Floor insulation, Roxul vs closed foam

[Arky217]

The foundation of my house (1152 sq/ft) is post and pier and there is no perimeter enclosure.
The bottom of the 2x8 floor joists are about 40" from the ground.

I am considering two methods of insulation.

The first method is 7.25" thick Roxul batts (R30) that are covered with 7/16" OSB sheets.

The second method is 1.5" (R10) of sprayed closed cell foam.

The cost to me of both methods (if I don't count my labor with the Roxul) is nearly identical, about $2000.

The Roxul has the advantage of about 3x the R value of the foam.

However, the Roxul has a couple of big disadvantages as well.
I would be doing all the labor with the Roxul method and since the floor joists are on 19.2" centers, it would require quite a bit of cutting the batts, since Roxul doesn't come in that width.

A big advantage of the closed cell foam is that I would not be doing any of the labor. Also, it appears that the foam would seal better against air infiltration.

The only apparent disadvantage of the foam is the lesser R value, however, I'm not sure that I really need more than R10 in the floor (The location is in western Arkansas).

I kind of leaning toward the foam (thinking about the labor with the Roxul, I'm 68).

What say ye ?

Arky

[MountainDon]

I don't like working "upside down" under a building if I can help it. I will be 68 in a little over a month.  You at least do have more height than I did/do.  But the closed cell foam definitely will seal better and stopping air infiltration is good.   Plus if you ever want you could add some batts at a later date. Maybe pay someone to crawl undermeath like I did.

[Adam Roby]

Why would you only spray 1.5" of the closed cell foam?  You may want to increase that amount seeing as how the cost difference may not be that much since they are already there spraying (just more material).  A hybrid solution like Don mentions is also something to consider, using the closed cell as the primary insulate. 

Air movement is a big factor in insulation, as is moisture barrier.  The closed cell acts as both an insulator as well as a moisture barrier.  There is no better moisture barrier than the spray since it creates the best possible seal (there are no taped seams, no staples, etc.).

[Don_P]

One caveat on flash and batt for others to think about, I hear more folks thinking about that route. This tale is on a roof so not sure how it applies. A coworker noticed a small drip spot on his new ceiling and removed a T&G board to investigate. He had hired a company to spray 1.5" of closed cell and batt with fiberglass, which should work here. The insulation was damp, beads of condensation on the foam. He probed the foam and they had skimped which allowed the dew point to occur in the cavity as the seasons changed. The company will come out after he removes the T&G, redo the work and will replace the T&G materials but not something anyone would want to happen. In this case I can only visualize that scenario in cooling mode but building science probably has info. A coathanger with tape marking the target depth stuck up thru the foam to check application is a very good idea, these guys probably knew what they were doing when they skimped.

[JRR]

If (IF) I build again, and because I live in a moderate climate, I will consider the following:  Allow the basement/foundation/floor joists to be totally "cold", with basement access only from the outside.  Inside, on top of the flooring, install sufficient layer(s) of rigid foam to exceed code recommendations.  On top of the rigid foam, install a finished floor surface ... perhaps wire reinforced grout and tile ... or perhaps, just a wire reinforced finished concrete layer...or a layer of T&G hardwood.

[Adam Roby]

That is an approach many people (are here anyways) use in their basements.  Rigid foam on the concrete floor, all the seams taped, rigid on the walls and taped, all the corners spray foamed together to create a complete seal.  Then you would build your stick walls on the and lay the flooring.  Many times this is done in order to be able to install hardwood flooring in the basement, where normally the humidity levels are too high for such a product.  This of course assumes the foundation has adequate draining and the water table is low enough not to intrude. 

[JRR]

Yes, it is an insulation plan many have used in the basement.  But I intend to leave the basement "not insulated" ...a simple space, not a living space...not even connected by stairway to the living space.   Oh, there might be an insulated equipment closet or bathroom/mudroom, but that's all.  Garden tractors, equipment, boats, trailers, vine cellar, etc.  The "heated/cooled" insulated living space would begin above, on the "first" floor.

[umtallguy]

flash and batt strike me as a bad idea in floor isulation, moisture would migrate up util it hits the foam I would think?

