Question re insulating the floor in my workshop

[Frank Pellow]

This thread is a spin-off from the thread entitled "Frank's Workshop Construction Project" (http://www.sawmillcreek.org/showthread.php?t=7769).

The workshop that I am building has 2x8 pressure treated joists on top of beams on top of piers. Thus, it is open below, so insulation becomes important. I had planned to install two floors. The lower one would be 3/4 inch pressure treated plywood nailed onto the joists. On top of that, I was planning to put 3" of rigid styrofoam insulation within structure of nailers. One top of that, I was going to put a plastic vapour barrier then 1/2 plywood.

Three problems with this are:

(1) it raises the floor about 2.5" more than I would like,

(2) the styrofoam insulation is expensive,

(3) I only get R15.

It occurred to me a couple of days ago that I could suspend fiberglass batts within the joists before installing the plywood. I could support the batts with 1x3 cross pieces every foot. The batts I have in mind are the same ones that I will use in the walls -Roxul Flexibatt which is moisture resistant and which is rated at R21.5. I would then put plastic on top of the 3/4 " plywood and 1/2 plywood on top of that.

The advantages of this are:

(1) the floor would be at about the height that I like

(2) the cost of material is about 1/3 the original plan

(3_ I get R21.5 rather than R15.

I have never seen this technique described anywhere so I don't know if there is some problem with it. I wrote to the manufacturer of Roxul Flexibatt insulation asking them if this is a suitable application but have not heard back from them.

I would appreciate hearing from anyone who can either tell me that the technique is OK, can tell me that it is OK with modifications, or can tell why it is wrong.

In case the suspension technique that I described is not obvious, I mocked up a small section and took some pictures.

[Paul Downes]

Frank, I would be somewhat concerned about pests and rodents getting into that insulation from the bottom and compromising it's integrity. Unless you could completely seal the outside perimeter, I would think racoons and mice and cats.........Also what will keep the snow from blowing underneath and getting the insulation wet during a thaw? I also am pondering on the up front cost of insulating a structure well. I keep reminding myself that it pays off in the long term. I wish the cost of sprayed foam would come down.

[Scott Stefanoski]

i insulated my shop similar to how you are describing. i put rolls of r-30 in the floor with the kraft facing up and stapled the paper to the jpoists. i then went under the joists and ran chicken wire accross the bottom of the joists to keep critters out. i probably should have used hardware cloth, but i have yet to see a bunch of loose insulation. although i haven't really checked since i moved the building.

[Kirk (KC) Constable]

I used chicken wire under the joists to hold the insulation on the house...

KC

[Chris Padilla]

My neighbor recently insulated under his house with batts. We have a crawl space under our houses.

When I redid the downstairs 1/2 bath, we found mice in the walls. They had hopped up on the plumbing and walked right into the wall and continued to follow the plumbing and managed to house themselves in 3 sections of wall. I foamed the hole closed and so far so good.

I think your idea will work fine, Frank. Chicken wire might keep out some of the larger creatures but it won't stop a mouse. Maybe some cheap plywood or chipper board might work?

[JayStPeter]

They sell little pointed metal rods made specifically to hold up insulation in ceilings and crawl space. Installation is quick and easy. They hold up fairly well over time. Chicken wire holds up for a while, but it rusted out in my old damp crawl space after <10yrs. The little rods occasionally pop out, but you just jam them back in. By occasionally, I mean that every few years I'd find a couple down in a 1100 sf area.
Hopefully, you'll have a foundation with vents and won't have to worry about rodents taking up residence in the insulation. I had my door latch break for the crawl space one year and had lots of visitors.

Jay St. Peter

[Andy London]

Frank, Although the fiberglass batts are cheaper, you will more than likely have problems. First as already noted are rodents or squirrels, not sure where you are in Toronto but most areas I have been to have lots of squirrels and they love this stuff. The best option is to have the joists sprayed with insulation.

If you do go with batts, make sure you have a thick vapor barrier on the underside. If this stuff gets any moisture in it and chances are it will, you will one again run into problems.

