Flat roof repairs 1

[TheBlacksmith]

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

 

[ishvaaag]

In this site

http://www.eota.be/html/endorsed.htm

you will find up to date downloadable european standards ETAG 005 and ETAG 006 that may be of your interest (plus other as well interesting on other subjects)

 

[bengineer]

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.
Another important point to remember is not if a flat roof will start leaking, but when it will start leaking.

 

[TheBlacksmith]

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

 

[LPPE]

Flat = bad.

Use some tapered rigid insulation to get some positive drainage, then apply your roofing membrane over that. Of course, apply flashing accordingly.

 

[Ron]

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.

 

[TheBlacksmith]

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

 

[Ron]

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!

 

[JAE]

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.

 

[Ron]

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...!

 

Blacksmith: Try searching the website listed below for info and you could post your problem on the forum there for input, as well.

http://www.taunton.com

Click on Fine Homebuilding, then on Breaktime.
Membrane roofing is pretty good these days, the problem areas tend to be the seams. I'm guessing you could get a seamless installation given the size of a "camp" building. Membrane manufacturers have their own fastener and drian details. Check those out as well.

 

[StephenEd]

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 !!

 

[Trussdoc]

Is it possible that instead of leakage, some or all of the water problems in the flat roof may be caused by condensation in the unventilated space?

 

[Ron]

Trussdoc...it does happen, but usually not the primary source of leaks.

 

[Taro]

No, condensation is probably not the most common source of leaks, but it does happen. My firm investigated leaking and deterioration in the wood roof of a winery a few years back. We discovered that there were no roof leaks. The problem was water vapor originating from inside the building, rising to the roof, condensing, and getting trapped above the batt insulation that was installed on the underside of the roof framing.

 

[TheBlacksmith]

To bring up to date. My roof is definitely leaking; the water came in very fast during a rainstorm. My Dad and I placed a large tarp over the bad section and now we get one bucket of water or less per rainstorm versus half a dozen buckets. The roof does slope approximately 1/4 inch per foot. (The bedroom is at the low end, hence the limited headroom.) I am thinking of the original conclusion, strip to bare wood, water dam style membrane for insurance, 3 layer roof cement and 15# felt BUR, then provide periodic maintenance - another layer of felt and cement as the top weathers, but before it deteriorates too much. Cost is an issue - this is a second home and the roof isn't the only repair for this year.


Blacksmith

 

[Ron]

Blacksmith...take a look at using a torch-applied modified bitumen or a cold process modified bitumen roof. Similar to built-up, but uses stronger material. You could probably get by with a two-ply system for this if you put a simple base sheet ply directly onto the wood deck.

I would not suggest a three-ply system with roofing cement as the interply bonding agent, unless you have done some roofing before. If you do it, use a squeegee to get a thin, consistent coat of roofing cement under the entire felt. Coat the entire surface with an aluminum emulsion coating, after the roofing cement bleed-out has cured out a bit. If you put the aluminum emulsion on too soon after placing the roofing cement, the cement will bleed through the aluminum emulsion.

Add an extra ply at all flashings.

Good luck.
Ron

 

[thaidavid]

TheBlacksmith,
We deal with ancient flat-roof repairs all the time here at Redstone Army Arsenel. Our solution: retrofit a conventional steel-framed pitched roof over them! I don't know if this option is open to you, but consider it for a long-term solution.
David

 

[TheBlacksmith]

Finally fixed the roof (was sick last summer). Used the torch-down recommended by several people, with the ice dam membrane in critical areas and a tie in between the two roofs (there wasn't one under all the tar and patches. There was a line of thunderstorms the afternoon after we finished all the details; nearly 1 1/2 inches of rain and not one leak! Thanks to all who gave suggestions.

Blacksmith

 

[Ron]

Hey Blacksmith....glad to see it takes you as long to get the "Honey-do" list done as it does for me. Way to go!