[Arky217]

Ok, after re-thinking this whole situation of floor insulation, I'm starting to reconsider my original plan of using cellulose,mainly because of cost and the labor involved.

I could go with one of two methods:

Method #1:  Cover the joists with OSB panels (would take 36 @ $8.75 = $315), then cut a hole in the middle of each bay (there are 90 bays, each one is approx. 17.75" wide x 93" long), then dense pack the cellulose with a box store blower (should pack to at least 2.5lb./cu.ft.). Approx. cost $330 for the cellulose, $315 for the OSB, total $645.

Advantage: $108 cheaper (also, I already have 30 sheets of OSB, but I could use them elsewhere)
Disadvantage:  If the cellulose in 1 or more bays ever got wet from a water leak (washing machine, busted hose, etc., it would take forever to dry out, would have to be replaced.

Method #2:  Cover the joists with insulweb, blow the cellulose, cover with 1/4" hardware cloth (keep out mice).
Since the dense pack cellulose is also resistant to air movement, it would seem that the hardware cloth would serve the same purpose as the OSB, supporting the celluose and keeping out mice.
Also, the subfloor is the air barrier, just like the ceiling below the attic is the air barrier.
Kind of like ceiling insulation inverted.
Approx. cost $330 for the cellulose, $333 for the hardware cloth, $90 for the insulweb, total $753.

Advantage: The cellulose would probably dry out if it ever got wet.
Disadvantage:  $108 higher cost.

What say ye ?

Thanks,
Arky

[MountainDon]

Do you think the big box store cellulose blower would work? I have borrowed them a few times and have actually had hose clogs occur (once on a long run of hose). The ones I have used did not seem to blow very hard and were labeled for loose fill attic only, or words to that effect.

[Arky217]

Thanks Don for the reply,

I think they will work because if I use the OSB, I plan to drill 3 holes adjacent to each other to make an oblong hole; this will enable me to get the hose at the very end of the bay, perhaps using a short pipe on the end of the hose.

Do you think the cellulose will dry out if I have a flood in the kitchen or bath (I've had them before, but on a slab) ?
Perhaps I'm just a worry wart, but that's really the only reason I'm considering insulweb and hardware cloth, otherwise I would probably just use the OSB.

Can you think of any reason to use the OSB vs the other ?

What do you think of 1/4" mesh 23ga for the hardware cloth; is it heavy enough ?

Thanks,
Arky

[MountainDon]

If it was enclosed with sheets of OSB and if it got wet I see little air movement so it stays wet and causes problems with eventual mold or rot on the subfloor, the joists or the OSB underneath. If it never gets soaked by a catastrophic plumbing failure there will be no problems. We've been through one failure and caught it within maybe 20 minutes of the failure. On a slab.  The repairs were not cheap, but were covered by insurance. That was our main residence. Our cabin has an elevated wood floor and batt insulation with plywood bottom. I don't see a chance of a catastrophic failure of the same magnitude there as the maximum amount of water inside at any one time is 15 gallons.

Maybe looking into a setup including water alarms and possibly automatic shut offs of some kind would reduce the water damage risk.

So, personally I get nervous about insulation is a pier / beam system. A crawl space has different solutions.



23 gauge would likely be okay for field mice but not larger rodents. I did not check the NPS handbook recently but I seem to recall it recommended a gauge in the "teens" not the "twenties".

[JRR]

Just thinking out loud:  If I were to try to insulate "upward" in between some joists, I would use plastic/paper bags to hold the insulation.  Put up a few strips of furring across the joists at one end ... stuff-up a few bags of insulation ... put up some more furring and continue onward to the other end of the joists.  Stuff with a lot of force, so that the cavity is well filled.  Now that last foot or two of joists may require a helper or two to keep the bags in place, until the final furring is secured.  But you get the general (bad) idea.
.
The plastic bags might help control water exposure.  The furring would allow air circulation.  This would be a fairly easy system to repair, I would think.
.
You could cover the whole system underneath with chicken wire, or what ever, for rodent control.

[Adam Roby]

I don't know about stuffing insulation... doesn't that reduce the R value?

