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Discussion Starter · #1 ·
This may sound like a stupid question but if I finish my basement but don't insulate ALL the walls, am I wasting money? Or is some insulation better than no insulation?


There are some areas that I just wont be able to get to and there are also a few areas that have so many wires (like above the circuit breaker box) that I'd rather just leave it as is.


Also, I won't be insulating inside the boiler room but do I need to insulate the walls that separate the boiler room from the rest of the basement? If not, won't the cold air in the boiler room make the basement cold?
 

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Yes. Some is better, but even better is the right amount.

You are more likely to create a moisture (mold and mildew) issue from the improper selection and application of insulation than you are not using it at all.

While not insulating makes the home leak energy and air like a sieve, the fact is that the room side heat/air will warm the walls up as it is letting all that energy go right to outside and will likely keep the surface temperatures away from dewpoint in most cases.

https://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf
 

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Windows on wash is right. There's also the fact of drying. When an open surface condensates, the water then begins to evaporate as well. When you enclose the surface, even with a vapor permeable solid like drywall, you still discourage/slow the drying process. Trapping the moisture leads to mold & rot.
 

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Your furnace loses a lot of heat to the air around it and if it is located in a cold room with little or no insulation, that energy is quickly lost.

If you can only get a little insulation into a particular place where all else is well insulated, that is very important to do. If you consider a 20' wall section where 1/2 is well insulated and the other half is not, then the heat loss will be dominated by the uninsulated half. If you were to add a small amount to the insulated side it would have almost no benefit. Add that same small amount to the uninsulated side and it could make a huge difference.

As stated, keep it tight to the walls to prevent air from reaching a cold surface, but add insulation where ever you can. Remember, an uninsulated concrete wall has an r-value below 2. References vary.

Bud
 

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Discussion Starter · #7 ·
Based on the info above, would this mean that if someone insulated their basement fully, but forgot to insulated one small section of the rim joist, then that uninsulated section would get moldy?


This goes back to my question about the boiler room. If I insulate the whole basement, except for the boiler room, would I be creating a breeding ground for mold in there? Or since there's room to breathe in the boiler room (i.e. no drywall/batts right off the cement walls) any moisture from heat trying to escape from there won't cause any problems.


Aside from mold issues, would leaving the boiler room unfinished and uninsulated make the entire basement cold and thereby negate the impact of the insulation in the remainder of the basement?
 

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Usually the boiler room will be well heated by the heat lost from the boiler and any areas of uninsulated wall will warm enough on the surface to avoid any condensation.

However, when sealing off a room you must consider how any moisture that gets in will get out. If the boiler is drawing combustion air from that room and there is an outside source to replace that air, yes it will get cold in there, but when the boiler cycles off the temp will rise.

As for that room contributing to cooling of the basement, yes, unless you insulate the interior walls.

Bud
 

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Discussion Starter · #9 ·
Usually the boiler room will be well heated by the heat lost from the boiler and any areas of uninsulated wall will warm enough on the surface to avoid any condensation.

However, when sealing off a room you must consider how any moisture that gets in will get out. If the boiler is drawing combustion air from that room and there is an outside source to replace that air, yes it will get cold in there, but when the boiler cycles off the temp will rise.

As for that room contributing to cooling of the basement, yes, unless you insulate the interior walls.

Bud

Is it safe to insulate walls near a gas furnace and water heater? The interior wall is a few feet away from both units. Do I have to drywall both sides of the interior wall?
 

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Interior walls should not present a moisture problem unless you turn that utility room into a second refrigerator. I had a 12' x 16' utility room with a big boiler and a big intake fan controlled by the boiler. I was worried that the room would freeze, but it remained reasonable even during very cold temps. Drywall the side you want to look good and optional on the other side. IMO

Bud
 

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Discussion Starter · #11 ·
Interior walls should not present a moisture problem unless you turn that utility room into a second refrigerator. I had a 12' x 16' utility room with a big boiler and a big intake fan controlled by the boiler. I was worried that the room would freeze, but it remained reasonable even during very cold temps. Drywall the side you want to look good and optional on the other side. IMO

Bud

So should I, or should I not, insulate that interior wall? The boiler room is pretty cold at the moment but I leave the door open to the rest of the unfinished basement. It may "warm up" once the rest of the basement is finished and the door is closed. However, not sure if adding a make up vent/pipe will make it extra cold in there.
 

