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Community and Q&A

Post your cut-and-cobble stories

User avatar
Martin Holladay | Posted in Energy Efficiency and Durability on

I have decided to write an article on the topic of Cut-and-Cobble Insulation. Even though I sometimes scoff at the technique, calling it an unprofessional method beloved by homeowners, I must admit that I have used cut-and-cobble myself. Sometimes, the method makes sense.

For those who don’t know, the term refers to the insertion of strips of rigid foam between studs or rafters. Each rectangle of rigid foam is sealed at its perimeter with caulk or canned spray foam.

So I’m asking for help.

1. Please post your cut-and-cobbles stories here — failures as well as successes. Would you do it again? Why?

2. Send me your cut-and-cobble photos. Post them here or e-mail them to me: martin [at] greenbuildingadvisor [dot] com.

3. Did Dana Dorsett coin the term “cut-and-cobble”? Or did someone else invent the term first?

4. Can you think of ways that cut-and-cobble might be risky or lead to failures?

All cut-and-cobble anecdotes will be cheerfully and gratefully received.

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Replies

  1. Ron Keagle | | #1

    The problem with the “cut and cobble” method of installing foam board is that it might not fit well. That requires sealant or adhesive to hold it in place and to seal the joints. The joints can leak, either at the outset from misapplication of the sealant/adhesive, or from the sealant/adhesive subsequently cracking from wood movement and a loose fit with too much reliance on the sealant/adhesive. The sealant/adhesive is also hard to apply because the joint is telescoping, so it tends to wipe the sealant/adhesive out of the joint as it is assembled.

    It is possible to cut and fit without the cobbling. This requires more care in the fitting, but it eliminates the need for sealant/adhesive, thus saving its material cost and effort to apply. The non-cobble method also results in a much more reliable joint seal and secure hold. With this precision method, the sealant/adhesive can still be used as a backup, but a much smaller quantity will be required. And since the sealant/adhesive is applied after the foam is telescoped into position, the application is much less effort and much more accurate.

    The non-cobble method requires the friction of an interference fit. The one requirement for an interference fit is that the framing members are parallel, or close to it. XPS lends itself to an interference fit particularly well because it is slightly compressible. You cut the foam on a table saw; taking the measurement with a tape, and then guesstimating a little interference when setting the saw fence.

    Then tap the foam into the telescoping fit with a hammer or mallet and piece of plywood to spread out the impact. Don’t go too far because you cannot pull it back. I would tap it in until the outer surface is maybe ¼” past the outer surfaces of the framing members. That way, you can be sure it won’t interfere with the drywall. Getting the proper fit by measuring and setting the table saw is surprisingly easy. Sometimes it pays to use a sanding block to break the edges of the foam board that will lead as the foam is telescoped into place.

    Placing the foam slightly deeper than the framing also leaves room for a fillet bead of sealant/adhesive. And the bead can be easily placed because the nozzle can be dragged right along the tiny inside corner of the recessed foam fit. For this, I would use either XPS compatible mastic adhesive or silicone, and not spray foam. If necessary, you can drag your finger down the wet bead to tool it out into perfect continuity and compaction. The bead can be very small because it can be precisely placed, and is only functioning as a sealant, and not to structurally retain the foam.

    Older construction presents a couple of problems. One is that the framing members are often not parallel, and the other being that the lumber is sometimes full dimension with rough cut and/or irregular surfaces. The rough and irregular surfaces require more care in the fitting, but the main problem is the non-parallel members. I have less experience in fighting that problem, but if one were doing a production job involving a lot of bays, some type of angle fixture could be made for the table saw. The typical angle would be very small such as ¼” in 8 ft. of length.

