Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Building & Construction

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 11-05-2012, 01:55 PM   #1
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Hey everyone!

Been getting a lot of wonderful information around here lately! Great forum! Hopefully you guys can help me with a project I have in the works, or at least on the drawing board, if you will.

The Room:

We have a 22x14 (ish) room that was added to our house at some point in the 40's or 50's. It is brick construction with a concrete slab floor poured inside. For some reason, the slab is just a mess. It appears to be sloped away from the house, and seams to have been poured in two sections, one stepped higher than the other. Sort of like an addition to an addition, if I had to guess. The slope is probably 2 to 3 inches over the length of the slab. It is also flat in parts and not in others.

Our Intentions:

We would like to put narrow oak plank flooring in this room, to match the rest of the house, and it is also going to be a family/TV/entertainment room. We will probably do surround sound in this room as well. I'm thinking of building a floor structure over the concrete. This would give me a nice level and flat floor that I can run wires under, duct work for HVAC, as well as give us a nice feel to the floor, instead of sub-floor and wood flooring right over a fresh level slab. I only want to raise it up a minimal amount. Just a few inches.

The questions:

1- What is the PROPER way to accomplish this? I'm assuming I will need a vapor barrier of some kind over the slab? What about air circulation?

2- What about insulation? What are my options?

3- Any links or examples I can refer to?

Any help would be appreciated!

Thanks everyone!

scootermcrad is offline   Reply With Quote
Old 11-06-2012, 06:44 AM   #2
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Back to the top for a new day...

Is this a dumb idea? I searched around for info on the web, but didn't see a whole lot.

scootermcrad is offline   Reply With Quote
Old 11-06-2012, 07:10 AM   #3
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


This is sort of what I had in mind.



Maybe I'm using the wrong terminology. They call them sleeper joists. Makes sense.

One thing I'll say, given the age of the slab and from what I've seen of the rest of the construction, the slab was probably poured right over grade with no vapor barrier or insulation, as shown in the above drawing. I could be wrong, maybe it WAS done, but I feel like I would be a fool to assume that there is a vapor barrier and insulation below that slab.
scootermcrad is offline   Reply With Quote
Old 11-06-2012, 07:59 AM   #4
DIY staff
 
Join Date: Sep 2009
Location: Kane county,Illinois
Posts: 21,851
Rewards Points: 2,350
Default

Floor Joists Over Concrete Slab


If the slab always remains dry--your plan will work-----
__________________
New members: Adding your location to your profile helps in many ways.--M--
oh'mike is online now   Reply With Quote
Old 11-06-2012, 08:47 AM   #5
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Quote:
Originally Posted by oh'mike View Post
If the slab always remains dry--your plan will work-----
Okay. So I can put sleepers right down on the slab without a vapor barrier of any kind? Once I've created a closed airspace below the floor will I need to provide some kind of venting for the cavity to prevent a moisture issue? should I maybe provide a slight gap between the wall and subfloor-finished floor to allow air to circulate?

Up until we bought the house, the slab actually had carpet over it for at least 5 years with no moisture issues and we found no mold upon removal of the carpet.
scootermcrad is offline   Reply With Quote
Old 11-06-2012, 09:01 AM   #6
DIY staff
 
Join Date: Sep 2009
Location: Kane county,Illinois
Posts: 21,851
Rewards Points: 2,350
Default

Floor Joists Over Concrete Slab


Lay the sleepers over a layer of tar paper--level and fasten to the concrete---then add your flooring--

I've done that twice without an issue----the key is a dry slab----

It's always a risk----let's see if anyone else has a suggestion.
__________________
New members: Adding your location to your profile helps in many ways.--M--
oh'mike is online now   Reply With Quote
Old 11-06-2012, 09:32 AM   #7
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Quote:
Originally Posted by oh'mike View Post
Lay the sleepers over a layer of tar paper--level and fasten to the concrete---then add your flooring--

I've done that twice without an issue----the key is a dry slab----

It's always a risk----let's see if anyone else has a suggestion.
Great! Thanks! I assume it's best not to penetrate the tar paper. What is suggested for securing the joists and shims to the floor?

