# Rim Joist Insulation



## ja191992stg (Jan 14, 2010)

I recently purchased a duplex in Buffalo, NY. House was built in 1920's about 2700 sq ft. I have no insulation in the basement or even the wall I believe. I will at some point have insulation blown into the walls but my first step is the basement. I have a side of the house where the house over hangs the foundation about two feet. So I have a huge cavity in between where the foundation ends and where the house actually ends. So a very deep rim joist cavity. I will try to post a picture. How do I insualtate this area? Foam board? I can feel the draft coming in the house. One thing that was cool about starting this project I have found several newspapers for 1920 in each one of these cavities. There is about 12 of these deep cavities between the floor joist, not the whole house. Point me in the correct direction.


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## Bob Mariani (Dec 1, 2008)

Spray foam is the correct way. Fiberglass is the wrong way and will not last or work. But you are correct that this is the most important place to insulate. 10-30% heat loss occurs here. Roxul insulation will also work.


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## gregzoll (Dec 25, 2006)

Fiberglass has been used for years for insulating Rim Joists and homes with no problems. Stating that it will not work, is only a misconception when not installed properly. Last layer used has to have the Kraft paper facing into the conditioned space.


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## ja191992stg (Jan 14, 2010)

Average cost? Ok I have only been in the house since late october, but when we did have some heavy rain, the lower part of the foundation would seep minor water. Only in a couple spots. But this would evaporate quickly probably because i had such a draft. So by doing this foam on the rim joist I am probably going to need a dehumidifer and good coat of drylock paint? The foundation is stone and cement and plaster like top coat. Its solid about two feet thick.


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## ccarlisle (Jul 2, 2008)

You have a few issues; first, use spray foam cans to block off the air leaks from under the sill plate where air, for one, is getting in. Then, do the same thing using butyl caulking compounds, from the outside to, again, prevent things (air, water bugs) from getting in.

Then insulate the area where you can with fibreglass material or polystyrene boards whatever is appropriate for that size area. That will slow down any heat loss from that area. Won't do anything if you don't do step1 above as fibreglass is not a good air barrier - good insulator but not good keeping down drafts.

Then the moisture issue; once the gaps are sealed as in 1 above, this should reduce the amount of buk water coming in. The ideal would be to cover that whole area from the outside with flashing etc - but this isn't a good solution for every case, so let us know when you done all of the above. Pictures would be nice - before and after...


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## Scuba_Dave (Jan 16, 2009)

The problem I have always seen with fiberglass is getting that complete seal
If warm air gets thru the the rim joist frost will form, then mold
I used fiberlgass when we 1st moved in, quick fix & what I was used to doing

I'll be going back & putting in rigid foam to totally seal each area
I have not found spray cans to be a great way to insulate large areas
Expensive buying the cans VS an entire sheet of rigid


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## ididit (Jan 31, 2008)

If I understand you right, your saying the house hangs over the foundation 2' x about 24'. Assuming that the joist are 24" O.C. like most houses ive seen that age. Spray foam is the top of the line insulation but that is not enough area to be worth calling in a spray foam pro unless your gona do alot more elsewhere in the home. Filling that area with canned foam will cost a fortune though. How high is the overhang off the ground. If you have room to get under there (from the outside) I would use fiberglass and put a bottom on the overhang (must use treated ply or a rot prof material if it is closer than 18" off the ground). If you compress fiberglass it will loose R value. So if your joist are 6 to 9" thick you can use r-19 batt and install with paper up TIGHT to floor. 10 to 12" use r-30 and install the same way. You say your getting the house walls blown later so what I would do is to go ahead and seal off the area with ply, spay foam, and caulk leaving out the insulation. Then when the insulators come they can drill holes into the bays and dense pack with cellulose the same way the walls are done.This will be second best only to spay foam and will save you the most money.
Just for your info, the correct way to blow walls with cellulose is to dense pack from the bottom. Aprox. 2" dia holes are drilled as close to the bottom plate as possible between every stud from the outside. The hose is then pushed in the hole and all the way to top plate. The blower is started and the hose is only pulled down about 2-4" when the blower starts to stall. Continue till the bay is compacted full. Plug the hole. If the insulators want to fill the walls from top then get somebody else! Sorry for the long post but im in the weaterization biz so I see this done all the time.


