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

Fine Homebuilding Project Guides

Roofing

Guide Home
  • Tools and Materials
  • Roof Replacement and Reroofing
  • Roof Ventilation
  • Waterproofing
  • Installing Asphalt Shingles
  • Installing Other Types of Roofs
  • Roof Maintenance and Repair
How-To

A New Roof Over the Old One

This homeowner found that replacing a worn out roof provided a good opportunity to insulate above the sheathing before installing new roofing.

By Pete Bennett Issue 190
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Synopsis: Vermont homeowner Pete Bennett needed to fix his poorly insulated roof, which was susceptible to ice dams, but he didn’t want to ruin the look of the interior’s cathedral ceiling. Because Pete needed to replace the cedar shakes on the exterior, he opted to strip the roof to the sheathing, then build a new roof over the old one. The area between the roofs was filled with closed-cell foam to provide an insulating value of R-45, and snow now slides off the new steel roof instead of building up and leading to ice dams.


My rustic 1930s post-and-beam home in Vermont had a definite roof problem: It was poorly insulated and susceptible to ice dams. But when I started working on a design for upgrading the insulation, I wasn’t willing to lose the look of the cathedral ceiling and the exposed-pole rafters by insulating on the inside. Because I needed to replace the 30-year-old cedar shakes anyway, it appeared an opportune time to fix the problem from the outside.

I had already installed one interior post to strengthen the roof structure and to help support snow loads, but the sagging ridge beam and the wavy roof surface still precluded the use of either SIPs (structural insulated panels) or rigid-foam board. A double-layer “cold roof” appeared too costly and prone to possible failure if snow clogged the upper vents. So in the end, I decided to build a second sealed, well-insulated roof directly over the first.

After the old shingles were stripped and the deck sealed with weatherproof polypropylene underlayment, a new straight, level ridgeboard was set above the old one. Rafters then were built in place, and closed-cell polyurethane foam was sprayed to fill this frame. The new roof frame then was capped with sheathing and a second layer of weatherproofing before the standing-seam metal roof was installed.

The closed-cell foam increased the estimated R-value from 11 to 45. The higher R-value and the fact that snow now slides off the steel roof have worked together to solve the ice-dam problems. Although not inexpensive (about $18 per sq. ft.), this high-performance roof lends solace to the worry of rising fuel costs. Not least of all, the increased comfort from a warmer ceiling makes it all worthwhile.

frame roof

Frame

After the roof is stripped, the old surface is sealed with a polypropylene underlayment (rooftopguard.com) and detailed with peel-and-stick bituminous membrane (graceathome.com) along the rakes and eaves to keep the roof weathertight during construction. A new, level 2×6 ridgeboard and rafters then are assembled over the old roof and are attached to the existing structure with nails and lag screws driven into the underlying wall top plates.

spray foam on roof

Foam

Closed-cell polyurethane-foam insulation is sprayed around the new roof frame, sealing edges and providing support for the rafters and the ridgeboard. Plywood sheathing is installed over the rafters and is covered with roof underlayment (bergerbp.com).

Finish

Finish

With the new framework insulated, sheathed, and weatherproofed, roofing can be installed without special detailing. A standing-seam metal roof (englertinc.com) was chosen for its long life and aesthetics, and also because its slick surface reduces the chance of snow accumulation, which can lead to ice dams and leakage.

finished roof


Pete Bennett is a retired engineer who enjoys improving his home in Underhill Center, Vt. Construction by Reap Construction of Richmond, Vt. Photos by the author.

From Fine Homebuilding #190

Fine Homebuilding Recommended Products

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

Staple Gun

Although powered staplers are very popular, you still need a manual stapler on the job site. This staple gun from DEWALT® is reliable and easy to fire, reducing fatigue over prolonged use.
Buy at Amazon

Utility Knife

This utility knife is well-made and comes in handy when cutting rigid foam insulation. You can extend the snap blade to cut through a 2-inch foam board.
Buy at Amazon

Flashing Boot

Adequately seal vulnerable vent penetrations through the roof with this galvanized flashing and flexible rubber collar.
Buy at Amazon
View PDF
Previous: Check the Roof for Square Next: Installing Asphalt Shingles over an Existing Shingle Roof

Guide

Roofing

Chapter

Roof Replacement and Reroofing

Sign up for eletters today and get the latest how-to from Fine Homebuilding, plus special offers.

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

View Comments

  1. lynntmp | Sep 21, 2023 08:33pm | #1

    How thick was the closed-cell foam?

  2. superblueapple | Sep 21, 2023 08:40pm | #2

    You know, if in many other professions the end of your life is rotten unless you know something about home building or really alot about home building or you made a huge amount of money to get it done through a trusted friend. Otherwise, your home is going to fall apart because of all the crooks out there no matter how much work you've paid others to keep it up or down in my case. Lying in bed looking at the sky every night with no roof or a rotten holey one is nice.

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Roofing

Roofing

A complete resource that includes the best materials and the right techniques to build a sturdy, leak-free, attractive roof on any house

View Project Guide

View All Project Guides »

Become a member and get unlimited site access, including the Roofing Project Guide.

Start Free Trial

Tools and Materials
  • Roof Coverings
  • Roofing Materials
  • Power Tools
  • Handy Helpers
  • Staging and Ladders
  • Safety Equipment
Roof Replacement and Reroofing
  • Preparing the Old Roof
  • Sheathing
  • Installing the New Roof
Roof Ventilation
  • Venting Basics
  • Installation
Waterproofing
  • Underlayment
  • Drip Edge
  • Flashing Adjoining Walls
  • Dormer and Skylight Flashing
  • Chimney Flashing
  • Vent Flashing
  • Gutters
Installing Asphalt Shingles
  • Calculating Shingles
  • Layout
  • Installation
  • Valleys
Installing Other Types of Roofs
  • Cedar Shingles
  • Metal
  • Low-Slope Roofs
  • Slate and Tile
Roof Maintenance and Repair
  • Assessing the Problem
  • Repairing Asphalt-Shingle Roofs
  • Other Roofing Repairs

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

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