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Thread: Historic home roof insulation solution

  1. #16
    Quote Originally Posted by Tom M King View Post
    Why not insulate at the ceiling joist level. We found a 1980 standing seam roof over an 1851 Cypress Shingle roof. I wouldn't spray foam against the wooden shingles. Not that it matters, but I doubt they're Cedar. Not sure about what was used up there in 1842, but around here everyone that doesn't know better also calls them Cedar Shakes.

    "Shakes" is probably a 20th Century term. Back then, they were all made by hand, including splitting, but they were called shingles.

    Here's a link to the page on my website about that roof we found. You can see the old roof in the first three pictures, which include one edge of the metal roof on top of the shingles. http://historic-house-restoration.co...sShingles.html All those pictures are thumbnails. You can click on one, and get a full sized version.

    Historic Associations don't like spray foam, but they're fine with the way we do it by wrapping a vapor barrier over, and between ceiling joists, and blowing in insulation. The blown in stuff can be removed later without damaging any of the original parts.

    It was not unusual for these old wooden shingle roofs to last 150 years. These days, they've engineered the life out of them by interlacing rows of tar paper. If one is put on according to specifications by the Cedar Shingle and Shake Bureau, they typically last about 35 years. The old ones would have lasted longer than that, had the fasteners not started to fail. The reason there were enough buildings left standing to save in the restoration of Colonial Williamsburg was because they still had the original Cypress shingle roofs on them.
    Tom, would you mind elaborating a bit on this method? Do you mean essentially insulating the ceiling of the third story/attic, and the leaving the sloped side walls without? Or enveloping the “room” space from above the ceiling joints and down along the sides with a vapor barrier, then filling the space between the vapor barrier and backside of drywall or plaster board with loose cellulose?

    The issue of moisture and roof venting comes from the conditioned spaced being exposed to the unconditioned space at the roof sheathing, correct? Moisture laden air permeating the plaster and insulation and then condensing on the cold roof sheathing. So if the conditioned spaced was completely sealed from enveloping from above with a air-impermeable barrier, the roof can stay invented. Is that right?

    I try my best to make nothing irreversible. I love the idea of it being easily removed in the future. Even the thought of spraying synthetic foam against 180 year old beams makes me cringe.

    Great website by the way and thanks for the clarification regarding shingles

  2. #17
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    Not getting a mental picture of "sloped sidewalls". Is there space between the ceiling joists, and rafters being used for living space? I'm not sure if my Insulation page makes anything clearer, or not. It's been years since I've worked on that website. Just a few days ago, I found hundreds of old pictures on old hard drives. I may have some pictures that can clarify.

  3. #18
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    There was a similar ventilation issue with that 1828 house on the Insulation page. Here's a picture that shows the gable end vents I added. There was no ventilation to start with, but also no insulation. The fourth floor is used in that house. There are knee walls under the rafters, and a short, flat ceiling below that gable vent.
    Attached Images Attached Images

  4. #19
    Quote Originally Posted by Tom M King View Post
    Not getting a mental picture of "sloped sidewalls". Is there space between the ceiling joists, and rafters being used for living space? I'm not sure if my Insulation page makes anything clearer, or not. It's been years since I've worked on that website. Just a few days ago, I found hundreds of old pictures on old hard drives. I may have some pictures that can clarify.
    sorry that was misleading. I just meant the walls, which in my case are sloped because they are against the roof rafters. Here is a photo. DC5395FF-5271-45DF-A14E-CA457AC260B7.jpg

    The third story isn’t very big, and I’d hate to lose any more cubic footage by dramatically extended the depth of the rafters, also because the chimneys are butted up against them.

    Your website is great. I see you or someone on your team can perform traditional plastering - something I’ve been fascinated by. I’ve attempted to skim coat with lime and have failed miserably.

  5. #20
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    My "team" is me, and two guys that no one else would hire, that can almost read a tape measure, if they work together.

    I have a method for skim coating old plaster, with nothing but finish plaster, without using Plaster Bonder. You will read everywhere else that it can't be done.

    That attic level looks very similar to the house in my picture. Will be off, and on here today, without much time to spend on it.

