Wednesday, September 7, 2011

What to Consider When Selecting a Roof System (Part 2)

You know you need a new roof, but where do you start? The most common method is to call three roofers to get independant proposals and then compare. But how do you know what to get proposals for? How do you pick a roof system that is best suited to your building? A step-by-step look at the various factors that affect the roof (and the needs of the building) is the best approach to answering those questions.

Yesterday we discussed regulatory requirements, aesthetics and fire codes. Today we will review the importance of the building's characteristics in regards to selecting the right roof system.

Building Characteristics
The building height, floor plate, location on the site, access to the roof, type and slope of deck, amount of equipment on roof and its location, drainage, and even the elevator's availability, load capacity and size are considerations that influence roof choice.

The building height will change the wind loads on the roof and so a roof's uplift resistance may be a major factor. The height may affect accessibility to the roof. This is further impacted by the availability, size and load capacity of the service elevator. If the height of the building or location on the site does not allow for a crane and there is no other way to get materials to the roof and debris off it, the choice of roofing system will be limited to what can be hand carried or brought in by helicopter.

The length and width of the floor plate of the building can also affect the design of the roof. If the building is a large industrial or retail building, the width may be too large to safely run extension cords for heat welding machines or to deliver asphalt to the work area at a hot enough temperature to assure adhesion. The length of the materials delivery run may encourage smaller pieces that can be delivered to the work area by wheelbarrow.

Take note of whether the building has parapet walls (the walls that extend above the roof line). Parapets over 3 feet high will change the wind uplift characteristics of the roof and will also trap snow that can drift above the tops of flashings. Most thermoplastic (TPO) single-ply systems are slippery when wet, so if there are no parapets there is the danger that staff working on the roof after a rain could slide off. The height of the parapet walls can also determine how they are flashed.

Tomorrow we will discuss how an evaluation of your existing roof should affect your decision of which roof system to have installed.

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