Floating An Insulated Sub-Floor On Concrete Floor
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- Опубліковано 30 вер 2024
- Floating a Floor Over a Concrete Slab Without Sleepers
Mike Hopp a RI remodeling contractor, and friend, asked us to help him frame out a large garage that was being converted into a studio apartment.
The garage was framed with 2x4 walls, a truss roof system and had an existing concrete slab floor. The trusses meant that we did not have any bearing walls inside the structure and meant that we cover the entire floor slab with no interruptions to the perimeter walls with insulating foam board.
We all agreed that this continuous foam board approach would be faster than installing pressure treated sleepers and then having to cut ridged foam to fit tightly between the sleepers, and spay foam them in.
Floating Floor Overview:
Mike’s plan called for an uninterrupted layer of 2” Owens Corning extruded polystyrene (XPS)foam boards directly on top of the concrete slab, with all the seams taped. This would be followed by two layers of 3/4-inch Advantech subflooring floating [not fastened] on top of the foam. The foam additionally allowed us to achieve a complete thermal break and obtain an R-10 insulating value above the concrete slab.
Creating a Thermal Break and Vapor Barrier
In an ideal scenario, the floor under this slab would have been insulated with rigid insulation such as XPS (extruded polystyrene) board, known for its high compressive strength. Utilizing XPS beneath the slab enables the concrete to retain heat effectively.
Our primary objective in covering the concrete floor with XPS foam board is twofold: to establish a thermal break and to implement a continuous vapor barrier.
Thermal breaks are essential for maintaining optimal heat retention within concrete slabs. Their advantages include heightened energy efficiency, enhanced comfort, and the prevention of condensation.
The absence of XPS foam board could result in cold air meeting warm, heat-generated air inside the studio apartment, potentially leading to condensation in the walls or floors and fostering mold growth and other issues.
Installing the Foam:
We sed Owens Corning FOAMULAR 400 Extruded Polystyrene (XPS) Insulation boards
designed for use in load-bearing situations, such as under slab, concrete floors, foundations, roadways and rail beds, parking decks, and cold storage installations.
We installed the 2” insulation boards on the concrete floor without glue. Installing the foam boards went quickly. The board cuts easily with a table saw lays flat on a clean, vacuumed concrete floor. Once the foam was fitted on the floor, we sealed all the seams with 3M #8067 All Weather Flashing Tape and sealed the perimeter seams at the concrete walls, and utility pipe penetrations with expanding foam.
This 3M tape is a self-adhering, waterproof flashing membrane designed for seaming damp surfaces such as polyethylene vapor barrier products, building materials and seal to around openings and penetrations in exterior walls. It has a unique acrylic pressure sensitive adhesive that aggressively sticks and stays stuck both at lower and higher application temperatures.
I will note that after installing the XPS foam boards on the floor we all noticed that the room felt warmer.
Note - we also covered the foundation walls, following the same procedure, but used 2” XPS 25 psi foam board as a cost saving solution.
Installing the Subfloor:
We then moved on to installed two layers of ¾” Advantech subfloor sheathing. The first layer of subflooring was installed perpendicular to the foam, taking care to stagger the ¾” Advantech and foam joint seams. We installed the tongue and groove plywood and ensured an 1/8-inch expansion gap at the butt ends.
Titebond subfloor adhesive was used to glue the first layer of Advantech plywood to the foam board. We used the larger 28oz tubes of glue and averaged approximately 2 sheets per tube.
Note - We recommend having a cordless caulk gun to assist in speeding up the process and save your forearm and grip strength.
The second layer or plywood was installed perpendicular to the first layer of plywood, again staggering our joints, and maintaining an1/8” expansion gap between subfloor sheets.
We then glued and screwed this second layer of plywood to the first layer, installing 1-3/4” screws every 6-inches to eliminate any squeaks between the subfloors.
After the subfloor system was installed, we installed our partition walls, and attached them directly to the sub-floor.
Conclusion:
The result was a strong and stiff subfloor without having to install sleepers that might loosen, squeak, or twist over time. The big win for us was achieving a thermal break with an R-10 insulation value and a continuous vapor barrier.
