Q: insulating a cantilevered area
Hi all:
My my kitchen wall has a cantilevered area that extends about one foot past the basement foundation wall. Recently, I had a concrete patio demolished that actually extended into the cantilevered area. I was looking up into that cantilevered area from the outside and the plywood used was 1/4″ material, cut sloppy with lots of gaps on the sides. I decided to replace it with some 5/8 plywood. When I pulled off these 12″ wide panels, I saw that the last cavity which comprises the width of the adjoining perpendicular wall, had no insulation. I could peer up into the cavity and see the floor sheathing above me. I figure I should stuff some insulation up into this last cavity but should it be faced or unfaced insulation – and if faced, which direction should the barrier face, up or down. Second question … the other cavities did have insulation but they were randomly oriented as far as kraft paper up and kraft paper down. Which way should they go?
Replies
Technically, we should know what climate you live in, but...
Doesn't matter IMO. Floors are under negative pressure. That's because warm air rises and leaks out of the top of a house (unless your house is VERY tight) which in turns pulls air in from the bottom of your house. So the warm moist air inside does not tend to push into floor areas. Add to that the fact that both floor plywood and floor coverings act as vapor/air barriers in themselves, it really is a non issue.
If it were mine, I'd use friction fit batts anyway, and overfill the joist cavities (using a batt designed for the next size up). Floors are notoriously difficult to insulate well.
If I just go with the FG insulation, should the kraft paper face up or down in the particular one cavity I discussed above? Also, how about the other cavities - kraft up or down?
Thanks
Fiberglass of any kind is not a good choice for this spot. As a previous respondent said, due to the pressure dynamics of a house, there is a lot of impetus for air movement through that cavity, and all the FG will do is filter that cold air beautifully before letting into your kitchen. I would suggest ridgid foam cut to fit and sealed around the edges with foam in a can. That will stop air infiltration much better than fiberglass.Steve
mmoogie:
I'm confused. I'm going to cover the entire bottom side of the cantilevered area (which is about 12 inches wide by 21 ft long) with new 5/8 plywood (primed and painted). If I carefully caulk or foam any gaps around the house sheathing and joists, won't this stop the air movement? Then, I think I would be OK with fiberglass batts.
I can't foam the entire cavities because they continue to extend into the basement.
Edited 10/26/2008 4:15 pm ET by Will92
There will always be leaks that you don't see or deal with...around siding, sheathing, rim joists, etc.Actually the last time it did a cantilever like that I used blown in cellulose at high density to plug any unforseeable leaks. Since you have access to the bays from the inside, it's easy to blow cellulose in. Just dam it off with a chunk of rigid foam, cut a hole with a hole saw just big enough for the hose and away you go.Messy though.Steve
Will92,
It is essential that you install blocking between each joist. The blocking goes directly above your foundation wall. Each piece of blocking must be air sealed, using caulk or spray foam. The blocking can be solid lumber or 2-inch thick rigid foam.
Insulation in the cantilevered area can be done with either spray foam (the best), rigid foam, cellulose, or fiberglass (the least effective). In all cases, attention to air sealing is just as important as, or perhaps more important than, the R-value of the insulation used.
As MHoilday and J Fink pointed out sealing the joist space is the way to go.
Since you are cantilevered over a basement foundation wall those joist bays are the lower end of an air chimnney. You are going to get more bang for your labor and money from air sealing that 21' air flue than you realize.
The first noticeable affect will be a less drafty and warmer basement, followed by some decrease in your heating cost.
mmoogie, what a great post. Thanks for sharing.I never thought of floor insulation like that. It really makes sense.
should the kraft paper face up or down in the particular one cavity I discussed above?
Niether. Any batt insulation you use under the bump-out needs to be unfaced. This will actually help you plunk bits of batting where you find yourself at the limits of arm's reach (trust me, you will find at leas t one spot you will want an extra foot of arm to reach).
Also, how about the other cavities - kraft up or down?
For "other cavities" we have to know your location/climate.
Majority heating is different than majority cooling; high humidty different than low humidity--all of which matters for placement of facing material. Especially since 50% time it's wrong, which can then invite the bad situation of trapping moisture in a wall cavity where it then condenses to become a problem.Occupational hazard of my occupation not being around (sorry Bubba)
Sorry for not mentioning location. It is Denver, Colorado. Since I am looking at new furnaces too, I have read we are a majority heating season.