When I do my cabin, it will be a post and pier, and I will use the big box store spray foam stuff.
http://www.lowes.ca/foam-insulation/touch-n-foam-low-pressure-polyurethane-foam-sealant_8789950.html



It will probably be pricey, but I won't have to worry about OSB, water, moisture and it will probably give the best possible insulation factor I can get.  IMO

[Arky217]

I don't know about stuffing insulation... doesn't that reduce the R value?

When I do my cabin, it will be a post and pier, and I will use the big box store spray foam stuff.
http://www.lowes.ca/foam-insulation/touch-n-foam-low-pressure-polyurethane-foam-sealant_8789950.html



It will probably be pricey, but I won't have to worry about OSB, water, moisture and it will probably give the best possible insulation factor I can get.  IMO

Key word with this product pricey.  The local closed foam spray company wants $2000 to spray 1.5" on my 1152 sq.ft.
If I were to use these kits from Lowes to spray the same 1.5", I calculate that it would cost with tax $3447 + me doing the labor.
That's based on the product specs of 200 board ft per kit and $349/kit.

It would be the best solution against a plumbing leak and for air sealing, however, that's an amount that I simply can't afford, or at least am not willing to pay for just a R9 or R10.  And it does not address the thermal bridging of the joists.

Arky

[Redoverfarm]

Arky they make a wire support for batt insulation. Easy to use. No mechanical fastening needed.  Just place your insulation batts up into the bay and spring one of the wire supports to hold it in place and keep going.   Here is what I am referring to.

http://www.lowes.com/pd_12336-41075-716225_4294858107__?productId=3125683&Ns=p_product_qty_sales_dollar|1&pl=1&currentURL=%3FgoToProdList%3Dtrue%26Ns%3Dp_product_qty_sales_dollar%7C1&facetInfo=

In regards to "rabbit wire" to prevent rodents from entering the insulation bays unless you are in an area of large rodents the 1/4" grid will do just fine.  I have a cage built in my outbuilding for livestock feed storage.  It is completely covered with wire.  It has prevented mice and larger rats from entering into the feed bags.  I would not go any larger than 1/4" or the mice will get through.

[Adam Roby]

Definitely an expensive option to go the spray foam route.  My cabin plan is a much smaller footprint of 16x16.  My thought was to go with 6 sheets of Expanded Polystyrene Insulation (2" x 4' x 8') to fill all the rafter voids, then use 1 container of the self spray that covers 200 sqft stretched mostly to fill the voids and help with the thermal break, with an additional thin layer over top.

http://www.lowes.ca/sheet-insulation/envirosheet-dr22s20004-2-in-x-4-ft-x-8-ft-expanded-polystyrene-insulated-sheet_10727729.html

My plan would look more like $140 of sheets, and $350 of spray, so $500 for the complete floor.  If I had more area I would go pro... but I like the idea of doing it all myself.  Ideally I would love the walls to be spray foam as well but cost is just too high.  Like you the idea of wet insulation under the floors is a scary thought... also considering being on piers there is a possibility of snow being blown under the structure and causing some moisture problems there.

[Arky217]

Well, I think I've finally settled on how I will insulate my floor.

I will cover the joists with the OSB sheets( I already have 30 of the 36 that I'll need) after I staple hard foam strips to the bottom of the joists to block the thermal bridging.

Then in each bay (17.75" x 93"), I will blow in the cellulose as dense as I can with the box store blower (should be able to get it at a density of at least 2 to 2.5 lb/cu.ft.

Approx. cost: cellulose - $330, 6 more OSB sheets - $53, 3 foam sheets - $33, total $416

As to the possibility of the cellulose ever getting wet from a plumbing leak, I'll just try to use preventative measures to keep that from happening and if it does, I'll just deal with it at that time.

But I do have a question about blowing the cellulose.
I was planning to just make an oblong hole in the center of the bay and push the hose in to the ends of the bay (about 4') and work toward the hole but I wasn't thinking about air relief, so I assume that besides getting a lot of dust being blown back out of the hole, that the back pressure might inhibit the packing of the cellulose.

I wonder if there a better way, such as making more than 1 hole for example ?
If more than one hole, where in the bay should they be and what would be the blowing strategy ?

Thanks for all the replies,
Arky