# Insulating an Overhang



## Tom Struble (Dec 29, 2008)

its probably just 1/4'' ply you could remove the nails with a catspaw or you could try to drive the nails thru the ply with a large nail set or punch


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## Scuba_Dave (Jan 16, 2009)

Do you know if there is any insulation in there ?
How far down does that front siding hang down over the plywood?
I'd be inclined to put up 1-2" rigid foam then another piece of plywood
Put a piece of trim on the very front if needed to hide it

I might even box off between the 2 beams & add R30


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## Hurriken (Jul 7, 2008)

I can't tell what if anything is under it. But I see no indication of any insulation at all. I'm wondering if I could remove the register in the room and slip something past the duct to reach that panel so that I could push it down.

I don't know how much that siding overhangs I will measure it tomorrow. I am in the Chicago area so it does get pretty cold.


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## burnt03 (Sep 20, 2009)

Scuba_Dave said:


> Do you know if there is any insulation in there ?
> How far down does that front siding hang down over the plywood?
> I'd be inclined to put up 1-2" rigid foam then another piece of plywood
> Put a piece of trim on the very front if needed to hide it
> ...


I've got a similar setup at my house, where the overhang extends from the crawlspace and there are chunks of fiberglass insulation stuffed in the voids.

If boxing in below the area, would vapor barrier need to be installed?


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## Scuba_Dave (Jan 16, 2009)

There will usually be a vapor barrier on the insulation facing the warm side
Then on the outside usually building paper/tar paper before finish siding
So as long as you aren't adding another layer...then yes
Problem is verifying if these 2 layers already exist


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## Gary in WA (Mar 11, 2009)

I'd add 2" XPS tight to the floor above. Add roxul insulation batt, unfaced (no air spaces), then a layer of foam (and canned foam the joints), and plywood , caulk all ends. No paper as the ply serves that purpose.
http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Gary


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## Hurriken (Jul 7, 2008)

What is XPS?


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## Gary in WA (Mar 11, 2009)

Second one listed: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11620

Gary


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## Hurriken (Jul 7, 2008)

Banzai!!! So today I said the heck with it and I went out and cut into it. There is insulation but it is the same stuff they put in the walls and it was bunched up. It is less than 4 inches thick. The beams are 2x6's. 









What worries me is that it is open going into the house. Notice the line with the glue drip on the left? that is where the overhang starts. the bedroom is behind above this. And the family room is below it.Shouldn't that be blocked off?









Where do I go from here?


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## Gary in WA (Mar 11, 2009)

Yes, at least around here we have to: "Solid 2X nominal blocking is required at ends of joists and over all bearing points. Blocking may be omitted where ends of joists are nailed to a header or rim joist." You may have gotten by because of the second sentence. 

I would add some rigid foam board as vertical blocking just over the wall. Fill as mentioned before. Caulk under the new ply on the joist bottoms try to air seal the ply similar to: http://www.buildingscience.com/docu...rs/air-barriers2014airtight-drywall-approach/ Add rim foam board to the cantilever: http://www.rd.com/57548/article57548.html
Plug any wiring holes to above exterior wall.

Gary


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## Hurriken (Jul 7, 2008)

GBR in WA said:


> I'd add 2" XPS tight to the floor above. Add roxul insulation batt, unfaced (no air spaces), then a layer of foam (and canned foam the joints), and plywood , caulk all ends. No paper as the ply serves that purpose.
> http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/
> 
> Gary


Isn't Roxul insulation more for fire and sound proofing? If I have this straight I should use 2" XPS to "box" off the openings where the overhang meets the wall. Then add a layer of unpapered batting. Followed by another layer of foam(2" again or is 1" OK) and capped with plywood. It had 3/8" plywood and it just so happens that I have two brand new sheets (my Dad was throwing it out) in my garage. 

It's a bigger job that I was expecting but I'm glad I'm tackling it, it should make my house better in the winter. 

