Roof Replacement


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Old 12-17-03, 03:00 PM
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Roof Replacement

Hello to all: It is time to replace our roof. I am currently working with a contractor (not a roof contractor but has done roofs before), who I think is an honorable person and willing to listen to suggestions. I would like to review the plan for our new roof in this forum and ask for your input. Thanks, here goes:
Our post and beam log home in Vermont is a modified cape with 2 full length shed dormers and a central chimney. Total square footage of the roof is 1,031. The dormer roofs which cover the majority of the area, are a 4-1/2/12 pitch. The original pitches at the gable ends are 10/12, which are about 3ft. wide. The house has cathedral ceilings upstairs (no attic or crawlspace at all). The existing roof consists of the following materials: Hand peeled pine timbers 3ft on center, 2X6 tongue and groove decking, one layer of 2in. rigid foam insulation with foil coating, asphalt shingles nailed directly on top. No ventilation, no vapor barrier. Ice dams have been a recurring problem on the dormer roofs.

The new roof proposal is to remove the asphalt shingles, retaining the 2in layer of rigid foam, add another 2in of rigid foam, Plywood decking, cover with bituthane (Iím guessing this is what you call ice and water shield around here), then architectural shingles. No extra insulation is proposed for the gable ends, where only about 1ft of the roof is actually over the heated living cavity and the rest is rake eave. No reflashing of dormer walls at gable ends. No ventilation. Suggestions please? Thanks, CT
 
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Old 12-17-03, 03:20 PM
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Replace all the foam insulation. Once it gets wet it is garbage. There is a special type of insulation, I believe you have installed. It's sole purpose is to be an insulated nailing base for cathedral ceilings. I'm at home now so I can't look up the name but I will tomorrow. You shouldn't need a plywood decking if you use this kind of insulation.

On your dormers install at least 6' of ice shield. Also install your asphalt shingles on the dormers, with a 4" exposure instead of 5".

On the steep slope areas you can get by with 3' ice shield and a 5" typical shingle exposure.

Tomorrow I will look in my National Roofing COntractor's Manual and tell you exactly how they suggest a roof be installed to your situation.
 
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Old 12-17-03, 04:13 PM
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Roof Replacement

Thanks for the quick reply, Grampy. I guess my main concern with this job is that I not have ice dams in the future. It's very bad the way it is now. Is there a way to do this without venting? I want this roof to last and not have to shovel it all the time like I'm doing now. I was considering one or two inch strapping, decking, vented drip edge and a continuous ridge vent. Does this sound like a feasible plan? CT
 
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Old 12-18-03, 07:16 AM
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Ice dams result from heat loss through the roof. The conventional way to fix this is to provide enough insulation to reduce the heat loss and use venting to dissipate the remaining escaping heat, before it reaches the roof surface. In your case, with cathedral ceilings in your dormers you will need additional insulation to compensate for the lack of ventilation. I'm don't know which brand and type of rigid foam insulation you are using, but the rigid insulation we have from Dow Corning has about R-5 for each inch. In Vermont, the desired R-value for cathedral ceilings is 38, so you would need about 8 inches of rigid foam insulation to take care of this - the 4 inches you're thinking of using won't be enough.

I don't feel comfortable with not having a wood deck surface. I would prefer to see 5/8" plywood sheathing installed over the insulation, then the Ice&Water sheild membrane (Grace is my preferred brand), and then the shingles. If you use enough insulation, then Grumpy's suggestion of at least 6' coverage by I&W membrane at the eaves of the dormers should be sufficient. Otherwise, I would cover the entire dormer surface with I&W membrane, and also run it along the end-walls. I would also suggest flashing the end-walls (where the vertical walls of the dormers meet the steep roof), to give you additional protection. Maybe it's overkill, but our roofs don't leak, and we have similar weather conditions to what you experience.

Finally, you may wish to consider a metal shingle or panel system, which would allow the snow to slide off the roof, and provide less material for forming ice dams. These come in steel, aluminum and copper, and there are a variety of manufacturers who can supply you. Of course, the cost is more, but you are trading up-front expenses for longevity and performance.
 
