Roof Replacement Process

A roof replacement, often called a re-roof, removes or covers the existing roof covering and installs a new one. The broad sequence is similar worldwide, although the materials, codes and trade terms differ by country. On a typical pitched house roof the work moves from the bottom of the roof (the eaves) towards the top (the ridge), so that each layer sheds water over the one below.

The steps below describe a common steep-slope (pitched) replacement. Low-slope membrane roofs follow a different but parallel sequence of deck preparation, insulation, membrane and flashings.

Planning and approvals

Work starts with an inspection of the existing roof, measurement of the area, selection of the new covering and a check of local rules. Many authorities require a permit for re-roofing, and some set limits on how many layers may remain on a roof. A written contract and the manufacturer's installation instructions define what will be done.

Typical sequence on a pitched roof

1. Site protection. Set up fall protection, ladder access, debris chutes or bins and protection for gardens, walls and gutters.
2. Tear-off. Remove the old covering, underlayment and worn flashings down to the deck, unless the code and conditions allow an overlay.
3. Deck inspection and repair. Replace rotten or delaminated sheathing and re-nail the deck where needed. Building America guidance for existing homes recommends checking that the roof plane is flat, because sagging can point to structural problems.
4. Eave and edge details. Install ice barrier where required by climate, drip edge and any deck-seam sealing.
5. Underlayment. Lay underlayment over the rest of the deck, lapped so water runs over each lap.
6. Flashings and valleys. Line valleys and prepare step, apron and penetration flashings so they can be woven into the new courses.
7. Starter course and field. Install the starter course at the eaves and rakes, then lay the main courses at the specified exposure and nailing pattern.
8. Ridge and hips. Cap hips and ridges and install any ridge ventilation.
9. Clean-up and inspection. Remove nails and debris, then arrange the final inspection where a permit applies.

Regional differences

In North America, decks are usually plywood or OSB sheathing and shingles are nailed through to the deck. In the UK and much of Europe, tiles and slates are commonly hung on timber battens over a breathable underlay, and fixing is specified under national standards such as BS 5534. In Australia and New Zealand, metal sheet roofing is widespread and is fixed to purlins or battens.

Daily weather protection

A roof under replacement is vulnerable to rain. Roofers normally strip only as much as can be made watertight the same day and use temporary membranes or night seals at the end of each shift, a practice the Canadian Roofing Reference Manual identifies as essential.