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I can't give you a definite answer as I'm not there, I said it should not be a problem but you will have to judge whether any surfaces are going to reach the dew point.

Since the furnace is right there, if you are terribly concerned, add a small supply and return to the room.

Bud
 

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Based on the info above, would this mean that if someone insulated their basement fully, but forgot to insulated one small section of the rim joist, then that uninsulated section would get moldy?
Specific to this - the answer is no. Because if the rim joist is exposed to the interior, it's surface will mostly remain warm (above the dew point) and it will have air circulation to dry if any condensation does develop.

If you insulate the interior wall, you should drywall & paint both sides & install a vapor retarder (kraft paper) to the warm side. This will limit vapor migration inside the wall, which will go from warm to cold.

Assuming the boiler room will be cooler than the other side of the wall, you may develop some condensation on the drywall when you open the door and the warm air rushes in. Since it's exposed, though, it should dry before becoming a problem. If you insulated the wall, but left the door open all the time, you may eventually see mold growth as it may condensate constantly and never dry out.

You want to isolate these areas and limit natural vapor migration so that you won't have condensation develop inside the wall.
 

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Hi Nick, not to get picky, but I just don't see the condensation issue. The room will be cool, not cold and it will be due to venting cold dry outside air. As that air warms up, its RH will go down.

As for warm inside air depositing moisture on the walls inside that room, those walls won't remain cool long enough to form condensation.

As for a vapor barrier, way overkill and technically, moisture moves from high concentrations to low concentrations, not warm to cold.

This is a simple issue and does not need a complex solution.

Bud
 

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Hi Nick, not to get picky, but I just don't see the condensation issue. The room will be cool, not cold and it will be due to venting cold dry outside air. As that air warms up, its RH will go down.

As for warm inside air depositing moisture on the walls inside that room, those walls won't remain cool long enough to form condensation.

As for a vapor barrier, way overkill and technically, moisture moves from high concentrations to low concentrations, not warm to cold.

This is a simple issue and does not need a complex solution.

Bud
You might be right on overkill & overthinking, Bud. I'm picturing this in my basement, where if I had a room on an outside wall that was not insulated, it would be cold; probably a 50+ degree delta temp.

I do however hold that if you're going to insulate, that you should use a vapor retarder. Besides, it makes hanging the batts easier anyway.

Barring some major dumping of moisture into the cold side, the cold side will be the lower concentration and generally is. Moisture will migrate through this wall because of that. If the dew point is met inside of the wall, that's a problem and why I suggest the vapor retarder to the warm side.

Following your thinking that the boiler will keep it pretty close in temp, a vapor barrier/retarder is not really necessary, but neither is the insulation then. If the backside was not drywalled and the insulation left exposed, there probably is no concern of condensate, but leaving exposed fiberglass is a poor practice and introduces it's own health risk.

Personally, I'd just insulate the exterior wall and be done with it.
 

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If you insulate the interior wall, you should drywall & paint both sides & install a vapor retarder (kraft paper) to the warm side. This will limit vapor migration inside the wall, which will go from warm to cold.
Interesting. I've never heard of kraft paper as a vapour barrier - only poly. Must be regional differences. I agree that un-covered insulation is a bad idea. I would only insulate interior walls for sound.
 

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Interesting. I've never heard of kraft paper as a vapour barrier - only poly. Must be regional differences. I agree that un-covered insulation is a bad idea. I would only insulate interior walls for sound.
Kraft paper is considered a "Vapor Retarder". Poly is pretty well impermeable, but kraft paper is designed to slow, but not stop vapor migration. Benefit being that, theoretically, water inside the wall structure could eventually dry through the retarder.

Selection or exclusion of vapor barriers and/or retarders is pretty important. The building science website that Nik333 linked to is a good source, but there are many other sources with great info. Depending on interpretation, though, some of them seem to contradict each other - newer seeming to supersede older, IMO.

http://energy.gov/energysaver/vapor-barriers-or-vapor-diffusion-retarders

http://insulationinstitute.org/im-a-homeowner/about-insulation/preventing-moisture-issues/

http://www.finehomebuilding.com/item/5090/whats-the-difference-vapor-barriers-and-vapor-retarders

http://www.energyvanguard.com/blog-...or-Retarder-Vapor-Barrier-Perms-What-the-Heck

http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barriers
 
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