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Old 01-22-2019, 12:46 PM   #1
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Insulating Floors


I need some insight on insulating the 1st floor in a very old antique yet renovated/modernized house.


We recently switched from LP forced air to radiant wood heat and are noticing a draft coming up from the 1st floor. right through the flooring. I guess we never noticed it when the forced air came on because it was mixing. Now with the steadier heat output, we notice it.


I'm not sure if I should insulate the floors when I pull them up for new flooring, or simply repoint and fix some of the air leakage in the basement walls, which is stone. I know these houses are supposed to "breathe" from the bottom up because they're not moisture locked. However everything else seems to have been torn down and insulated including the walls (I think) and attic (for sure).


Currently the condition of the floor is plywood over beams, then 3/4 pine for finish. No underlayment. I was thinking for the insulating, pull up flooring and add 1/4" foam board over plywood, then new flooring over top of that.


I would also like to note that when the forced air is off, cold air is coming up from the floor registers. All of the duct work from the furnace (which is relatively new) is wrapped and insulated. Not sure why cold air is being sucked through them into the house.


Thank you.
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Old 01-22-2019, 01:19 PM   #2
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Re: Insulating Floors


During cold weather all houses experience "stack effect" with cold air pushing in the lower portions and forcing warmer inside air up and out the upper leak areas. Seal all leaks and the drafts will go away, I know, difficult.

I have seen a few stone foundations covered with a couple inches of spray foam, fantastic results. Most building codes will require a thermal covering and they make a special paint that can qualify. But the application can cover the walls and the rim right up to the bottom of the floors above.

What type of wood stove are you using, air tight, sealed combustion?

Your thought about pulling up the floors to add a 1/4" layer of foam might air seal a little but nothing for insulation. With plywood under the floor there are few paths for air.

If you can see the bottom of that plywood from below you can seal just about everything with caulking.

Wrapping the ducts with insulation does not mean they sealed all joints and seams, just hides the fact. A little inspection and you can determine if they foil taped or coated in mastic all potential leaks. Without that everytime the blower comes on it creates pressure differences blowing good air out while sucking cold air in.

Bud
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Old 01-22-2019, 03:25 PM   #3
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Re: Insulating Floors


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During cold weather all houses experience "stack effect" with cold air pushing in the lower portions and forcing warmer inside air up and out the upper leak areas. Seal all leaks and the drafts will go away, I know, difficult.

I have seen a few stone foundations covered with a couple inches of spray foam, fantastic results. Most building codes will require a thermal covering and they make a special paint that can qualify. But the application can cover the walls and the rim right up to the bottom of the floors above.

What type of wood stove are you using, air tight, sealed combustion?

Your thought about pulling up the floors to add a 1/4" layer of foam might air seal a little but nothing for insulation. With plywood under the floor there are few paths for air.

If you can see the bottom of that plywood from below you can seal just about everything with caulking.

Wrapping the ducts with insulation does not mean they sealed all joints and seams, just hides the fact. A little inspection and you can determine if they foil taped or coated in mastic all potential leaks. Without that everytime the blower comes on it creates pressure differences blowing good air out while sucking cold air in.

Bud

I figured the draft is probably coming through the floors from the gaps in the basement foundation. Repointing the foundation walls seems like it's going to be the project for the summer. The rest of the house is pretty tight aside from two entry doors.


The stove is a Jotul F500, it's an EPA tube stove.


Insulating the floors, or sealing them I don't know which would fit this application best. I'm just trying to keep the cooler basement air from coming up through the floor. The air getting sucked in through the floor boards actually seems colder than the basement itself.


The issue with the ducting is I'm getting colder air coming up through the registers with the furnace and blower off. So when it's not running, which we haven't been doing due to the stove, cold air is coming up through them. Almost like we turned the A/C on. We've resorted to covering the registers with rags to keep it at bay.
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Old 01-22-2019, 03:48 PM   #4
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Re: Insulating Floors


A wood stove needs make up air so it's going to sucking in air anyplace it can.
If the old registers are not being used you can buy magnetic covers for them, or better yet do away with the old ducts.
Balloon wall constrution?
If so have the walls been fire blocked?
Not sure why you think pulling up the flooring will do any good, it can all be done from under the floor.
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Old 01-22-2019, 03:54 PM   #5
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Re: Insulating Floors


A "pretty tight" house will normally exchange all of its inside air every 3 hours. To get tighter than that requires a lot of effort and some deliberate ventilation. Leakage is normal and air exchange is necessary. Modern homes just control the air paths.