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Awesome job, it looks fantastic Rob
This would be an excellent bone and joint saver in a shop,and allow electrical to be in/under floor for tooling!
I like the idea of this process. Couple question. What do you think would happen if water would get between the concrete and foam board. Do you think it would cause mold growth? Will it dry out? I would really like your thoughts on that aspect. If that was a concern could you lay down a dimple mat as a barrier to act as a drying plane. Lastly what are your thoughts of using say rockwool comfort board or rocktop instead of the pink foam insulation? Thanks Rob.
I don’t think either material supports mold growth. The plywood would though. I’m not familiar with rock wood board- does it have an R-Value?
Why wasnt a vapor barrier needed? Over the concrete / under the foam?
@@samputrah because the XPS board is a vapor barrier when it’s taped and sealed
What a great idea. Could you also grove and layer pex for in floor heating in this at the same time?
I’m looking to do this exact same project on a concrete pad under a covered patio. Was this garage pad sloped? And if so was there any concern with leveling the pad prior to installing the xps and subfloor? Thank you!
Not sloped
Do you think I can get away with only one layer of 3/4 Advantech? I have a garage that was converted to studio a few yrs ago. I put down an epoxy floor at the time. But the floor is cold in the winters. A couch,chair, dresser and refrigerator will go on top. I’m thinking of a low pile rug on top of the subfloor. Cost is a consideration. I will go with the two layers if really needed for the floor to function well. Thanks for the video, appreciate it.
This video was awesome. Thanks for sharing this clever and unique solution.👍👍
Great idea. How did you resolve doorways?
Rob, South Florida here. We have an upcoming podium slab or elevated slab, seaside. What's your take on using this type of floor here? Added note; we are using steel beams and columns with the base plates raised and using non-shrink grout. Clear span beams.
@@davidbruce5377 not sure, we don’t have those kind of conditions
No worry of termites or carpenter ants getting in the foam board?
Long time ago we used R-Max for wall sheathing on exterior under the siding and we had a terrible time with carpenter ants building tunnels and chewing up all the foam between the foil surfaces. From the outside I could put my hand on the vinyl siding and could just barely feel movement of them crawling around but we could easily hear them. Ended up removing the siding and ripping what was left of the R-Max. Thank God we only used it on 2 houses.
A friend said he had same type problem with an ICF house they poured years ago also, but I've not heard that being a problem more recently.
Just curious about putting foam on top of concrete, he have used it under slabs on a few projects, but no way really to monitor under a slab, what goes on.
Great questions. 👍
No more worry than the sleeper method. We do t see termites as much as we do carpenter ants. Either way you need to monitor the property and treat if needed
Cordless 29oz caulk gun eh? I have a Cox 41002 gun which is pretty nice but with that amount of goop to dispense, I think you're right that a electric tool is the way to go.
It was worth it’s weight in gold, but it will probably sit in the shop for another year
Excellent work Rob!
I live in a small building with townhomes over a concrete slab with an open garage underground. In the winter my house is always freezing. This method probably would work as a good insulator.
Would you mind giving me your 2¢ if installing only the insulation boards and skipping the two layers of plywood would suffice to create a thermal barrier before installing a floating wood floor. I won't have enough height clearance to afford the 2 layers of plywood. Thanks!
@@hermenegildoluisgasparotto7881 I think you need to have a sub floor under a wood floor you need to have at least one layer
@@hermenegildoluisgasparotto7881 Even just 1.5" or 1" of foam then a layer of plywood/OSB would be better than nothing.
Why was Foamular NGX 400 chosen instead of Foamular NGX 1000?
NGX 400 on subfloor? Isn't that overkill? Seems like NGX 250 would be fine unless you have some really high point loads. In that case, why not 600? 800? Advantech is extremely stiff, too, especially two layers. Just saying.
This is a really helpful video. Thank you for making this. Question though. If I wanted to connect my radiant heater system to this and run pec through this. How would you suggest doing that? I was thinking of either running 5/8 plywood rips to channel around the pex pipe (as opposed to buying that crazy priced quik trak stuff) Then cement board, decoupler, then tile. That brings the total height to 4.75 inches above concrete. Is that overkill?
