huangyhg

flat roof repairs
recently the family "camp" has passed to me. it was built in three phases over the years, a gable roof going north and south, a second addition gable roof east and west and the final, a flat roof going east and west. it is leaking between the second and third sections. as an advanced diy, i intend to reroof it myself. i am looking at the new "rubber" sheet systems as an improvement over the built-up and roll roofing materials. i figure on running the sheet 3-4 feet up the gables and the valley. cost is a concern, and it’s a second home, albeit with sentimental value, so cost is a concern (and i don’t wish to alter the appearance), prohibiting reengineering the roofline to eliminate the flat roof section. suggestions or web sites/books would be appreciated.
thank you in advance. blacksmith

in this site
european standards compare to american about as well as soccer does to football. you don't say where the home is, but it sounds like maybe snow build-up is your problem. if this is the case, you need to roof or flash up the side of the end wall adjacent to the flat roof as high as the snow that drifts against this wall. it would probably be wise to enlist the services of an architect in the design of the new roofing system as the building envelope is an architectural and not a structural concern.
bengineer-
thank you. yes the camp is on the tug hill of nys, noted for an average of 220 inches of snow a year. but the flat roof is about 35 years old and has only leaked for 2-3, so there is hope. i figured on running the new system 3-4 feet up the side of the gable. also, i know we didn't ventilate the flat roof well, part of the addition is an unheated garage, part is a bedroom added in 1970, with insulation and no air space, that's where the roof is leaking. probably "cooked" it in the summer sun until it failed.
blacksmith
flat = bad.
use some tapered rigid insulation to get some positive drainage, then apply your roofing membrane over that. of course, apply flashing accordingly.
flat is not the issue...membrane integrity and flashing tie-ins are critical in this case.
i'm not a fan of "rubber" roofs for a variety of reasons, not the least of which is that i have performed numerous failure investigations on this type of roof system. in consulting on over 15 million square feet of roofing membrane systems, i have seen few "improvements" over the basic built-up roof (bur) system.
the built-up system you have on there is now 35 years old. i would say it has performed quite well, considering you didn't develop leaks until the last 2 or 3 years. considering its performance and age, it is likely a coal tar built-up system.
keep in mind that the bur system offers several advantages...
1)redundancy of plies (if something punctures one ply, you will have others below to resist...not so with a single ply system)
2)ease of repair...readily available and compatible materials at local hardware store to fix in emergency. again, not so with most single-ply systems. in fact, some repair materials, if used on rubber membrane, will destroy the membrane material.
3)track record...your application speaks for itself. i'd be shocked if you can find a rubber roof in your area that is older than 15 years and has performed as your system has.
ron,
thanks. as i hinted in my original post, i think part of the problem is that the flat roof was the last addition and the joint between the adjacent pitched roof and the flat roof is suspect, that's why i want to run the new material or flashing up under the gabled roof. also we did the bedroom conversion and packed the joists with r-25 right against the sheathing, but i was 15 and not an engineer yet. when i get the roof fixed, i'm only using 4 inches and will ventilate the air space above the batts. (can't lower the ceiling, only have 75" now - it’s a camp). what about the use of an "ice dam" rubber membrane under bur or roll roofing? the roof does have a slight drainage pitch.
blacksmith
i agree with the use of an "ice dam", but you can use one of the modified bitumen materials for that (w.r. grace, ice and water shield). your approach to extending the tie-in farther up-slope is good. make your tie-in flexible by using a "dry" sheet right at the transition, below your waterproofing/roofing membrane. wasco and others have good flexible flashings for applications such as this.
regarding ventilation under shingles...that's more an excuse by manufacturers to evade warranty issues than it is an engineering/scientific fact. while "heat sinking" in the shingles does lower their ultimate life, convective ventilation below the shingles does little to lower the actual shingle temperature.
good luck from a fellow diy'er!
ron,
i understand what you speak of when you compare performance records of built-up vs. single ply (epdm) roofs. however, i keep hearing from roofers that in recent years the single ply roofs have used quite a bit of r & d to produce a considerable upgrade in the integrity of these roofs. for the ones you investigated, were they older than say 10 years? have you heard similar information regarding their performance improvements in recent times?
also, fixing a built-up roof requires peeling back multiple layers in staggered sections to allow proper staggering/splicing of new plies. this, assuming you know where the leak actually is.....and with a built-up roof, sometimes its hard to find as the outflow below doesn't always line up with the leak above.
with single ply...yes it only has one line of defense, but you can quickly find the leak. the trick, as you mentioned, is finding the correct patching materials.
i'm not arguing the actual cost/benefit of either system. and i am certainly not a roofing expert, but the above are some pros i've heard for the single ply roof.
jae...newer technology has produced some improvement in the membrane materials but not necessarily so in their seaming techniques and training of installers. manufacturers still "qualify" their installers by financial performance not roofing capability. some of the more "exotic" polymers used to produce roof membranes actually are pretty good materials...the weak link being the manner in which their seams are bonded and their flashing details.
epdm roofs have not improved a great deal since their inception. in some cases, their experimental "improvements" have been disastrous. many of the failures i investigated were 10 to 15 years ago, though have done several in the last few years. one reason i have seen for a lack of complaints with many roof systems is that owners do not keep the buildings long enough to know if the roof is performing properly or not. often failures result in the second, third, or fourth ownership, thus precluding a claim against the original roofer and the manufacturer of the membrane, if either is actually known at that point.
regarding patches to a bur, the process is not to peel back successive layers, but to put back successive layers. finding a leak in a bur is tremendously easier than finding a leak in most single ply systems. since bur's are usually fully bonded systems, leaks don't travel a great deal from their source (there are notable exceptions, but generally this is the case). for fully bonded single ply systems, the same is true. for mechanically attached or ballasted single ply systems, the leak may be in the membrane on one side of the building and show up as a leak in the building on the other side! in short, once through the membrane, it is free to travel laterally until it finds its way into the building.
i know my bias against single ply systems comes through readily. i've just seen too many problems with them to treat them as equivalent to a quality built-up roof system. yes, there are relatively good single ply systems on the market and, yes, there are even ones that i would specify under the right conditions, but as a class of system, i consider them inferior to a quality built-up roof or to a quality modified bitumen system. they are usually much less expensive ($1.50 to $3.00 less per sf than a good bur), and if an owner looks at the cost vs. the expected time he will have the building, they often win.
in developing and following the management of roof systems for several school districts as well as "a major theme park", the owners who will "live with" the building for its life see the life cycle cost benefit of quality bur systems and proper maintenance.
sorry for the diatribe...!
march84 (visitor)31 jan 02 15:05
blacksmith: try searching the website listed below for info and you could post your problem on the forum there for input, as well.
i second the tapered insulation idea, though certainly not the least expensive option. many codes require a minimum of 1/4" / ft slope on any roof.
single ply roofs can be a maintenance headache if they are unballasted and the uv has it's way with the roofing.
how about a gravelled built-up?
good luck! if only your next roof were to last 30 years !!

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