  2. User avatar
    Aaron Birkland | | #2

    I look forward to this article with great interest. I posted a question a while ago, but due to family medical issues haven't been able to implement it this year. Basically, the house we're rehabilitating presents a situation in which I can't really think of any approach other than cut 'n cobble that meets our requirements:

    The situation:

    We have an 1850s house with no sheathing - clapboards are directly on the studs
    The clapboards are largely original, old growth wood, and are in surprisingly good condition for their age. We do not want to remove or cover this original siding.
    Exterior wall studs are between 4.5-5.5 inches deep, with varying widths and spacing.
    We have gutted the house, so have easy access to the stud bays for sealing. (The exterior walls previously were stuffed badly with fiberglass and covered in 3/8" drywall due to an unfortunate renovation in the late '60s. As there was no original plaster and trim left, and lots of critters living in the walls, we had no qualms about gutting it)

    Cut 'n cobble looks desirable to me because:

    The rigid insulation boards can be placed so as to maintain a 1/2" air gap behind the clapboards, to provide enhanced ventillation and drying ability.
    The rigid insulation boards provide a degree of air sealing, as they'll be foamed in on all edges
    (but won't form the primary air barrier - airtight drwall will play that role)
    They serve to physically contain one side of the cavity insulation,
    preventing the insulation from contacting the sheathing, and preventing significant air leakage into the insulation cavity
    With EPS especially, the foam insulation boards will have some vapour permeability, allowing some drying capability to the outside

    In response to Ron Keagle: Our stud bays are definitely nonuniform, not perfectly parallel, and rough cut (i.e. you can see a distinct sawtooth profile from an up and down saw). I'm thinking of dealing with that by cutting a 1" chamfer or rabbet around the interior perimeter of the insulation boards to accept the foam sealant, allowing a sloppy fit otherwise.

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Thanks, Aaron and Ron.

    Keep those comments coming!

  4. Michael Brahmey | | #4

    If there is a way to do it wrong, then I have tried it. I've been slowly retrofitting my 45+ year old colonial in Virginia. My first choice to improve the envelop is always airsealing with caulk and foam gun and add cellulose. I've used that model for most of the exterior walls plus attic.

    However, there are several exterior walls where foam was appropriate to maximize thermal effectiveness while minimizing depth. In those walls, I have tried all the cobble methods. I've friction fit, used caulk to seal edges, used foam gun to fill edge gaps - these all are terribly time consuming and quality is suspect. Virtually all stud cavities are unique with wires, outlets and plumbing runs preventing standardization. Also, I'm pretty cheap - I use lots of recycled (free) materials on my projects and I dislike paying for labor I can reasonably do myself. Closed cell spray foam is the obvious choice for these targets, but it's expensive. So, I found the optimal balance is using very loose fitting pieces of glued up polyiso, use construction adhesive to attach them to backside of drywall leaving 2 inch gaps between rigid foam and studs. I finish by using diy closed cell foam to fill the gaps. Its not perfect, but gets the job done at my pace and my price point. Here's a couple of picts from the backside of my kitchen wall. Black is glued up polyiso (2"+1.5") that I salvaged. Before - look closely and you can see mouse nests. After - insulated and sealed.

    Cheers!

  5. User avatar GBA Editor
    Martin Holladay | | #5

    Michael,
    Since I've opened up many mouse walls over the years -- many filled with droppings and caches of stored dog food (gathered by mice) -- I appreciate the improvements shown in your photos. Nice job.

  6. Eric Nutis | | #6

    Martin,
    First off, I'd like to thank you for all the great information on this site! It has been a great resource for trying to fix issues with our house.
    Background info: House is in St. Louis, Mo on the border between Zones 4-5. Two story built in 1993 with major thermal issues. Some of these issues are: HVAC wall stacks ( supply) located in exterior walls, master bedroom over garage that was insulated with R-19 FB in 2x10 joist bays that extended into conditioned living space, cantilevered second floor joists over 1st floor exterior walls with R-19 FB in 2x10 joist bays, bump out bay with 2x10 floor joists with fiberglass R-19 in 2x10 bays, etc
    I've used cut n cobble to seal a majority of these leaks along with closed cell spray foam in floor joist bays. When using the cut n cobble method, I usually try to do a belt and suspenders method of using adhesives (PL premium), Great Stuff Pro foam, and tape with XPS foam..
    Problems with cut and cobble:
    1. Very time consuming!!
    2. Finding tapes that stick and stay stuck without peeling off.(tried foil tapes, housewrap tapes, tuck tapes, etc. Budget has been tight but will try Siga tapes when funds allow in the future.
    3. Lots of scrap materials left over.

