Base sheet installation

It was time to waterproof our roof. Several days had passed since we tore off the old roof. The dry weather did hold, but we didn’t want to push our luck.

We opted for a modified bitumen roofing system, which I mentioned in my roof insulation discussion. This system consists of a base sheet and a torch down membrane (or cap sheet).

The base sheet comes in the form of 39 inch wide rolls with an adhesive backing. When I say adhesive, I mean aggressively adhesive. I sometimes felt like a fly that got a little too close to a glue trap while working with the base sheet.

To install the base sheet, Pablo, our roofer, carefully lined up the sheet on the roof. The adhesive backing is protected with a light blue plastic cover that is split along the middle of the sheet. This way we could lift one half of the sheet, tear off the protective cover, glue it down, and repeat the process for the other half of the sheet.

The sheets were installed from the bottom of the roof to the top to have the overlap in the direction of the water flow, in the same manner as regular shingles. The base sheets came with markings to facilitate lining up the overlap for each row. This made it easy to keep everything neat and square.

Along the parapet, Pablo pulled the base sheets over the cant strips and terminated them a couple of inches above them.

To assure full contact and proper adhesion, the base sheet gets rolled a couple of times. That should assure a fully adhered roofing system that does not lift off during a storm.

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About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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