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ja191992stg 01-13-2010 10:57 PM

Rim Joist Insulation
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.

Bob Mariani 01-14-2010 07:22 AM

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.

gregzoll 01-14-2010 07:51 AM

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.

ja191992stg 01-14-2010 09:18 AM

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.

ccarlisle 01-14-2010 10:04 AM

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...

Scuba_Dave 01-14-2010 10:35 AM

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

ididit 01-14-2010 10:51 AM

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.

Gary in WA 01-14-2010 01:22 PM

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:

First I would seal the rim joist of that overhang with foam: 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

ja191992stg 01-14-2010 04:51 PM

3 Attachment(s)

ja191992stg 01-14-2010 04:52 PM

3 Attachment(s)
I would like to paint the foundation with drylock again, what does anyone think

ja191992stg 01-14-2010 04:55 PM

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

gregzoll 01-14-2010 05:14 PM

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.

ididit 01-14-2010 07:02 PM

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.

Scuba_Dave 01-14-2010 07:14 PM

CA has already "reversed" this due to studies


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.

Local jurisdictions may or may not adopt the NEC’s requirement. The California Electrical Code, for instance, allows insulation to be in contact with knob-and-tube wiring, provided that certain conditions are met, such as, but not limited to, the following:
  • A licensed electrical contractor must certify that the system is safe.
  • The certification must be filed with the local building department.
  • Accessible areas where insulation covers the wiring must be posted with a warning sign. In some areas, this sign must be in Spanish and English.
  • The insulation must be non-combustible and non-conductive.
  • Normal requirements for insulation must be met.

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

http://www.renovation-headquarters.c...n%202%20cr.gif http://www.renovation-headquarters.c...ation%20cr.gif

ccarlisle 01-15-2010 07:32 AM

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

I don't...

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