplane hangar.

        1. DanH | Feb 21, 2012 06:42am | #9

          If the condensation is coming from outside air, and you install a vapor barrier and ventilate above it, there will still be outside air in contact with the metal roof.  In addition, there will be outside air in contact with the vapor barrier, which will be nearly as cold as the roof.  How is the "vapor barrier" an improvement?

          1. davidmeiland | Feb 21, 2012 09:56am | #12

            The successful solution

            would be one that keeps the bottom of the roof assembly (whether that's the roofing itself, a vapor barrier, a deck, or whatever) above the dewpoint.

            A VB itself won't do this. In some cases the dew drops roll down along the top of the VB instead of dripping inside.

  3. KDESIGN | Feb 21, 2012 09:50am | #10

    Question:

    So, as I understand it, this moisture condensation is caused by the temperature drop both inside and outside with high water vapor content both inside and outside.  So when the temperature everywhere drops below the dewpoint, dew forms on every physical object it can find.  Or does it just form on the ceiling of buildings?  If so, why only there? 

    1. davidmeiland | Feb 21, 2012 09:54am | #11

      Google

      "night sky radiation"

      Surfaces facing the sky on clear nights can be quite a bit colder than the air temperature. The roof gets colder than the rest and condensation forms on one or both sides of it.

      1. DanH | Feb 21, 2012 08:27pm | #16

        Interestingly, the best fix for potential interior condensation on a metal roof is a "hot roof" of sorts -- one that has an insulating layer in direct contact with the roofing.  The insulation prevents any radiative cooling from conducting down to the "ceiling" surface, and the lack of an air gap prevents condensation on the back of the metal.

        The insulating layer doesn't have to be much, of course -- 3-5 degrees difference is all it takes.  A layer of spray undercoating would likely work, building paper somehow laminated to the back of the metal, etc.

  4. DoRight | Feb 21, 2012 11:32am | #13

    One more comment from someone else in the NW who knows about condensation in metal pole barns.  We had one built not so long ago and the contractor quoted the building with the plastic covered insulation SO AS TO REDUCE condensation.  Then he started pushing to use plywood sheathing under teh metal roofing instead of insulation.  He wanted about $1000 for an up charge.  I did not wish to pay this.  He wished to do the plywood so badly he did for the cost of the material.  I don't know if the insulation is a pai in the but for the guy or if if he did not want complaints about condensation (leaky roofs) or what. 

    Well, the plywood looks great making for a beefy looking building.  No condensation.  ANd I do know the insulation sags over time, and BIRDS LOVE TO TEAT IT OUT AND BUILD NESTS IN IT!  Think about that mess.

  5. glacierfergus | Feb 21, 2012 04:25pm | #14

    Give the customer the option...

    If you can present options and potential consequences to the customer, then they will understand what they are getting and what they are paying for. 

    I live in an area with relatively low hunidity (Central Montana), but extreme temperature fluctuations in winter. (60 above to -35 F)  When the temps outside drop 50 degrees overnight, we get some condensation issues in uninsulated metal buildings.  Most shops around here are built with just the frame and purlins, as you described. Some end up spraying foam on the underside of the metal, and others just live with the occasional "indoor rain."

    Since you are already planning to have trusses at 2' on center (many will go with trusses at 4' on center with 2x6 purlins) you could easily just sheath the roof with ply or OSB.  Then put a good synthetic underlayment (Titanium or similar) and screw the metal to that. Makes a very solid roof structure and any condensation on the underside of the metal drains down the underlayment and out the eves. Occasional condensation on the walls doesn't present as much of a problem, at least in my climate where everything gets dried out pretty quickly.

    Give the customer the option, and explain how condensation works. Then they can make an informed decision...

    1. hammagic9 | Feb 26, 2012 03:17pm | #17

      That why i thought it might be best to set trusses and then titanium overtrusses, then purlins, then metal roof.  Cold air would still be over titanium but atleast warm air will not come in direct contact with metal 1st.  Figured the space above the titanium would have some sort of chimney effect between the soffits and ridge vent and would cause the condensation to be less and would dry faster (more air flow acrossThe bottom of metal roof).  What did condensate on roof panel would drip on titanium and run down to soffit, instead of dripping on floor. 

  6. glacierfergus | Feb 21, 2012 04:26pm | #15

    Give the customer the option...

    If you can present options and potential consequences to the customer, then they will understand what they are getting and what they are paying for. 

    I live in an area with relatively low hunidity (Central Montana), but extreme temperature fluctuations in winter. (60 above to -35 F)  When the temps outside drop 50 degrees overnight, we get some condensation issues in uninsulated metal buildings.  Most shops around here are built with just the frame and purlins, as you described. Some end up spraying foam on the underside of the metal, and others just live with the occasional "indoor rain."

    Since you are already planning to have trusses at 2' on center (many will go with trusses at 4' on center with 2x6 purlins) you could easily just sheath the roof with ply or OSB.  Then put a good synthetic underlayment (Titanium or similar) and screw the metal to that. Makes a very solid roof structure and any condensation on the underside of the metal drains down the underlayment and out the eves. Occasional condensation on the walls doesn't present as much of a problem, at least in my climate where everything gets dried out pretty quickly.

    Give the customer the option, and explain how condensation works. Then they can make an informed decision...

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

Two Ways to Test Windows

New devices showcased at the Builders' Show make it easy to measure glass performance, u-factor, SHGC, window thickness, and more.

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 695: Saving Bricks, Cut-and-Cobble Insulation, and Waterproofing Foundations
  • FHB Podcast Segment: Waterproofing Below-Grade Foundation Walls
  • Midcentury Home for a Modern Family
  • The New Old Colonial

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 333 - August/September 2025
    • A Practical Perfect Wall
    • Landscape Lighting Essentials
    • Repairing a Modern Window Sash
  • 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

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