This is the general layout of the room. Should the sleepers run the longer length of the floor, I assume, with blocking between?

scootermcrad is offline   Reply With Quote
Old 11-06-2012, 09:45 AM   #8
DIY staff
 
Join Date: Sep 2009
Location: Kane county,Illinois
Posts: 21,851
Rewards Points: 2,350
Default

Floor Joists Over Concrete Slab


How high are you raising the floor?

You will penetrate the vapor barrier with the fasteners----can't be helped----I would use .22 caliber studs---or Tapcons
__________________
New members: Adding your location to your profile helps in many ways.--M--
oh'mike is online now   Reply With Quote
Old 11-06-2012, 10:13 AM   #9
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Quote:
Originally Posted by oh'mike View Post
How high are you raising the floor?

You will penetrate the vapor barrier with the fasteners----can't be helped----I would use .22 caliber studs---or Tapcons
The least amount I can get away with. I need to figure out exactly how much slope there is to the floor and where the slope is at, first. I have a feeling that half of the floor is sloped on the end by the stairs (closer to the house) and the other half is not as sloped (further from the house).

My first thought is to actually start with a 2x6 sleeper joist (on end, like normal) and cut it to match the slope of the floor. It would be incredibly time consuming and every joist would have to be cut individually and placed, but I have a feeling that would give me 3"+ nailing depth for my sub-flooring at the high end.

Is that a bad idea?? Am I in the wrong frame of mind on how to set up these joists? The room has a pretty tall ceiling, but I don't want to lose anymore ceiling height than needed.
scootermcrad is offline   Reply With Quote
Old 11-06-2012, 10:41 AM   #10
Bombastic Idiot
 
notmrjohn's Avatar
 
Join Date: Aug 2012
Location: Mesquite, Texas
Posts: 761
Rewards Points: 500
Default

Floor Joists Over Concrete Slab


" provide some kind of venting for the cavity to prevent a moisture issue?" No. Barrier on slab keeps moisture from coming up from below. If water vapor can enter space from above thry flooring, it can also exit to above. Have you done the ol' plastic taped to the concrete moisture test? 18 to 24 inch squares of at least 6 mil plastic taped around all sides, wait 24 hours, see if moisture condensed under neath?

At least 6 mil plastic , edges overlapped 6" and taped might be better barrier than felt. Bring edges up walls and seal to them at least as high as top of sleepers.

Run sleepers across short dimension, easier to handle and level. But compare cost of number of 22' vs 14' you will need.They should run at right angles to final floor planks. And random lengths with joints offset from each other are better than full span. There are no real joints between lenghts.Lessee if I can explain that. To cross the 14' space, you lay a 4' sleeper from one wall, at other wall you lay another 4' in line with first leaving 6' gap.You span that distance with a 7' sleeper about 1/4" to side of first two, ovelapping both ends 6" Make sure they are level and are really fastened securly to slab, loose ones are gonna squeek. Shim them up to level, a dab of construction adhesive between shims and sleeper and fasten to slab thru shims. Use lots of fasteners, so you'll want to use a power driver.

Alternativly use pressure treated sleepers, foam between, vapor barrier over that. That way you can use adhesive between sleepers and slab.
The type of subfloor, type and placement of vapor barriers, underlayment are gonna depend on your flooring.

Ah, I can shut up, take a look here. http://www.hardwoodinfo.com/articles/view/pro/28/241

BTW have you thought about radiant heat floor? There are some combination subfloor radiant heat products, I dunno a thing about installing or reliability as sub-floor or heat.

Another BTW, are you sure slab was poured inside brick wall? From slope it sounds more like it was a patio deck, that was later bricked in. If that is case it probably does not have a barrier under it.
__________________
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.