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## Gary in WA (Mar 11, 2009)

SPF and Roxul is best. (As Bob said) My second choice for a 24" cantilever would be a mix of all the other posts. Cellulose or Roxul, then rigid foam board sealed for air *applied to joist bottoms*, then plywood on the bottom. You need that thermal break of foam board. Science site of why: http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/


First I would seal the rim joist of that overhang with foam: http://www.rd.com/57548/article57548.html If your B.D. requires a vapor retarder, staple asphalt paper to the floor decking. Then, if not already, solid block (same size as joists) the bays over the wall (to prevent rotation), air sealing and adding foam board to all the other rims.

Be safe, Gary


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## ja191992stg (Jan 14, 2010)

pictures


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## ja191992stg (Jan 14, 2010)

I would like to paint the foundation with drylock again, what does anyone think


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## ja191992stg (Jan 14, 2010)

The wood in the pictures is not wet, it looks like it was wet at one point but not anytime recently. Leaves in the one joist area shows that alot of air is coming in


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## gregzoll (Dec 25, 2006)

The bays with Knob & Tube cannot have any insulation covering the wires. You are kind of SOL on those areas, unless someone can come up with a suggestion in how to leave an air gap behind the wires and around them.


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## ididit (Jan 31, 2008)

I see the bays already have bottoms so if its in good shape then leave it alone. Dont look wet either so another +. I would just caulk and foam the cracks in the bays and do the blocking that bgr suggested. The blocking will add support (not really neccessary cuz the house is 80 years old and if the joist have not failed yet, prolly never will) and to keep cellulose from falling out as stated in my last post. Like gregzol said your SOL on the bays with knob and tube. Its likely your entire house will need rewiring before any competent insulator will touch it. DO NOT LET ANYBODY INSTALL ANY KIND OF INSULATION OVER KNOB AND TUBE! Its in the walls too. Water profing the basement wall is a whole nother story. Dry lock is just a bandaid and not a good one at that. There are only a few good ways to do it wright. Here is one check out the others too. 
http://www.youtube.com/watch?v=_mY1EHGAqmk


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## Scuba_Dave (Jan 16, 2009)

CA has already "reversed" this due to studies



> *Insulation:*
> Insulating walls and attics in conjunction with knob and tube wiring can be a problem. The National Electrical Code is very specific about NOT *burying* knob and tube wiring under insulation and although some US jurisdictions, such as California, have over-ridden this code, those that have, have specifically stated that the knob and tube wiring has to be inspected by a licensed contractor prior to the installation of the insulation.





> *Building Insulation:*
> K&T wiring is designed to dissipate heat into free air, and insulation will disturb this process. Insulation around K&T wires will cause heat to build up, and this creates a fire hazard. The 2008 National Electrical Code (NEC) requires that this wiring system not be covered by insulation. Specifically, it states that this wiring system should not be in…
> _hollow spaces of walls, ceilings and attics where such spaces are insulated by loose, rolled or foamed-in-place insulating material *that envelops the conductors. *_
> 
> ...


What I find interesting is that they say *envelope* or *bury*
Nothing really about insulation being under or in contact on one side
But pics show non-contact on one site


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## ccarlisle (Jul 2, 2008)

Who said there was K+T wiring there, and in which picture do you all see it?

I don't...
:huh:


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## Bob Mariani (Dec 1, 2008)

ccarlisle said:


> Who said there was K+T wiring there, and in which picture do you all see it?
> 
> I don't...
> :huh:


They are looking at the old (very old) style round romex. These are not knob and Tube.. but what can you do?


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## gregzoll (Dec 25, 2006)

Last picture appears to be K&T, but without another picture of the wires somewhere else running, it is hard to tell. Yes, it appears to be Romex, but need a second picture to tell.


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## ididit (Jan 31, 2008)

On second look that may not be k&t. Especially that its touching the wood. K&T has insulators every so often that keep it from touching anything. Usually, not always tho. Given the year of house. Its still possible that K&T is there somewhere so my previous post still stand.


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## Scuba_Dave (Jan 16, 2009)

My MIL's house has knob & tube & romex
There aren't any insulators where it goes thru the floor in the basement up into the walls

The house in this thread was built in the 20's


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## ididit (Jan 31, 2008)

yea I know. Im an accessor for the weatherization program so ive been in alot of old attics. About half of K&T that I see have insulators 2-3' apart and at the corners where it comes up through the open wall seals and plates. Dont really know if it supposed to be that way and the rest are just hack jobs or if touching wood was ok and the others where done by and obsesive electriction. Anyway I apoligize to the O.P. cuz we sure have gotten way of track from his questions.:whistling2:


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## Bob Mariani (Dec 1, 2008)

no insulates were required when going through studs. These were used to support runs along the studs.


