I have a question. Does anybody have an easy way to insulate I Joist floors? The web at the bottom is too low to hold the insulation, and putting the insulation in the middle results in a sloppy fit. Other than ripping long strips of insulation, I can’t think of anything. Regular insulation stay wires seem too loose. Thanks for the advise. Chuck
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
Fine Homebuilding's editorial director has some fun news to share.
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
I believe fiberglass Insulation comes in slightly wider widths so that it will fit snugly between I-joists. This is commonly used in metal stud buildings too. IE: it comes in 15" & 16", 23" & 24" You may need to go through an insulation contractor to get the wider stuff. I've never seen it at home centers.
If you're a DIYer and have the time..... You could fasten 1x2 ledgers to the webbing, then lay (glue?) 1x sheets on the ledgers, then lay the insulation on top of that.
AFAIK that is how my 75-yo bathroom floor was insulated: 1x T&G planking sitting on 1x ledgers between the joists, and a bunch of construction debris that I'm surmising was supposed to be insulation. It's the only other explanation I can think of for it (or the debris could be leftover from previous demos). If anyone has an alternative explanation, I'd love to hear it.
Taylor,My guess is that what you have is construction debris, and the 1x was to keep the rats out. If you ever remodel from the top, you can quickly tell if the stuff was demo trash, or purposely laid there. I have seen this more than once.Bill
Bill, interesting. But this is 2nd floor and I think you are thinking of keeping rats getting from a crawlspace into the joist bays?Ow I'm going back to put in those 1x's!In any case, what I suggested is one way to put in insulation, for those that have time on their hands....
Tap roofing nails most of the way into the bottom of the joist about every 16", leaving the head slightly exposed. Then string piano wire zig-zag under the insulation to hold it in place.
happy?
My house has I-joists on 24" OC. The insulation they used was 24" wide and they used these metal wire/rods to hold it into place. Funny thing is that the code requirement for the unfinished basement was to insulate either the floor joists (to the first floor above) or the exterio walls of the basement. They chose they harder route, IMO.
You can order or buy direct insulation in wider widths and use some 1/2"x1" pieces of wood if you cannot find wire/rods to help support the insulation in your joist cavities.
I have seen it supported by a stapled up plastic mesh, w/ squares like 1-2". I know my local yard supplies it, but only by the roll. What they sell it designed for this.
The thing is that the insulation is supposed to be pressed pu against the bottom fo the subfloor... Overall though I think the issue is getting a good friction fit with I-joists. A loose fit with airspace above would be.... well you know...
No major reason why the insulation must be pressed against the bottom of the subfloor. Yes, it will improve its insulating quality a bit, but you can improve it more by covering the bottom with Tyvek or some such.
If ignorance is bliss why aren't more people
happy?
>> No major reason why the insulation must be pressed against the bottom of the subfloor. <<
I'm think that is incorrect. When I was building Energy Star houses, Advanced Energy, the consulting company that was overseeing the implementation of Energy Star program required it. What they taught me was that fiberglass insulation had to be in contact with an air barrier on the interior of the building envelope to work correctly. Otherwise air currents between the interior covering and the insulation would greatly deplete it's insulating effect. For example, they told me that they had used heat sensitive photography (I forget the correct terminology - infared?) in finished houses and that they see cold pockets where the insulation was not up against the sheetrock on walls - which is BTW the reason they require wall insulation to be face stapled. Using the same methods they could also see insulation installation problems in batted ceilings. Also, for example, behind prefab fiberglass tub-shower units they required us to install insulation and then a rigid air barrier like 1/4" plywood, or rigid foam (we used the 1/4" thick fanfold stuff) before the tub was installed.
Another point is that the building inspectors require floor insulation to be up against the floor with the vapor barrier toward the living space in the 3 inspections jurisdictions in which I build.
We use those wire insulation supports to install floor insulation.
Some readers might think Well OK - but what the heck in fiberglass insulation doing in an Energy Star house anyway? Which I asked these Energy Star guys, and their answer was that for the SE USA, the performance of fiberglass insulation was fully acceptable as long as it was meticulously installed.
If you've got the FG insulation up against the floor, with the VB on the top side, the entire bottom side is open to air circulation (exactly what pressing the FG against the floor is supposed to prevent). You'll lose about half the effectiveness of the FG.
If ignorance is bliss why aren't more people
happy?
If you've got the FG insulation up against the floor, with the VB on the top side, the entire bottom side is open to air circulation (exactly what pressing the FG against the floor is supposed to prevent). You'll lose about half the effectiveness of the FG
Not disputing that.... BUT... if you have air circulating on both sides, then you have a much worse situation. The insulation blanket is never going to be 100% because of mechanicals penetrations, etc, etc. which is how the unconditioned air is gonna get above the low-mounted insulation. If you are that concerned about unconditioned air below the insulation, install R-30 insulation - the cost uplift wouldn't be that great - my guess would be about $150 per 1k sq ft.
Attached is a simple drawing of how one air leak - around a plumbing pipe as an example - basically renderers the entire joist bay uninsulated if the insulation is not up against the subfloor.
Covering the bottom of the floor system with house wrap is an intriguing idea, but is not a very workable solution, especially in, say a 2' high crawl space. The reality of it is that there are all kinds of wires, ducts, duct hangers, pipes, pipe hangers, etc in the way, and getting any kind of a good seal on the air barrier would be very difficult if not impossible. Also you have just added another step to the building process - Is there now 2x the opportunities for air leaks? What is the associated expense? Do you actually do this? If not who, who is gonna do it? - my $8/hr laborers who can't even do a good job at picking up trash? - an insulation contractor's guys who won't really want to do it anyway, much less do a good job?
The previous poster's suggestion for spray foam is a good one, but then there may be issues with the flame spread value, smoke development ratings. Where I live there are very specific rules about covering foam plastics in accessible spaces, which include any area were there are any serviceable items like mechanicals, pipes, etc. not to mention the extra expense. If it is a basement, than it could be covered with sheetrock, but now you have still more expense.
Given the poor seal at the edges of the insulation, I doubt that you're going to see much difference between the two layouts. In any event, if the sheathing and underlayment joints are staggered the leakage through the joints should be negligible. Infiltration could be cut to essentially nothing if VB or rosin paper is placed between the two layers or under the sheathing and other penetrations are appropriately foamed -- much better than relying on the FG facing.
If ignorance is bliss why aren't more people
happy?
First off- fill in your profile info.
Secondly, this is an excellent place to use spray foam insulation. It is self supporting and sticks directly to the ceiling you are trying to insulate. You also get a perfect fit every time.
Of course it does cost more but you will get what you pay for.
Stu
If your I joists are 16 inch centres, buy some steel stud insulation. I usually buy "quiet zone". It is a full 16 inches wide and fits snuggly. Up here it comes in silver packaging.
If your I joists are at 19.2 inches, call in your neigbourhood foam guy!
Merry Christmas
Cliffy
To hold 19.2 in place you cut your old tape measures into strips and use them like the wires. That's why they have those diamonds there, you know -- so you'll know where to cut an old tape.
If ignorance is bliss why aren't more people
happy?
I used the 24" insulation stay wires and cut them shorter.