Just to be clear, the cantilevered area only extends about a foot from the foundation wall. So, when I go down to the basement, I can also reach into these 12" deep cavities that I am now viewing from the exterior of the house. Actually, I can insert new FG insulation from either down in the basement or outside (since I have the plywood removed from the underside of the cantilevered area). The FG batts that were installed were R30 and the joists are 16" on center. These batts were only about a foot long so I could see the ends of them from down in the basement when I look up at those cavities. The basement is unfinished. The last cavity that I can NOT access from the basement is a smaller cavity, and I have confirmed that this cavity is within a wall that runs perpendicular to the cantilevereled wall. Hope this makes sense.
If I were you I would tear out the old FG and foam all the cavities. That is a critical area and stopping air movement is just as important as R value.
You won't be sorry if you do this.
http://www.rhhfoamsystems.com/
http://www.tigerfoam.com/?gclid=CMD7sZespo8CFRFSagodWlt5Rw
You are right to be concerned, this is a HUGE energy waster...and actually pretty common.
Best practice is to put blocking above the foundation wall (extending from the mudsill to the underside of the floor sheathing). Cover the blocking with rigid foam, then seal around the edges with spray foam (the canned "great stuff" works fine...a little goes a long way here). I
f you like fiberglass insulation, that will be fine, but fiberglass does not stop air flow and that's the big concern here. I would apply rigid foam either above or below the fiberglass batts, again foaming the edges to stop air flow. to me, the easiest would be to apply foam right to the underside of the floor sheathing, then unfaced fiberglass (you can pull the paper off if you need to), then seal it up with plywood. seal the edges of the plywood as well...air that gets into the space can still lead to conductive loops under your floor, which negates some of the r-value in the fiberglass.
Justin Fink - FHB Editorial
You really should follow Mmoogies advice .. it's good, solid, and valid..
So is it insufficient to just use my R30 batts in those cavities and cover the entire length with 5/8 plywood primed and painted? I already have my plywood cut and painted. I was planning on getting those panels in place and doing a good job with caulking/foaming joints, etc.
I really don't understand the concept of "blocking". How about this.... place the plywood panels I have cut, up against the joists from the outside and get it caulked or spray foamed in really well. Then, I could go down to the basement and press fit individual panels of rigid foam against the plywood. Then I could insert the unfaced R30 into the cavities. What sort of rigid foam should I use? Styrofoam? How thick? I am very conscious of indoor air quality and understand styrofoam can off gas styrene (carcinogen).
I think that, if you can do an impeccable job, the fiberglass and plywood will do as good of a job at stopping air infiltration from below the cantilevered area as the spray foam.The nice thing about spray foam is, if done correctly, it will eliminate air movement on all six planes. Your approach will only deal with one plane.Fortunately for you, the only other plane that is an issue is the rim joist. I would inspect the rim joist and caulk or foam any areas where air could move through.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
So, I don't think anyone has answered my proposal of buttoning up this cantilevered area with my plywood panels and then coming in from the basement side with some foam panels I can cut to the dimensions of the cavities. Then I could put in the FG batts. I think that once it is buttoned up solid and FG installed, this might be enough, but I wanted to put the idea out to the group about the foam panel approach AFTER I get the plywood installed.
Regarding the plywood panels, on front side, there is wood running the entire 21 feet perpendicular to the joists, but at the back side (going into the basement cavities), there is only what I think is called the rim joist. So, on this back end, there is nothing to fasten the plywood to. In other words, I can use screws to hold the plywood up to the joists, and along the front piece of wood, but in the back, there is no wood border to fasten to. I would caulk this joint, but as pointed out, caulk can fail and I don't want there to be a gap opening up - mainly for rodents! So, should I install some furring strips at the back end between each joist to give some additional wood to fasten to in the rear?
<< So, I don't think anyone has answered my proposal of buttoning up this cantilevered area with my plywood panels and then coming in from the basement side with some foam panels >>
There's nothing wrong with buttoning up the bottom of the cantilever, insulating the space from inside the basement, and then installing blocking to stop air flow out of the cantilever...but it may make your life more difficult. You will have much better access to the cantilever from outside - you can apply foam board, foam edges, etc without having to shove your arms through a tiny hole in the rim joist.