    Attached are pics of wall separating first floor garage wall and kitchen. Construction was from exterior side to interior: 5/8" drywall, 2x4 studs, R-13 fiberglass kraft faced batts, and interior 1/2" drywall. HVAC wall stacks are located in the stud bays with mold showing. No insulation was over ductwork and ductwork was detached at bottom run at elbows.
    Removed drywall and attached 2x2 to exterior edge of studs with PL premium and screws. Then cut and cobbled 1 1/2" XPS between studs over HVAC ducts for a R-7.5 over ducts. Caulked and foamed XPS around perimeter and then taped edges.
    Eventually. the garage is to become enclosed in the thermal envelope and become living space, so I couldn't justify the costs of SPF for this repair.
    However, after cut and cobble of rim joists in basement, attic vent chutes with XPS, blocking open floor joist bays to interior with cut and cobble, all I can say is that thank god my labor is free!! lol

    1. Trevor Lambert | | #30

      3M 8067 tape will stick to just about anything, and while it's a lot more than tuck tape, it's a lot cheaper than Siga.

  7. Eric Nutis | | #7

    Sorry, pics didn't attach first time. Please add if possible. Thanks

  8. Eric Nutis | | #8

    I've found a few benefits of cut and cobble:
    1. You can do what you can as budget allows versus having a SPF crew come in where its more feasible to have everything opened up at one time.
    2. During remodeling, cut and cobble may be cheaper and less of a hassle than having a SPF crew come in or even using a DIY SPF kit. SPF goes everywhere when sprayed and cut and cobble eliminates having to plastic everything off.
    3. After having a SPF failure, using a product that has been manufactured in a controlled environment has its benefits. SPF was applied too thick per pass and shrank away from framing. After the joy of tearing the SPF out, used cut and cobble to build up R value with SPF used to air seal perimeter. Cut and cobble can also be used when temperatures are too low for SPF installation.

    Risks of cut and cobble:
    1. Tape, canned SPF, or adhesive failure that allows air/moisture penetration without a way to dry out. I've had adhesives and tapes fail that were supposedly ok to use on XPS.

  9. User avatar GBA Editor
    Martin Holladay | | #9

    Eric,
    Thanks for your comments. I think that the reason your photos aren't being displayed is because the files have "illegal" characters in their file names. I tried to rename your files, but was unnsuccessful.

    I suggest that you reload the photos once more as attachments to a new comment, after renaming them something innocuous, like Cobble 1, Cobble 2, Cobble 3, and Cobble 4.

  10. BOB ALSOP | | #10

    I've also found a few other advantages to the "cut and cobble" method.
    If you're building during cold weather, and spray foam is not an option, and you want to insulate the enclosure enough to get heat in, then cutting in sheets of 2 inch thick foam will get you a structure that can be heated. Then trades can rough-in the wiring, plumbing, cable ,etc runs and later more layers can be added to build out the depth. if done correctly you get a middle layer of 1 1/2 foam spaced around wires,etc, and then a final 2 inch layer (2x6 walls) that will cap everything off.
    Layers will be can foamed as needed, and the final assembly will be taped at all seams using a good tape such as 3M 8067.
    A little slow and fussy, but makes a nice, tight enclosure.
    I mostly rip the sheets on a table saw, which coats your sawblades with melted plastic, but doesn't dull them much. Think safety, though, as a "jammed" sheet of XPS can kick like a mule.
    Bob

  11. BOB ALSOP | | #11

    I'll try to add a few PIX

  12. BOB ALSOP | | #12

    Here's another one.

  13. User avatar GBA Editor
    Martin Holladay | | #13

    Bob,
    It looks like the photo you intended to post with your last comment didn't load properly.

