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Spider2k (Spider2k)
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Registered: 10-2015
Posted on Tuesday, October 20, 2015 - 05:18 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Another question....

I have a 1932 home with a gabled slate roof and a "finished" attic. I've attached a picture of it. It has a floor and is finished with Celotex panels, an early version of fiberboard. There are eves but they are solid wood and not vented. There is one gable fan but no vents. Two old drafty windows in the other two gables. It's slate on wood. No tarpaper. The attic was not insulated (except that Celotex) until I added some last year when I reacted to my heating bills at $400+ for a 1800 square foot home. I had bat insulation added behind those Celotex panels, which now are up against the slate roof. I'm now thinking that was a mistake, as I've screwed up the air circulation for the slate. Even before I added the batting, I had huge ice dams form on the eves. Long story short: How can I lower my heating bills and/or fix the ice dams? I'm thinking of removing the bats and laying them on the attic floor. I use the floor for storage, but I think I could live without it. When I get central AC, however, the attic is where the air handler will reside. House is in Mid-Atlantic.

Any budget-friendly suggestions?

(Message edited by spider2k on October 20, 2015)
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Brycenesbitt (Brycenesbitt)
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Registered: 08-2012
Posted on Wednesday, October 14, 2015 - 11:09 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Bill B: could you upload a sketch of the roof? Details matter.

Basically every part of a building needs to be able to dry out, and to equalize in humidity. If you put foam below the rafters then one system needs to dry to the inside of the attic, the other through the slate to the outside.

Don't have two vapor barriers: inevitably the space between will get moist and never dry properly.

Ceiling insulation could work, with a vented attic above. Use http://www.slatespacer.com/ to increase venting.


Trapped water will even rot stone (the idea behind slate spare is to dry the stone).
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Bill_b (Bill_b)
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Posted on Wednesday, October 14, 2015 - 02:08 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Question,

We are building an addition on to an older fire station, which has a slate room which seems to be in good shape. The City wants to use slate on the new addition to harmonize with the existing slate. Excellent decision I think. But,I have to insulate the new roof. We are using wood trusses and solid t&g deck and I would love to spray foam the underside of the deck, but there is a lot of conflicting information about venting the deck versus not venting the deck under slate. Any thoughts? This is in North Carolina.
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Elizebethwoodhall (Elizebethwoodhall)
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Posted on Tuesday, March 11, 2014 - 07:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Jamesriverarchitectscom liked the solution you shared with us. Just one thing I was wondering whether it works for open celled spray foam insulation?
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Bob_wewer (Bob_wewer)
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Posted on Thursday, November 07, 2013 - 11:30 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

The most critical element here is the moisture. You should not look to ventilation to cure a moisture problem any more than you would look to Ice and Water Underlayment to cure a leak. Deal with the moisture. Whether you foam against the roof deck and just make the attic conditioned space or deal with the moisture at the ceiling level, keep the moisture in its vapor state on the living side of the insulation. The whole ventilation craze (and ventilation is a good thing) started with the fiberglass roofing shingle. No longer a two part asphalt but just the adherent asphalt (cause fiberglass mat cannot be saturated)the shingles were susceptible to heat and had to give off that heat to the inside of the attic. The ventilation craze started with tighter homes (good thing) but with bypasses in retrofit situations, concentrations of moisture pushed upward and condensation occurred.
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Steveb (Steveb)
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Posted on Tuesday, September 04, 2012 - 02:59 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Todd,

That roof design still isn't going to breath even with those spacers. The air under the exposed sheathing is stagnant because there is no push from below or inlet.

These houses were never designed for air movement. The only way is to build a secondary roof and vent the whole thing. That probably isn't going to be done so as long as you have real boards up there you won't have to deal with it in your lifetime. If its plywood then it will deteriorate eventually.
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Branden_wilson (Branden_wilson)
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Registered: 03-2008
Posted on Wednesday, February 15, 2012 - 10:59 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

" I am much more concerned with leaks going undetected and where rot can occur."

that's exactly what happens with these modern "advancements". trouble is, all the contractors will be pushing these new techs and when they create new problems and you are in what old school refered to as the "reaction" stage, the contractors will sell you another new tech to "alleviate" that problem. sounds like you are protecting yourself and your client from this type of destruction by objective evaluation and truth searching. all the best, branden

REAL SLATER
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Old_school (Old_school)
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Post Number: 673
Registered: 01-2009
Posted on Saturday, July 30, 2011 - 03:26 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

If you have two of the eyebrow dormers, (we could only see the one in the picture) why not install a exhaust fan in one and let the other become an intake and allow for the cross ventilation? Not perfect mind you because they are designed to let air out, but you may be able to install a screen in front of the one that the air will be coming in on to deflect the water. If there are any other areas where the air can "intake" the fan will draw it in and mix with outside air.

