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Old_school (Old_school)
Senior Member
Username: Old_school

Post Number: 676
Registered: 01-2009
Posted on Saturday, August 06, 2011 - 11:30 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

If it can't "breathe" in, it can't "exhale" out.
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Newengroof (Newengroof)
New member
Username: Newengroof

Post Number: 1
Registered: 08-2011
Posted on Tuesday, August 02, 2011 - 04:09 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

i'm repairing an existing slate roof for a cathedral ceiling. old roof shingles were mortared and no ridge ventilation. needless to say there was a moisture problem. currently has high back copper gutters. in addition to adding a ridge vent should there also be any type of 'drip edge venting' or soffit venting?
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Timtrain35 (Timtrain35)
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Username: Timtrain35

Post Number: 4
Registered: 03-2011
Posted on Friday, April 01, 2011 - 04:20 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Who said anything about fireproof? And how would you adhere the rigid to the underside of the roof deck?
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Lucerne96 (Lucerne96)
Junior Member
Username: Lucerne96

Post Number: 19
Registered: 03-2011
Posted on Friday, April 01, 2011 - 01:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Who recommended fiberglass? I would recommend rigid insulation as far cheaper than sprayfoam. If you want fireproof, use foamglas.
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Timtrain35 (Timtrain35)
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Username: Timtrain35

Post Number: 3
Registered: 03-2011
Posted on Friday, April 01, 2011 - 12:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Exactly my point, as stated previously. There needs to be an adequate amount of SPF in order to prevent condensation from happening. If you ventilate the roof deck, there's no point in using SPF, it's a waste of money. The SPF insulates more effeciently than fiberglass because, at the correct thickness, it also acts as an air barrier. It performs exactly what your theoretical wall will do, which is seperate the inside from the outside effeciently enough where there aren't any condensation issues or need for ventilation to counter act condensation. Condensation occurs when warm, moist air comes in contact with a cold surface. The SPF insulates effeciently enough where this isn't possible. You're thinking you need the ventilation because this condition will be present. With fiberglass, you would be correct, however this isn't fiberglass. Check the data for yourself as far as what the R value is for SPF per inch versus fiberglass (although just looking at R value doesn't give you the whole picture, but that's another arguement).
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Lucerne96 (Lucerne96)
Junior Member
Username: Lucerne96

Post Number: 18
Registered: 03-2011
Posted on Friday, April 01, 2011 - 11:20 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Returning to the original question.

If you use spray foam insulation on the underside of the slate, you are, in effect adding a vapor barrier to the underside of the roof. If the SFI is of insufficient U value (ie. not thick enough), then the dewpoint will be on the surface of the foam insulation; you will have condensation. This condensation will lead to mold growth.

So, to prevent this scenario, you need to either have alot of insulation (in Philadelphia area, the standard here is R-70 ceilings, R-50 walls; and/or CONSTANT ventilation.

European Passivhaus standard buildings feature both in a shell that is extremely airtight (max .6 ACH @50 Pa vs US average of 10 to 12 ACH @ 50 PA. This is part of the reason that they are built without the need for a primary heating system.

I would think a better solution would be to build a super insulated, thermally bridge free, interior wall with a vapor barrier on the warmside & provide for ventilation air to flow between the underside of the roof & the interior wall. It is really extremely difficult to retrofit a truly airtight vapor barrier.
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Timtrain35 (Timtrain35)
New member
Username: Timtrain35

Post Number: 2
Registered: 03-2011
Posted on Friday, April 01, 2011 - 08:26 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Lucy, if the house is that poorly built, then you've answered your own question. If the whole house is sealed up tight, then the HVAC system needs to introduce the proper amount of fresh air into the structure and ventilate. This is usually done with an ERV. However, is it's just the attic, then the typical exhaust fans located in the kitchens and bathrooms should suffice.
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China_ad_slate (China_ad_slate)
Junior Member
Username: China_ad_slate