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Old 12-18-03, 07:31 AM
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Lightbulb Ice dam

You could put up some Thermwire Melt It a snow and ice melting cable there on the roof Its made by Chromalox ED
 
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Old 12-18-03, 06:25 PM
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product and Intall Options

Thanks to all for the input so far. I'm still hoping to hear from Grumpy after he consults his books. I payed a visit to the local building supply store and was shown an interesting product. It is by Atlas Roofing and called the Vented R. or Cross vent Nail Base Insulation. This is a prefabricated 4X8 sheet consisting of "polyiso insulation board with 1", 1.5" or 2" vent spacer strips separating a 7/16" APA/TECO rated OSB (I think the staff called it Aspen board) from the polyiso foam insulation to create a cross ventilating airspace..." It is .. "designed for use over sloped uninsulated roof decks." Has anybody used this product and what do you think? If I get the 5.5" nominal thickness with the 1" vent space and install it over my 2" of existing rigid foam, I would, according to the brochure, have an R value of 25 + 14(for the 2"), which would bring me up to code, right? But they say a lot about vapor barriers under the polyiso foam and I'm wondering, since I have no vapor barrier now, how to incorporate a vapor barrer with this system. Can anyone tell me if they've used it? Thanks, CT
 
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Old 12-19-03, 04:51 AM
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Yes, we've specified Atlas (and comparable other manufacturer's) on our commercial projects and it works just fine. You may still get some minor ice dams, but it shouldn't be bad at all. The trick is to pay attention to the roof edge details so the air can get into that vent space at both top and bottom of the roof; also, our Atlas catalog says they reccomend the 1" air space.

You're on the right track for the total R value you are looking at. The problem you have is that the vapor barrier really should be directly on the deck. Grumpy is right, if any of that old insulation is wet, it's garbage. If it were me, I'd just bite the bullet and take off all the old insulation, put the vapor barrier where it belongs, and put down the new nail base insulation. You're going to spend a lot of money on this roof, why take a chance just to save a few dollars?

The Atlas web site is {www.atlasroofing.com}. I haven't been on their web site, but I would hope they have suggested details that you coud adapt for your project.

Just my 2 cents worth.

Bruce
 
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Old 12-19-03, 07:53 AM
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Insulation Garbage?

Thanks for the replies. I'm getting conflicting opinions regarding the 2 in. foil faced insulation I now have down on the deck and am considering whether to keep it or not. Most of this material hasn't been wet, only along the eaves and in another couple of problem areas. The vapor barrier is another problem. An Atlas tech person suggested I take up the 2in and lay the vapor barrier, then put the 2in. back down. At that point I could replace any of the 2in. that looks like it's crumbling or swollen, etc.. Then the cross vent goes down, taking care to stagger the placement over the layer underneath, to avoid thermal bridging. What other condition problems am I looking for in this material (the 2in. foil wrap stuff)? Why are you sure it's all in bad condition? It was installed in 1984. Thanks again for all the good imput, I've learned a lot from this forum. CT
 
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Old 12-19-03, 11:16 AM
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I guess I didn't mean to infer that all the existing was in bad shape, I just thought you should take it up to get a vapor barrier directly on the roof. If you can remove the existing, put down a vapor barrier, then re-set the existing, then there's no reason to trash it, other than the stuff that shows signs of damage.

If the insulation you have now is foil faced both sides and you re-use it, I would suggest that you punch the foil that faces up full of small holes to be sure you aren't dealing with a double vapor barrier ( the foil acts as a vapor barrier).

Bruce
 
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Old 12-19-03, 05:47 PM
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Vapor Barrier

Wow! I wouldn't have thought of punching the upper sides of the foil wrap. Great idea. This would also allay my concern that water had wicked into the material from the edges and the foil barrier had retained it. I think I may have the information I need to create the design now. If anyone has any other ideas that haven't been covered here they think I should consider, please post it. Thanks much, CT
 
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Old 03-28-04, 08:57 PM
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Roofing Qoute/Vapor Barrier

Hello again, I'm hoping this message will connect to the thread I began back in December. I have a few more questions. First, What should I use as a vapor barrier and how do I install it on the tongue and groove decking? How do I seal the pieces of vapor barrier together?

The other question is this: it is hard to get roofers out to even look at this job and I have only received a quote from a general contractor. Here's his breakdown (As I calculate, this roof is under 11 square) Could you tell me what you think of the price?:

Strip one roof layer and dispose of shingles- $1800
Remove current 2" insulation, install vapor barrier and replace 2" foam (does not include new 2" foam if needed) $2400
Install 6-1/2" cross vent on dormer $4350
Trim roof $1850
Install new shingles according to manufacturer, new drip edge and ridge vent $3600
Added cost for 4" exposure on dormers $1300
Added cost for 6-1/2" cross vent on 10/12 pitches $2000

Total: $17,300.00




Thanks, CT
 
 

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