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Old 02-20-2009, 01:54 AM   #1
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Insulating to stop air infiltration in the basement.


I bought a home last summer that was built in 1920. At that time, I thought the house was well kept and probably had very little issues or problem. At least, that's what the home inspector told me after checking my house. However, I learned it the hard way when fall and winter finally arrived. The whole house was just cold nearly as cold as outside. After spending over $1,000 in insulation for my attics and my basement and sealing off my leaky windows, finally the house is brought to a comfortable level. However, my first floor always seems to be cold especially in the corners along the floor and the drywall even though my newly installed thermostat says the air is warmer. So, I did some further investigation and found out that there is a huge air infiltration through my basement rim joists and the sill plates. There is a gap of 1 inch between the basement wall and my first floor rim joists. Also, there are holes here and there between my joists at the rim that you can stick a finger or two and feel gush of outside air flowing through the joists. Now, I know what the problem is how do I go about fixing it or stopping it air? I am frustrated that the fix is pretty simple but getting at these gaps is going to be very hard. But what do you put in these gaps? spray expanding foam (Polyurthene Foam), stuff installation batts into the holes, or stuff anything that will stop the air running through my joists. I want to make sure that the solution is reliable not half-baked fixes that it makes no difference after spending $100s of dollars. Please, any advise or hints or help will be greatly appreciated. Our feet always feel cold. So, my wife always raising the thermostat no matter how much I explain or yell at her that she shouldn't raise the temparture.
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Old 02-20-2009, 05:34 AM   #2
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Insulating to stop air infiltration in the basement.

Is it the rim joist or the mud sill that lays on the foundation. and if so is the foundation block or concrete. if its block make sure the hollows in the block are filled..I would recommend using some mortar mix to fill these gaps. only because your saying they are an inch high. this will also help in supporting the sill. gaps that size will more then likely attract mice to come into the basement when the temp outside drops.
Foam would be the easiest thing to use and the best to seal all gaps as long as you don't have problems with mice. they will eat there way into the house through the foam. it would all depend on the access to the area. GOOD LUCK BOB
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Old 02-20-2009, 12:02 PM   #3
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Insulating to stop air infiltration in the basement.

Thanks for your reply. I guess I didn't give complete details. This is a two story house - Basement is the lowest level in the house followed by the first floor and second floor. My basement is directly underneath my living room. I am not really sure but the basement wall looks like a solid stones stacked up on top of each other on which the first floor sits on. In the basement, the walls are finished and insulated. There is this coal room they call it that is sitting right underneath my porch, which is basically opened to outside elements even though this coal room has walls and windows. I am second guessing that this air infiltration is because of my coal room which I am not using or will ever. Let me give you some idea of what my sill plate and rim joists look like by drawing an image and where the air infiltration is. This gap is all around my first floor joists. Any kind of help will be greatly appreciated. Thank you.

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Old 02-20-2009, 12:21 PM   #4
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Insulating to stop air infiltration in the basement.

Ok first some terminology so we're talking about the same thing. All those joists running across the ceiling of the basement are floor joists. The one running around the perimeter of your house is the rim joist. The rim joist and ends of the floor joists sit on the sill plate which sits on the stone foundation.

That 1" gap you feel between the basement wall and floor joists is the thickness of the sill plate and is normal. Since you have a stone foundation there probably are also a lot of gaps between the sill plate and stone foundation that will allow air in and must not have been filled when the wall was insulated.

It sounds like the rim joist itself has also not been insulated and that you have access to it. I would insulate the rim joist. I prefer cutting foam board to fit between the floor joists tightly against the rim joist and spray foam in these panels to seal them tightly. You could also use fiberglass batting.

The area around the sill plate should also be spray foamed to seal the gaps.
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Old 02-20-2009, 01:24 PM   #5
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Insulating to stop air infiltration in the basement.

First off, jogr is right,,you need to seal those areas. My question is,,,is the red in your drawing really touching the stones? Or you think they are?? My best guess is there is a gap ALOT of places. Best way of checking I know of is,,,put as strong of light you can down in this area.(up in floor joists area) Go outside when it is DARK. You see light coming from someplace,your losing heat and gaining mice!! You may have to lay down and look up if you have siding on your house like mine has. I looked everywhere when it was warm too,,,forgot to lay down and look UP!! I have same problem and as soon as I can it WILL be fixed. Caulking needs warmer temps. ONE temp fix is the foam cord backing type stuff. You can put that into the worst of spots and caulk over later.

The stat dont know how cold the floors are,,my floors are 58-60. Head tall sitting at my puter is 66. My basement is 55. It will be warmer next year!!ONLY other way is to heat your basement warmer than upstairs so heat comes up thru floor. Quite wasteful to say the least. You can also seal the area where the basebord meets the wood floor. They sell 'Great stuff' at the box stores for pretty cheap sometimes. How thick is that foam insulation against foundation wall now?? 2" pink foam is R-10,,,thats BEST material for the rim joist area!!
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Old 02-21-2009, 03:19 AM   #6
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Insulating to stop air infiltration in the basement.