  14. BOB ALSOP | | #14

    Sorry....let's try that again.

  15. User avatar GBA Editor
    Martin Holladay | | #15

    Bob,
    Looks like a nice, neat job. Thanks for the photos.

  16. Keith Gustafson | | #16

    I did what was posted above. For the roof I had a great deal of leftover iso board. I cut it with at least 1 inch gap all around and filled it with 2 part spray foam. The foam needed no support, just push it onto the siding nails protruding through the sheathing.

    I had bought pallets of the iso for the roof as the most economical means, so it was in a sense 'free' and certainly much cheaper than the store bought spray foam kits

  17. Hobbit _ | | #17

    It wasn't rafter or stud bays, but was definitely as little
    "cut" as I could manage and a *whole* lot of cobble when I
    added the extra layer of "waste" polyiso to the basement wall:

    http://techno-fandom.org/~hobbit/hse/log/257215/25.html

    Anti-convection sealing was caulk at the bottom and low-E
    great stuff along the top. I had the luxury of a flat
    surface and could just tape joints like they'd done on
    the exterior retrofit. In some early depressurization
    tests I realized that air can actually diffuse fairly
    quickly right through the concrete block *and* the 1"
    layer of EPS that's behind all that, so it's all nicely
    encapsulated away now.

    Hopefully this thread won't get buried under spammer attacks.
    Strongly suggest y'all perma-ban large netblocks encompassing
    wherever they're coming from.

    _H*

  18. John Sheridan | | #18

    Hi I restore and Convert antique Timber frame structures. Most of our clients like to see the original roof sheathing, rafters and purlins exposed on the inside of the home. To facilitate this we usually build a new roof over the existing structure. This gives us room for insulation, as well as it Takes care of any structural issues in the antique framing. It is easy in my area to get tractor trailer loads of used 2, 3, and 4 inch poly iso for 15 % of retail cost ,. Here is our method which seems to work well so far , it is very warm , and there have been no condensation issues. this method allows the frame to dry to the in or out.

    First we apply 30 # felt over the original Rough board roof sheathing. We then apply 5/8 plywood sheathing over the 30 # felt. This helps Stiffen up the old frame as well as provide some fire separation between the foam insulation and the interior.
    Next we frame over the original roof, using 2x10 or 2x12 depending on span. This gets the roof load off of the old purlins which are often undersized.
    We thenRip the foam , using the table saw, and cut to length with a hand saw. Strips of poly iso are used to fill the rafter bays with 2 layers of foam , we install the first layer tight to the rafters and install the second layer leaving about 1/2 inch on each side against the rafters.
    We then install 2 inches of spray foam over this. It gets in Tight to the rafters and seals everything up tight.
    We leave about 1 inch of space between the top of the rafter and the underside of the roof sheathing that is attached to the rafters. We install a soffit vent and ridge vent . This allows free airflow between the top of the spray foam and the bottom of the sheathing.
    We then install roofing as normal .
    This sound very labor intensive, but we find the insulating goes very quick , one guy on the ground ripping with the table saw and 2 men on the roof we can insulate an entire roof in 1 day. The cost savings over using 8 inches of spray foam are substantial.
    We used to use SIP panels, But we found Due to the Nature of these antique frames a lot of shimming was needed to make everything look right. It also required lots of panel cutting to get the loads to dump onto the principal rafters. In the end this system is much cheaper to install and is more user friendly. The drawback is that once you install the poly iso , you have to keep everything dry until you get the sheathing and roof paper on.

    We have also used this method on sidewalls using 6 inch studs , 1.5 inches of poly iso and a 1/2 inch airspace between the studs and sheathing.

  19. John Sheridan | | #19

    Hi Martin I just Posted above, I would like your feed back on this system. I am ready to insulate another 1 of these barns and I would like to know your Thoughts.
    thankyou.

  20. Mark Hays | | #20

    Cut and Cobble worked well for this major remodel

    We are nearly finished with a to-the-studs remodel of a 1950-era home on the Cape in Massachusetts. It was originally built with no insulation, so a complete upgrade was needed.