I've attached a quick drawing to show you where the blocking should go. The idea is to stop any air that flows into the cantilever floor from traveling along the floor joist cavities, basically short-circuiting your insulation system. The blocking can be foam panels or framing lumber, doesn't matter - just make sure to foam the edges after it's installed. Extruded or expanded polystyrene is your best bet (blue, pink, or white boards) - I wouldn't use polyiso here because it has a vapor barrier and if this is your first go at this, it's easy to create a situation that holds moisture.
View ImageJustin Fink - FHB Editorial
Thank you Justin. Excellent picture and this is exactly my situation - but of course you knew that!
Now I understand "blocking"
While I have it all open, do I need to install any furring strips between the joists so I can fasten along the entire perimeter, or will fastening the plywood to the joists be sufficient?
If the joists are spaced 16" or 24", you should be fine nailing or screwing directly to their underside, and along the 3 outside edges.Justin Fink - FHB Editorial
Hello again everyone and thanks for all this great information! JFink's illustration was excellent and now I understand "blocking". My plan is to finish this project this weekend. It this sounds reasonable, what I will do based one what I understand from everyone is to install short pieces of R30 insulation in these cavities (I will remove the Kraft facing per recommendations here, right??) and then I will attempt putting in some polystyrene blocking from inside the basement. I looked and it is no problem to access these cavities from the inside the basement for the blocking.
Now, more questions regarding the last cavity at the end of the wall. This cavity is only like 5" wide and there is no access from the basement. This cavity is where my cantilevered wall meets the next wall at 90 degrees so it is between the exterior joist/sheathing and another floor joist. When I look up in this cavity I can see the plywood (actually I think it looks like OSB) above. The cavity runs from the front of the cantilevered section and back along the adjoining wall (which has a sliding glass door) for probably like 15 feet. In that cavity was just some unfaced insulation but there was alot missing in the front part of the cavity (towards the cantilevered area). Shall I just cut some short sections of my R30 and try and slide sections down the line until it is filled? This doesn't look easy but I think I can do it. There are lots of nails extending down into the cavity from the plywood above so I'm sure my FG sections will snag a bit along the way. I could try and fasten a small piece of plywood or something perpendicular to the end of a broom stick and gently stuff the pieces down the line. My guess is that since the space above this cavity is within the wall, it isn't really conditoned space so I should remove the Kraft paper from my R30??
Thanks for any additional input.
You are aware that wood shrinks and expands depending on moisture and humidity aren't you?
That wood shrinks in one direction and not the other? Sooner or later the chaulk will fail.. it's not a matter of if but rather when..
Foam isn't affected that way.
Foam provides not only a water/vapor barrier but also superior insulation.. Fiberglas is what furnace filters are made of (cheap ones) thus air flows through it readily) Heat rises cold air settles. What you want is as tight a barrier as possible to prevent air movement outside the conditioned space..
As for off gassing, everything off gases to some extent.. your carpet, the glue used in plumbing, OSB, Plywood, paint, etc..
The trival amount we're discussing isn't going to decrease your air quaility mainly because instead of heavy air movement you will have effectively blocked such air movement..
My home is made with foam. I used ICF's for my foundation and SIP's for my walls..
My house is super insulated.. energy costs have been cut in 1/3 inspite of doubling the size of the house and tripling the windows. That in spite of using the same furnace an dA/C units..
As for any detectable smell form the foam, neither I nor my hyper sensitive wife can detect any smell. to date nobody who's viewed my home has noticed any odor either..
I had a house in Western Washington built on a hillside with about 12 feet past the foundation supported on posts. We got in on a government-sponsored insulation package and the contractor stuffed oversized unfaced fiberglass batts between the joists and covered them with a brand new product called "tyvek" to allow it to breathe and keep moisture out. Actually, it worked very well. Kept the floor warm anyway :-).
Edited 11/7/2008 9:44 am ET by Ray
Thank you Ray:
Anyone else with suggestions on insulating the cavity at the end of the wall as I've described above?
First, let's remember you're in Denver. So am I. I wouldn't necessarily call it a "heating climate." Just as much emphasis is on cooling.
Denver's weather changes fast. Faster than the other places I've lived in. So on the days that I'm freezing and looking to stay warm, the next, I've got the windows and doors open. Therefore, I've found that tightening up the house has only momentary advantages.
In a perfect world, you'd use the sprayed foam as suggested early on.
In a more practical world, the cut to fit pieces of foam (and sealed by small cans of foam) makes much more sense.