The red blocks in my drawing is my brick wall and it is sitting on the edge of the basement wall. It looks like the previous owner had done some sort of poor masonry work where the last row of bricks are sitting. I am not sure if the air is actually coming in that way, but then again I could be wrong. I think I will try your idea with a light. After spending considerable amount of time in my basement, I came to realize that part of the infiltrating outside air is entering my basement through these open holes right in the bottom of my rim joists and hitting my basement ceiling. So, I did spend about a day going around fixing them by stuffing a small garbage bags with insulation batts into these holes. On top of that, I also blocked the whole Rim Joists with rigid foams up against the basement ceiling and the against the rim joists. It made a huge difference that my furnace don't run On and Off all the time like it use to. However, as I explained to you guys earlier. The air is still traveling through my rim joists although now it is not directly hitting underneath my first floor. Still, it could be better by completely filling these sill plate gaps with something. I am thinking of this spray foam that I have been reading about. You guys might know this. It is called spray foam. That expands to fill all holes and gaps as it expands. They usually come in canisters and are expensive. But, can I spray foam insulation into the sill plate gaps? Is that dangerous to do? My thinking is that since I can't see the gap very well with my eyes and don't even know how the air is comming in spray foam will fill all the gaps and seal it good. Plus, it will be very easier on me. I can get the job done in a half a day rather than the whole weekend.

My second floor always at around 60 to 67 and the first floor is at 69 to 72, but the first floor feels like 60 or 59. My basement on the other hand it is at around 59 to 65 all the time.

Any help will be appreciate it. Thank you.
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Old 02-27-2009, 07:58 AM   #7
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Insulating to stop air infiltration in the basement.

I sorely want to just stuff something into these sill plate gaps and I am just desparate guys. I don't know what to do. Our 80% furnace is running every 8 mintues even though it is 40 degree outside. Plus, we just feel cold as if we are inside an icebox. As a result, my first floor and the walls just feels cold to the touch. It is as cold as outside.

So, I am looking for some cheap but reliable solution to fill these sill plate gaps. I have looked everywhere and the type of foams I want to get for this project is not sold in our local hardware stores even at HomeDepot and LOWES but only online. Since this gap is not easily accessible and can't be seen hardly. Pretty much I am going to be shooting dart in the dark hoping that it fixes the problem. So, I need a type of foam that I can just pour or squeeze into these gaps. I found out that there are 3 different types of foam that I can really use - Spray, Pour and Retro (like a paste). These are not sold locally and also you have to get contractors if I am going to want anyone of these foams.

Can someone please direct me to a company or a website that you dealt with before where I can get more information or get someone to come out? I would appreciate it. Thanks.
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Old 02-27-2009, 08:26 AM   #8
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Insulating to stop air infiltration in the basement.

Can you take some pictures of the areas?
That would help to see what you have

Any old windows leaking air? Poorly sealed door?
Old dryer vent not sealed up?
New dryer without a flap vent?

These are some of the issues I have seen
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Old 02-27-2009, 08:36 AM   #9
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Insulating to stop air infiltration in the basement.


Here's a link to Great Stuff website. I can get this stuff at Home Depot.
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Old 02-27-2009, 01:13 PM   #10
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Insulating to stop air infiltration in the basement.

I just insulated and sealed my rim joists with 2" thick extruded polystyrene from Lowe's and caulk and spray foam. It made a big difference and, counter-intuitively, made the top floor warmer by reducing the stack effect.
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Old 02-27-2009, 05:00 PM   #11
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Insulating to stop air infiltration in the basement.

Foam is great but in your case the KISS principle may apply. Just stuff and fill any gaps with fiberglass insulation. It wont cost much, will be done pretty quick, and should have immediate benefit. Worst case you pull it out and hire a spray foam contractor and you are only out a few bucks and a few hours.
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Old 02-27-2009, 08:06 PM   #12
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Insulating to stop air infiltration in the basement.

Fiber glass will get wet with the moisture transfer and should not be used. extruded polystyrene of spray foam only is the way to go.
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Old 02-28-2009, 11:03 AM   #13
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Insulating to stop air infiltration in the basement.

DIY: There is a product which may interest you called Roxul Flexibatt.
It is an insulation which is used in the same fashion as that horrible fiberglass pink. With pink, it won't do you any good to stuff it into holes, because that will pack it. Pink relies on the millions of air spaces to create dead air.
Roxul, on the other hand is quite solid. It can be cut very easily with a bread knife, has a higher R-value than pink, doesn't have that charming itch you get with pink. It will not burn. Water doesn't hurt it. It's made from rock.
You can stuff it into little holes as tight as you like and it WILL stop the air infiltration, which is very obviously your problem.
I have nothing but good things to say about this stuff, and since I discovered it a few years ago, I have not had to go anywhere near pink since.
I get it from Home Depot.
This is what it looks like.
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Old 03-03-2009, 09:47 AM   #14
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Insulating to stop air infiltration in the basement.

I really wanted to use this stuff in my application, for some reason its not available in NY
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Old 03-03-2009, 10:34 AM   #15
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Insulating to stop air infiltration in the basement.

Use an infrared thermometer to find the coldest areas.
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