# insulation question



## Stirdy (Jan 24, 2010)

I have a dirt basement (almost a crawl space) that stays fairly warm in the winter. I think its because of all the exposed duct work. But, the master bedroom is an addition with its own crawl space that gets cool. Rolled insulation is stuffed into the floor joist and has fallen out or sagging in areas. I was thinking about stapleing some plastic up to hold the insulation in place.

I was wondering if this would be ok, not sure if it pose some sort of vapor barrier issue....


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## gobug (Dec 10, 2003)

A plastic layer under the insulation on the bottom of the flooring would definitely improve the insulation value of fiberglass beneath the master bedroom. Fiberglass with an air flow through it has almost no insulative value. 

It used to be code here that crawl spaces and basements have air ventilation. IIRC, that is no longer code and considered to be not the best. Perhaps you have entirely different factors that influence the different temperatures in your crawl space and basement.

I suggest you get a temperature gun and measure temperatures in various spots of the spaces below. This will help you identify where you lose heat or gain cold air.

Insulation of the inside walls of the basement or crawl space does not work as well as insulation along the outside surface of the crawl space. Inside insulation along the crawl space walls also creates an opportunity for mildew and other molds. Unfortunately this is easiest in the early stages of construction, not after construction is complete.

I would consider using a foam board insulation beneath the heat duct work. The foam board is a lot easier to attach to the basement/crawl space "ceilings". Duct tape could be used to close up the gaps along the foam board edges.


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## VaFarmer (Mar 2, 2011)

where are you located? more cold days than hot or more hot days then cold? Your climate determines proper location of a vapor barrier. Cold climate it goes closest to your heated interior to prevent warm air from condensating in the insulation, in area that has more warm days than cool weather the vapor barrier goes toward the warm side/ furthest from your conditioned interior suchas bottom of your floor joist would be OK. You state that insulation is falling down this is typically a condition of crawl space air-water vapor condensating in the insulation, when converts to water the insulation gets heavy and starts falling down. Sounds like you need to start with 6mil plastic covering the dirt floor, run it all the way to block walls and install nailing strip or epoxy chaulk edge to block (seal it somehow). with out the vapor barrier and humidity above 20% you have mold growing, and not all mold is visable, if cleaning wear at least a dust mask min. If you clean the wood use a hydrogen peroxide mix, chlorine does not kill the roots of molds only makes the mold dorment untill humidity gets above 20% again and then mold will start to grow again.


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## Ross (May 9, 2002)

If you don't seal it tight its not an issue. I've seen chicken wire used and then you have a larger animal barrier too.


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## boiledfrog (Jun 2, 2011)

I'd staple a criss cross of string under the insulation. Having a cold crawl space is not a real problem. Having the cold rise into the room is.


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## wharton (Oct 9, 2011)

Hhere in northern Pa. a properly designed, built and insulated crawl space can be as dry and warm as an Egyptian Tomb. That said, most vary from barely acceptable to wet, moldy disasters. The best method was mentioned in the second post. It's called a sealed conditioned space. The idea is to seal the floor with plastic, or a concrete slab over plastic. Then block all the vents with foam board and insulate the walls with more foam board. There is no insulation in the floor joists, and the space can be conditioned (heated and dehumidified) in several ways. One is to add ductwork from the hot air heating system. It doesn't need much, just a very small feed and return. When I build new homes I install a medium sized dehumidifer and a small electric garage type heater that hangs off a bracket. I either have the walls spray foamed with r-10 or install 1-1/2" thick sheets of the foil faced foam. This end result in new construction is that the dehumidifer will run full out for a few months to get all the construction moisture out, then it will only run occasionally to keep the humidity below 50%. The electric heat only would run in a real ugly cold snap, since the space is kept pretty warm from the building sitting on top of it, and the fact that it's buried in the somewhat warmer earth. Having built six of these in the last few years, I can say that they stay warm, dry and continue to impress me.
This technique presents two possible health issues that need to be considered. First, if you have a potential radon issue, the time to deal with it is when you are building or upgrading the crawlspace. An old style, fully vented crawl space in a heavy radon area may have very low reading in the home, but have the numbers spike after properly sealing and insulating. The second is fire safety. Foam is flammable, and the code requires a fire rated covering over it. Dow makes a foil faced foam listed as thermax, which is rated. Spray foam gets an addition coating or a thick rated paint to meet code. 
When I encounter conditions like the OP has, I do a few things that radically improve the crawl space and reduce the heat bills.
#1 Remove all fiberglass insulation, mitigate mold and repair any structural issues, block all existing vents. 
#2 Correct and grading and drainage issues on the outside of the home. Gutters cleaned, repaired and functioning properly. Grade pitched away from the house. Downspouts extended 10' from the foundation.
#3 Install a thick (15MIL) plastic vapor barrier on the floor, seal all joints with the proper tape and secure the sheet to the walls about 1' up. 
#4 The insulation contractor then sprays high density ureathane foam from the plastic covered dirt floor up to the bottom of the wooden subfloor. In this area R-10. 1-1/2" is enough. 
#5 Install a dehumidifer. In the event that it cannot be gravity drained with a small section of garden hose, it can be drained into a condensate pump, and drained outside through a small tube. this is a simple, inexpensive pump that is used to drain condensate from central AC systems.
Then end result is a warm, dry space, lower heat bills, and no mold. In mixed climates like here, vented crawl spaces are generally failures, and additional venting, or adding a layer of plastic to the bottom of fiberglass filled floor joists, only makes things worse.


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## fishhead (Jul 19, 2006)

If you are considered about creating an unwanted vapor barrier I think you could use a house wrap like Tyvek to stop air movement but allow moisture to travel.

I just insulated a floor in a room with an uninsulated crawl space underneath. I put down 1" of blue foam covered with 5/8" stained particle board followed by 4 coats of floor quality water based polyurethane. It came out looking pretty good and isn't cold anymore.


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## fishhead (Jul 19, 2006)




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## Gianni (Dec 9, 2009)

Venting a crawl space is one of the first things to do to eliminate a Radon build up. If there is Radon gas in the area I would vent it and put the plastic under the insulation. If there is ducting in the room the small air space will vent some from the insulation to the room.


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## Seymour (Dec 15, 2011)

fishhead said:


> If you are considered about creating an unwanted vapor barrier I think you could use a house wrap like Tyvek to stop air movement but allow moisture to travel.
> 
> best info i've heard, i'm a building inspector in canada and run into this problem lots, house wrap is your best option, also if you use Roxul batt insulation (mineral wool) rather than fiberglass you will get better r-value and a stiff piece of insulation as well as a rodent barrier.


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