You may be able to erect several "baffles" in the attic to make the air move in a circuitous pattern through the attic to move the air around to where you want it. For instance, it the vents are directly opposite each other the air would flow from one to the other, and with this method, you could make it go down to the floor and around before it made it out the other vent via the fan. Just a thought. Sounds like they have created their own monster. Oh, and as Joe said on the other post, fix the missing slates.
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Old_school (Old_school)
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Posted on Saturday, July 30, 2011 - 07:04 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Interesting, I read and answered the post on the the other topic you posted and then I came to read this and it is exactly what I thought. For every action, there is an equal and opposite reaction, and they are getting their "reaction" on this roof now. If the nails are dripping water (read the moisture has no where to go and it is condensing on the cold metal of the nails) and the wood is wet, the house is rotting in place as we speak. You have to get the moisture out! Is there a humidifier? Can it be turned down a bit? Are they venting the bathrooms and such directly outside, or into the house envelope? Did they replace the windows and such when the house was redone? If so, they stopped areas where the house vented (it was drafty and venting itself) Quite a can of worms. It may be that the only answer now is to try and seal the envelope of the house and cross your fingers. It is tough to retro the old houses without causing a lot of problems.

If you are free next week, you should drive down to Landcaster PA and come to the slate convention and talk to us. There will be a lot of different slateres ther and we love to talk slate.
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Jamesriverarchitectscom (Jamesriverarchitectscom)
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Posted on Friday, July 29, 2011 - 11:13 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

I have a very similar conundrum for a project in the Mid-Hudson Valley. I am consulting for a historic home with a slate roof that was put on only 7 years ago. It looks great at first blush, but there are a lot of the basic errors that Jenkins talks about. The protruding nails drip condensation from the warm moist attic air that has no where to go thanks to the total blanket of ice and water shield. The first slate contractor brought in to look at the issues of random broken slates and a leak in the valley suggested spray foam.

As in Todd's example, there is spray foam installed at knee walls, a cathedral ceiling, and at a spire- the slates in these areas don't appear to be any worse for the wear. My big concern was for the boards in the deck. I can assure you that the closed cell foam is not perfect, and therefore is not air tight- air being the vehicle for water vapor which condenses on the cold nails and underside of the underlayment.

I am very concerned with the wholesale sprayfoam insulation approach. I am leaning toward having the insulated attic floor thermally scanned to find gaps in the foam insulation and to have a vent added at the top to help the small eyebrows vent the space better. I am also certain that I will have an insulated hatch cover put over the access to the attic- currently closed off with only an interior door at the bottom.

I am not as concerned with small areas such as the knee walls not being vented as hopefully there can be some drying laterally, and the painted ceilings help reduce vapor drive. I am much more concerned with leaks going undetected and where rot can occur.
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Old_school (Old_school)
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Posted on Wednesday, July 13, 2011 - 08:56 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Todd, I believe you are wrong on that. Air movement is the most critical component you are dealing with in this instance. You are going to be spending a LOT of money trying to save money, and I think you will eventually (sooner than later) end up with a hell of a mess and then the bills will really start to come in.

Step back a bit and think this thing through. What is the expense, what is the potential payback, and what are the risks? I can tell you what the results are going to be before you do it, but you seem to be a very intelligent person that has time and thought invested. I have been there and done that on other things and the results were bad. Take some advice on this one and save yourself a lot of hassle.
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Toddmanqa (Toddmanqa)
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Posted on Wednesday, July 13, 2011 - 09:47 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

The slate that is over the section of the roof that has spray foam applied to the underside of the solid lumber roof deck has had no problems. That being said, it's only been in service for a few months.