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## ja191992stg (Jan 14, 2010)

yes old wiring, old romex, no ground, those two wires are coming from pole outside to fuses. Yes needs to updated. Back to the insulation question. How beneficial would it be to place foam board in the face of the cavity, leave the cavity empty. just 2 inch foam, with foam or caulk aorund the seams to make it seal better.


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## Bob Mariani (Dec 1, 2008)

This will be beneficial. Be sure to seal it well. Stopping air flow is you main concern.


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## Gary in WA (Mar 11, 2009)

http://en.wikipedia.org/wiki/File:Knob-and-tubes.jpg

"in the face of the cavity," The rim and the bottom, one without the other would give you 1/2. Unless you mean between joists, that would do nothing for the floor above. 

Be safe, Gary


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## ccarlisle (Jul 2, 2008)

ja191992stg said:


> yes old wiring, old romex, no ground, those two wires are coming from pole outside to fuses. Yes needs to updated. Back to the insulation question. How beneficial would it be to place foam board in the face of the cavity, leave the cavity empty. just 2 inch foam, with foam or caulk aorund the seams to make it seal better.


It's highly unlikely that you have both K+T _and_ Romex wiring, it's usually one or the other, and by the looks of it, wth your confirmation, you have Romex. It just doesn't correspond to the K+T I have seen...I'm not an electrician tho'.

Your insulation approach is fine*. Caulk all four sides of the face board facing you, cut pieces of 2" styrofoam XPS to the right size i.e approx 16" wide by 9" high, for each bay), wedge that in there tight against the face, then caulk the gaps you might have made with the can spray foam. 

That takes care of the insulation + air drafts; but in theory you still need a vapour barrier on the inside...Or, do the same thing with 1" polyisocyanurate board with the aluminium vapour barrier facing inside. That takes care of all three elements. Again, theoretically you still have a thermal transfer through the wood but that's relatively small. Once you've insulated and stopped the air drafts, you've accounted for most of the heat loss.

* Now while you're there, you might just as well stuff in some fibreglass batts in there, no? The fact that you are doing _something_ is far more important than the _exact_ method you use -you know what they say about inertia...go thumbs up for tackling a bit problem in your house.


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## ja191992stg (Jan 14, 2010)

no its not knob and tube, just old romex.

yes between the joist. it would do nothing for the floor above but it would stop the draft coming into the basement. should i just build a box with the foam board inside the cavity between the floor joist? If i just put some on the underside of the above floor and then face the cavity will that help the floor? Do i need foam with the foil on it or the plain pink stuff.


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## Bob Mariani (Dec 1, 2008)

use spray foam and resolve all issues at the same time and with much less effort. buy the DIY kits for about 600 sq ft area.


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## ja191992stg (Jan 14, 2010)

place foam on top of cavity and then face it close??


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## BlueBSH (Oct 29, 2009)

ja191992stg said:


> place foam on top of cavity and then face it close??


Wouldn't you want to do all sides of the cavity and the back and bottom to just to make sure there are no gaps or holes in it? That's what I always seen done with spray foam...


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## ccarlisle (Jul 2, 2008)

No, no...*IF* you go with spray-foam - either professionally applied or the DIY kits - then you spray the top and bottom of that box and the back, in each bay. But it's tricky doing that but easier than crawling in there on all fours...expensive too. And you may just fill in the whole thing.

That's the best, from a contractors point-of-view and from the technical point-of-view. But *IF* you go the polystyrene route, I suggested you cut a piece the size of the back part, caulk and seal with canned spray-foam ie cover the part that faces outside. Then fill the rest with fibreglass to cover the pink portion you showed us. 

The professionnally-applied foam is the best as it deals with the insulation, the vapour barrier _and_ the air infiltration aspects of the job in one shot. But it's tricky in closed-in areas like that. Now what we suggested may not be doable either because you can't reach that far, but it'll be cheaper than foam.


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## ja191992stg (Jan 14, 2010)

Got an estimate this morning for 3-4 in foam sprayed along the rim joist and the cavities for 975.00. Good price? what questions should i be asking


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## ccarlisle (Jul 2, 2008)

How many board-feet does that mean? or did they give you that figure. A board-foot is 12"x12"x1" thick and usually costs around $2/bdft.

Otherwise, ask open-cell or closed cell?