Following that, the use of blown in cellulose becomes sensible, but with such a small area...
Then comes your fiberglas batts.
Your description of caulking and sealing the leaks is assumed and expected in any and all of the applications.
Go the the big boxes and get yerself a piece of 2" thick insulating foam. Blue or pink. It doesn't itch like fiberglass and does a much better job of insulating.
If the entire "box" the last joist created is closed except for the cantilevered section, dense pack cellulose is the direction I would take. And if I was going to dense pack that joist bay I'd do the entire cantilever. I like the cost/performance of cellulose. Then while I had the machine rented/borrowed I'd look to see if I could add insulation to the rest of the house, ie the attic, or any other problem areas.If that is not an option, stuff FG in the best you can, then caulk the inside of the joist to the sillplate in the basement to slow air movement.Garett
Hi all:
I just took another look at the last cavity I need some help with. The cavity measures about 5 1/2" wide and probably 12 feet deep. Therefore, some of the space IS below the kitchen floor on that wall (both in the cantilevered area and back into the house). Should I stuff R30 into that cavity best I can and should it be faced or unfaced? Additionally, should I try and make a styrofoam block for this cavity too that would extend from the mudsill plate up to the plywood sheathing above so that the cavity is sealed from any air infiltration from the cantilevered area. Again, the cantilevered area extends only about 12" beyond the foundation wall.
I want to say that above all, I DON'T want to create a mold and mildew situation. I would rather not have ultimate insulation than risk mold and mildew. Would it be sufficient to just stuff this last cavity with sections of R30 and make sure I do a good job with buttoning up my plywood soffit panels??Should the R30 be faced or unfaced in this scenario?? All that was in this cavity was some unfaced R30 and there is NO evidence of moisture problems/damage - so perhaps that is good enough??
Edited 11/9/2008 12:27 pm ET by Will92
Edited 11/9/2008 12:30 pm ET by Will92
R-30 unfaced... then block it off with foam the best you can,Garett
Thanks Grott:
When you say "block it off with foam, are you saying I should insert a small piece of rigid styrofoam block - just like the other cavities? Or are you saying unfaced R30 even in the cantilevered section of this end cavity and then seal up the plywood "soffit" with Great Stuff??
Also, I noted that one of the cavities that does extend in to the basement has a heating vent that comes out into the cantilevered area, past the mudsill, and then penetrates into the upper flooring for the kitchen. Should I put a piece of vertical styrofoam blocking in FRONT of this heating vent (closer out to the cantilevered wall in other words) to better isolate it?
Hi folks:
Please delay any further advice until I can post a few pictures. I don't want anyone to spend their precious time on this until you can see what I'm talking about. I think a few pictures are necessary at this point. Specifically, I found that that last cavity does extend partially in the basement. The joist sits on top of the mud sill timber and I can see into the cavity from down in the basement. I pulled out old insulation in this cavity from down in the basement because it was full of mouse droppings and even a few carcasses. Yuck. I will need some help knowing what to do with this and will post a few pictures in a day or two. Thanks again for all the help folks. It is greatly appreciated!
Hello everyone:
I had a chance to take some pictures I hope will help.
One picture shows the cantilevered area that extends about 1 foot from the foundation wall. There was a concrete slab patio that I had removed (note they poured the concrete without forms so it flowed under the cantilevered area).
All the cavities I can view under the cantilever area are 16" OC wide. The last cavity in question is at the left corner of the wall and is only about 5" wide. I didn't realize this cavity also ran clear through to the basement until I carefully looked in the basement. You can see this cavity in the other two pics I took in the basement of this corner. "Basement Joist" picture shows the corner and the last cavity. I then stepped back a bit and shot "Last Cavity" pic. Note the joist is close to the foundation wall in this cavity but there is a gap. I pulled out the filthy, mouse infested FG insulation through this gap. I should be able to insert new FG insulation from both the outside cantilever area and inside basement from both ends.
Questions...
1)Should I also put some sort of rigid foam blocking in that last cavity? Because I can't access the full width of the cavity from the inside of the basement except for at the very end, my only other option is install a small square piece of foam blocking vertically from outside, in the cantilever area. Would this be a good idea to have foam blocking on this end cavity as well?? Note, I will install the vertical blocking foam pieces from inside the basement.