If you were to do a concrete garage floor would you recommend a dimple mat underneath the foamular board first? And if I was to do rolled rubber gym flooring would that replace one of the advantech sub flooring layers ?
Couldn't moisture migrate up through the slab and get trapped under the foam insulation unable to dry?
i was thinking condensation build up and just sitting there too?
Applying a vapor barrier on top of the slab and under the flooring underlayment prevents moisture (and the alkaline salts that moisture can pull from the concrete) from diffusing through the concrete slab. It slows or prevents water in the concrete from damaging the floor. Moisture can break down the water-based adhesive used to secure costly floor coverings and discolor or deform the flooring products. To avoid moisture imbalance and flooring failure, choose a concrete floor vapor barrier with lower permeance than the flooring cover above the slab.
Excellent video and information. I have a similar situation in my "this old house" basement. I appreciate the product inforomation to help guide me on my project. Thanks again.
That Titebond adhesive is not good for foam. It’s solvent based and will eat that foam. You need something like PL Premium!
Other than that, a great install!
Can this be done on a basement floor? I have a sump pump, but I want to make sure no mold grows under the lvp I’m planning to lay down in my basement.
How long are the screws for the boards?
@@SandyEdgley I forgot to click on the link and read the article
this is well thought out, but I have to wonder if that Titebond is rated for the foam or if it will eat through it like most non foam board rated construction adhesive?
No issues - check tech sheet
Is the concrete slab all perfect and level? Partitions screwed into the subfloor penetrate below subfloor into concrete or nah?
@@fooflateka level enough
@@ConcordCarpenter what about the second part
@@fooflateka We only screwed into the double layer of plywood
What is the detail for the outside framed walls? I saw that you had double bottom plates 1:58 but those would not be accessible for drywall installation once you stack all this material (insulation + 2x subfloor) on top
@@crabkilla in that case I guess you’ll just have to make sure you fasten into the studs
@@ConcordCarpenter I suppose you would need to do 3x bottom plates or frame block it.
Being a garage, isn’t the concrete floor sloped for drainage? How did this method correct it?
(Or is this a Washington St only code)
this one was not sloped, had it been I'l probably do an SLP
"promo sm" 😬
How could you integrate a radiant floor system into this?
@@cna5018 if electric you could glue down a Electric decoupling mat. If hydronic then you install plywood designed for the hydronic tube
@@ConcordCarpenter thanks. Would you sandwich that between the plywood or just go on top of both and then put my walls up?
Sorry. I would use hydronic and tie into my current boiler system.
@@cna5018 either
how much total height does this add?
less 1-3/4"
Is this more cost effective?
Than what? Not insulating.
What was the cost per square foot?
For what they used probably $5.25 sq’
Great question- I’d have to do the math- our labor rate prob skews that a bit too
@@ConcordCarpenter yes. I should have said, DIY homeowner price per square ft. Thanks
@@compton3611I disagree. When asking the installer what his “cost” was it goes without saying you mean materials only. When asking what he “charges” it would mean how much does the customer pay
Vapor barrier beneath the slab?
You mentioned no insulation but I am more concerned with vapor barrier.
Need to stop coming up through slab and go where
The foam is your barrier
@@ConcordCarpenter
Is there a vapor barrier beneath the existing slab?
I am not understanding how this stops or prevents vapor drive through the slab.
@@thelunatick1993 probably not under the slab - unknown. it prevents moisture from getting in the building space
Can you run radiant through the foam?
I had the same question. You could cnc groves for the pex right into the foam i would think
No but you could’ve installed a radiant ready board under the top layer of plywood.
2 layers of advantec!! What did this guy win the powerball? Why didn’t the home owner just use one giant garage size piece of polished marble ?it would have been cheaper!! 🤣😂 ✌💖🗣Mackeater!
Haha
What was the purpose of the glue? I’ve read about the floating floor and plan to do it but have never seen the glue detail under the plywood.
more secure - no squeaks
Nice, should have offset joints 2ft. This us a good system, some install this over compacted stone, no concrete