Crawl space encapsulation help
* Updating this as I go, in case it will help anyone.
I just want to make sure I understand all this correctly so that I can do a professional looking job, or make sure it get done correctly should it be out of my skill set. This way if I ever sell my home I don’t have any problems with Home Inspections.
Here is my info and plan of action followed by a few questions:
Project area : 1000 sq Feet, 15-16 inches between ground and floor joist. ( 2 hollow blocks)
HVAC Supply Duct vents in crawl.
CODE: IBC, IRC ……. (2006) (looks like not much changed in this area compared to 2018)
Climate zone 4A
CrawlSpace Wall: R-10 Continous, R-13 Cavity.
” Crawl space walls insulation shall be permanently fastened to the wall and Shall extend downward from the floor to the finished grade elevation and then vertically or horizontally for not less than an additional 24 inches.”
DOW ESR-2142 report says it can be installed without ignition / thermal barrier. I can’t find it reasonable priced no local store within 100 Mile carry it.
Alternate: Mineral wool batts.
Rockwool or Owens corning Thermafiber
StegoCrawl 10mil, With stego glues, tapes, etc.
(this is pricey, but seems to be “the best”)
RodenHouse has many different types
PMF plasti-grips, Look nice but costly.
I found this nice PDF by Rockwool for permanently fastening Mineral wool.
Plan of install:
lay the vapor retarder all the way up to the end of the wall ( not just 6″ up. then install the Mineral wool.
Address details of rim joist, sill plate, before or after vapor retarder depending on moisture content. If its too high give it a chance to dry with vapor retarder and dehumidifier installed.
Address Detail of: top of block foundation wall before Vapor retarder is installed.
Rim joist and sill plate Details:
Use a 2 part foam or cut and cobble for rim/sill if they are a candidate for sealing.
Whats this about candidate for sealing? I was reading about wood rot problems. If the moisture content was to high and you sealed it in Or sealed / insulated without knowing why the moisture content was so high.
Seems there was 2 cause for concern:
1. capillary action due to missing capillary break between foundation wall and sill plate.
2. improper exterior setup ( siding, drainage plane, air barrier, flashing) allowing the sill to get wet. once insulated it will not dry.
before sealing up you seems you need to check:
1. Moisture content
2. The way the exterior sheathing + siding are installed ( to see if there will be or is a moisture problem / drying problem of sill/rim)
3. make sure there is a capillary break between the sill plate and block foundation.
While I Know the steps I still need to fill the details Like What is okay moisture content, What is okay way of sheathing + siding setup and is the thick hard black looking felt paper a capillary break.
Questions About mineral wool Batts:
1. Is mineral wool batts okay code complaint application? They will be protected and in the conditioned space via the Vapor barrier.
Seems this is a legit approach, but there is concerns about moisture transport via air motion.
so while it looks like an good alternative to foam, it realistically still needs an air barrier and may cost more from fasteners and install vs Foam board.
2. Can you rip / split Meneral wool batts in two along its Thickness? AKA take a R23 5.5” thick and make 2 R11 ~ 2.6” thick.
Not worth the effort and issues involved, seems it may be hard to cut even setup with a jig.
3. How is rockwool (roxul) batts vs Owens Corning Thermafiber batts? (owens is 70% recycled).
Thinking greener, but don’t know how it is in terms of the quality and longevity. Like how poly vapor retarder degrades over time if the recycled content is to high.
4. permanently fasten batts. I would like to refrain from filling my foundation full of holes / nails ( structural integrity, thermal bridging, expansion and contraction of fasteners working lose are the concerns).
Has anyone seen or came by a code legal system that lets you “permanently fasten” by:
(these ideas are assuming I am installing the batts in a continuous fashion similar to foam board, because in my application the standard width of the mineral foam will cover my crawl space wall with one batt.)
4A: drop lumber from the joist and make a frame to press like a clamp to hold batts in place?
4B: Think strapping but with the strapping attached to Floor joists.
4C: Friction fit between Vapor retarder (floor) and floor joist (or running board perpendicular to floor joists.)
4D: Friction fit between vapor retarder (floor) and floor joist, but install a 2×4 perpendicular to floor joists say 3.5″ out for r-15 to creat a L-channel.
4E: (see image)
Knauf and NAIMA
I was reading an install by Knauf and then NAIMA where they run the batts in a continuous fashion similar to friction fit between stud bays, but there are no studs. Batts are longer than the wall and are fold in an L at the floor. The batts are pressed tight to each other, then fastened using nailer strip into the sill plate compressing the bats, then using weights or 2×4’s placed on top of the floor portion of the batts. Taped can be used on the floor (vapor retarder) and batt edge.
That lead to this Idea:
I will be installing a “board” at the top of my vapor retarder to give me a lip to mastic or caulk. I could install a 2×4 there then Install in a method like NAIMA, but use fastener and washers through the batts into the 2×4 that holds / gives a sealing joint to the vapor barrier.
Questions About the install:
5. What is the deal with an additional 24” of insulation? (They don’t state it on basement walls. Maybe its assumed basement walls will be over 24” past grade then?)
6. I am retrofitting and I am going to have to go Horizontally with that 24″.
I interpreter the code to say the vertical insulation on the wall needs permanently fastened, but it does not state the additional 24″ needs fastened.
Am I reading that right?
7. How would you address the 24” of horizontal insulation? ( I have my reservations about using some type of fastener that will puncture the vapor retarder.)
8. All that I have read and seen in videos people omit the 24″ additional insulation. when retrofitting? any clue why? ( I just got prime and have to finish reading the papers here.)
Thank you all for your time and expertise.
(p.s. If you know of better or cheaper but okay products let me know)
Don’t feel you need to give 100% answers. guidance, search terms or reading links are all good.
(edited to clean up)
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