Post Number: 13
Registered: 01-2011
Posted on Friday, April 01, 2011 - 02:53 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Who do know West Europe and North American market of roofing slate??? what quality do they nee? S1 or S2??? And their market price... It will be appreciated.
Nancy Rao
Shanghai AD slate Co., Ltd
ASTM-S1/EN12326 T1 S1 A1
Roofing slate manufacturer.
WEB: www.cnslate.com
TEL: 86-21-61910796
FAX: 86-21-62199550
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China_ad_slate (China_ad_slate)
Junior Member
Username: China_ad_slate

Post Number: 12
Registered: 01-2011
Posted on Friday, April 01, 2011 - 02:52 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Who do know West Europe and North American market of roofing slate??? what quality are suitable for them? S1 OR S2???
And their market price... It will be appreciated.
Nancy Rao
Shanghai AD slate Co., Ltd
ASTM-S1/EN12326 T1 S1 A1
Roofing slate manufacturer.
WEB: www.cnslate.com
TEL: 86-21-61910796
FAX: 86-21-62199550
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China_ad_slate (China_ad_slate)
Junior Member
Username: China_ad_slate

Post Number: 11
Registered: 01-2011
Posted on Friday, April 01, 2011 - 02:50 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Who do know West Europe and North American market of roofing slate??? what quality do they nee? And their market price... It will be appreciated.
Nancy Rao
Shanghai AD slate Co., Ltd
ASTM-S1/EN12326 T1 S1 A1
Roofing slate manufacturer.
WEB: www.cnslate.com
TEL: 86-21-61910796
FAX: 86-21-62199550
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Lucerne96 (Lucerne96)
Junior Member
Username: Lucerne96

Post Number: 17
Registered: 03-2011
Posted on Thursday, March 31, 2011 - 08:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Timmy; I think this is a retrofit of a existing, poorly built standard US house; not a european Passivhaus standard building.

Unless you totally gut the building; deal with the inherent thermal bridging issues; and provide proper ventilation, you will have problems with moisture if you are in a climate with winter.

How can you not? Where is the moisture you put in the air from cooking, showering, breathing etc. going to go? As soon as the warm interior air of the conditioned space begins to cool, it will give up the moisture.
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Timtrain35 (Timtrain35)
New member
Username: Timtrain35

Post Number: 1
Registered: 03-2011
Posted on Thursday, March 31, 2011 - 04:46 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Wrong. If the dew point calculation is at the roof deck, then you didn't figure on enough foam insulation. The dew point should occur within the insulation. Fiberglass thinking doesn't apply to SPF in regards to vapor barriers in cold climates, the SPF is so much more effecient than fiberglass that it doesn't need one, when applied at the correct thickness. The ventilation for the roof deck is also incorrect. On big selling point for using SPF to insulate is that it seals off all points of air infiltration. You seal the attic space to make it part of the building envelope, regardless if it gets finished or not. As far as having an unvented deck with a slate roof, well, the jury's still out on that one because of the relative "newness" of SPF versus slate. However, shingle companies are starting to come around and still honor their warranties when an unvented, SPF insulated attic assembly is used. Make sure your client uses the proper amount of SPF, professionally installed (no DIY kits) and stay away from "hybrids" and "flash and batt" systems.
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Lucerne96 (Lucerne96)
Junior Member
Username: Lucerne96

Post Number: 16
Registered: 03-2011
Posted on Wednesday, March 30, 2011 - 09:37 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Assuming you live in a climate with winter; the problem will be that the dew point will be the underside of the roof if there is no vapor barrier keeping the warm moist air from coming into contact with the underside of the roof.

What you want is a vapor barrier on the warmside of the roof, before the insulation; with ventilation airflow between the insulation & the shell of the building.

see this... http://www.inspectapedia.com/Energy/Dew_Point_Calculation.htm
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Mjpl (Mjpl)
New member
Username: Mjpl

Post Number: 2
Registered: 03-2011
Posted on Wednesday, March 30, 2011 - 04:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

I have a home owner with a 3 year old slate roof, with gable end vents only, on butted 1x 8s and 30 # felt, I&W on eaves and valleys. He is in the process of finishing out the attic space, and is planning to use spray on foam insulation. What, if any, ventilation concerns should he have.

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