Leaking into the basement is one thing, but it isn't leaking through that layer of plywood except for holes and seams, both of which can be addressed from basement it ceiling is exposed.

Another source of that cold air at the floor level could be the rim of the floor framing. Being an older home I don't know how your frame and floors were constructed. If balloon framing then the edge of those floors could be exposed to the wall cavities. A picture of the rim area might tell us, but if you can reach up into the wall cavities from the basement it is probably balloon.

Even if platform framed the exterior walls probably sit on the plywood with the new hardwood floor spaced off to the inside. That gap and lack of an underlayment provide a path for cold air.

Nothing absolute here as hard to see from my chair.

Do you have any supply or return ducts in the basement?
Is the furnace in the basement?

Bud
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Old 01-22-2019, 06:02 PM   #6
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The house is timber framed if it helps.

i don’t know if the walls are fireblocked, I’m not entirely sure I know what that means. There is 2x6 framing in between the post span. The posts are something like 8”x8”.

From what I gather, there’s not much I can do about the air being exchanged aside from slow it down a bit. Really I just want the floors to stop pulling up so much air. So my options are sealing the seams in the plywood from below or putting in some insulation from below. Would a rigid type foam friction fitted work adequately?
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Old 01-22-2019, 06:13 PM   #7
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Re: Insulating Floors


Air doesn't usually blow in. It is usually sucked in like a vacuum. Wood fire, fans, bathroom and range as well as people all are using the air in the house causing a vacuum, nothing will stop that replacement air from getting in.
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Old 01-22-2019, 07:42 PM   #8
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Re: Insulating Floors


Would it be possible to get some pictures of the floor joists from below, the perimeter?

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Old 01-22-2019, 09:32 PM   #9
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Quote:
Originally Posted by Bud9051 View Post
Would it be possible to get some pictures of the floor joists from below, the perimeter?

Bud
Yes I will try to upload some pics tomorrow evening. I will need to shovel the snow away from the cellar door.
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Old 01-22-2019, 09:41 PM   #10
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Re: Insulating Floors


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The house is timber framed if it helps.

i donít know if the walls are fireblocked, Iím not entirely sure I know what that means. There is 2x6 framing in between the post span. The posts are something like 8Ēx8Ē.

From what I gather, thereís not much I can do about the air being exchanged aside from slow it down a bit. Really I just want the floors to stop pulling up so much air. So my options are sealing the seams in the plywood from below or putting in some insulation from below. Would a rigid type foam friction fitted work adequately?
That doesn't sound like you have to worry about fire stop.
Balloon framed houses had studs that went from the foundation to the roof so a fire in the basement could go right to the attic.
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Old 01-23-2019, 08:48 AM   #11
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Re: Insulating Floors


I did some searching but didn't find anything related to how they were built long ago. I have worked on some older homes where a large beam was placed around the perimeter where we would normally place the sill plate. It is from there up that I'm trying to identify how the floor joists were installed, on top of that beam or butting into it and thus how the plywood above was installed.

I suspect the extra cold air is coming from the rim area and some sealing from the basement may be productive.

Input welcome.
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Old 01-23-2019, 07:53 PM   #12
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A little late coming but I had to clear a 4’ snowdrift off the cellar door.

I think I got the types of pics you’re looking for. Disregard the old floor timbers. They aren’t supporting much weight if any at all.

Looks like I was mistaken. There’s no plywood under the flooring. Just two layers of floor boards.

There was some insulation stuffed between the joists at some point. Looks like it has been removed since. Probably due to too much moisture.
Attached Thumbnails
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Old 01-23-2019, 08:22 PM   #13
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Re: Insulating Floors


A lot of seams to seal but that's where the air is coming from. You could cut and fit some foil faces rigid insulation and caulk or leave a gap around the edges and use can foam.

Bud
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Old 01-24-2019, 10:24 AM   #14
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Re: Insulating Floors


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A lot of seams to seal but that's where the air is coming from. You could cut and fit some foil faces rigid insulation and caulk or leave a gap around the edges and use can foam.

Bud
You mean between the joists correct?
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Old 01-24-2019, 10:51 AM   #15
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Re: Insulating Floors


End to end side to side all seams. Seams that pass over the top of each joist are isolated by caulking the full length of each joist. Sounds like a lot and some spots are tricky but using your 5 finger multi-tool can get most.

I use the large tubes of construction adhesive from loctite.

Bud
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