Andy

[Frank Pellow]

First of all I would like to thank everyone who let me know that something along that lines what I had contemplated is a farily common technique.

Paul and Chris, you both make good point about mice and critters. I had not thought of that. Thanks!

I am going to put lattice right down to ground level and that should keep out most of the snow.

I will not really have room to crawl underneath so anything I put on will have to be done before I put down the floor. Among other things, this means I will not be able to jam in the rods that you suggest Jay.

Chris, your idea of cheep plywood sounds good. I think I can get some bottom-of-the-line stuff for about $10 (US) a sheet (including taxes). I guess that I should paint the underside. I figure that I will need about 14 sheets. That still leaves me with a big big saving over using styrofoam

Jay, I don’t have a foundation, just piers. That means there will be plenty of ventilation.

[Frank Pellow]

Andy, I had not seen your response when I posted the above reply. Do you think that enclosing the bottom with plywood will solve the problem?

Also, you suggest a vapour barrier on the outside. I guess that I could line the plywodd with plastic before installing it. If I did this, do you think that I also need a vapour barrier above the pressure treated plywood sub-floor?

[JayStPeter]

Frank,
I'm not an expert, but everyone poopooed my plan to put ply on the underside of my crawl space. Said it was kind of like not having ventilation under your roof. Good chance it will rot. Again, not an expert, but closing in your floor joists just doesn't sound right to me.
Make sure you put a vapor barrier down (i.e. plastic over the dirt underneath). Damp = bugs that eat wood.

Jay

[Chris Padilla]

Hmmm, I think Jay has a good point. I had thought about enclosing it but thought that since it it close to the ground and not an attic, ventilation might be different some how. Now I think not.

Frank, do you plan to excavate at all under the shop? You know, dig down several inches, maybe back fill with rock or something...something good for drainage. I guess if you seal the floor, you need to vent it...does make sense. Hmmm....

[Frank Pellow]

I am going to cover the ground with 6 mil plastic then about 10 cm (4 inches) of chipped stone. You can see that ground cover in my photos at the start of this thread.

Ventialtion -hmmm I need to think about it. I think the problem will be that mice can probably get through any vents.

Perhaps, if I used the thinest pressure treated plywood I can find to close in under the insulation, that would prevent rot. That will cost a lot more than the $10 stuff I mentioned above but it would mean I don't need to paint and it still be a lot less expensive than my original plan.

[Ed Weiser]

Frank---
In your climate the ONLY place to put the vapor barrier is between the subfloor and the joists, as close to the heated interior as possible. Otherwise you will have moisture and rot problems as condensation collects in the insulation with nowhere to go. The pest problem is real and should be considered. Rodents will chew through almost anything short of masonry and other than erecting a subwall around the perimeter these pests are difficult to stop. Galvanized wire mesh with openings of about 1/4" is probably your best bet. Hope this helps.

Ed

[Frank Pellow]

Frank---
In your climate the ONLY place to put the vapor barrier is between the subfloor and the joists, as close to the heated interior as possible. Otherwise you will have moisture and rot problems as condensation collects in the insulation with nowhere to go. The pest problem is real and should be considered. Rodents will chew through almost anything short of masonry and other than erecting a subwall around the perimeter these pests are difficult to stop. Galvanized wire mesh with openings of about 1/4" is probably your best bet. Hope this helps.

Ed

Thanks Ed but I am confused. You say the vapour barrier should be as close to the heated interiaor as possible but go on to say that this is between the subfloor and the joists. Why not above the subfloor? That is closer to the heated interior. Recall that the subfloor is pressure treated plywood. I would not think that that stuff should be above the vapour barrier.

I will check to see if I can get galvinized wire mesh with such small openings.

[Frank Pellow]

I have been thinking more about whether or not ventilation is needed. The suggestion was that it is needed because it is needed in ceilings. On the other hand, ventialtion is not needed in walls. So we have two examples to choose from. My hunch is that, because we do not have rising hot air in floors, the wall eample should apply.