Last edited by notmrjohn; 11-06-2012 at 10:45 AM.
notmrjohn is offline   Reply With Quote
Old 11-06-2012, 11:15 AM   #11
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Quote:
Originally Posted by notmrjohn View Post
" provide some kind of venting for the cavity to prevent a moisture issue?" No. Barrier on slab keeps moisture from coming up from below. If water vapor can enter space from above thry flooring, it can also exit to above. Have you done the ol' plastic taped to the concrete moisture test? 18 to 24 inch squares of at least 6 mil plastic taped around all sides, wait 24 hours, see if moisture condensed under neath?

At least 6 mil plastic , edges overlapped 6" and taped might be better barrier than felt. Bring edges up walls and seal to them at least as high as top of sleepers.

Run sleepers across short dimension, easier to handle and level. But compare cost of number of 22' vs 14' you will need.They should run at right angles to final floor planks. And random lengths with joints offset from each other are better than full span. There are no real joints between lenghts.Lessee if I can explain that. To cross the 14' space, you lay a 4' sleeper from one wall, at other wall you lay another 4' in line with first leaving 6' gap.You span that distance with a 7' sleeper about 1/4" to side of first two, ovelapping both ends 6" Make sure they are level and are really fastened securly to slab, loose ones are gonna squeek. Shim them up to level, a dab of construction adhesive between shims and sleeper and fasten to slab thru shims. Use lots of fasteners, so you'll want to use a power driver.

Alternativly use pressure treated sleepers, foam between, vapor barrier over that. That way you can use adhesive between sleepers and slab.
The type of subfloor, type and placement of vapor barriers, underlayment are gonna depend on your flooring.

Ah, I can shut up, take a look here. http://www.hardwoodinfo.com/articles/view/pro/28/241

BTW have you thought about radiant heat floor? There are some combination subfloor radiant heat products, I dunno a thing about installing or reliability as sub-floor or heat.

Another BTW, are you sure slab was poured inside brick wall? From slope it sounds more like it was a patio deck, that was later bricked in. If that is case it probably does not have a barrier under it.
Great info! Thanks! And yes, the explanation helped! And, since I want to run the flooring length-wise in the room, that makes sense.

The slab, oddly enough, does appear to be poured inside the walls. The addition to the house was used for the original builder's wife to have a little shop in. Eventually it became a family room of sorts, as times went on and the house changed hands several times. If I dig down below the level of the slab outside, the brick continues below the level of the slab. So, it does appear that it was intentionally built that way and not a patio slab with walls built on top.

I will try the moisture test with the tape! Thanks! And I will definitely check into the radiant sub-flooring products. That would be super nice for the winter time.

So, QUESTIONS, then... If I put 2x4 sleepers down and level them out over the 22 foot length (14 foot length is level. Slab only seems to slope the length of the 22 foot dimension). By the time I get to the other end of the room, I'll probably be a 4x4's worth of height, or more. What about the shims themselves?? Various thicknesses of plywood? How far am I spacing these sleepers apart?? Also, what would be the suggested sub-floor materials?

Gonna pull out some string and level to see if I can figure out the slope behavior of this slab. Now it's going to drive me crazy if I don't do this soon! HAHA!

The flooring I'm going to be using will be reclaimed 1-1/2" wide x 3/4" thick red oak. Using reclaimed because we want it to match the character of the existing floors in the house as much as possible, plus we have a connection to get it at a very reasonable price.

