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Roofing/insulation for apprentice house
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 2:35 pm    Post subject: Roofing/insulation for apprentice house Reply with quote

I own an apprentice house which was built in 1967. The entire interior is cathedral style with finished cedar plank ceilings. I have the original plans which show the structure as 3" T&G decking, Visqueen, 1" rigid foam insulation, shingles. The house was last re-roofed in the late '90's, well before owning it, but it looks like nothing has changed other than going from wood to asphalt shingles. The entire roof is a 12 in 12 slope. There is no venting or eaves. Being in MI there is obviously severe heat loss which also results in substantial ice dams.

From my research it seems the best way to get this insulated is to use something like a Ray-Core 5.5" SIP (R42) attached directly to the decking. The SIP is sided with the vapor barrier from the factory. It would then get OSB sheathing directly on top of that and then the shingles. Would this be sufficient without having to try and vent the roof? With no eaves I'm hesitant to go down this path by altering the look of the house too much.

The problem I may have is adding this much to the stack height of the roof could interfere with windows that cannot be altered. I'll need to confirm this in the spring when taking measurements is possible. It seems even adding 3.5" SIPs at R26 would be an enormous improvement over what I have now. I've read that the code for my region calls for R38 or R30 if under 500 sq ft. If it is just not possible to get R38 due to the original design of the house I assume any improvement would be accepted by an inspector?

Any thoughts on this approach or other suggestions?
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SDR



Joined: 17 Jun 2006
Posts: 14824
Location: San Francisco

PostPosted: Thu Dec 28, 2017 3:07 pm    Post subject: Reply with quote

"The problem I may have is adding this much to the stack height of the roof could interfere with windows that cannot be altered."

I assume these are second-story or clerestory windows whose sills are a short distance above the present roof surface ?

SDR
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 3:14 pm    Post subject: Reply with quote

SDR wrote:
"The problem I may have is adding this much to the stack height of the roof could interfere with windows that cannot be altered."

I assume these are second-story or clerestory windows whose sills are a short distance above the present roof surface ?

SDR


Yes, that's correct. There's 54 ft worth of clerestory windows running across the front of the house.
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SDR



Joined: 17 Jun 2006
Posts: 14824
Location: San Francisco

PostPosted: Thu Dec 28, 2017 6:11 pm    Post subject: Reply with quote

Perhaps the added material could be tapered below that band of windows, at say 30º, and flashed with color-matched metal. Your 45º roof pitch comes in handy here . . . ?

It is always troubling to contemplate altering the appearance of a significant building. Consistency -- of, for instance, the width of roof fascia -- is the key principal, of course. Others here will no doubt have reliable counsel.

SDR
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 6:47 pm    Post subject: Reply with quote

SDR wrote:
Perhaps the added material could be tapered below that band of windows, at say 30º, and flashed with color-matched metal. Your 45º roof pitch comes in handy here . . . ?

It is always troubling to contemplate altering the appearance of a significant building. Consistency -- of, for instance, the width of roof fascia -- is the key principal, of course. Others here will no doubt have reliable counsel.

SDR


That's a great idea about cutting the SIP at an angle where it meets the row of windows. I do have one other window on the side of the 2nd story where this method probably wouldn't work though since the window faces the side of the roofing that's over the garage.

I'm not crazy at all about introducing a fascia board (there isn't one now) but having essentially no insulation for the roof is causing lots of problems. The first winter of owning the house the ice dams got to be almost 12" thick and there's about 90' of it. Now I know I need to rake the roof when it snows heavily, but if I'm not around when that happens I come home to breaking the ice dams off with a dead blow hammer. It's a ton of work to maintain, not to mention lots wear and tear on the house.

The 3.5" SIP with no venting sure sounds more appealing from an aesthetics standpoint, but there is little point in doing that if it can't solve the ice dam issues. The other option would be to only vent the roof. That would add about 2" of height but would do nothing in regards to making the house easier to heat.
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SDR



Joined: 17 Jun 2006
Posts: 14824
Location: San Francisco

PostPosted: Thu Dec 28, 2017 7:23 pm    Post subject: Reply with quote

I assume there are no gutters, so I'm wondering what the edge of the roof looks like now.

