Originally published in Interiors & Sources

09/10/2008

Roof Surveys and Plans

By Richard L. Fricklas

 

When the building owner does not wish to face the expense of removing superfluous equipment, polyurethane foam can be sprayed over the units and associated ductwork, serving as an air barrier and as thermal insulation, reducing heat loss dramatically.

If equipment removal cannot be readily or practically performed as part of routine maintenance, it almost certainly makes sense prior to any reroofing operations. Roof-deck manufacturers and deck-trade associations (e.g. Steel Deck Institute and National Roof Deck Contractors Association) provide guidelines on how to fill in the gaps to make the deck level and remove and replace damaged decking. The profile of the existing deck needs to be established (see Fig.1) so that, when unneeded equipment is removed, you have replacement decking with the same profile on hand so it will nest with the adjacent decking. Finding replacement types A and F deck, however, can be a challenge, and special accommodations using more readily available, type B deck will be required.

Many existing roof decks have inadequate slope. Ponding is undesirable on all roof systems. Locating puddles on a roof plan where they remain for more than 48 hours after a rainstorm may indicate where drainage needs to be addressed. (Some authorities recommend only dealing with standing water that remains after 48 hours; some exert requirements that are more stringent.) One option is to add new roof drains or to reset existing drains so water can flow freely off of the roof. Another option is to look at where the water is impeded. Saddles (see Fig. 2) can be constructed on the upstream side of curbs to deflect the water around the obstructions. Tapered roof insulation, plywood, OSB, fabricated metal diverters (on metal panel roofs), or even tapered spray-in-place foam can resolve some of these issues, at least until reroofing is done. At that time, thermal insulation will probably be needed to meet the new energy codes, and tapered materials can be easily added.

The question comes up: What do I do if existing windows or doorsills are too low to accommodate thicker insulation layers? Creating new valley lines and rows of drains is one option. Another option is to not elevate the thickness of roof insulation all the way to the wall, but to treat the first 4- to 6-foot width as a separate roof area with its own drains and install raised curbs just beyond this area that are fully elevated (so that the rest of the water is flowing away from the curbs, perhaps toward a newly created valley-line).

Some years ago, most building codes called for a minimum of a 0.25-inch-per-foot slope, tempering this somewhat for existing buildings where increasing slope would be a burden. Nowadays, the codes require positive drainage. If a roof is ponding 48 hours after rainfall has ceased, one could conclude that drainage is not positive (even if the roof intended to have a 0.25-inch roof slope). With this new definition of positive slope, installing tapered insulation needs to be sufficient to overcome slope loss from deck deflection. Crickets and saddles should kick water away from obstructions; the new valleys formed by insulation build-up require positive slope to drain as well.

What are the objectives of all this mapping and inspection?

  • It’s easier to associate defects on the roof with active leaks.
  • It enables development of long-range (and immediate) financial plans for roof maintenance and replacement.
  • It enables corporate management to objectively compare roof conditions (i.e. using ROOFER) between all buildings in the inventory, and to prioritize repair or replacement.
  • It enables comparisons of performance between differing roof systems to determine which are actually providing the lowest life-cycle costs and enable realistic estimates of roof life.

For building managers, consideration should be given to establishing an in-house roofing expert. Some of the courses from the now-defunct Roofing Industry Educational Institute are available through the National Roofing Contractors Association, including Roof Inspection, Diagnosis and Repair. The NRCA also has a maintenance manual for low-slope roofing, which was developed in cooperation with the Asphalt Roofing Manufacturers Association (ARMA) and the Single Ply Roofing Industry (SPRI). Educational programs are also available from the University of Wisconsin-Extension (e-mail hmartin@dcs.wisc.edu for more information) and RCI, as well as from major roofing manufacturers.

Meanwhile, if you do not have current roof plans and a program for roof inspection, maintenance and replacement, what better time to create one than now?


Pages: 1  2  View All  
 

 
Noteworthy Design News
12/18/2014
12/16/2014
12/15/2014
12/11/2014
12/10/2014
comments powered by Disqus
©Copyright 2014 Stamats Communications, Inc. All rights reserved. / Interiors & Sources