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Insulate between the trusses under the house or not?


Jwhitman's Avatar
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CAL

04-15-16, 10:55 AM   #1  
Insulate between the trusses under the house or not?

Recently, I remodeled my bathroom and installed electric heated floor coils and tile. It seems like insulating the space underneath would make sense. The crawl space is cover with 6ml plastic and the ground under it gets moist. There is no mold issues or condensation seen. There are areas where the distance between the trusses exceeds 24" so i thought about spraying in insulation, but that seems to get mixed reviews. If I use matting where can i find really wide matting? Also is it a good idea to do it at all. I live in Northern California so we see some 30deg weather in the Winter, but nothing severe. The other thought is the grout will allow moisture through to the sub-floor and trap moisture in the insulation cause a problem? Any help appreciated.

Thanks,
J

 
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04-15-16, 05:05 PM   #2  
If you have web truss floor joists... or even standard joists... professional spray foam would be best. Hopefully that crawlspace is ventilated.

 
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04-15-16, 05:43 PM   #3  
That grout should be sealed, moisture from above is not an issue.
The fact that you still have a moist crawl space is.
It can cause mold and fungus to form.
This can be caused from several reasons.
No gutters, or down spouts just dumping the water close to the foundation.
No grade way from the foundation.
Foundation below grade was never sealed before it was back filled.
Mulch pilled up against the foundation, flower beds forming ponds.
Just to name a few of the most common issues.

 
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04-19-16, 09:03 AM   #4  
One last question

The moisture under the house is just the dirt is damp. The dirt is adobe and all around the outside of the house it's the same way. There is heavy plastic over the dirt. If the moisture down through the grout in the tile is not a problem then the only question i have left is the usefulness of the insulation and what type is best. Matted or spray in. It seems like the spray in will be easiest,but will it absorb what moisture may be under the house? The matted will be harder to to get up in place. There are some areas under the house that have 47" between beams. Any ideas or suggestion welcome.

J

 
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04-19-16, 09:11 AM   #5  
The moisture under the house is not really as damp as I may have lead it to seem. There is heavy plastic on top of the dirt and the dirt is adobe that is always kinda damp(Summer or Winter) But the insulation idea is really what i need help with. The spray in seems O.K because of the wide span between supports, but the matting seems easier to remove if problems occur. Will the heat from the coils under the tiles try to go up into the room or into the crawl space below. Any ideas or any of these thoughts would be appreciated.
J

 
Jwhitman's Avatar
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04-19-16, 09:14 AM   #6  
Crawl space is ventilated. I was planning to use the cans of spray foam. The bathroom is 4X6, but how do i get the foam to stay vertical? Will this work?

 
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04-19-16, 09:20 AM   #7  
how do i get the foam to stay vertical?
Sorry, don't understand what you mean.

 
Furd's Avatar
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04-19-16, 12:39 PM   #8  
I was planning to use the cans of spray foam.
If you mean the crap that takes several hours to harden then I would advise you to forget that plan UNLESS, you are going to first cut rigid foam (polyisocyanuratre) panels to fit and then use the spray foam to simply "glue" the panels in place and seal the edges.

If you want to do a full foam treatment then you need to use the two-component packages available over the Internet or from larger builder supply stores. (I've never seen them in a homecenter.) These two-component packages have the same instant rise foam that sets in 90 seconds or less that the biog time insulation co0mpanies have on their job trucks. I'll admit that there IS a learning curve and also that it is quite expensive but it is also fun to see that stuff spray on like thick paint and then almost instantly fill the entire space. It is EXTREMELY sticky and done correctly it will harden in place before it has a chance to sag.

Will the heat from the coils under the tiles try to go up into the room or into the crawl space below.
The heat will go in all directions. The wood flooring will offer some insulative properties but adding additional insulation below (from the crawl space WILL help, especially if you can add a reflective component such as foil-faced foam insulation board.

I personally would NOT use fiberglass in the crawlspace unless your utility is paying for it and you don't expect much of an improvement.

 
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