Author Topic: Questions about crawl space encapsulation  (Read 1546 times)

intellectsucks

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Questions about crawl space encapsulation
« on: January 09, 2018, 11:50:58 AM »
Corrected accidental double post. See below.
« Last Edit: January 09, 2018, 01:09:36 PM by intellectsucks »

intellectsucks

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Crawl space sealing questions
« Reply #1 on: January 09, 2018, 12:03:41 PM »
This weekend I'm planning on sealing my crawl space. I have some questions:
1. I'm planning on sealing the foundation vents by sticking rigid foam in them, covering it with plywood and sealing the edges with spray foam. Will this work? Will spray foam be enough to keep it attached or will I need to secure with something else?
2. I'm planning on putting the vapor barrier on first, then rigid foam boards on top of that on the walls. Some places online recommend to reverse that (foam boards first then vapor barrier). Does it matter?
3. Is there any reason to put insulation on the floors of the crawl?
Thanks in advance for your response.

TheWifeHalf

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Re: Questions about sealing crawl space vents
« Reply #2 on: January 09, 2018, 12:03:54 PM »
My son, under his Dad's direction, just used the rigid foam.
We don't insulate ours, don't know why, but I think it's important to open the vents in the spring (my job)

intellectsucks

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Re: Questions about crawl space encapsulation
« Reply #3 on: January 09, 2018, 10:50:31 PM »
Just did measurements and the crawl appears to be divided into four sections (see attached sketch).  This brought up some more questions.
1. The four sections are separated by cinderblock walls. Is it necessary to encapsulate them as well or is it OK to just seal and insulate the exterior walls?
2. The cement sections don't appear to have moisture issues (no visible moisture and no musty smell). Is it necessary to seal the floors of those sections with vapor barrier?

poko

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Re: Questions about crawl space encapsulation
« Reply #4 on: January 09, 2018, 11:27:07 PM »
I had mine professionally done. It was a mess down there (dirt nearly to the floor joists!) and very expensive to have it done right. I can't offer much in the way of what should actually be done, but mine is now all lined with heavy duty plastic (no foam that I can see). I'm in the south though so I'm not sure if they did any insulating at all, but definitely none on the floor.

I would think you'd need to run it over the concrete as well otherwise how would the transition from concrete to vapor barrier work? Mine has a dehumidifier running down there as well. I recommend sticking a bluetooth hygrometer down there to track humidity from inside the house. Mine has been great for identifying when the dehumid goes out or something is going wrong. Good luck!

Rcc

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Re: Questions about crawl space encapsulation
« Reply #5 on: January 10, 2018, 03:45:02 PM »
I had mine professionally done. It was a mess down there (dirt nearly to the floor joists!) and very expensive to have it done right. I can't offer much in the way of what should actually be done, but mine is now all lined with heavy duty plastic (no foam that I can see). I'm in the south though so I'm not sure if they did any insulating at all, but definitely none on the floor.

I would think you'd need to run it over the concrete as well otherwise how would the transition from concrete to vapor barrier work? Mine has a dehumidifier running down there as well. I recommend sticking a bluetooth hygrometer down there to track humidity from inside the house. Mine has been great for identifying when the dehumid goes out or something is going wrong. Good luck!

Ditto here back in November. Crawlspace walls first covered in 20 mil plastic (held on with adhesive). Then 2" of foam board insulation on top of that - secured with masonry anchors. Same 20 mil plastic to cover the bare dirt ground, with overlapping and taped seams. All piers have the plastic running up them skirt style at least 24". All gaps, cracks and penetrations (HVAC, plumbing, electrical) sealed with foam. Finally, since my HVAC is in the crawl space - a 4" duct was added to the plenum so conditioned air is blown into the space. To avoid a dehumidifier (expensive and one more damn thing to maintain) I had them install a drain to daylight drain in lowest spot of the space.

I too have been monitoring before and after with a remote for temp/humidity and it runs no more than 10% higher humidity than the house. But, this was done when humidity was running 40% or lower, its (quick eyeball) currently 69F/31% in the house (kitchen) and 64F/37% in the crawlspace. I'm curious what it looks like in Spring & Summer.

Looking at OPs questions ...

1. The plywood on vents may be overkill with your plans. Why not use the same foam board
2. The cinderblock walls probably dont need complete covering, just enough to keep moisture from seeping in where they meet the ground. Ie: running the plastic up 12-24" etc
3. Concrete is porous - moisture can get through. However, how much would need to be quantified - maybe do everything except concrete and measure over time ?

dollarchaser

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Re: Questions about crawl space encapsulation
« Reply #6 on: January 28, 2018, 07:24:09 PM »
I did this DIY project a few years back. It returned a better reduction on cold/drafty floors than adding insulation to all joists in the crawlspace.

Things went bad spring 2017 when mega rains came in. Below the vapor barrier the water rose high enough to trip my water alarm sensor. But the noise was so muffled and I had forgot about using it. Once we caught on, I had to reopen the vents, drop a pump into the crawlspace and pump down the water. UGG ! Underground waterbed!! Most of my caulk has separated so a redo is needed.

Monitoring the humidity level sounds like a good idea. Thanks

ncornilsen

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Re: Questions about sealing crawl space vents
« Reply #7 on: January 29, 2018, 09:49:09 AM »
My son, under his Dad's direction, just used the rigid foam.
We don't insulate ours, don't know why, but I think it's important to open the vents in the spring (my job)

this is a really common mistake people make.   In the summer/spring, warm air comes from outside. Warm air contains moisture. This warm air then goes under your house, where your floorjoists, support columns, etc are likely cooler. The moisture then condenses on those things and can feed mildew and rot.

the best thing is really to keep the vents open year round, or even close them in the summer. nobody does it because they don't like cold floors!  This is why I like the idea of conditioned crawlspaces. 

Rcc

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Re: Questions about crawl space encapsulation
« Reply #8 on: February 07, 2018, 12:01:57 PM »
Some reference. This firm geared their work for the SE US, but still useful info, free videos and PDFs:

https://www.advancedenergy.org/portal/crawl_spaces/

Sibley

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Re: Questions about sealing crawl space vents
« Reply #9 on: February 08, 2018, 08:13:14 PM »
My son, under his Dad's direction, just used the rigid foam.
We don't insulate ours, don't know why, but I think it's important to open the vents in the spring (my job)

this is a really common mistake people make.   In the summer/spring, warm air comes from outside. Warm air contains moisture. This warm air then goes under your house, where your floorjoists, support columns, etc are likely cooler. The moisture then condenses on those things and can feed mildew and rot.

the best thing is really to keep the vents open year round, or even close them in the summer. nobody does it because they don't like cold floors!  This is why I like the idea of conditioned crawlspaces.

My vents don't close. They're just there. I won't change that!