[Ed Weiser]

Frank--
It all depends how you will cover the subfloor. If you plan resilient tile or wood flooring, the vapor barrier goes beneath the subfloor. For masonry products it can go directly beneath the product.

Ed

[Frank Pellow]

Frank--
It all depends how you will cover the subfloor. If you plan resilient tile or wood flooring, the vapor barrier goes beneath the subfloor. For masonry products it can go directly beneath the product.

Ed
Ed, my floor is going to be wood so I guess the barrier goes below. the sub-floor.

You did not answer my question about the fact that I am planning to use pressure treated plywood in the sub-floor. Is that a mistake?

[Ed Weiser]

Frank--
Since the vapor barrier is beneath the subfloor, ordinary T & G 3/4" subfloor-rated plywood is fine. The additional expense of pressure treated plywood is unnecessary. If you are still worried about drifting snow up against the insulation, you could also use housewrap-type product (e.g. Tyvek, etc.) which is moisture permeable to offer some additional protection beneath the joists. It is not particularly expensive.

Ed

[Rob Russell]

Frank,

You want to find a way to keep ground moisture from bleeding up into the fiberglass batt insulation. Water vapor that seeps into the batt insulation will greatly reduce the effectiveness of the insulation. You might need a layer of housewrap on the bottom of your joists.

I agree that, with a vapor barrier just beneath the plywood, you don't P/T plywood. I'd use a minimum of 3/4". If you want a really stiff floor, put a layer of 1/2" over the 3/4". Stagger the joints.

I'm still working on the DC schematics - had to create a bunch of standard symbols for the various electrical components (switches, contacts, coils, etc.)

Rob

[Gary Sutherland]

Awhile back, I ran some speaker lines for an elderly friend who lives in a mobile home. It had a very tough black 'fabric' (plastic? It was dark under there!) of some sort stapled under the joists, with fibreglas insulation above that, which I had to get the wires through.

It seems to work very well and hold up; try giving a mobile home mfg. or dealer a call and see what they use.

Good luck!

gary

[Andy London]

Andy, I had not seen your response when I posted the above reply. Do you think that enclosing the bottom with plywood will solve the problem?

Also, you suggest a vapour barrier on the outside. I guess that I could line the plywodd with plastic before installing it. If I did this, do you think that I also need a vapour barrier above the pressure treated plywood sub-floor?

Frank I think for the most part that yes plywood on the bottom will solve the problem. I think for the effort you are going through rigid insulation with 1 X 3 strapping would be easier and less of a problem down the road.

I had my joists sprayed for the most part, due to the way the grade runs on bedrock, the back 20 feet of the shop has 2" rigid. Then to help things out a bit I built a knee wall and insulated it.

If you go with fiberglass, house wrap or plastic will work, you do not require air movement under a floor like you do in an attic where there is drastic temp changes.

The other option Frank, give the inspectors a call and ask what they would do, they will give you a quick answer, I've built quite a few homes/buildings here in Halifax and know what I suggested will pass in our area.

Have fun!!

[Frank Pellow]

Ed, I did not make it clear but the reason I asked whether it was a mistake to use the 3/4 inch pressure treated plywood above the plastic is that I already have the plywood. I can't return it. Do you know if there will be problems if I use it? Just how bad is it if I put the plastic above the plywood sub-floor and below the plywood floor?

Ed and Rob, I will check into what types of housewrap are available here starting with Tyvek (which I have never heard of). I am definitely going to put something solid at the bottom of the joists.

Rob, I am planning to put 1/2" plywood over the 3/4" plywood sub-floor and I going to place it so that the joints are in different places.

Gary, I will see if I can find fabric of the type you mention.

Andy, I am relieved to hear from you that "you do not require air movement under a floor like you do in an attic where there is drastic temp changes". That is what I suspected but it is good the hear it from someone else.

Andy, I spoke to the inspector assigned to my building and he did not seem to know much (in fact, he did not seem to know anything) about floor insulation under open spaces. Everything I suggested he seemed to go along with and say that I should try it and see how it works out.