2) Not shown in the pictures is a heating supply duct that extends out into the cantilever area (and feeds the kitchen above). Should I install a piece of vertical foam block in front of this duct in the cantilever area to seal it off from the outside? I suppose I could sort of make a box around it with foam insulation. Would I want to stuff some unfaced R30 around it before boxing it in?
3) Referring back to Mr. Fink's illustration, is vertical foam blocking in the 16" OC cavities sufficient along with R30 FG in the outside cantilever cavities and my 5/8" plywood soffit panels screwed and caulked into place or do I need additional foam panels on top of my plywood panels or up against the bottom of the kitchen floor sheathing above? I found some Carlisle InsulFoam R-Tech white rigid foam board at Home Depot and some foam compatible caulk/adhesive. For the FG, I want to use UNFACED R30 right?
4) Back in the basement, once I have my foam block panels installed, do I need to install matching sizes of drywall against them or can they be left exposed? I read somewhere you can not leave foam exposed. The basement, as you see in the pictures, is unfinished.
I appreciate all the help everyone has generously extended.
Edited 11/13/2008 12:11 am ET by Will92
Edited 11/13/2008 12:34 am ET by Will92
Sorry. Forgot the cantilever picture and couldn't figure out a way to add to the last post.
You can get rigid foam in 1/2, 1, 2" sizes.
Use two strips of 2" plus one 1", and a 1/2" strip to make long laminated sandwitch and slide it into that last 5 1/2" cavity. If that last bay is straight all the way back it will slide right in. I likely won't be, so leave the 1/2" strip untill last.
Another method would be to slide the pieces in individually and then run a bead of spray foam on the last piece as you quickly slide it in place. That is going to be messy, but the spray foam ( the canned stuff) will finish expanding in the bay and seal/hold the others tight.
>>I pulled out old insulation in this cavity from down in the basement because it was full of mouse droppings and even a few carcasses. Yuck. <<Another reason not to use fiberglass again. I re-iterate my recommendation for cellulose. Critter don't like it , and it seals everything up nearly air-tight.I can't tell you how much nasty old nest-and-tunnel-laden fiberglass I have removed from literally hundreds of places.But it seems you are set on fiberglass.But now I'm really confused by your pictures. Where is the cantilever? From the outside everything looks like it's sitting on a cellar wall, and nothing is cantilevered out over it. Am I missing something? Steve
Edited 11/13/2008 12:36 am by mmoogie
Hi Steve:
I can see why you may be confused with my cantilever picture. The cantilever extends out from the basement foundation wall by only a foot or so and the last cavity I have asked the board about it the end one on the left corner. Some of the siding is missing on the house because the old concrete slab can completely rotted the siding since they poured the concrete above the lower course of the siding. I think they cantilevered this area to just make the kitchen a bit bigger. Right under the cantilevered floor is that big chunk of concrete you see in the picture. This remaining concrete under the cantilevered area was also finally removed. Also, when they poured the concrete, it completely flowed underneath the cantilevered area and even forced its way up between the plywood panels underneath fastened to the joists. Does this make more sense? I could take another picture if it would help.
Edited 11/13/2008 7:04 pm ET by Will92
ok, so if I'm understanding everything correctly...the concrete I'm seeing in the exterior shot is the remnants of the old slab, which has now been removed, leaving you with a short overhang. Again, from what I understand, the outermost bay of this cantilever is 5 1/2" wide.
Assuming I got all of that correct, m first choice would still be to insulate from the outside by removing the plywood from the underside of the cantilever. If there isn't enough room, or you don't feel comfortable with that approach, I would then try from the basement.
Stuffing fiberglass into that long narrow bay isn't going to be very effective. Fiberglass needs to be loose and fluffy to be effective. Think of it like a million little pockets of air. If you squeeze the fiberglass and cram it into a restricted space, you've smooshed all of the little pockets, rendering them ineffective.
Actually, I think the idea of using long strips of ridgid foam is a good possibility, though it's hard to tell from the photo. My first choice in your situation would be as someone else mentioned - blowing in dense pack cellulose from inside the basement. If you decide against that, then I would try from the outside.
If you can get at it from the outside, rip off the plywood from the underside, pressure fit a long 5 1/2" wide strip of 2" foam into the joist bay (doesn't have to be against the underside of the kitchen floor), foam or caulk the edges, and then replace the plywood. Though it's less R-value than fiberglass, the foam will do more to stop the air flow, won't interfere with the protruding nails, and solves the conflict of the heat vent thats in the way. Heat moves on air. Stop the air, you stop most of the problem.
didn't realize you were in Denver...I was just there earlier this week for a trade show!
