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mfitzsimons 04-20-2009 03:27 PM

Chimney Flashing
We're having a new roof put on our house. Seems that one of the brick chimneys needs some new flashing. We're in Maine, and up here, lead is the most commonly used flashing material. That is what our roofer intends to use, but... Everything I have read seems to indicate that the standard practice is to step flash the shingles, having the flashing extend up the chimney, and then counterflash from the chimney, with the flashing imbedded into the morter lines, and extending over the base flashing on the roof. Two separate pieces of lead. OK, so what our roofer proposes, and what he sayes has worked for him over the years, is having the lead flashing installed as one piece. The topmost part imbedded into the chimney grout lines, and re mortered, and the bottom part directly step flashed into the shingles. There's Grace Ice and Water Shield around the chimney, and that will come up ehind the flashing. I know nothing at all about roofs, but to me, it seems that if the house and chimney move differently, having the flashing attached as one piece as he proposes... things will eventually weaken, and the flashing may pull from the morter. He sayes the two piece method is "the old way"... He seems to have done a good job on the rest of the roof, though, using better quality materials, working neatly, etc. Any thoughts or suggestions? Thanks!

jaros bros. 04-20-2009 06:44 PM

There are hundreds of roofs that have one piece flashings, and for the most part have shed water just fine. However, no professional who does meticulous work would do a one piece flashing in my opinion. Every construction manual that I've ever read uses a two piece flashing and counterflashing. The reason being for the movement in the deck and masonry, more protection against water infilitration, ease of roof replacement down the road. For what it's worth, I have never liked the lead, but in your neck of the woods copper is the only other alternative and that cost a bit more. Two step flashings also take more time and require a little more finesse.
One piece is probably the norm where you are so unless it's spelled out in the contract for a two piece, that's what you're getting. If you want a two piece, ask for it, and if need be throw in $100 extra for his labor and material. Most contractors don't mind the extra work and are glad to negotiate.

Ed the Roofer 04-20-2009 09:12 PM

If a one piece chimney metal flashing is used, there will be movement between the two separate structures and either the portion connected to the shingles will pop up the fasteners or tear the lead, or the embeddment into the mortar will be tugged at suffiently enough, to prematurely loosen the seal.

Depending on how much mivement your home experiences, it could wind up looking like 99% of all of the older chimneys, which have roofing cement caked on to try to inhibit the influx of leakage.

No specifications from either the NRCA or SMACNA advise a one piece system, nor do any of the shingle manufactuers written instructions.


mfitzsimons 04-20-2009 09:37 PM

Thanks for the replies. I guess my suspicions are confirmed. If we're going to go to the trouble of having the flashing redone - which is needed in the first place because an earlier job wasn't done properly - I think we'll just ask our roofer to humor us, and use the two piece method, even if it costs a bit more... By the way, he's charging us $300 for a one flue chimney. Does this seem reasonable? I think it is, but again, we've not got all that much experience with all this. Again, thanks for the advice!

Ed the Roofer 04-20-2009 10:00 PM

It depends on th e pitch of the roof and what the man values his craftsmanship at what type of wages get paid in your area.

I charge slightly more, but I think that when things are done the Right Way, it merits the value provided for a long term solution.


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