What things to know a new Modified Roof?
Part 3 of 5 to my “Re-Roofing Event”:
Late next week the 1-1/2-12 pitch roof on the patio is getting replaced. The roof framing is 2×6 on 24″ centers with half the porch having doubled 2×6’s for possible future solar hot water panels. The max open span is 12ft between home’s 2′ overhang and tripled outside wall header. The original decking is 1/2″ CDX. The overall size of the patio roof is 16′ x 44′. The current hot tar roof is 14 yrs old but has never leaked. Although it has that “Alligator” look….
I’m leaving the old roof intact and 2-2/2 weeks ago rolled-on/sealed it with 10 gallons of non-fiber asphalt. New 1/2″ CDX was nailed through the old roof and into the rafters and covered with 30# felt.
I’m told it is to be hot-mopped on a 43# base sheet nailed to the new decking and felt, and topped the Cedar colored Modified Bitumen.
What will I expect to see, and what should I lookout for, as this roof is put on the patio?
Thanks so much for your help,
Bill
Edited 10/12/2008 4:30 pm ET by BilljustBill
Replies
Sounds like you are adding a lot of weight to your old roof. Did I get that right ... on top of your old roofing ... addiing sheathing and new roofing to it? and your span for 2x6 @ 24oc is 12ft? or was it more? you said 12 in one place and a 16 ft size in another ... not sure what I read. Maybe you're stressing the structure a bit? That's my reaction. ... but it's a little late, too ... so take it w/ a grain of salt.
Thanks for you info. The open patio 2x6's are attached to the house wall with Simpson hangers and also sistered to the 2' overhang rafters of the house. The open span starts after the house overhang and is 12' to the triple 2x6 header and extends 2' passed it. That header is supported with six 2" steel pipe columns on 8' centers. Half the length of the 44' long patio have rafters are side-by-side doubled.
The clarification change anything?
Thanks,
Bill
Since you have no snow loads to be concerned with, I don't think the extra weight is a concern.
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Don't know. 12' span for roof load on double and single 2x6. No snow loads. Didn't ping the concern of other posters. You might just check a roof joist span table to see if you are well w/in the limits. I'm not a structural expert. 2x6 aint a whole lot, but it's only a 12 span. No real feel for it really. These other guys got more experience seeing stuff like that I suppose. But I I think I would consider the span starting at the face of the wall, not on the tail of the eave/joists. While the connection is OK, I don't think I would consider it a 'bearing point'.
The labels on the base sheet will specify that it is 43# base. It will feel thicker than 30# tarpaper and have a slightly gritty feel to it.
biggest concern would be how it is nailed on. When I was doing this, the plasti-cap nails were forbidden, because the plastic can melt from the hot tar, leaving you with nothing much holding it in place. Since the mod-bit top surface is attached to t he 43 base sheet, there is then nothing holding much on. Preferred methods were to use tin tabs and nails, a metal type of the cap nails, or to spot mop the base sheet down to the deck, but you already have 30# interferring with that last choice. I suppose it is possible that new pasticaps have been developed that hold under hot tar, but I think not.
The other concern is detailing the edges and flashing, but there are so many ways of attending to that, I hesitate to start...
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you forgot burning the house down.
carpenter in transition
I think I recall that in some other thread, he had mentioned they were planning to use hot instead of a torch to mop this modified down. I don't understand that, but figured there must be new or diff methods since I got out of BUR
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There's no way to do BUR except with a kettle, but there is cold process modified. Instead of a torch, you use a heat gun. I went to the school a couple of years ago and basically wasted a day. I haven't found an application for it yet, that I can't do with a different product. The big sell is that you can buy different colors to match your shingles, but the two times I wanted something other than black, I had to buy way more than I needed 'cause nobody stocks it around here.View Image
So if they are telling him they are hot mopping on a modified, that suggests that they are applying it off-label, or that they are hot-mopping 90# roll and calling it modified.
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I've seen some companies hot mop 1 layer before installing modified. Don't know the spec on it, but they hot mop and come back later to install the modified. I guess they're using the hot mop as base sheet.View Image
i have had modified put down a couple times,they hot mopped it down,one crew did a real nice job with the mop another slopped tar all over the exposed part,looked pretty tacky.if a man speaks in the forest,and there's not a woman to hear him,is he still wrong?
We used a Tremco cold applied BUR two years ago on our Data Center.
http://www.tremcoroofing.com/products.asp?pselect=1#1
Same step by step process as the hot mop, but know hot tar smell. The guys installing don't care for it a whole lot because it is slower and messyier then a hot mop. Has the same warrenty as the hot mop Tremco BUR, as long as you continue to purchase extensions, and they inspect annually.
Any idea what your type of roof cost was a square?
I remeasured my patio roof and deducted the house roof 2' overhang's tie-in that was shingled with the GAF impact shingles.
So, it's 6.5-sq.s of my patio comes to about $468.50 a square which includes 43# base sheet, perimeter metal and rolls of modified Bitumen top granulated sheet. It's to be hot tar applied.
Does that seem like a high cost?
Bill
Edited 10/16/2008 1:11 pm ET by BilljustBill
What we had done was a commercial roof on our Data Center. In fact it wasn't in the budget to do the whole roof, so they just did half of it. I could round up the numbers, but they would not be comparable to what you are having done. Our building is a 35' to the top of the parapet wall and has a structral poured concrete deck.
I was just pointing out that Tremco does have a cold applied BUR that is an alternative to a hot mop BUR. We had the same cold BUR put on our main office building about 10-12 years ago. Thus far I can't see any differance in preformance between it and a hot mop BUR.
I expect the cost is higher for the cold BUR. It is slower and thus more labor intensive than a standard BUR.
Dave is right, a large commercial can be done much less expensively than a smaller portion of a residential.And you don't get 6.5 squares. You get 7 - possibly more with tie-ins.
I wouldn't have set up hot mop for less than $300 a square twenty years ago, so with all costs gone up since then, your calculated price sounds fair, if you calculated right.
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