I often post images sent to me by readers, if you do not have linkable pictures to share. My email is below.

SDR
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pharding



Joined: 25 Jun 2005
Posts: 2205
Location: River Forest, Illinois

PostPosted: Thu Dec 28, 2017 7:31 pm    Post subject: Reply with quote

Stacking insulation up is a bad idea. It is better just to use the foam insulation between the joists and keep the roof profile..
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Paul Harding FAIA Owner and Restoration Architect for FLW's 1901 E. Arthur Davenport House, the First Prairie School House in Chicago | www.harding.com | LinkedIn
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 8:35 pm    Post subject: Reply with quote

SDR wrote:
I assume there are no gutters, so I'm wondering what the edge of the roof looks like now.

I often post images sent to me by readers, if you do not have linkable pictures to share. My email is below.

SDR


There are no gutters. A previous owner tacked some up across the rear of the house and it looked awful. I removed all of it except for one run on the back of the garage to keep all the water off a below grade patio.

The edge of the roof ends flush with the siding. There's standard (2"?) drip edge along the perimeter. It's not an ideal design since all the water coming off this large steep roof runs right down the windows. If there were going to be any changes to the roof it would make sense to extend the edge a few inches past the siding.


Last edited by vortrex on Thu Dec 28, 2017 8:42 pm; edited 1 time in total
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 8:36 pm    Post subject: Reply with quote

pharding wrote:
Stacking insulation up is a bad idea. It is better just to use the foam insulation between the joists and keep the roof profile..


That's the thing, there are no joists to do that. There is no air space between the inside finished wood ceiling and the roof.
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 8:48 pm    Post subject: Reply with quote

Here's a picture from the blueprints showing the roof detail at the front of the house.

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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 8:54 pm    Post subject: Reply with quote

And here's the house. The upper row of windows are slightly different now. At some point a previous owner replaced the 1/4" single pane glass with 1/2" insulated. The windows do not extend as close to the roof as shown in this picture.

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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Thu Dec 28, 2017 8:59 pm    Post subject: Reply with quote

Here's a detail of the front of the house for the garage section. You can see this has traditional framing. There are no ice dam issues there.

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DavidC



Joined: 02 Sep 2006
Posts: 6111
Location: Oak Ridge, TN

PostPosted: Fri Dec 29, 2017 10:19 am    Post subject: Reply with quote

One thing you may want to consider if you do go with the SIP's is to remove the existing VisQueen poly vapor barrier. Having two vapor barriers sitting against one another could possibly cause a situation where moisture gets trapped in between them.


David
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vortrex



Joined: 24 Dec 2013
Posts: 59
Location: Ann Arbor, MI

PostPosted: Fri Dec 29, 2017 10:36 am    Post subject: Reply with quote

DavidC wrote:
One thing you may want to consider if you do go with the SIP's is to remove the existing VisQueen poly vapor barrier. Having two vapor barriers sitting against one another could possibly cause a situation where moisture gets trapped in between them.


Yes, would remove everything down to the decking and start over. I'm guessing there will need to be some repairs made anyway. Unfortunately, this house was not always taken care of and has had water leaks in the past. I had a roofer on the house once doing a small temp shingle repair and he says the nails are rusty/brittle, which leads me to believe there's moisture getting trapped in the existing roofing.
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SDR



Joined: 17 Jun 2006
Posts: 14824
Location: San Francisco

PostPosted: Fri Dec 29, 2017 11:36 am    Post subject: Reply with quote

I was toying with the idea that the 3" T&G decking was the interior ceiling surface. Would that construction provide spans like those shown in these realtor photos ?

http://www.wowhaus.co.uk/2013/10/21/on-the-market-1960s-larry-brink-designed-midcentury-modern-property-in-ann-arbor-michigan-usa/

Further inspection of the construction set would clear up the question. I'm scratching my head.

SDR
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