Rob, thanks for letting me know about the DC schematics. I hope that you are not just doing the symbols for me and that you will be able to use them elsewhere. I really really appreciate the electrical advise that you have given to me.

[Jim Becker]

One point..."house wrap" (Tyvek, etc.) does restrict air flow, but it is not a vapor barrier. It is a moisture permeable material. That is on purpose to avoid a double barrier and cause moisture retention in any wall/floor materials, including insulation.

Were I building this floor-on-piers design, I'd put a layer of 1/2" Ext plywood below the deck, construct the floor structure and insulate in the bays with the vapor barrier on the floor side. Given the northern climate, I'd use R30 batts for fiberglass which are also self-supporting in the bays due to the slightly wider width and stiffness they come in.

[Frank Pellow]

Jim, I would put the house wrap below the fiberglass so I would not want it to be a vapour barrier. I want it to at least slow down "critters" who want to nest in the insulation. I am also going to see about using galvinized 1/4" mesh if I can find some with . I would use both with the hope that this combination would actually stop mice.

I will think about R30 but I expect that I will still go with the R21.5 from Rexul. When you add in the R value of tyhe two floors, that brings me up to R23 and the government recomendation for floors over unherated spaces in this part of Canada is R25. Also, I expect that R30 would be too thick. The R21.5 from Roxul is only 5.5 inches thick and they say that it is mosture resistant.

[JayStPeter]

After thinking about it last night, I was prepared to make the same arguments against my previous statement.
I agree w/Jim that Tyvec is a wind barrier, not moisture. There is a very good water resistant versions of osb out there these days. Local Lowes has a piece in a jar of water as a demo. I can't remember the name of the stuff, something with "tech" in it I think. I think the price was relatively in-line with other osb, but am not sure how it would fit into your budget/plan.

Jay

[Frank Pellow]

After thinking about it last night, I was prepared to make the same arguments against my previous statement.
I agree w/Jim that Tyvec is a wind barrier, not moisture. There is a very good water resistant versions of osb out there these days. Local Lowes has a piece in a jar of water as a demo. I can't remember the name of the stuff, something with "tech" in it I think. I think the price was relatively in-line with other osb, but am not sure how it would fit into your budget/plan.

Jay

Jay, what does OSB stand for?

[JayStPeter]

oriented strand board

It's the stuff that looks sorta like particle board, but made with larger chips of wood.

Jay

[Frank Pellow]

oriented strand board

It's the stuff that looks sorta like particle board, but made with larger chips of wood.

Jay

Sounds like what I would call "aspenite".

[Chris Padilla]

OSB at the local orange box is nearly $20/sheet for 7/16" thick stuff. I was kinda surprised at the cost. It must have had some kind of chemical treatment because it was blue. I don't recall any other name attached to it but I wasn't really paying attention to it.

[Jim Becker]

OSB at the local orange box is nearly $20/sheet for 7/16" thick stuff. I was kinda surprised at the cost.
OSB "used to be" about $7.95 per sheet...as recent as two years ago when I did my shop expansion.

[Rob Russell]

Rob ... I hope that you are not just doing the symbols for me and that you will be able to use them elsewhere.



This is not solely for the DC schematics. I need to do an electronic version of the schematic for my phase convertor and will use the symbols from the DC when I do that diagram (plus more - you don't need capacitors, a phase monitor, potential relay etc. for the DC contactor).

[Frank Pellow]

Well, I found some galvanized wire mesh with a 1/4 inch opening.

The good news is that it certainly looks like rodents could not get through it.

The bad news is that it is really expensive (a little over 70 cents US a square foot, including taxes).

I am now considering using only the mesh (not wood of any kind), stapling the mesh to the underside of the joists, and inserting the insulation at the top of the joists where I am told by the manufacturer it will stay. The quote from a Roxul rep is "the product is designed for friction fits and therefore you likely wouldn't need any strapping". Since the insulation is 5.5 inches thick and the joists are 7.5 inches thick, this will leave two inches between the mesh and the insulation; making it even harder for critters to get at.

