# Is it worth it to insulate my basement ceiling / 1st floor joists?



## HolyWhip (Oct 6, 2021)

I spent all last weekend putting up batt insulation between the joists, and sealing the perimeter - thinking it is going to be cold down there this winter. There are even holes where you can see outside (through the rusty basement door leading outside), and a vented crawl space that shares the same air volume (looks like someone busted a hole through a block foundation wall at the top to make that happen).

Tonight is the first freezing night, and my basement is not even chilly.
which makes me wonder if I'd be better served taking all this batt insulation and using it my attic instead (which only has old dark fluff beneath the floorboards).
Or just leave the ~$500 worth of insulation as it is...

Any advice? 
It is worth it to do more than seal the rim joists in this basement considering my gas boiler and a radiator are down here too?


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## stick\shift (Mar 23, 2015)

Personally, I don't like to see insulation between floors if both spaces are conditioned. If not, then go nuts separating the spaces thermally.


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## Nealtw (Jun 22, 2017)

If the crawlspace is vented. insulate that floor and close it off from the basement and insulate that door. 
Leaving the basement cold with out vents is a good way to start moisture problems


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## HolyWhip (Oct 6, 2021)

Nealtw said:


> If the crawlspace is vented. insulate that floor and close it off from the basement and insulate that door.
> Leaving the basement cold with out vents is a good way to start moisture problems


So basically I should do a good job sealing up my basement. Don't insulate where I did because it'll be somewhat temperature controlled down there (with the gas burner and there is a radiator down there). Then isolate the crawl space, which is on an addition on the side of the house.

I was worried about air sealing my basement too much, because the gas burner and water heater need oxygen. A gas company worker told me yesterday that the oxygen demand is more of a volume thing, and I don't need to worry about sealing up the basement. Enough air should find it's way in for the gas burning devices.


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## Nealtw (Jun 22, 2017)

HolyWhip said:


> So basically I should do a good job sealing up my basement. Don't insulate where I did because it'll be somewhat temperature controlled down there (with the gas burner and there is a radiator down there). Then isolate the crawl space, which is on an addition on the side of the house.
> 
> I was worried about air sealing my basement too much, because the gas burner and water heater need oxygen. A gas company worker told me yesterday that the oxygen demand is more of a volume thing, and I don't need to worry about sealing up the basement. Enough air should find it's way in for the gas burning devices.


Most older basements leak enough air. If you seal the walls up tight you need to bring air in ( duct)
If not then air would find a way to come down from above with all it;s moisture and mix with the cooler air in the basement and then the moisture will find some cool place to condense.


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## quatsch (Feb 4, 2021)

> my basement is not even chilly.


So the walls & floor are not very cold, at least not yet. The earth around your basement is probably at 50F.

"Divide room volume (Step 1) *by total/1000* (Step 2). If less than 50, additional air is needed. If greater than or equal to 50, no additional air is needed."
But I'd think you need to know the BTU/hr rate.


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## Old Thomas (Nov 28, 2019)

I would not insulate between the basement and first floor. Heat migrating down is very slight and insulation is not helping. I did insulate between my first and second floors. We like our upstairs bedrooms cool and noise is reduced. Our kids’ bedrooms are above our tv watching room and noise was never a problem.


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## Missouri Bound (Apr 9, 2011)

Was it chilly before you insulated it?
Insulation is never a bad thing to have.
But you can't leave it like it is. 
What are you doing to cover it?


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## Jim Port (Sep 21, 2007)

quatsch said:


> So the walls & floor are not very cold, at least not yet. The earth around your basement is probably at 50F.
> 
> "Divide room volume (Step 1) *by total/1000* (Step 2). If less than 50, additional air is needed. If greater than or equal to 50, no additional air is needed."
> But I'd think you need to know the BTU/hr rate.


What is the additional air needed for?


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## Dave Sal (Dec 20, 2012)

Info-512: Crawlspace Insulation


Read this in depth information sheet discussing crawlspace insulation, addressing issues from condensation and drainage to how to approach vapor permeance.




www.buildingscience.com


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## Ronnie833 (Jan 9, 2021)

Exposed fiberglass batting like that is a health hazard and should never be exposed in spaces you're likely to use. I see a work bench down there. I took all the insulation out of my basement. It made no difference to the 1st floor temperature. But....my basement is airtight. You'll need to fix any air leaks to the outside.


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## HolyWhip (Oct 6, 2021)

Missouri Bound said:


> Was it chilly before you insulated it?
> Insulation is never a bad thing to have.
> But you can't leave it like it is.
> What are you doing to cover it?


If I was going to leave it between the joists, I would cover it with 3/8" drywall where I could (of course there would be some gaps for pipes and wires).


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## HolyWhip (Oct 6, 2021)

Ronnie833 said:


> Exposed fiberglass batting like that is a health hazard and should never be exposed in spaces you're likely to use. I see a work bench down there. I took all the insulation out of my basement. It made no difference to the 1st floor temperature. But....my basement is airtight. You'll need to fix any air leaks to the outside.


I started putting up 3/8" sheet rock. It's hard to tell in the picture but one panel is in the back already up. 
Now I think I'll take down all the batt insulation (except near the rim joists, which I've sealed with rigid board and foam), and move all those Batts up to my attic. 

I was concerned about making my basement air tight, because I have a gas furnace and gas hot water heater down there.
From what I'm hearing, I should have enough air coming in even if I seal it up relatively tight.


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## HolyWhip (Oct 6, 2021)

Jim Port said:


> What is the additional air needed for?


I have a gas furnace and gas hot water heater down there in the basement. So I was concerned about sealing it up too tight and running out of oxygen. But then I also don't want a ton of cold outside air coming in and raising my heating bills either. Seems like a delicate balance, but from what I'm hearing, I could seal it up pretty good and still have more than enough oxygen coming in for the combustion.


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## turbo4 (Jan 30, 2021)

You most likely have enough cracks and holes to provide air even if you seal up everything you can find. A well sealed basement will not get very cold even with no heat at all added. Definitely seal up anything where you can see outside from inside. All that cold air coming in the basement is pushing warm air out the upper floor. With well sealed basement you dont need a radiator. My underground basement stays above 70 with just the heat coming off the boiler with no added heat at all and its 1000SF . Also i have no insulation at all in the walls or ceiling.


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## Ronnie833 (Jan 9, 2021)

HolyWhip said:


> I started putting up 3/8" sheet rock. It's hard to tell in the picture but one panel is in the back already up.
> Now I think I'll take down all the batt insulation (except near the rim joists, which I've sealed with rigid board and foam), and move all those Batts up to my attic.
> 
> I was concerned about making my basement air tight, because I have a gas furnace and gas hot water heater down there.
> From what I'm hearing, I should have enough air coming in even if I seal it up relatively tight.


Yes, that is an important concern. Probably better to ask in the HVAC forum. In any case, there are products specifically for bringing in "replacement air" for your gas furnace and HW heater. So, having gas equipment should not prevent you from making your basement fully airtight.


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## Missouri Bound (Apr 9, 2011)

I doubt you need this....but if you want you certainly can do something like this.


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## Missouri Bound (Apr 9, 2011)

HolyWhip said:


> I have a gas furnace and gas hot water heater down there in the basement.


When you say furnace.....you mean that boiler, correct?
Any idea how old that is? Or how big?
Boilers can last a long time but when you replace it the new one will most likely be much smaller and may even have a high efficiency burner that brings in it's own combustion air.
Take a look at the tag on the boiler. You will have input and output of the BTU rating.
That will tell you it's efficiency. Perhaps you can save some money by replacing it.
Not that is anything you want to hear right now


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