One more question, look at the 2nd to last picture. That piece of batting goes back into the house. Should I cut it off or roll it back inside?


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## Gary in WA (Mar 11, 2009)

Glass batt is ok. The foam as you said if fine. If a finished basement, the batt doesn't do much good in the room's ceiling, use it at the cant'. 

Gary


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## Hurriken (Jul 7, 2008)

A few more things as I get going. 

The Joists are 2x8's and not 2x6. 

I understand sealing the blocking foam and I understand sealing the piece that is flush with the bottom of the floor. I also understand adding unfaced batting which I will glue to the top piece of foam. But why do I need a second sheet of foam between the batting and the plywood facing? Will that actually have an effect? I guess that should be sealed as well?

If I understand correctly I should glue the plywood facing to the joists and then seal it with caulk as well? If so it's a one way road. Once I glue that I will never get it off again! No mistakes.

I know there are two heating ducts up there. Should I try to box them with foam or butt up against them and cover them with batting? What can touch the ducting, foam, batting, expanding foam, acrylic caulk? Maybe I can coat them with expanding foam?


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## Gary in WA (Mar 11, 2009)

The ducts should be wrapped with duct insulation so as not lose any heat on delivery. Just wrap them at the cant'. 

Don't glue the ply or even caulk it (sorry), use some sill sealer for the air/thermal break there instead. You want to isolate the cold ply from the joist which would transmit warm/cold/moisture through it. 

Gary


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## Hurriken (Jul 7, 2008)

After removing the entire cover panel I have found that between two of the joists there was no insulation at all. Near the windows the board was wet on top. I am pretty sure that rain came in and made its way around the registers. I will have to seal that somehow.


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## Hurriken (Jul 7, 2008)

Is this what you mean by Sill Sealer?









If so do I just staple it to the ply and then secure the ply? (I plan on using screws for the ply is that OK?


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## Hurriken (Jul 7, 2008)

Can I put canned foam directly on heating ducts? I am planning on foaming around the mouth of the duct under the floor where the register is mounted.


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## Gary in WA (Mar 11, 2009)

"If so do I just staple it to the ply and then secure the ply? (I plan on using screws for the ply is that OK?" ----- 
Staple and screws are fine.

Read the warnings on the can foam of different brands, may need fire-stopping foam if under the aprx. 130* for gas furnace heat delivery temp. Foams are toxic when burning.

Gary


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## Hurriken (Jul 7, 2008)

There was a big gap between the register and the floor. I could stick my fingers through and up into the bedroom. 









I secured it and lined both registers with spray foam.









Then I wrapped them in duct insulation.

















I am going to start cutting the foam to fill the rim joists tomorrow. I bought foam glue to install them. I will seal gaps with foam and caulk the whole thing. BTW, my utility room on the other side of the room is unfinished and I discovered that there was nothing blocking air from the room from going up and through the rim joist and traveling all the way to the over hang...that is a lot of wasted money over the years.

I still have not decided how to insulate the top. The joist are 9 inches. R30 batting is 9 inches. If I put 2" foam on the top (bottom of the floor) then I would have to crush the R30 by two inches and reduce the R# by doing so. I have to think about this some more.

One more question. If a rim joist is blocked by a piece of 2x10 is that good enough or should I still add foam?


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## Gary in WA (Mar 11, 2009)

Compressing you would still have an R-25-. Bottom of page: http://saveenergy.owenscorning.com/2009/02/question_where_can_i_find_your_2.html


The 1-1/2" thick block has an R-1.88, not much: http://www.coloradoenergy.org/procorner/stuff/r-values.htm


Gary


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## Hurriken (Jul 7, 2008)

The 2" I have is R10 so does it add up? If so with the batting compressed I would end up with R35. The nice thing would be that I have 3/4's of a roll of unfaced R30 left over from the attic job.


