Built Up Roofing

8/7/2019 Built Up Roofing

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You know what it’s like when you’re

old and reliable. People are alwaystrying to nd something better,even while they take you for granted andkeep coming back to you when they needsomething they can count on.

Built-Up Roo ng (BUR) systems areused to it. People have been doing it tothem for more than 160 years.

For a at roof that achieveswaterproo ng and drainageexcellence, it’s hard to beat a

multilayered system whosecornerstones are among the mostwater-resistant combinations knownto man – asphalt and coal tar.

So why does it get such eetingrespect?

“We’re seeing built-up go to sleepfor a little bit, waiting for the next bigfailure,” said Mike Brigham, founder of Mount Ranier, Maryland-based Built-Up Roo ng Systems. “It has a history of

going away for awhile and then coming

back. People who believe in it strongly –school systems, municipalities – believein hot, rubberized asphalt.”

BUR dates back to the 1840s, whenit was known as composition roo ng.

e concept was so basic and viable thatit rose to capture more than 90 percent of the at-roo ng market by the 1960s. Butthe emergence of other systems, along

with a decline in workmanship amongBUR practitioners, saw the method’smarket share decline in the 1970s to aslow as 40 percent.

e key to BUR’s strength and

durability lies in the fact that all plies of

the roof are fused together into a single,monolithic barrier that applies to theentire surface.

at eliminates numerous problemsinherent to other systems, including:

No need for fasteners, which create•

additional risk of leakage.No need for ballast, which is o en•

laid loose in the form of stones andcan be blown o by heavy winds.

Less movement in the form of •

expansion and contraction, whichleads to buckling, ridges and splits.

Roo ng elongation does notcreate an alarming risk of leakage so

long as the roof maintains its elasticity.e problem arises, however, as roofs

age and become more likely to pull away from themselves during expansion.

e key to long-lasting water-

Built UpRoongBy Dan Calabrese

The key to long-lasting water-resistance is to install a roof that limits movement and maintains its elasticity.

22 WATERPROOF!



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resistance is to install a roof that limitsmovement and maintains its elasticity.

e idea of a BUR system is to attack the problem on both ends. First, BURsystems are designed to limit movementwith high tensile strength well beyondrecommended industry standards of 200 pounds per square inch. Second, theblending of all materials in a monolithiccompound preserves elasticity far longerthan single-ply roofs. At the sametime, single-ply membranes essentially o er just one shot to stop a leak. If themembrane is compromised, water willget through.

When roo ng contractors installa BUR system, they fuse the multipleplies together with hot-mopped asphalt,resulting in a compound that self-adherescompletely to the roof at all points.

e natural water-resistance of asphalt only adds to the BUR’s systeme ectiveness as a waterproo ng strategy – estimated at ve times the water-resistance of a typical single-ply system.

Basic installation of a BUR systeminvolves the following steps:

Base sheets are mechanically •

fastened, generally nailed, to thedeck or substrate.Felts are installed with either hot•

asphalt or coal tar. You can alsouse a cold-applied liquid adhesive,sometimes known as solvent-basedasphalt or cutback asphalt.Application of hot asphalt runs at•

20 to 25 pounds of coal tar per 100square feet between each ply, orthree-to- ve gallons of cold-applied

adhesive per square.For the surfacing, install a cap sheet•

with the same amount of bitumenor lap cement as is used to installthe plies. en apply a ood coatof roughly 60 pounds per squareof asphalt or 70 pounds per squareof coal tar. en embed 400-to-500pounds per square of gravel, or 300to 400 pounds per square of slag.

For emulsion surfacing, use aboutthree gallons per square and apply analuminum re ective coating a er theemulsion cures to re ect UV rays.

You can install a BUR on just aboutany type of roof deck, but you don’t alwaysdo it the same way. You need to knowsome basic di erences for applicationwith di erent types of decks, including:

You can’t mop a BUR system to a•

wood roof deck without puttingdown a rosin sheet and base sheet.Steel roof decks need a thickness•

of 22-gauge, minimum, along withsome approved insulation, whichshould be mechanically attached tothe deck to provide a substrate.Before you mop felts directly to•

polyisocyanurate insulation, besure the manufacturer will stillwarranty the roof. You might needa coverboard, such as wood beror perlite, in order to preserve thewarranty. e same goes for the useof adhesives to attach insulation.