In regards to the question posed by 'Old School', in which he asked why I don't just open a window and install my AC unit up in the attic, the reason is that Albany, NY, experiences great temperature extremes depending on the season. If I put my second AC unit/furnace and supply vents in the unconditioned attic, I'd lose an enormous amount of energy due to extreme heat and extreme cold.
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Timtrain35 (Timtrain35)
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Posted on Wednesday, July 13, 2011 - 07:51 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

In my opinion, you're asking for trouble with that confined 2" airspace. What you risk doing is having the dew point occur within that void and nowhere to go. To try and verify this, you could (or have someone) perform some modeling on your roof assembly. That will take into account your particular climate zone and the specifics of the materials used. You can google WUFI and there are a couple of online tools you can use to do it yourself, but it's not a task for the faint of heart.

I understand you want to be energey effecient, but if you're not going all out with SPF, you risk doing more harm than good. BTW, how's the SPF performing on the other section of roof? How's the slate on that section?
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Olde_mohawk_masonry__historic_restoration (Olde_mohawk_masonry__historic_restoration)
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Username: Olde_mohawk_masonry__historic_restoration

Post Number: 162
Registered: 04-2007
Posted on Tuesday, July 12, 2011 - 07:00 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Todd,

Some Joe Jenkins knowledge I've never forgotten: "You want a slate roof to be water tight, not air tight." Once you stop the roof from breathing moisture will have trouble escaping from behind the slate.

I've pulled slate off roofs in the Capitol Region in which the attics were spray foamed five or less years ago. Slate are found to be delaminating, roof deck rotting and steel nails rusting. Yeah, you'd like to think they used copper nails 80 years ago. Betcha they didn't.

We slated a new education center in Rotterdam Junction this past Fall. When we returned in the Spring to lay up the brick and stone some spray foam clown was there filling the space between the rafters. He stopped me to ask how the roof was going to breath, since there was no ridge vent. "It's not going to breath," I snapped.

Needless to say I wasn't consulted in the design phase.
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Old_school (Old_school)
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Posted on Tuesday, July 12, 2011 - 05:42 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Question, why do you need to have the space "conditioned" to install the Ac / heater in the attic? I would think you would be better off just opening up one of the widows up there and putting a screen over it and leaving it open all the time, and THEN install your units in the space. Unless there is a specific reason to do so, I believe you are making more problems than what you started with.
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Toddmanqa (Toddmanqa)
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Posted on Tuesday, July 12, 2011 - 03:01 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Adding PDF file of roof diagram for those who can't read the TIFF file.
application/pdfroof diagram-pdf
roof diagram.pdf (71.5 k)
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Toddmanqa (Toddmanqa)
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Posted on Tuesday, July 12, 2011 - 02:59 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only) Ban Poster IP (Moderator/Admin only)

Background - 80 year-old, 2-story Colonial in Albany, NY, with Vermont green slate over 1" solid-lumber roof deck with ~1/8" space between the roof deck boards. Appears to have tar paper over roof deck/under slates.

The roof is un-vented at the top and there is no overhang at the eaves. In fact, the second-floor ceiling was raised for additional headroom, and part of the roof joists impinge on the edges of the room (as part of the original house construction).

To place a second air conditioner/furnace in the attic, I want to bring the attic into the conditioned air space. To that end, I am in the process of adding tongue and groove plywood to the attic deck and wanted to get advice on insulating the roof joists.

My initial plan was to spray the space between the roof joists with closed-cell spray foam, but I abandoned that idea due to the excessive cost of the spray foam (about $1.00 per board foot).

I then opted to use a combination of DOW Extruded Polystyrene (about 50 cents per square foot) and the spray foam to seal the edges of the foam to the roof joists and get an airtight seal.

However, my research has indicated that the solid lumber boards under the slate/tar paper need to breathe.

Question - Would the following configuration work?

2x2" squares of insulation glued to the underside of the roof deck spaced about two feet apart. Then, two layers of the 2" sheet foam glued to the spacers and then the edges and ends sealed with spray foam. See option 1 in schematic below.

Note: One of the rooms already has spray foam in the angled portion of the second floor roof and in its walls.

Follow-up question - If the answer is no, the airspace alone is not enough, and fresh air is required, what about drilling some air holes in roof joists in the planned two-inch air space area, and then venting to the side of the house? See option 2 in schematic below.
image/tiffroof diagram
roof.TIF (87.8 k)

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