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## Gary in WA (Mar 11, 2009)

R-25 is recommended for your area: http://www.ornl.gov/cgi-bin/cgiwrap?user=roofs&script=ZipTable/ins_fact.pl

I would also caulk a bead at the joist/brick area to stop any air there. Run a backer rod before caulking to get the perfect hour-glass shape for optimum stretch between the different materials. http://www.coastalcontractor.net/article/117.html
If the backer rod is a tight fit (assorted sizes avail.), you could leave off the caulking as the plywood soffit will cover, or caulk it instead.


Gary


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## Hurriken (Jul 7, 2008)

GBR in WA said:


> I would also caulk a bead at the joist/brick area to stop any air there. Run a backer rod before caulking to get the perfect hour-glass shape for optimum stretch between the different materials. http://www.coastalcontractor.net/article/117.html
> If the backer rod is a tight fit (assorted sizes avail.), you could leave off the caulking as the plywood soffit will cover, or caulk it instead.


The Plywood didn't cover it. There was a strip of trim along the bricks that did. I was going to fill that with canned foam. I had no idea. I am assuming polythyrene backer board can be purchased at most HI stores. I will go that route. The farther I go in this project the more I slap myself in the head over all those years of wasted energy. The article said to use a better caulk. Can I determine that by the price of the caulk? I assume I use a window and door caulk?


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## Stillwerkin (Nov 24, 2008)

That cantilever looks familiar.

First thing is to double-check the structural. 
The whole side of the house is resting on cantilevered 2x8's, 16" on center? -Optimally, you will probably want a beam supporting that front rim joist, resting on posts, resting on concrete pads at least 42" below frost.
-The load spans, and materials, should be calculated by a qualified engineer. 
-Double check if everythings square(i.e. joists level).

The next thing is insulation.
-I'd recommend a spray-foam company to do it all. That's a lot of overhang, and they should be able to seal between the joists and under the plywood easily. The farther past the brick the better. 
-Seal every crack well.
-If using batt, double up the ductwork insulation. Steel and concrete transmits heat/cold well as opposed to foam and dry wood..


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## Hurriken (Jul 7, 2008)

I installed the foam into the rim joists. 









Then I filled gaps with canned foam and caulked the joints.




















> First thing is to double-check the structural.
> The whole side of the house is resting on cantilevered 2x8's, 16" on center? -Optimally, you will probably want a beam supporting that front rim joist, resting on posts, resting on concrete pads at least 42" below frost.
> -The load spans, and materials, should be calculated by a qualified engineer.
> -Double check if everythings square(i.e. joists level).


I can't imagine that I have a problem here. This house is 30 years old and there doesn't appear to be any problems because of this. 



> The next thing is insulation.
> -I'd recommend a spray-foam company to do it all. That's a lot of overhang, and they should be able to seal between the joists and under the plywood easily. The farther past the brick the better.
> -Seal every crack well.
> -If using batt, double up the ductwork insulation. Steel and concrete transmits heat/cold well as opposed to foam and dry wood..


Well, I've already done what I've done so I'm going to keep going. I am trying to seal everything as tight as possible. It would have been nice if the original builder would have done it right. 

BTW, I went to the hardware store and asked for backer board and was greeted with blank stares. can you post a picture of what I'm looking for?


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## steveel (Sep 10, 2010)

Is there an issue with mixing and matching types of foam sheets in these situations? I'm just thinking out loud here, and my own reading hasn't turned up anything. What I'm wondering is whether there is an issue of potentially trapping any water that does get into the batts, if both layers of foam have low-permeability. 

SteveEl


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## steveel (Sep 10, 2010)

backer ROD comes in a plastic bag. It is coiled up roll of foam, sort of like the kids pool noodle only much smaller in cross section. You jam in gaps so you don't need as much caulk/blowfoam to fill them. Sold in weatherstripping section in my stores


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## Hurriken (Jul 7, 2008)

There was moisture in there when I first opened it up. That is because the window had been left open and it rained and went in past the register which was bent causing a 1/2 inch gap between the floor and the duct. I fixed that and sealed it now. 