    Major work started in November, when temps were too low to safely spray foam. With many changes planned to window and door openings, we also needed an incremental solution for insulation that we could install wall by wall. Cut-and-cobble was the answer.

    We cut XPS panels to fit each stud bay space, and carefully sealed the edges with the 'windows' version of Great Stuff, which remains flexible. This should prevent cracks as the assembly expands and contracts. A couple of photos are attached. With two layers -- 2" and 1" -- we could nearly fill each bay for a rough R value of 15 for the interior walls.

    To boost insulation, reduce thermal bridging and block condensation on the sheathing, we also installed new housewrap over the exterior, covered by 2" of XPS foam board carefully sealed with Great Stuff. All of the panel joints and edges around window / door openings were also covered with a thick layer of flexible DAP 230 sealant. (For panel joints, empty a few tubes of the DAP sealant into a paint tray and apply it with a 3" paint roller. With pole extensions, it is easy to reach high up on your walls without a ladder.) A photo is attached.

    In short, the cut-and-cobble approach took more time, but matched the rest of our upgrades and project schedule. We ended up with ~R25 wall assemblies and a tight air seal. The next step: 8" of closed cell spray foam on the underside of the roof, which will create a 'conditioned space' attic. (Cut-and-cobble is not a good option for the interior side of a roof!)

    Mark

  21. S L | | #21

    I am in the process of doing Cut and Cobble in my home.

    When I calculated the cost of 2" of spray foam diy kits vs 2" rigid foam boards from the local big box, the cost was significantly less to use the 2" rigid foam boards.

    Even though the rigid foam boards approx. half the cost, it is significantly more labor intensive. I could have done the spray foam for all walls in one day. With the rigid foam board, it took me 5 days to cut and place all the foam board.

    There where other benefits of going with the 2" rigid foam board vs the spray foam in my situation:

    1 - Knowing for certain that I had 2" of coverage throughout the wall so I knew the dew point was inside the foam board.

    2 - Decreased risk of harmful off gassing from diy spray foam kits. I don't personally think this is a problem with current diy spray foam kits but my wife and the rest of my family had concerns - just spraying around the edges of the foam board instead of the entire wall decreased the risk, and removing the insulation would be easier if there was a problem.

    I used small blocks to hold the rigid foam board in place while I sprayed the foam around the edges. This let me do several studs at once, and I didn't have to worry about the rigid boards moving until the spray foam hardened.

  22. TVCarpenter1 | | #22

    Hi All:
    I am the project manager on the restoration of a home built in 1735, and this building is on the National Historic Registry. Due to many years of shoddy construction we were forced to remove all the plaster and wood lathe. Then we removed all the brick nogging in the exterior walls with the thought of now insulating it properly. I have attached a picture of what we now have before starting the "Cut-and-cobble" process, as we believe this is the only way to go. We are prohibited from disturbing the exterior of the structure, so our only option is to work from the interior.
    We are thinking of using 1x1 furring strips and attaching them to the posts, then cutting in 1-1/2" XPS board staying tight as possible, then sealing any gaps with Master Seal NP1. Finally we would finish off with spraying closed cell insulation.
    I would appreciate any advice on how to proceed. I have read a bit of back and forth on EPS, XPS and Poly-iso, and I would appreciate any information on which way to go. I have also read that the insulating boards should be faced on the exterior facing side to diminish permeation. Looking forward to any help. Thanks!

    1. Andy CD Zone 5 - NW Ohio | | #23

      TV, for the most suitable answer, you'll need to provide your Climate Zone, at minimum. Also, what's the thickness of the wall, what's presently on the exterior (looks like cedar shingles only), what's the final interior treatment?

    2. User avatar GBA Editor
      Martin Holladay | | #27

      TV,
      I suggest that you read this article: "Insulating Walls in an Old House With No Sheathing."