Hope this helps, Justin
Justin Fink - FHB Editorial
Edited 11/15/2008 6:16 pm ET by JFink
Thanks Justin:
Yes, you are correct. The concrete you see is remnants of the concrete patio. That piece of concrete is now removed and I have removed flimsy 1/4" plywood soffit panels from the cantilevered area giving full access to the bays.
For the last cavity, couldn't I just install a piece of vertical rigid foam blocking 5" long x 9" hight (to fit the width and height of the last cavity)??. I bought some InsulFoam white board at home depot. I would do it as you illustrated earlier in your picture - except I would do it from outside since it would be impossible to do it from down in the basement (that last rafter is an inch or so above the foundation wall and I can peer into the cavity from the sides, and have full access from the very end, but NO access to right at the cantilevered area like I do for all the other cavities. I tried to show that in the pictures I took. A piece of small vertical blocking would stop any air infiltration into the basement from the short cantilevered area. I'm not sure how I would even blow in cellulose insulation into the last cavity because as I mentioned, full access to the cavity is at the very end run of the cavity (probably 15-20 feet long) - again, I tried to show the end of the cavity in the picture. Therefore, my plan would be to install the vertical piece of foam board as described above, and carefully stuff a piece of R30 FG insulation into the small cavity I have created in the cantilevered area. Make sense?
By the way, the heat supply I mentioned above is NOT in this last cavity. It is in one of the other 16"OC cavities and extends well into the foot long cantilevered bays. Should I "box" in this heat supply vent somehow either with rigid foam board from the outside - effectively cutting off air infiltration into the basement (and to the air vent) in this cavity. Again, I would carefully stuff a small piece of unfaced R30 into the smaller cavity I have now created (without the vent in it) between the foam box and the outside cantilevered wall. Does that sound reasonable? Is the white styrofoam rigid board OK close to a heat outlet or is there a flammability risk? Should I make a plywood box instead?? I would leave a gap between the rigid foam box and the vent and those heat vents don't get THAT hot anyways, right?? It would seem something should be done around this vent since from down inside the basement I can not obviously put in a vertical piece of rigid foam blocking like the other cavities since the heat ducting runs into that cavity. OR... should I just use my unfaced R30 in this cavity (like it originally was done) and forget about blocking or boxing it in altogether just for this one cavity? Justin, I understand your idea of sliding in a horizontal piece of rigid foam board but (1) it will touch the hot heat vent; (2) it will not close all the gaps in this cavity.
For all the other cavities that are 16" OC my plan is carefully insert pieces of UNFACED (?) R30 batts into the cantilevered bays and then seal them off with vertical pieces of white rigid foam board blocking pieces as illustrated by Justin.
Also, could someone address my other question about whether I can leave my InsulFoam white foam board blocking pieces as is, or whether I need to fasten identical sized pieces of drywall to them so when viewing them down in the basement, they would be covered with drywall. Again, I would install them as Justin illustrated in his diagram. So imagine them now covered with identical sized pieces of drywall (if this is necessary).?
Edited 11/16/2008 1:41 am ET by Will92
Edited 11/16/2008 1:44 am ET by Will92
Edited 11/16/2008 5:20 pm ET by Will92
Edited 11/16/2008 5:41 pm ET by Will92
Here is a modification of your cantilever picture that I hope better explains my ideas about boxing in the heat vent with white rigid foam board. Note the duct work coming into an existing cavity (of course there is no blocking there now) and extending up to feed a heat register in the kitchen floor above. In the adjacent cavity, I tried to illustrate my idea on a horizontal piece of rigid foam board press fit and caulked along the bottom plane of the joists and then another piece of rigid foam board vertically placed to essentially make an L shape. With the floor joist side and top OSB, it would box in the heat register. I could not get my drawing of the two pieces of foam board to fit in the cavity with my illustrated duct work without obscuring the view of the heat duct so you have to imagine this rigid foam board pieces in the same cavity as the duct work. Does this sound reasonable? Would I need to fabricate any sort of collar piece where the duct work exits the cavity above the foundation wall into the basement?
Edited 11/18/2008 7:52 pm ET by Will92
Hi all:
I am finally getting back to finishing putting my 5/8" plywood panels under the cantilevered area. The panels are about 12" wide by 8 foot long and I will have three of them to button up the cantilever.
