Another "shop floor" question - advice appreciated

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Forum topic by glen posted 01-27-2014 05:47 AM 1334 views 0 times favorited 13 replies Add to Favorites Watch
View glen's profile


172 posts in 3159 days

01-27-2014 05:47 AM

Topic tags/keywords: question shop floor

Hi Everyone – I’ve read a bunch of blogs and posts on shop floors, and while I think I got a lot of info, I have one or two questions that remain unanswered.

I live in rural Alberta in Canada, so yes, it gets cold. My sweetheart (the sweetest of hearts – keep reading) has said that I should make a shop out of 2 of the 3 stalls in our garage. Yup – she’s a keeper. I will have a 20×22 ft space with windows, etc. The floor is a concrete slab with 2 floor drains in it.

I would like a wood floor, but don’t want to damage the slab by glueing or screwing (or ramsetting) down the sleepers in case we ever move. Can anyone think of any problems with floating the floor? I would use 16”on centre set of pressure treated 2×4 sleepers and put 3/4” T&G ply over it, with rigid foam in-between. I’m guessing that would be strong enough for the weight of the machines and keep my feet warm. I would shim it so the floor was level but the slope of the concrete would still be there in case water got in under the floor. The remaining stall will have a car in it, so there is likely to be snow and water brought in.

As well, and this may be a question more for my electrician, but can anyone see a problem with running some conduit between the sleepers so I can have in-floor power?

And lastly – vapour barrier. Needed? I’ve seen where the moisture then gets trapped between the poly and the concrete causing a mould problem. Air circulation is needed to avoid mould – thoughts anyone?

Thanks for your advice. Like I said, I’ve read a lot of the posts on this and I’m not sure i have my answer. If you think this was appropriately answered in another thread, please point me in the right direction.

high five


13 replies so far

View Nicholas Hall's profile

Nicholas Hall

352 posts in 2713 days

#1 posted 01-28-2014 03:13 AM

You are a tougher man than I. I lived in Calgary and Ft McMurray for a year or so and I was blown away by the cold. Since I’m from Maine, I thought I knew what cold was, I was totally unprepared for -40 degrees for days on end. I can see why you would want a subfloor!

I don’t have an answer to your question, but I just wanted to wish you luck and bump the thread back up to the top of the forum where it will hopefully be seen by someone with the answers you’re looking for.

Good luck & post pictures when you’re done!

-- Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read. -Groucho Marx

View HerbC's profile


1801 posts in 3465 days

#2 posted 01-28-2014 03:42 AM

I think you’d do well to use CertainTeed Platon to prevent or at least minimize problems with moisture between the slab and the wood subfloor.

Good Luck!

Be Careful!


-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View glen's profile


172 posts in 3159 days

#3 posted 01-28-2014 06:20 AM

Nicholas – thanks for the bump! I’ve worked in Ft McMurray in the winter and it does get pretty cold there. Mind you, I grew up in Winnipeg – middle of the prairies with arctic air whipping across the country and hitting you smack dab in the keester! Playing hockey outside as a kid, we’d cover our faces with vaseline so we wouldn’t get frostbite! I’ll post pics of the shop when done. Might start a blog about this journey…

Herb – that’s a great solution! I forgot about that stuff, but have seen it at the flooring store when I was doing my basement. I might put the sleepers on top of that so I could still have space for electrical to be run, if my electrician agrees. Thanks for the advice!

View widdle's profile


2072 posts in 3605 days

#4 posted 01-28-2014 07:32 AM

go for it…Alot of floor guys down here are just gluing down the ply straight to the clean concrete.And either wedging 1x ’’s down from the ceiling or buckets of sand to keep it flat until the glue dries..

View TheWoodenOyster's profile


1332 posts in 2541 days

#5 posted 01-28-2014 04:06 PM

Hey there. Texas guy here so I don’t know too much about the cold other than I stay as far away from it as possible. I thought I’d throw in my two cents here. I have some commercial construction experience, so hopefully that will help.

I think the wood floor is a great idea. I think your 16” OC stud floor with t+g plywood will work great. I d not see any problem with making it a floating floor and I would actually recommend that because it will allow movement due to temperature and humidity change. If the floor starts getting loose, you could just wedge it at the walls to get it tight again, but I seriously doubt this will be an issue.

As far as electrical under the floor, I don’t see any issue with it. It is just like running electrical under a pier and beam house. Something to think about that might be a cool option though: You could use 2×6 for the floor joists and have the option to run dust collection thru your floor. That might not be applicable, but it is a decent question. Also you could have floor outlets near machines so that you don’t have cords strung all over the place. A “trap door” system where some of the floor panels were removable might give you some flexibility with putting things under the floor at a later date. A local licensed electrician could tell you for sure about the electrical under the floor. Your codes in Canada are likely different than the ones in Texas.

As far as the “mould” AKA mold (you guys up north crack me up), you are correct that air circulation is needed. Waterproofing might very well be necessary in your situation. I’d consult a local homebuilder about that one. Anytime we put down wood floors, we put a vapor barrier down as well. I lean towards putting it in.

Hope that helps.

-- The Wood Is Your Oyster

View glen's profile


172 posts in 3159 days

#6 posted 01-29-2014 04:06 AM

Thanks for the feedback everyone. Oyster – good ideas. I’m not sure I’ll do the ductwork in the floor as I’m hoping to run 6” ductwork all the way to the tool. The shop has 12ft ceilings, so it would be possible to have the floor that high, but i’d have to do the floor in 2×8” in order to get that ductwork in there and that seems a bit thick The windows will be at a weird height. This is the first “Real shop” i’ve set up, so I’m not exactly certain where tools are going to wind up, and to route all that ductwork and then have to change it, might be a bit of a pain. A couple floor plugs should give me the flexibility I need and hopefully avoid having to reroute electrical.