But it's probably based on half-a-day or so, two men+truck.


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## Bob Mariani (Dec 1, 2008)

you will want to ask that they are using closed-cell. Also what prep is any will be required by you.


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## ididit (Jan 31, 2008)

ja191992stg said:


> Got an estimate this morning for 3-4 in foam sprayed along the rim joist and the cavities for 975.00. Good price? what questions should i be asking


 About 4 times what I would want to spent on such a small area. Then again I dont live in NY :no:. Ask yourself how long will it take to lose $1000 worth of energy through that one area of your home? LONG TIME even with todays energy prices. I would do something simple and cheaper till you can afford to get the whole house insulated at one time. You will get a better deal that way.


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## ccarlisle (Jul 2, 2008)

Look at 'foaming' it another way: if your overhang is about 2' deep, and you have a dozen bays of about a foot high, you're looking at about 45 cubic feet of foam to fill it. 

That's the equivalent of 600 board feet, or a DIY spray-foam kit costing about $600 from Home Depot...two-pound density i.e. "closed cell" is what you want actually, as already pointed out.


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## ja191992stg (Jan 14, 2010)

No No, this price of 975.00 is for the whole basement. The basement is pretty long, here is a pic


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## ja191992stg (Jan 14, 2010)

Plus the wood on the far wall pictured is a storage closet, another 6 feet behind that. The stoage closets on the right are half of the width of the basement. The est was for the whole basement with 3-4 inch of foam, now how is that price?


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## Bob Mariani (Dec 1, 2008)

cheap... makes you think if you will get what you need and have it done correctly.


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## ididit (Jan 31, 2008)

If you mean the overhang of the house past the basement all the way down then thats better but still kinda high. If you mean spaying the entire underside of the house floor (very good idea) then I would pay that and im cheap. But like Bob said study up and make sure your getting what you pay for and not only that, get what you need. When spay foam is done it has to be done complete. If you leave Any cracks or openings unsealed, moisture will get in and not back out.


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## ja191992stg (Jan 14, 2010)

Got another est. They were cheaper, 900.00. No iam not doing the underside of the floor. I am just doing all the joist in the basement. I was told by both companies doing the underside of the floor is a bad idea. I forgot why but they would not do that.


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## ididit (Jan 31, 2008)

The joist in the basement IS the underside of the floor:confused1: I thought. Or is it not a full basement house? Its not common down here in the south to insulate floors (some do) in a non basement crawl but is it not up there?


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## ja191992stg (Jan 14, 2010)

I am just doing the rim joist and the cavity between the joist. Not the whole underside of the floor. That would be a lot of money


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## Bob Mariani (Dec 1, 2008)

it will be worth it. 30% is returned as a tax credit during 2009 or 2010 up to $1500


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## jordao (Feb 8, 2010)

Correct on the spray foam: two part, closed cell. More durable than fiberglass and it insulates at a higher R-value per inch.
Provides: 1. Air sealing 2. Insulation 3. Vapor and moisture barrier.
It's a slam dunk. 
Fiberglass in the rim joists is the older, more traditional way.
Kraft paper is useless, it becomes old and cracks, does not seal at the joints. 6mil poly, caulk or foam and *unfaced* fiberglass is only the second choice.


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## jordao (Feb 8, 2010)

*Condition your crawlspace, not your floor.*

Insulating the floor in a crawlspace area is not recommended, especially if there is ductwork, and double especially if ductwork is not insulated.
If it is a crawlspace: 
1. lay down 6 mil poly (Visqueen/plastic sheeting) over the soil, overlap any joints, caulk joints if possible.
2. Have the rim joists(box sills etc) and the crawlspace walls insulated with 1.5" of 2 part closed cell foam, and have them overlap the 6 mil poly. 
3. Ensure that all vents are blocked and sealed and foamed over.
4. insulate any access door with minimum 2" blue styro (Polystyrene type III) board

This way you have a conditioned crawlspace, it now takes care of insulating your floor and ducts. 
Creates a pressurized area, which will decrease leakage in ductwork and increase flow to the registers
It will also reduce moisture in the crawl from walls and from soil
It will also reduce radon infiltration from the soil (2nd leading cause of lung cancer in the US)

Ask for more info at the DOE or WAPTAC.ORG (government assistance for low income families to weatherize homes)
Jordan


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## jordao (Feb 8, 2010)

The average low income family home that we Audit and Weatherize saves $346/annually on Energy bills after the work is done. Studies in several states (Ohio, Indiana, Iowa). The focus of the whole program:
1. Air seal entire house
2. Insulate Attic
3. Insulate Crawl/basement
this usually costs around $3500 to $5000 depending on house size, including initial, interim and final audits with tech measurements done (blower door, manometer, etc)
The required ROI (return on investment) or SOI (savings on...) is complete in most homes within 10 years. 
If you are paying for the work yourself, with $4500 spent you will receive a dollar for dollar tax rebate (not a tax deduction!) of up to $1500; i.e. 30% back as a tax REFUND.

