Table 11-1. Typical Code--Allowable Reroofs Over Existing Roofing

CEMP-ET

TI 809-53

01 May 1999

Table 11-1. Typical Code--Allowable Reroofs Over Existing Roofing

(Inspection and Written Approval Required by Code Official Prior to Application)

New Overlay Roofing

Built-Up

Wood

Asphalt

Tile

Metal

Modified

Shake

Shingle

Roof

Bitumen

SPF

Existing

Roofing

Built-Up

Yes

NP

Yes

(3:12)

(2:12)

(2.5:12)

1

2

Wood Shake

NP

Yes

NP

1

3

4

2

Yes

Wood Shingle

NP

Yes

NP

(4:12)

3

4

Yes

NP

Asphalt

NP

Yes

1

(4:12)

(3:12)

(2.5:12)

Shingle

2

Asphalt Over

NP

Yes

NP

Wood

Asphalt Over

NP

Yes

NP

Asphalt

Tile Roof

NP

Metal Roof

NP

Yes

NP

Modified

Yes

NP

Yes

NP

Bitumen

(3:12)

(2.5:12)

NP = Not Permitted

Note: (Minimum Roof Slope)

1

See specific requirements

2

Board and batten leveling system must be firestopped

3

One layer 500 mm (18-in.) Type 30 nonperforated felt interlaced between shake courses required.

4

Type 30 nonperforated felt underlayment required for reroofing.

b. Climate/Weather. A complete tear off requires good weather as the building is occupied and

nightly tie-offs are not perfect. The demands of protecting the building sometimes result in accepting

phased construction especially when a thicker insulation system is being added and it is unfeasible to run

from eave to ridge in a single day.

(1) Nightly Seal-Off of New Penetrations. When new structurals are added it is necessary to

carefully seal where the anchor bolts penetrate the old roof system. This seal might be little more than

asphalt mastic (figure 11-2). Verify that the old drains are in working order until the new sloped roof and

associated drainage system is completely functional.

(2) Upgrading Insulation. Adding new insulation and/or an air space above the existing roof will

change snow-melting characteristics and will generally reduce, not create vapor condensation problems.

c. Logistics. Tear off is complicated especially if asbestos-bearing materials are present or if landfill

or recycling rules and regulations require separation of construction materials. Chutes are efficient for

material removal provided that dust management is used. Vacuuming of aggregate-surfaced roofs prior to

tear-off removes a great deal of surface dirt as well as loose aggregate. Staging of new materials is

11-2