  6. #21
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    Quote Originally Posted by Dan McGonigle View Post
    I had read that closed cell foam has a maximum thickness spec. Such that it cannot be installed in greater thickness than “x” (I believe it varies, maybe based on climate?). Did I read that wrong?
    There's no maximum thickness relative to ability to apply it. We have 10+ inches of it in the roof of our major addition...at R 7.5 per inch, that's not too shabby and it made the attic "conditioned space". That said, there are diminishing returns with closed cell spray foam beyond 6" or so due to the cost of material and application. In some circumstances to fully fill a given area, 2-3" of closed cell is applied and the remainder of the space is filled out with fiberglass or rockwool for cost reasons. But in other situations, the spray foam is the way to go because of fit or difficulty getting other materials in, etc. Every situation has to be judges by itself. In your home, you have 6" joists and then purlins---you have nearly 8" for the foam. You have enough space to meet or get very close to the new-construction specification without adding any sticks to the rafters.

    Relative to venting, someone who knows what they are doing can replace the current cap with a vented cap and it will not stick up much more or at all from what you are used to. Modern materials permit airflow while closing off the venting to critters. They will just have to trim the steel back a little more than it likely ise now and slice out the cedar parallel to the ridge line before installing the new cap. You also need to vent the soffits to complete the task and with traditional insulation methods, you'll need baffles (air channels) up each rafter bay on the underside of the roof deck to keep insulation from closing off the venting. *** If you do the spray foam, you eliminate this work and the cost may very well cover the premium cost of the spray foam while getting you much higher R-value than you can get with anything other than closed cell spray foam. ***

    To your question posed to Tom about the envelop, yes, you want the entire envelope around what will be essentially living space insulated. In space like this, the "roof" is also the walls in many situations. That means you insulate the roof (ceiling/walls) as well as the end-walls of the gables, etc. If you do install knee walls, you can technically stop the roof insulation there and then come down the knee wall, but the floor (ceiling of what's below) would also need to be insulated to complete the envelop. Assuming the space is all open now, it's easier to do the envelope all the way to where the roof meets the outer limits of the space, even if you intend to install knee walls. In fact, that makes it easier to embed storage in those knee walls because there's no faddling around with insulation in the knee wall, itself. Many folks like to do cabinets and drawers in knee walls because otherwise, it's wasted, non-walkable space.
    Last edited by Jim Becker; 01-16-2021 at 9:41 AM.
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  7. #22
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    couple more pictures of up there. I also had to figure out a way to get real ductwork in the house, without being visible other than the registers, and not using the small, high velocity stuff.
    Attached Images Attached Images
    Last edited by Tom M King; 01-16-2021 at 11:12 AM.

  8. #23
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    The screen was so we could see what was going on when the insulation was blown in, and to let air out. Over that went the vapor barrier. The plywood had enough fasteners in it to hold it in place. The plywood was because I had to squeeze in there, and didn't want splitters in my back. We insulated the hell out of it everywhere we could. Between the rafter at the roof slope was the only place that we just had to accept what we could get. Baffle stapled to roof sheathing from soffit up to open air above the 24" of insulation on the flat part of the ceiling.

    The metal shingles were already on that house when we started to work on it, and being a museum house, no place for a ridge vent. They want me to put a Cypress shingle roof on it, like it had originally, but I'm 70 years old, and have more work lined up than I can possibly ever get done. I only work within 10 miles of home. I'd like to think that I will get to it, but have other, more important things on the to-do list.

  9. #24
    Thanks. I’m getting a better idea of the system. I’m currently looking into a product called “Intello” - claiming to be a “smart” vapor barrier that allows one to use traditional batt or fill insulation without roof venting.

    Again, I’m really impressed by the work you’ve done. I’d love to focus more on historic preservation. Thanks for all your input.

    In hindsight, I should have never preemptively contacted my building inspector. I normally wouldn’t, but was planning on getting a small dumpster for the some of the work and I know several people in town are friendly with him. In fact, my father was the inspector for a few of the surrounding towns and knew my towns inspector very well. I hope that grants me some leeway!

  10. #25
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    Dan, it's an attic, not an occupied space, at least for your use. Staple some fiberglass batts in the purlins and include a moisture barrier to keep moisture from the house out of the insulation. Then drywall it. Even without any heat it will stay above freezing in the coldest weather. You will want some ventilation in summer. A gable vent on the south or west end and a powered one on the north or east end that you close for winter would make it a really good space to store crafty stuff for your kids to go thru someday.

    In the meantime, lath and plaster might be fun.

  11. #26
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    With no venting, it's critical to use an insulation method that is designed for that situation to avoid what can be serious issues over time.
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