Meanwhile:
1. Lower your annual fuel bill
2. Lower your energy usage - less energy plants need to be built
3. Lower your carbon footprint
4. Have a warmer house in the winter, and a cooler home in the summer.

Just do it! Take advantage of your tax dollars.
Jordan


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## ccarlisle (Jul 2, 2008)

Nice picture - an accountant might buy that - but it's a picture nonetheless. A pipe dream some would say...

Meanwhile, such a "low income family" continues to use their four cellphones and buy HD TVs, drives two SUV's to drive four blocks to McDonalds for supper three times a week, shops at Walmart and is, on average, 100 lbs overweight each...

That's the _real_ picture. 

Life is too good to cough up $5K to save what the kids spend on sneakers. 

:yes:


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## brons2 (Jan 25, 2010)

Rants in French notwithstanding (yes, we know how to use Babelfish and Google Translate), I agree with CCarlisle. Lots of vendors come in and promise 30% savings: the insulation guy, the windows guy, the appliance guy and the tankless water heater guy. Clearly they can't all come in and save you 30%, otherwise you'd have no energy bill at all. 

I do agree that the tax credits as opposed to regular tax deductions are a good deal.

I personally did end up getting a tankless water heater because as a single male taking 1 shower a day and doing a few loads of laundry a week, it makes no sense to keep 50 gallons of water hot 24 hours a day. I'm also considering the installation of Celbar spray in cellulose. I don't trust the foam, it's highly flammable.


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## jordao (Feb 8, 2010)

I have nothing to sell. 
Your choice of water heating is excellent. Unfortunately, the payback is greater in other countries where the products are less expensive and the energy costs are higher. 
You are doing your part, sincere kudos. 
Babblefish doesn't know the animosities, and intended inflections in idiomatic expressions. Babble this :thumbsup::

Jordan

_Keep it in English_
_Personal attacks will not be tolerated & are grounds to have your posting priveleges taken away_
_Moderator_


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## jordao (Feb 8, 2010)

I apologize, the point of my original comment was not to share my view on poverty in the US, and I would appreciate *focus* on the part of all interested in this subject of Weatherization (Wx).
The point is the cost effectiveness of the measures being used and promoted by proactive experts around the world. The U.S. has lagged behind the rest of the world in construction and renovation. These measures are what is accepted as the best 'band aids' for deficient energy-conscious construction methods.
This forum is not designed to discuss personal views on anything but DIY suggestions by experienced ones in their fields.
Thanks, Jordan


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## beenthere (Oct 11, 2008)

Bob Mariani said:


> use spray foam and resolve all issues at the same time and with much less effort. buy the DIY kits for about 600 sq ft area.


Yep. Spray foam will do a two fold job, insulate, and reduce infiltration. Fiberglass insulation won't do near as much to reduce air infiltration.


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## mferguson0414 (Jan 6, 2009)

In the end I hope you have all your problems answered. I still do not understand why both companies said to no insulate the part of the house that hangs over with no thermal break. I am kinda in the same situation with an addition some years back that is about 4' deep with no protection/thermal break from the elements and that area of the kitchen is always super cold in the winter. Right now my problem is that I have no access to that area accept for ripping up the floor and somehow insulating that area from the interior of the house..oh well.


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## Bob Mariani (Dec 1, 2008)

beenthere said:


> Yep. Spray foam will do a two fold job, insulate, and reduce infiltration. Fiberglass insulation won't do near as much to reduce air infiltration.


fiberglass should never be used in this area. The moisture is trapped and deteriorates this material.:no:


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## JayKay (Mar 16, 2010)

There is a structural insulated rim joist available.
It comes in 16' lengths and is pre-cut to typical joist depths.
There are two thicknesses: 2-5/8" which meets R-8
and 3-1/8" which meets R-11.

It is not suitable for retro-fitting which is really what this post is about however, it is a good solution for new construction.
Contact me for more information: [email protected]
John aka JayKay


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