I also ran across this as well...

http://www.february-11.com/2h_floors_o.html


Last edited by scootermcrad; 11-06-2012 at 11:24 AM.
scootermcrad is offline   Reply With Quote
Old 11-07-2012, 06:41 AM   #12
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Should the sleepers by about 16" OC, like normal, or should they be closer?
scootermcrad is offline   Reply With Quote
Old 11-07-2012, 07:07 AM   #13
DIY staff
 
Join Date: Sep 2009
Location: Kane county,Illinois
Posts: 21,851
Rewards Points: 2,350
Default

Floor Joists Over Concrete Slab


16" spacing will be fine-----plywood shims will work----stick with exterior grade plywood---

For sheeting use BC exposure one---or CDX tongue and groove
__________________
New members: Adding your location to your profile helps in many ways.--M--
oh'mike is online now   Reply With Quote
Old 11-07-2012, 08:53 AM   #14
Member
 
Join Date: Jul 2012
Location: Concord, NC
Posts: 60
Rewards Points: 75
Default

Floor Joists Over Concrete Slab


Quote:
Originally Posted by oh'mike View Post
16" spacing will be fine-----plywood shims will work----stick with exterior grade plywood---

For sheeting use BC exposure one---or CDX tongue and groove
Fantastic! Thank you sir!
scootermcrad is offline   Reply With Quote
The Following User Says Thank You to scootermcrad For This Useful Post:
oh'mike (11-07-2012)
Old 11-07-2012, 10:23 AM   #15
Bombastic Idiot
 
notmrjohn's Avatar
 
Join Date: Aug 2012
Location: Mesquite, Texas
Posts: 761
Rewards Points: 500
Default

Floor Joists Over Concrete Slab


You are lucky on the direction of slope, lots easier to shim entire sleeper length equally than having one end higher than other. You could even use plywood of proper thickness, ripped down and running full length of sleeper. I wonder if slope was intentional so floor could be sluiced down with hose or bucket back when it was a shop.One end is 3 1/2" lower than other? That is considerable, perhaps the room was a garage at one time. I once had to level a shorter span of almost that slope by ripping 2X4's on a taper from full to nothing.

"Gonna pull out some string and level " This is a great excuse... er... need to buy a rotatable laser level. http://www.walmart.com/ip/Trademark-...ndingMethod=rr Strike a level chalk line an inch above high end, then all around room at that level. Stretch your strings across and along room from the lines.

You can space sleepers closer, but as mike sez, 16" is fine, that's what they'd be if they were joists. Comparing your pic and link I posted, you can see pic has gapped butt joints of sleepers, instead of off set laps. The butt jointed sleeprs should be used under butt joints of your sub-floor, or plan your offset ones to be at least 5 foot long at those joints, 6" past long edge of plywood each side. Short sleepers between long ones for side seams are not needed but would add stiffness. Note that butt seams of sub-floor are staggered.

I'd use the T&G CDX. The mastic under plastic is up to you, would keep plastic from bunching up as you work wouldn't hurt under sleepers areas, might help seal the nial holes thru plastic, watch your step, plastic can be slippery. Figure out what thicknesses of shims you'll need, buy a "shim set" of plywood, from 1/8", 3/16"/ 1/4, 5/8, 3/4 what ever to make your different thicknesses. At low end you could double 2x's, adhesive between them, if butt joints, stagger them, not joint right over another. Fasten one to floor, over shim if needed, then fasten top one to it, I'd use deck screws. Which reminds me, screws and nails should be rated for use with pressure treated. Ram-Set has such rated fastener called Ram Guard.

Po'lly take you less time to do job than it took me to one finger peck all this blather. Let me know how that new laser level works out, I need a new one. Mines getting so dim I can't see it, or mebbee its my eyes.

__________________
Measure twice, cut once.
Look at the nail, not the hammer. Watch the fence, not the blade.
If you hook your thumb over your belt you won't hit it with the hammer or leave it layin on the saw table.
notmrjohn is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Concrete Basics for the DIYer Mort Concrete, Stone & Masonry 7 11-22-2012 11:19 AM
concrete porch slab questions Queso Bandit Building & Construction 2 06-29-2011 10:31 AM
Fix or Replace Porch Concrete Slab Majoram Building & Construction 10 06-25-2011 02:45 PM
Help stone over concrete slab Johnnyquest Flooring 0 05-20-2011 03:36 PM
Concrete slab to foundation work tntgarv Building & Construction 3 02-28-2010 12:23 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.