[Chris Padilla]

Do what you can to keep the critters from getting under your shop to begin with and you'll have a shot. Critters are remarkably resourceful and the underside of your shop will be quite inviting and tempting...they will tax themselves striving for that beach-front property! :)

[Frank Pellow]

Chris, I plan to install rigid wire fencing at least 6" into the ground around the perimeter of the building and extending up above the ground by about a foot to meet the siding. I will then cover that with lattice stained the same colour as the siding.

The only thing that I am still in doubt about is whether to put the vapour barrier below or above the sub-floor.

[Robert Ducharme]

The vapor barriers main purpose is to isolate materials that should not have humidity from the interior living spaces which have humidity (showers, breathing, etc).

assuming you have

flooring
sub-flooring
insulation


I would place the vapor barrier below the sub-flooring and above the insulation. I do not think you will have enough moisture to really bother sub-flooring especially if you do the flooring okay. Also, if the floors are pretty water proof (painted, etc), I am not even certain why you are putting any in at all. I can see it more if you have drywall.

[Frank Pellow]

Today I installed the first section of insulated sub-floor. I am attaching some photos that illustrate the structure that I decided upon. I thank all of you who contributed to me deciding upon this method.

The insulation is mineral wool (40% recycled) rather than fiberglass. A local guy that I talked to told me that he used it in his crawl space and that raccoons hate it.

I also included a photo of the tool I am using to screw the strapping under the joists. I sure could use a Festool CD 12 FX drill with a right angle chuck, but I don't have one, so the improvised tool will have to do. Actually, it is surprisingly fast.

[Jim Becker]

Lookin' good, Frank. The mineral wool is a pretty good solution...I had forgot about it since it doesn't get used that often, especially in residential work around here. Do wear gloves, long sleaves, eye protection and take a cold shower after working with it, however! (Same actually applies to fiberglass, too...)

[John Miliunas]

I also included a photo of the tool I am using to screw the strapping under the joists. I sure could use a Festool CD 12 FX drill with a right angle chuck, but I don't have one, so the improvised tool will have to do.

Sheeeesh Frank! I feel the pain of having to screw the strapping up in that fashion way down here! :eek: The Festool would be the hot tip! But, I think I've seen right angle attachments for regular drill somewhere. Don't thing they were that expensive, either. Even a cheap one would have to do better than what you've got going there. You're going to end up with Carpal Tunnel doing too much of that! Ouch!!! :( I'll grant you this: You shore do have a lot of moxie! Like I said on the other thread, I'd still probably be staring at the painted circles about now! Kudo's, my friend! You deserve it! :cool:

[Ed Weiser]

Frank--
Great job!! I realize it must be a real pain to get under that floor system to attach the mesh but I think in the long run you'll be quite pleased. It looks like you've got 8+ inches of mineral wool insulation. What kind of R-value will that give you? Looking forward to the next group of photos!!

Ed

[Frank Pellow]

If I can find a right angle attachment that fits my electric drill (a cheap Ryobi), I would cetainly be interested. I briefly looked into such a thing about a year ago and was not successful.

I am going to Home Depot tomorrow morning early to pick up more insulation and will check to see if they have such an attachment.

[Frank Pellow]

Frank--
Great job!! I realize it must be a real pain to get under that floor system to attach the mesh but I think in the long run you'll be quite pleased. It looks like you've got 8+ inches of mineral wool insulation. What kind of R-value will that give you? Looking forward to the next group of photos!!

Ed

The insulation in 5.5 inches think. The R value is R21.5.

[Chris Padilla]

Frank,

Look for a flexible cable for your drill as well...it might work for you. I have the right angle attachment for my Festool CDD12 drill...pretty nice however the eccentric drive is bloody awesome!

[Frank Pellow]

Lookin' good, Frank. The mineral wool is a pretty good solution...I had forgot about it since it doesn't get used that often, especially in residential work around here. Do wear gloves, long sleaves, eye protection and take a cold shower after working with it, however! (Same actually applies to fiberglass, too...)