    3. User avatar
      Dana Dorsett | | #33

      >"We are thinking of using 1x1 furring strips and attaching them to the posts, then cutting in 1-1/2" XPS board staying tight as possible, then sealing any gaps with Master Seal NP1."
      ..............
      >"I have read a bit of back and forth on EPS, XPS and Poly-iso, and I would appreciate any information on which way to go."

      Can I convince you to change the foam type to polyisocyanurate?

      XPS is blown with a mixture of HFCs, the predominant component of which is HFC134a a powerful greenhouse gase with a 100 year global warming potential of ~1400x CO2. HFC134a is banned for most applications as of January 2019 under the Kigali Amendment to the Montreal Protocol. The US did not sign on to the Kigali amendment, and the major manufacturers here have not changed blowing agents to be Kigali-compliant.

      Over several decades the bulk of the HFCs diffuse out, and as it does the performance of the foam drops toward that of EPS of the same density, or about R4.2 per inch.

      EPS and polyiso are blown with comparatively benign hydrocarbons, usually variants of pentane at about 7x CO2, (with some proprietary mixes for polyiso). With EPS most of the pentane escapes the foam and is recaptured at the factory, not vented into the environment. With polyiso it's more complicated- aluminum facers can hang on to the blowing agents for much longer, but even so it's a far more benign blowing agent. There is some slow degradation inperformance over time with polyiso, but not with EPS. Still, even after many decades foil faced polyiso would still be outperforming EPS in your type of climate. See:

      https://materialspalette.org/wp-content/uploads/2018/08/CSMP-Insulation_090919-01.png

      Then there is the fire hazard aspects. EPS and XPS are polystyrene, which melt while burning, which can spread fire downward (against the convection) in a fire situation. Polyisocyanurate does not melt, but chars in place. With heavier facers polyiso can even qualify as a timed thermal barrier. One product (among a few) of fire-rated polyiso is Dow's Thermax line of polyiso.

  23. TVCarpenter1 | | #24

    Andy:
    Thanks for the come back.
    We are in NY, 4a zone. The thickness of the walls are 6", and you are correct, the exterior is Cedar shakes (about 280 years old). The final interior wall treatment will be 5/8" drywall.
    Art

  24. User avatar
    Michael Maines | | #25

    On the few occasions when I have used the cut and cobble approach, it's been in isolated stud bays or sometimes roof bays to allow for plumbing or other utilities. Not ideal, but sometimes you have to make do.

    I thought you, Martin, invented the term but apparently not?

    1. User avatar GBA Editor
      Martin Holladay | | #28

      Michael,
      This is an old thread, dating back to 2013. No, I didn't invent the term "cut-and-cobble." The first place I saw the term was in a comment posted by Dana Dorsett.

      1. User avatar
        Dana Dorsett | | #32

        That's my enduring contribution to the 'merican lexicon, I guess. :-)

        1. Yupster | | #34

          A general Google search and a domain specific search of greenbuildingadvisor.com and greenbuildingtalk.com offered up the 12th of February, 2010 as the earliest use of this term. And it was indeed Dana. http://www.greenbuildingtalk.com/Forums/tabid/53/aff/14/afv/topic/aft/77438/Default.aspx
          Not really sure why I just spent time on that...

  25. Tim R | | #26

    This my cut & cobble on a low slope roof addition in Southern California.
    The middle area is a porch infill 5'x7' moved to be interior space. The building is a 1985 tract house, with 2x10 ripped to the roof slope(1/4&12). The original install was 2x8 fiberglass batts with no ventilation to the cavity. This is an unvented assembly. The drywall was installed first then cellulose was installed. I put the cellulose in a cardboard box then beat it with a drywall mud mixer to loosen it and placed it in the rafter bay. Then friction fit the 1.5" foam in place. Then 5/8" sheathing with blocking at the panel edges. The roof is a built up hot mop roof.
    I do see moisture lines on the finished roof on cold mornings (50 degree F) It has only been 2 years so no problems yet.

    1. User avatar
      Jon R | | #36

      I'm curious - why the extra work of cut-and-cobble when continuous foam (on top) would perform better and more cellulose (and no foam) would perform similarly.