I’ll likely put something like HerbC recommended, that way I get vapour barrier and don’t have to worry about mould or wood rot.

And i’m glad all the gratuitous use of the letter “u” gave you a chuckle! I had actually spelled it “mold” to start but my mac flags it as a spelling error, and autocorrects to “mild”... Not quite! Long live the u.

Take care everyone, and thanks for the advice.

View rustfever's profile


781 posts in 3916 days

#7 posted 01-29-2014 04:44 AM

A vapor barrier is required to prevent sweating/moisture migration/mold. Talk to a local design professional.

-- Rustfever, Central California

View Dan Lyke's profile

Dan Lyke

1520 posts in 4731 days

#8 posted 01-29-2014 03:01 PM

Normally on a slab construction you put a vapor barrier under the slab. In this case I’d use a moisture barrier, like lapped tar paper. That’d keep the water out and let there be a little more vapor migration than 6 mil plastic.

And, yes, I think you’ll be fine floating the floor.

As Wooden Oyster suggests, I’d be okay with wiring under the floor. I didn’t go with floor sockets in my shop because everyone warned me about sawdust in the sockets, but (check local codes) I don’t even see a reason why you couldn’t just run Romex under there. Staple it to your “joists” to keep it in place.

-- Dan Lyke, Petaluma California,

View Manitario's profile


2797 posts in 3489 days

#9 posted 01-29-2014 03:25 PM

I live in Sault Ste. Marie, and while not as cold as Alberta, we still have our share of chilly weather. I have done both of my shops with 2×4’s laid on the concrete floor (wide side down) with 3/4” ply on top. My first shop I nailed the 2×4 to the concrete, my new shop I just placed the 2×4 on the concrete and screwed the ply to it; the ply and the weight of my machines are enough to keep the floor in place. 3/4 ply with the 2×4’s every 16” are enough to support my 900lb planer. If you want more insulation, for my first shop I cut styrofoam board and put it between the 2×4’s. For my new shop I did away with the styrofoam and just vapour barriered between the plywood and 2×4’s.

-- Sometimes the creative process requires foul language. -- Charles Neil

View blazer50's profile


4 posts in 2307 days

#10 posted 01-29-2014 04:45 PM

Great question, Great Idea and yes, Great Wife, luckily I have one too that encouraged me to build a dedicated 28X32 shop by our house.
First, your concrete slab should already have a vapor barrier under it when it was poured. Is your slab sealed with concrete sealer?? If not I would consider that first. You have already thought of shimming the the subfloor joists. Shim below and only occasionally. Think about the floor slope and access to drains if water does get in, and it will. Allowing a good path will give the water an exit point.
Are the drains tied to your sewer or septic system? I hope not, if they are, plug them tight. Over time they will dry out and emit sewer gas. Or leave access to them and periodically run water down them.
As far as mold goes there are so many factors, like how are you heating or air conditioning the space and a dehumidifier is always a good option for the health of your wood and equipment. Don’t overthink this too much from the alarmists posts. There are always reasonable solutions if it occurs.
Think about layout before you start which will help with under floor wiring as well as extra joists in certain areas.
I built a storage building for my completed projects and excess wood supply a few years back and got a bargain on some good hardwoods. I actually collapsed a small area where I had some 8/4 walnut stored vertically and it was sitting on 2 layers of 3/4 plywood. It just happened to fall between the 24” floor joists spacing.OOOPs.
Anyway I hope this helps some. You sound like you have thought this through and should just go for it.
Best of luck.

View Jim Finn's profile

Jim Finn

2780 posts in 3528 days

#11 posted 01-29-2014 08:40 PM

I did just what you want to do but with no insulation or vapor barrier. I live in a high desert. It works great. I had that floor in place for six years and just last year dissassembled it when I moved and the new owner could not tell that there was a floor in there at all. I put it together with screws so it was easy to disassemble.

-- No PHD just a DD214 Lubbock Texas

View glen's profile


172 posts in 3159 days

#12 posted 01-29-2014 11:17 PM

Thanks again everyone. Lyle – I never even thought of those traps drying up. The drain is hooked up to our septic tank and field… I was thinking of putting a subfloor underlayment that allows water to get around it and provide a bit of vapor barrier, as suggested by Herb. That way any water off the car will get in there, but I think I should also make access panels for the drains. It would likely come in handy if there was a plumbing problem as well. I believe the concrete is sealed already.

I think there are special floor outlets with covers that I can use. I watched the Wood Whisperer’s latest shop tour (that mausoleum of a shop) and he has some outlets covered in the floor. I’d really only need a couple, and I should be able to keep the sawdust out.

I will post a blog with some pictures in the near future so that anyone wanting to revisit these issues can follow along.

Thanks for all the help, everyone!

View Dan Lyke's profile

Dan Lyke

1520 posts in 4731 days

#13 posted 01-29-2014 11:29 PM

I suspect that if you get the little dummy plugs that you can put in to keep toddlers from sticking things in sockets, and be religious about using them, you’ll be fine with floor outlets. I just went with ceiling outlets.

-- Dan Lyke, Petaluma California,

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