Built-Up Roof: A roof consisting of multiple plies of roof felts laminated together with bitumen. Built-up roof material can consist of bitumen-saturated felt, coated felt, polyester felt or other fabrics. A surfacing is generally applied and can be asphalt, aggregate (gravel or slag), emulsion or a granule-surfaced cap sheet.

This section was written simply to give people an idea of what a Built-Up Roof (B.U.R. for short) is and how it’s put together. The materials and information listed here are not comprehensive nor do they represent all types of built-up roof materials available.

Built-Up Roofing is one of the oldest and most reliable ways of installing a new roof. It was first known as composition roofing and started in the 1840's. B.U.R.’s come in two basic types, asphalt and coal tar, and three basic components – (1) the waterproofing component, (2) the reinforcing component, and (3) the surfacing component which is used to protect the other components from the elements.

There are many different types of materials used in Built-Up Roofing. Check Here

A built-up roof can be installed over just about any type of roof deck as long as the proper substrate is used. BUR's can't be mopped to a wood roof deck. In this case a rosin sheet and base sheet are needed first. With steel roof decks, the thickness of the deck should be a minimum of 22 gauge and some type of approved insulation should be mechanically-attached to the deck to provide a substrate. Manufacturers should be consulted before mopping to Polyisocyanurate ("iso" for short) insulation. Many manufacturers will not warrant a roof if the felts are mopped directly to the iso and a coverboard such as wood fiber or perlite is needed. In some cases adhesives are being used to attach the insulation to the deck but be sure the roofing materials manufacturer is consulted before this is done. With structural concrete roof decks, the roof is often mopped directly to the deck after it's cleaned. Sometimes a thermal insulation is used to provide a substrate. Thermal insulation can be attached by mechanical means, adhesives, or even hot-mopped. If the insulation is hot-mopped with bitumen, then care needs to be taken so as not to allow the bitumen access to the interior of the building at joints in the roof deck. Also, if Isocyanurate insulation is used, only 4' X 4' sheets can be mopped due to its propensity to warp and curl. With lightweight insulating concrete, pre-cast gypsum panels, or poured gypsum, venting base sheets are attached with special fasteners and then insulation may or may not be installed over the base sheet and then the roof membrane installed. In some cases a vapor barrier will be necessary. Built-up roofs cannot be mopped directly to lighweight insulation or gypsum. Cement fiber roof decks should have a base sheet or insulation mechanically-attached to it before installing the roof. Insulation should be installed in two layers with all joints offset and staggered a minimum of twelve inches.

How long do the last?
The service life of a roof is dependent on many factors: geographical location & weather conditions, foot traffic, materials used, conditions under which the roof was installed, slope of roof, type of surfacing material, etc. Under ideal conditions, a 3-ply built-up roof should last at least fifteen years, a 4-ply should last at least 20 years, and a 5-ply should last at least 25 years. This author has seen ten year old 4-ply roof that needed to be replaced and twenty year old 3-ply roofs that were still functioning.