  26. Brian Barlow | | #29

    I used cut and cobble with spray foam and caulk to seal in my 50's ranch bathroom and basement. We renovated the bath room, as it was all pink. Pulled out the rockwool and using used xps foam board, removed exterior wall outlet, foamed in between and screwed 1/2 inch of foam board over the interior studs. It had a cast iron in wall radiator that we pulled out too. No heat in the bathroom, but it doesn't get too cold. Still have a lot to do in the basement with this. Want to insulate the walkout exterior properly, and all the exterior wall joist bays.

  27. User avatar
    Robert Opaluch | | #31

    I used cut & cobble two ways on a home built back in 1982-3. The first was to use leftover XPS strips to fill in the 5.5" x 2" x 92 5/8" empty space at the intersection of an interior 2x4 partition and the exterior 2x6 stud wall. Would still consider this okay for infill. Advantage is easy to do and high-R cut&cobble for this small space, and pretty much limiting any airflow in the space. Beats using fiberglass or leaving the airspace unfilled. I wouldn't use XPS today, rather use EPS or polyiso.

    A few years later, the second cut and cobble job involved insulating the sloped ceiling of a storage room to convert it into a study/spare bedroom and large storage closet. Given the low ceiling height, I wanted to infill between [email protected]" rafters (9'8" span, 5 in 12 slope). I wanted to avoid lowering the ceiling except for drywall. (Project was barely doable given the low and sloped ceiling.) . So I cut foil-faced polyiso to fit tightly between the rafters. Just push it in place tightly. With new ply sheathing/building paper/cedar shake roofing, and adding drywall, I didn't think air sealing would be too bad, but of course didn't consider water vapor (foil-faced polyiso and no ventilation). Even in very dry Colorado, not good even if avoiding roof leaks over time.

    Advantages include ease of installation (really not hard if you have identical bays to fill);
    about as high R-value as possible without lowering the ceiling or changing the new roof.

    Sorry no photos.

  28. DCContrarian | | #35

    Amazon used to sell a 600 board foot closed cell foam kit from Fomo, although it has now stopped. I used the kit along with 2" RMax foil-faced polyiso to insulate the rim joists and one wall in my basement. I am very pleased with the result.

    My basement has one wall that is above grade with a walk-out door. It is framed with 2x4's. The siding had been leaking and I had to have the siding and sheathing replaced along with removing the interior drywall and fiberglass insulation. To insulate this section I cut strips of polyiso to fit between the joists (13.5"), pushed them into place and then sealed with about an inch of spray foam. I did this after the siding was on so the siding nails came through so there is a half inch gap between the sheathing and the foam, I like to think this gives extra insulation. Two inches of polyiso is R13.1 and an inch of closed cell is R6.5 so I get R19.6, much better than the 3.5 inches of fiberglass that was there.

    The joists are 2x10 so I cut rectangles of polyiso to fit -- 9.25x 13.5 inches. I found there was almost no waste. The foam came in sheets of 48x96. I would cut the 48 inches into either five strips of 9.25 -- 46.25" total -- or two 9.25 and two 13.5 -- 45.5" total. So at most there is 2.5" of waste. I used the 9.25 strips for the joists and the 13.5" strips for the stud bays. A 96x9.25 strip can be cut into 7 13.5 pieces with 1.5" of waste.

    It took me about an hour to spray out the 600 BF of foam. The tanks were heavy, about 120 lbs full. I put them in a four-wheel garden cart so I could wheel them easily, the cart was also handy as a place to stand while spraying the joist bays. Before spraying I rehearsed the whole thing, wheeling the cart through the path I would take and making sure I could reach everywhere I needed to spray. The actual spraying I was able to do in a single pass without stopping. I wore a Tyvek suit, gloves, glasses and a respirator.

    I've been very, very happy with the results. The house is noticeably warmer, less drafty, less damp and quieter. I used to get field mice coming in every fall and haven't had any since doing this.

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