Question, should I leave a small gap (1/16" or so) between adjacent panels (where they share a floor joist) to allow for expansion/contraction or not even worry about this? I recall that when a contractor replaced my plywood sheathing on my roof, he left small gaps between adjacent panels.
Thank you.
Edited 1/16/2009 3:14 pm ET by Will92
I really don't think you need to be concerned. If you can't see it then leave the gaps, if you can see it then don't leave any gaps.
Hello gang:
Can I revive this thread? After we discussed my cantilever insulation project, life got in the way and this project was delayed. I am now ready to resume this project.
I called a big insulation contractor firm here in Denver in the hopes they would take on this job but they are currently too busy for a small job like this. However, they provided some instructions I wanted to run by the board. Basically, they have proposed something quite different than installing wood or rigid foam board insulation vertical blocking in each bay extending from the mudsill plate to the floor sheathing above (as illustrated by Mr. Fink). I was told that blocking is not necessarily a good idea. The insulation fellow told me you actually want to have basement air circulation into the cantilever area so that it can help to heat the upstairs floor above. Mind you, the entire basement is unfinished and the heat registers are kept closed. Therefore, he said the proper approach is to install pieces of rigid foam board in each bay but flush back vertically against the rim joist faces. He also said I want pieces of rigid foam board sections cut to fit on top of the plywood soffit panel horizontally (again in each joist bay). Finally, he said on the ends of the cantilever (right and left), I should install pieces of foam board vertically. Basically, he emphasized that I want rigid foam board everywhere there is contact against a cold outside surface. Does this seem reasonable? Personally, I sort of like the idea of interior air circulation into these bays rather than sealing them off entirely. If I properly seal my 5/8" plywood panel with caulk and expanding foam to eliminate air infiltration, would this be an OK approach??
Seems to be good advice. Having a bit a garage air to balance humidity under the subfloor is a good thing, IMO. The heating effect is secondary.A La Carte Government funding... the real democracy.
May depend on the type of insulation. If you allow e.g. basement air to circulate into that space, you may have to protect any exposed insulation ... i.e. drywall. Rigid XPS, e.g. must be in "substantial contact" with drywall or other approved fire barrier.
While your intent/concept is OK, it mayb be difficult to achieve.
Thank you.
Another general contractor (home builder) I had look at some other projects said I could basically do the same thing but use two pieces of batt fiberglass insulation in each bay in an "L" shape. One piece would be cut to lay horizontally on top of the plywood soffit and the other piece would be placed vertically against the rim joist. Maybe this is the better way to go in light of fire codes and rigid foam board. ??
Any other input gratefully welcomed.
I've seen that done in your configuration. May have to think about the vapor retarder, then. I think some have run it up the lower wall straight to the floor which encloses the entire cantilever at the face of the inner wall. The floor sheathing should be the vapor retarder running horizontally.
Some of the foil covered polyiso is approved for exposed insulation in non-habitable areas..
William the Geezer, the sequel to Billy the Kid - Shoe
Maybe the face, but not the edge, I think.
I went back to your original post. Your overhang is 1 foot. I have a few overhangs like yours. They are the biggest energy loosers there is. You should be able to insulate the area really well yourself with some effort and not cost you a fortune. Cut 2" Blue of Pink foam insulation about 1/2" narrower that the joist opening. Tack it up against the subfloor. Then take can foam insulation like you can get in Home Depot or Lowes and fill the 1/4" gap around the permitter of the tacked in place ridge insulation. Then do the same thing again pushing the second piece of ridge against the first. Foam around it like the first. Keep doing the above until you get close to having the joist bay full. Then measure the distance from the bottom of the joist to the bottom of the insulation. Then purchase the thickness of insulation to make up this last void. Install as above. If you have space to put a 1/2" piece if rigid insulation across the bottom of the joist before you put your trim boards back on do so. This will mitigate some bridging of cold through the joist themselves. On the inside of the basement put pieces of Thermax between the joist up to the subfloor. These pieces will be vertical covering the ends of the ridge insulation previously installed. Thermax is code approve to be left exposer. Yes some work but materials won't be costly. The return for the labor will be worth it because 1) You won't get a better insulation job than the one you just did and, 2) punchouts that have an exposed overhang like yours are real big energy drain on the house and wallet.