Does it make sense to put the heat registers directly in front of a window in in a cantilever?


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## steveel (Sep 10, 2010)

I don't see why not. Registers are frequently placed in front of exterior windows. If a window is left open to admit rain, that's a problem, cantilever or no.


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## Hurriken (Jul 7, 2008)

steveel said:


> I don't see why not. Registers are frequently placed in front of exterior windows. If a window is left open to admit rain, that's a problem, cantilever or no.



I'll admit guilt there! Water and wooden houses don't get along very well do they?


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## Gary in WA (Mar 11, 2009)

"“Oh, you mean I don’t have to put in a suspended ceiling here? You mean I don’t actually have to take the duct to the outside wall?” Well, of course you don’t. If you insulate your walls sufficiently and provide good windows, you don’t have to provide a duct to the outside wall; you can provide the heat at the inside wall and simply blow the air over there. If you have a piece of junk wall and a piece of junk window, yeah, not only do you have to put the vent right below the window, you’re still going to be uncomfortable. But the duct savings are significant; it’s just that they’re not usually reaped." From: http://www.greenbuildingadvisor.com...-moves-through-homes-building-science-podcast

Gary


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## steveel (Sep 10, 2010)

That was a very useful and timely clipping for my situation too Gary.


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## Hurriken (Jul 7, 2008)

Slowly I advance...
This weekend was absolutely beautiful and I used it to work on this project. I cut all of the top foam boards and caulked them in. 




















I found the backer rod and so I installed that and ran a line of caulk above the bricks. I was surprised how much caulk I needed...8 tubes!










Here is a bonus picture. My burning bush is beginning to change color.











Tomorrow I am off work. I am going to try to finish it off. I will install the batting and then the sill sealer and the plywood. One question about the sill sealer. Should I just cover the joists with it (staple it up) or cover the up side of the plywood with it?


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## Gary in WA (Mar 11, 2009)

Good job! Just the joists to make a thermal break at the plywood soffit to house. 

Gary


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## Hurriken (Jul 7, 2008)

Placed all the batting and sill seal.










Cut the plywood and rolled a coat of stain on it.









Screwed most of it in place...I forgot to recharge the cordless driver.

















I'll put the last piece in soon and then mount some trim against the bricks.


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## cole123 (Oct 30, 2010)

Nice job! This thread has been really useful to read.

I have almost the exact same overhang detail in my house...I was thinking of insulating in a slightly different way:
1) Remove plywood from underside of overhang.
2) Cut 2" XPS to fit between joists, and attach directly to rim joist, seal with great stuff foam.
3) Attach continous 2" XPS foam slab to underside of overhang. Caulk to seal all contacts between rim and floor joists
4) Attach plywood to underside of XPS using 3" screws into joists, trim around the edges of XPS slab.

Are there reasons to attach to XPS to the floor sheathing rather than to the underside of the overhang space?


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## Hurriken (Jul 7, 2008)

Interesting question. You would have to ask the experts though.


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## moopey (Sep 14, 2010)

this thread is awesome. I'm in the same situation with my raised ranch that I purchased july of 09. The first winter in the house my living room was incredibly cold. The room had a large bow window that was very very drafty. This summer I replaced the bow window with 3 anderson 400 series double hung windows and made sure to insulate around the window. Well now that the weather is getting cold I'm noticing that room is still colder than other areas of the house, especially when sitting on the couch in front of the new widows.....this is right above the overhang.

I can tell that the window is not drafty so I've been wondering how well the overhang is insulated. 

I think I'm going to do some investigating in the house to find out. I can't really get into this project right now, so I'll do it with no demo.

I would be curious as to how much it would cost to have it all spray foamed if the structure was already opened up.


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## burnt03 (Sep 20, 2009)

Hurriken,

Now that it's gotten a little cooler, have you noticed any difference in the room??


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