# Insulation with no subfloor?



## Nealtw (Jun 22, 2017)

You really want to do your home work before taking on this job. What you have right now might not be good for people but the house has done well as it can breath. 

When you want to bring a house up to today's standards you can make it bad for the house. 

You almost have to treat your basement like a crawl space.
We deal with crawl spaces in two different ways.
A sealed crawlspace is much like a modern basement where we insulate the perimeter walls and condition the air. The problem you have with that is your foundation was not likely waterproofed in any way and you likely don't have a perimeter drain to take water away from the foundation. 

A vented crawlspace would need a sealed floor between the basement and the house with insulation in the floor with venting in the basement so any moisture in there can get out.


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## APA (Jul 13, 2018)

pss2103 said:


> We have a house built in 1879 and our floor is the original hardwood floor made of heart pine with no subfloor under it - laid right on the beams. We have an unfinished basement underneath that is about 6 feet in height with our HVAC, boiler, etc. If the light is on underneath, you can see through some of the floorboards to the basement.
> 
> There is no insulation on the underside of the floor boards. Because the basement area isn't part of the HVAC system, some of the unfiltered air is coming up into the house through the floorboards. What should I insulate the bottom of the floor with to prevent that? I was thinking of using something like basic reflective bubble foil - or should I use something else? We have a baby so looking for something without allergens/dust.
> 
> It's mainly to keep the cruddy basement air from seeping through the whole house but sound and heat benefits would be welcome too. Thanks!



Not sure how much air would get through a finished hardwood floor. The house has lasted this long, so I would not bother with it. I hear this all the time from these encapsulation experts. 30% of the air you breathe comes from the crawlspace! The crawlspace air comes from the outside. Seal up any huge penetrations with foam and be done with it. Would be easier to install a few air filters in your house.


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## APA (Jul 13, 2018)

APA said:


> Not sure how much air would get through a finished hardwood floor. The house has lasted this long, so I would not bother with it. I hear this all the time from these encapsulation experts. 30% of the air you breathe comes from the crawlspace! The crawlspace air comes from the outside. Seal up any huge penetrations with foam and be done with it. Would be easier to install a few air filters in your house.



I misread. Just put an air filter in your basement...


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## 3onthetree (Dec 7, 2018)

So you probably have an airy, musty, dampy basement that really just houses mechanical equipment and a little storage, and you really aren't seeking soundproofing or insulating value? I would want to stop the floor pass thru just in terms of spiders and toddlers dropping shredded cheese falling thru the cracks, let alone the mustiness. 

- thinking spray foam in the joist spaces as a bigger expense and easy- but you'll see it in the cracks, 
- then thin rigid insulation board on the bottom of the joists where you can tape butt seams (I see houses where DIYers use polystyrene to brighten it up). Probably existing piping and stuff makes this difficult.
- finally white scrim sheeting on bottom of joists would be easiest to install, not fully airsealed though.


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## carpdad (Oct 11, 2010)

I think tarpaper first, cut approximately to the joist bay and get the paper as flat against the floor boards as possible. Staples. If floor boards have gaps, black would minimize the sense of those gaps. Some air/dust barrier but vapor will pass. Then fiberglass batts with kraft paper side down. How thick depends on you. Even r13 will help. Maybe a mix? R30 where the bay is clear, r13 if there are pipes or such in the way. If bsmt smell, and if you have a window, small window fan running all the time. But you must have enough air coming in for the water heater/boiler. Look at the btu of those units and search how much air you need.


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## APA (Jul 13, 2018)

APA said:


> I misread. Just put an air filter in your basement...



Also a dehumidifier.


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