Check with manufacturers rst.e BUR system is o en mopped•

directly to structural concrete roof decks – a er the deck is cleaned –although you can use mechanically attached thermal insulation as asubstrate. But with lightweightinsulating concrete, as well aspre-cast gypsum panels or pouredgypsum, you’ll need to attach venting base sheets with fasteners,a er which you might installinsulation in between the basesheet and the roof membrane.Cement ber roof decks will•

de nitely need a base sheet orinsulation mechanically attached.

As a general rule of thumb, a BURroof lasts longer if it has more plies –although that is obviously impactedby outside factors such as climate, foottra c, materials used, workmanship androof slope.

E cient drainage is crucial to theoverall e ectiveness of your BUR system.

Spring 2008 23



e design of the deck and roof substratemust drain to enough outlets – situatedin the right spots – to remove water suchthat it can never pond longer than 24hours.

Many roo ngsystems aredesigned withintegral drainagechannels, butcontact betweenthe membraneand the insulationcan impede water ow. Installers shouldtake care to ensure that the nishedroof membrane has su cient slope tominimize the amount of water retaineda er rain.

Steve James of St. Petersburg-based Florida Southern Roo ng saidthis old system is regaining momentum

partly because of improved materials,particularly berglass felt.

“ e biggest improvement of latehas been the berglass felt as opposed

to rag felt,” James said. “ is goes back a few years, but combined with properpractice and old-school workmanship,you get what you get with a built-up roof – a good many years of service with areasonable price tag.”

Brigham says roofers are takinga heightened interest in new roo ng

materials – not only berglass felt but a variety of hybrids and other new options.He worries, however, that they are notalways doing so for the right reasons.

“Architects,it seems, overthe years havelost sight of whatthey’re really buying,” Brighamsaid. “Now some of them are buying awarranty instead of

a roo ng system.”e proven nature of BUR systems,

combined with the constant quest fornew concepts, is creating new marketopportunities for those ready to seizethem.

Carlisle, Pennsylvania-based CarlisleSynTec o ers a variation on the BUR that

Reective Roof Coating

Asphalt

Ply Sheet

Cover Board

Asphalt

Rigid Roof InsulationDeck Surface

The proven nature of BUR systems,

combined with the constant quest for new concepts, is creating new market opportunities for those ready to seize them.

24 WATERPROOF!



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Waterproofing

System.

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Designed for use as part of a completewaterproofing system from W. R. MEADOWS,MEL-DRAIN is the ideal choice for enhancedwaterproofing and positive drainage protection.Used as part of a worry-free, single-sourcewaterproofing solution, MEL-DRAIN incorporatesa high compressive strength core combined

with a varied selection of geotextile facingsto suit specific project needs. Its high flowcapacity prevents clogging and relieveshydrostatic pressure buildup. Use MEL-DRAINas part of your next waterproofing system.

it calls FleeceBACK. e product wasintroduced 13 years ago.

It features multiple membranesand is promoted as having outstandingUV- and ozone-weathering ability, aswell as an ability to last 50 years withoutdropping below 200% elongation.

“Built-up roo ng has been around along time, and you have building ownersout there who may have had a satisfactory experience with them, so they’reinterested in going back to that multi-layer approach,” said Ron Goodman,FleeceBACK product manager forCarlisle SynTec.

“ at would be one market driver.Another one we run into is compatibility with existing asphalt roofs. Buildingowners are looking to conserve costsand extend the life of the existingroof. Either they have an existingsmooth built-up roof, where we can goin and put on an EPM or TPO cap sheetthat’s hot-mopped to the smooth built-up roof.”

One variable among BUR systems

usually depends on geography. BUR

systems in the south most likely includea white-re ective roof – which fends o UV rays and reduces air conditioningusage in the building. BUR systems inthe northern U.S., by contrast, are morelikely to be dark colored so as to helpretain heat.

e currently heightened interestin energy-e ciency is helping to drivethis trend, particularly builders’ interestin seeing their buildings certi ed underthe U.S. Green Building Council’sLeadership in Energy and EnvironmentalDesign (LEED) Program.

On the surface, you might say,

BUR systems seem relatively foolproof,which is probably why the concept hasremained in use for the better part of twocenturies.

But the success of any particularinstallation always depends on the rightmaterials, the best workmanship and asound design. As more roofers masterthese techniques, BUR systems improvetheir chances of being around a century from now.

Spring 2008 25

Built Up Roofing

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