FHB Logo Facebook LinkedIn Email Pinterest Twitter Instagram 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
SUBSCRIBE TODAY

Save up to

70% off

the cover price

In-depth articles, up-close photography, and detailed illustrations in every issue.

Subscribe Now!
Subscribe
  • How-To
  • Design
  • Tools & Materials
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
  • Join
  • Log In
Subscribe

Discussion Forum

Discussion Forum

Flat Roof Venting – Screened Porch

jc_tn | Posted in Construction Techniques on February 19, 2021 10:43am

I’m in the planning process of building a screened porch 20’w x 16’d replacing an old deck on the back of my house. Due to the location of second story windows, the roof will need to be flat (1/4″ / ft slope) and butt up to the brick veneer of the house. I plan on using 2×10 ceiling joists/rafters running perpendicular to the house, then cutting tapered 2x pieces to glue to the tops of the 2×10 to give me the appropriate slope, then cover that with 5/8 ply. This Old House had some good details on doing this. I plan on installing EPDM or a similar one-piece covering. The inside of the porch will have a T&G ceiling attached to the bottom of the 2×10 joists/rafters.  The porch will also have a vent-less fireplace installed. 
I’m concerned in the warm months that heat will be trapped in the cavity above the T&G ceiling, and also concerned that in the cooler months when we’re using the fireplace that moisture will accumulate above the T&G ceiling.
I’ve researched this on the web and it seems that most flat roof information comes from the UK. Polyroof has a Ventilated Abutment drawing showing a vent where the flat roof meets the wall. Does anybody know of a US company that offers a similar solution? Should I be concerned with venting?
Thanks in advance!

File format
Reply

Replies

  1. User avater
    UncleMike42 | Feb 19, 2021 09:15pm | #1

    Are you going to insulate that roof? (vapor barrier and six inches of batt insulation would leave 3.5 inches of vent space above. Not code anyplace, but you said this is a screen porch...)

    Sounds like you will end up with 4 inches of space above the 2x10 at the wall. you can leave gaps in your slanted 2x spacers near the wall to let air circulate between joist cavities. if you vent the soffit at the low end (away from the house) and vent both ends of the soffit near the house, you might be ok without venting along the house wall, or using a mid-roof vent.

    for a 320 sq ft roof, 1:300 would call for 77 square inches at each end. (top and bottom) If you split the top end (near the house), 38.5 square inches. at 4 inches high, this would need 10 inches of gap. Two five inch gaps with a couple inches of nail catcher between would work too.

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

Designer Kitchen Cabinets on a Budget

This Danish manufacturer has found a way to bring modern, architect-designed cabinetry to the masses.

Featured Video

How to Install Exterior Window Trim

Learn how to measure, cut, and build window casing made of cellular PVC, solid wood, poly-ash boards, or any common molding material. Plus, get tips for a clean and solid installation.

Related Stories

  • Podcast 471: Members-only Aftershow
  • Podcast 471: Adding Outsulation, Sealing Leaky Bump-Outs, and HVAC for a Shed Office
  • Schneider Electric Recalls Line of Electrical Panels
  • Podcast 470: PRO TALK With Builder Mike Knoche

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

Sign Up See all newsletters

BOOKS, DVDs, & MERCH

Shop the Store
  • Pretty Good House
    Buy Now
  • Code Check Building 4th Edition
    Buy Now
  • 2021 Fine Homebuilding Archive
    Buy Now
  • Outdoor Projects
    Buy Now
  • Shop the Store

Fine Homebuilding Magazine

  • Issue 308 - July 2022
    • Pretty Good House Book Excerpt: Copper Farmhouse
    • 10 Dos and Don'ts for Electric In-Floor Heat
    • A Sturdy Rail for Outdoor Stairs
  • Issue 307 - June 2022
    • How to Raise a Post-Frame Home
    • Trimming Deck Stairs
    • Evolving an Energy-Efficient Envelope
  • Issue 306 - April/May 2022
    • Framing Stairs to an Out-of-Level Landing
    • Building a Zero-Energy Home for Less
    • Good-Looking and Long-Lasting Traditional Gutters
  • Issue 305 - Feb/March 2022
    • The Steady Surge in Residential Solar
    • The Fine Homebuilding Interview: William B. Rose
    • How Good Is Your Air Barrier?
  • Issue 304 - Dec 2021/Jan 2022
    • Why You Need Blower-Door Testing
    • Passive-House Standards for Everyone
    • Window Replacement With a Side of Rot Repair

Fine Homebuilding

Follow

  • twitter
  • facebook
  • instagram
  • pinterest

Newsletter

Get home building tips, offers, and expert advice in your inbox

Sign Up
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences

Taunton Network

  • Green Building Advisor
  • Fine Woodworking
  • Fine Gardening
  • Threads
  • About
  • Contact
  • Advertise
  • Careers
  • Copyright
  • Terms of Use
  • Site Map
  • Do not sell my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2022 The Taunton Press, Inc. All rights reserved.

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
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Account

  • Log In
  • Join

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

Shop the Store

  • Books
  • DVDs
  • Taunton Workshops

More

  • FHB Ambassadors
  • Reader Projects
  • Podcast
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Sign Up See all newsletters

Follow

  • twitter
  • facebook
  • instagram
  • pinterest

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

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