Sealing crawlspace plan for review


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Old 01-16-16, 09:34 AM
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Sealing crawlspace plan for review

Hello!

I am starting my project to seal my crawlspace, and just wanted to run this by you to see if I am missing anything or you have any suggestions. My thoughts are that I am not going to be living down there or storing anything in there, so 10 mil (100' x 20" rolls) is good enough plastic. I am also undecided about whether I should rigid insulate the walls since it's already 60F down there anyway which seems like a good temp. The vents outside are already sealed.

The plan:
•Penetrations in subfloor and walls: EXP FOAM all holes (cable holes, water pipe holes, etc.)
•Vent holes: GLUE plastic on top and bottom (to cover up the concrete block holes), then 2" HARD FOAM, EXP FOAM all around to fill the cavities and bring them even with the wall).
•Tops of walls: PLASTIC and THIN HARD FOAM (for the concrete block holes)
•Door: PLASTIC AND HARD FOAM.
•Joist spaces:PLASTIC, HARD FOAM, and EXP FOAM.
•Support columns: PLASTIC, GLUE, and TAPE all seams.
•Walls: PLASTIC, GLUE, and TAPE all seams.
•Floor: PLASTIC, GLUE, and TAPE all seams.


I contacted DAP, Liquid Nails, and Loctite customer service for gluing tips (I am going to glue the plastic to the walls and the foamboard to the plastic rather than use hammer-in fasteners), so I wanted a glue that would work for plastic to concrete. Loctite never responded, DAP said they didn't have anything that would work for this, and Loctite said to use their PL-950. (I was thinking to use butyl tape, but it's $11 for 30' and I think I can get more than 30' out of a $8 10 oz tube of adhesive (still going back and forth on this one.)

Questions: 1) For the door, I'm was going to glue the plastic to the wood, and then the foamboard to the plastic, but is a vapor barrier necessary everywhere that the foamboard is going? (walls, yes, but door? Joist spaces?)

2) This is the "uninsulated approach" (just plastic everywhere). Does anyone know if someone makes a rigid foamboard that has an attached vapor barrier so that I can just glue that to the walls? (So the vapor barrier and insulation are one piece rather than two separate things)

3) At some point, I would like to remove the insulation from around the crawlspace ventilation pipes because that insulation is bulky and would make it less crowded, has been wetted, I can't see what's going on with the pipes (leaks, etc.), etc. But removing it would increase heat transfer through the pipe walls. Any thoughts on this?

That's all I got. I always miss something or there may be a better way to do this, so I appreciate all the help and ideas.

Regards,
Leaning
 

Last edited by leaning; 01-16-16 at 11:12 AM.
  #2  
Old 01-17-16, 04:17 AM
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Normally sealing crawlspaces in Georgia is not necessary. I have been involved in only one, and it was a disaster due to the planning of the general contractor. No provision was made to air condition the space, and it condensated to the point where it formed a small rivulet on the floor. We "glued" the plastic to the walls using air conditioner duct sealant, which works rather well. Formerly the Southern Building Code, which your house may have been built under, provided that cross ventilation was provided on all sides of the crawl. It took care of moist air during the summer months. The only drawback was the cold air in the winter, requiring closure of the vents to prevent freezing of exposed pipes.

I will PM one of our pros on sealing crawls and have him stick his nose in here for advice.
 
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Old 01-18-16, 08:17 AM
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Update: I got the glue info all wrong. Here's the info from the manufacturers:
Liquid Nails: "I would use the LN-950 Polyurethane"
DAP: "We do not have a product suitable for this application."
Loctite: "We do not make any product that will adhere 10 mil plastic (polyethylene plastic) sheeting to concrete block foundation walls."
 
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Old 01-28-16, 10:54 AM
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Update: In case anyone is interested, I would NOT use LN-950 (Liquid Nails Polyurethane Construction Adhesive) for this. I bought 5 tubes from Amazon, and several days ago, applied the LN-950 from XPS to XPS, from polyethylene to wood, and from polyethylene to XPS. It stuck to the wood and XPS great, but it didn't bond at all to the polyethylene and just peeled away cleanly. Good thing I did this on a sample before I went around my crawlspace sticking sheets of plastic to the block. I have one other option (Masterseal NP1) which I have used before to bond aluminum sheet to ceramic. That stuff works great, and it would take a jackhammer to separate those two. I ordered it, so when it comes in, I'll give it a try on these same materials. So, LN-950 with polyethylene? Not from what I see. HTH. Leaning
 
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Old 01-28-16, 05:21 PM
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Very few adhesives stick to polyethylene and those that do are fairly expensive. I would suggest that you use battens, about 3/8 or 1/2 inch thick and at least a full inch wide. Use some sealant between the poly and the concrete and then the battens over that. Drill holes through the battens and into the concrete and use the plastic "pins" that have a nail to spread the wings of the pins.

https://www.fastenal.com/products/details/50806

Space the pins according to the thickness of the batten and the flatness of the concrete, about 12 to 24 inches apart.
 
 

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