Thanks for the advise Jim. I did wear gloves and long sleaves today and am off shortly to take a shower.

[Frank Pellow]

Frank,

Look for a flexible cable for your drill as well...it might work for you. I have the right angle attachment for my Festool CDD12 drill...pretty nice however the eccentric drive is bloody awesome!

Flexible cable, that sounds NEAT. I never knew that there was such a thing.

[Jim Becker]

Thanks for the advise Jim. I did wear gloves and long sleaves today and am off shortly to take a shower.
Cool water is best in this case as it will not open your pores to any fibers that happen to "be there". Once you are completely rinsed, you can kick up the heat to normal! I worked for a couple of years for an insulation contracting company owned by a former father-in-law and learned that one really quick!

[Frank Pellow]

Cool water is best in this case as it will not open your pores to any fibers that happen to "be there". Once you are completely rinsed, you can kick up the heat to normal! I worked for a couple of years for an insulation contracting company owned by a former father-in-law and learned that one really quick!

Too late, by the time you sent this, I had already had my hot shower and was off to bed. However, I will remember this tip for the next time.

[Frank Pellow]

Flexible cable, that sounds NEAT. I never knew that there was such a thing.

I found one today and it was not very expensive so I bought it. A picture is attached.

It works OK but I do have some trouble keeping the bit in the screw -and I am using Robertson screws (known to some of you a square head) which are the best type of screws for holding a bit.

[Jim Becker]

The reason you're having trouble with the bit staying in the recess is that it's very hard to put any pressure on at all with a flex shaft. The recess is still slightly tapered and with the torque of driving, it's gonna fall out. An angle chuck would probably be more effective, if only because it may be easier to put pressure on the fastener.

[Frank Pellow]

The reason you're having trouble with the bit staying in the recess is that it's very hard to put any pressure on at all with a flex shaft. The recess is still slightly tapered and with the torque of driving, it's gonna fall out. An angle chuck would probably be more effective, if only because it may be easier to put pressure on the fastener.

Jim, you are correct about the reason I am having trouble and you have the proper solution too. But, I am not willing to pay for a drill with a right angle chuck right now.

[John Miliunas]

Jim, you are correct about the reason I am having trouble and you have the proper solution too. But, I am not willing to pay for a drill with a right angle chuck right now.

Frank, I know what you mean. I found this at McFeely's:
http://shop.store.yahoo.com/squaredrive/ra-5301.html

For $45.00(US), might be worth it. :cool:

[Frank Pellow]

Thanks for doing the research John. Yes it would be worth it if I could have the chuck NOW. But, I think that, if I orderted it today, the earliest I could expect to have it in my hands would be next Monday and the job should be finished by then. Even if I paid extra to have it shipped fast, it would have to clear Cnadian Customs and that almost always takes a couple of days.

[John Miliunas]

Thanks for doing the research John. Yes it would be worth it if I could have the chuck NOW. But, I think that, if I orderted it today, the earliest I could expect to have it in my hands would be next Monday and the job should be finished by then. Even if I paid extra to have it shipped fast, it would have to clear Cnadian Customs and that almost always takes a couple of days.

Understood. Too bad stuff has to get tripped up at that little expansion crack between CN/US. :( Good luck with the rest of the insullation. I'll keep checking progress. :) :cool:

[Frank Pellow]

Understood. Too bad stuff has to get tripped up at that little expansion crack between CN/US. :( Good luck with the rest of the insullation. I'll keep checking progress. :) :cool:

Yes, supposidly we have free trade between our two countries, but free trade never seems to work to the advantage of ordinary people.

:(

[Frank Pellow]

Today I worked smarter. :)

I figured out that, if I gripped the flexible drill near the bit with vice grips, then I could put sufficiant pressure on the bit to keep it from slipping out of the screw recess.

[John Miliunas]

I'm starting to think you've got stock in "Vice Grip"! :D Good solution! :cool: