QC Radiant Heat plan with couple specific questions

Gordy

As to the concrete on main floor. I really don't know if sistering the 2x10's with 2x8's is sufficient to carry 3 1/2-4" of concrete. That's a lot of extra dead load compared to gypcrete. That's why gypcrete is used for such. It is a light weight concrete. Not suited for your finish wants however.

Even the 4" of concrete the floor will see movement with live loads. No guarantee it won't crack where you don't want it to.

4" of concrete is 49.5 lbs a square foot extra dead load. Verses a standard framed floor detail. I would consult with a structural engineer.

Usually thin pours with tubes embedded in concrete have a finish floor over top, so minor cracking is not a huge concern. Except where you can get a decent full 4" in a basement, garage etc.

Sukhoi29SU

@Gordy , I asked him to see if it would work at 3” pour. 36 psf dead load plus 2.5 for 3/4”OSB. I don’t expect to need 4 inches on a concrete floor I’m not driving a vehicle on. I figured 3” would be max but I was hoping to get away with 2 - 2.5”. As with any concrete I’ll expect cracks, but hoping to utilize a high psi concrete that will minimize it.

It’ll really be nice if I can put the insulation within the floor joists to conserve ceiling height upstairs.

Thanks for those diagrams! I’ll plan on that for the lower level.

Gordy

Forgot yes you would insulate those joist bays with r-19 bats to prevent back losses to the basement.

RetrosPex

Concrete/basement floor:

Several people have stated pretty well the problems of over-pouring to add radiant. Basically, what you are trying to do is avoid the work and mess of taking the concrete out, and you are going to end up with a compromise that is going to cost you forever. Energy is getting very expensive, in any form. I've done a lot of renovations over the last 35 years, and pouring over an existing slab is something I'd only do if there were no other options. If you go thin, it is going to crack. Well, all concrete cracks, for that matter.

I'd get some guys in there, bust it all out, use 2-3" of good quality rigid insulation board, put your tubing in, and enjoy it for a long long time. While you are at it, fix any drains, add any desired drains, another bathroom, etc.

As for supporting the building: this is a big job you are talking about. You might want to look at doing it in more than one stage, more than one pour. It is a bit less disruptive that way, but takes longer. Buy yourself some adjustable steel shoring posts, and sell them when you are done.

One last point...if you pour over the slab, and then need to do work later on, you have to take out 2 layers. By the way, I'm doing some of what you are talking about right now myself, so I understand your pain.

Good luck.

Sukhoi29SU

> @RetrosPex said:
> Concrete/basement floor:
>
> Several people have stated pretty well the problems of over-pouring to add radiant. Basically, what you are trying to do is avoid the work and mess of taking the concrete out, and you are going to end up with a compromise that is going to cost you forever. Energy is getting very expensive, in any form. I've done a lot of renovations over the last 35 years, and pouring over an existing slab is something I'd only do if there were no other options. If you go thin, it is going to crack. Well, all concrete cracks, for that matter.
>
> I'd get some guys in there, bust it all out, use 2-3" of good quality rigid insulation board, put your tubing in, and enjoy it for a long long time. While you are at it, fix any drains, add any desired drains, another bathroom, etc.
>
> As for supporting the building: this is a big job you are talking about. You might want to look at doing it in more than one stage, more than one pour. It is a bit less disruptive that way, but takes longer. Buy yourself some adjustable steel shoring posts, and sell them when you are done.
>
> One last point...if you pour over the slab, and then need to do work later on, you have to take out 2 layers. By the way, I'm doing some of what you are talking about right now myself, so I understand your pain.
>
> Good luck.

@RetrosPex
I think you might have misread my last post. I am, in fact, busting out the concrete in the lower level. They are starting this Friday and it was surprisingly affordable. The price included temporary structural supports and all of the concrete removal and was not even close to five figures. I’m doing the lower level the right way. It will be insulated properly and a new 4” slab will be poured over the pex.

My question regarding ‘minimum thickness of pour’ was in reference to the main floor - and the pour would be over subfloor,
not an existing slab. I will be beefing up the floor joists to do so.

Thanks

RetrosPex

Sorry about that, I did misread it. Sound like you have it under control. I'll have to re-read it. Did you consider underfloor transmission plates?

Sukhoi29SU

@RetrosPex

I was going back and fort between staple up between the existing floor joists for the main floor, or gyp-Crete with a floating floor on top. After a bit more research, though, and since everything is exposed and now is the time to do so- I decided to beef up floor joists and pour concrete for the main floor.

Are the underfloor transmission plates you are referencing the plates that go underneath staple up insulation within the floor joists?

hot_rod

I've poured concrete mix down to 1-1/2". My home in Utah had concrete thin pour on the main level.

It needs to be a pea gravel mix and you need to "soup up" the mix a bit. Double the fiber in the mix 3 lbs/ yard, add SRAs to reduce shrinkage. Some plants have access to lightweight aggregates.

Typical redi mix is 150lbs / cubic foot, light weight is around 115 lbs/ cubic foot.

Use 3/8" tube so you get more aggregate coverage over the tube. ideally 1-1/8" over any tube.

Don't water down the mix! Plastic over the plywood, you do not want it to adhere like you would with gyp-crete type mix.

Plan on covering it as it will crack and not be a viable finished surface. Smaller aggregate reduces the strength a bit. I glued wood parquet tiles over mine, hey it was 30 years ago

A small grout pump will move a pea gravel mix, no need to wheel or get a large boom truck.

Movement in the framing is the biggest concern, sounds like you addressed that. Usually a deeper joist helps eliminate flex, not doubling joists so much. Unless you sandwich steel between the joists and bolt thru them. That will really stiffen a spring floor.

Sukhoi29SU

@hot_rod
Thanks for response. You’re talking a bit over my head on some of the concrete stuff. I won’t be pouring the concrete myself but hope to find someone that knows what the hell they are doing. If I was to show them your notes I imagine they’d have a better idea.

If I plan on a 2.5” pour. Are you thinking this would not be able to be finished , stained / polished and used for final floor?

The guy who is helping with the plans changed his mind on sistering the 2x8’s and advised to sister the joists with Versa lam 7.25 x 1.75. Not familiar with Versa lam but he thinks it will do the trick. I hope it will. 2.5 in of concrete will be 30lb dead load by itself, plus 3/4 osb.

Gordy

The problem is @hot_rod the concrete surface will be the finished product with stained, and or polished finish. Not very pretty when it’s cracked. Sistering 2x8’s to 2x10’s adds dead load. It’s also a WAG how much you would gain in stiffening the span.
As your floor is with 2x10’s, 16” on center, 13’ span it’s an L/458.

For tile the minimum is L/360

For stone the minimum is L/720

The higher the number the less deflection, and less opportunity for cracking.

The deflecto calculator will not plug in for the type of joist sistering so it would be a WAG.

Typically you would reduce joist centers, joist depth, joist span ,or a combination of such to gain on the deflection rating.

Gordy

In using the calculator I did some assumption calculations based on the inputs allowed.

I went with a joist depth of 8” since the difference between a 2x10, and a 2x8 is 2”.

Your joist spacing would drop to 14.5 but 14 is the only input so I used it.

Same span 13’

Gets you an L/723 just makes allowable limits for stone.

Sukhoi29SU

@Gordy these were the words from the guy doing the building docs:

“I changed my mind about attaching (2) - 2x8.
Instead, screw a 7.25” - 1.75” versa lam. It will hold 70 pounds per lineal foot or 53 pounds per square foot at 16” on center. You need to hold 40 pounds live load, 10 pounds dead load, and 30 pounds of concrete for a total of 80 pounds. Your existing 2x8s all ready are good for 40 pounds live load and 10 pounds dead load for a total of 50 pounds. “

I think he meant ‘existing 2x10s’- I don’t have any 2x8s now.

Hope this will work. I would hate for that concrete to crack up due to deflection.

Gordy

I was going to suggest LVL but they are very pricey.

Also is there wiring, and other obstacles to navigate trying to sister the joists?

Gordy

My point on favoring on the safe side is any deflection will crack the concrete over time. Well placed saw cuts will control them. If you opt for a smaller aggregate based mix design, and a thinner pour it becomes even more prudent.

Gordy

I did a sistering job for an old 1900’s home which was converted to a men’s club.

The joists were rough sawn 3x12’s. Above a was kitchen more commercial as time went on to the point the joists were sagging from all the equipment in the now commercial kitchen.

We jacked everything back up to as level as possible with out cracking the mud bed kitchen tile.

Sistered every joist with 1 3/4” thick x 12” tall LVLs. I don’t have to say it sucked trying to navigate 14’ long LVLs along the existing joists in a confined space......

Sukhoi29SU

> @Gordy said:
> I was going to suggest LVL but they are very pricey.
>
> Also is there wiring, and other obstacles to navigate trying to sister the joists?

I’m redoing all the electric but imagine there will have to be some wiring to navigate around.

There’s a company called speedfloorusa.com I was researching. Ideally I’d like to avoid pulling up subfloors and replacing all my joists with something like this. My idea to do concrete on main floor was if it would be relatively simple to beef up existing joists.

Anyone used Versa lam in combination with existing floor joists?

Gordy

Yes see last post. Price them, and get back to me. Don’t be in the middle of a sip off your beer......

Gordy

1 3/4”x7 1/4” around 5 bucks a foot.

Sukhoi29SU

> @Gordy said:
> Yes see last post. Price them, and get back to me. Don’t be in the middle of a sip off your beer......

Sorry, I didn’t initially realize LVL is the same thing that my planner is recommending - ‘versa lam’.

$5/ft might be a little pricy but I’m saving money on not having to pour gypcrete and then put a fancy engineered hardwood over that. I’ll have to measure how many feet i’d be looking at getting.

I’d be securing this to my existing 2x10s I imagine?

I just need to hire you for a couple months to come out to Illinois, Gordy! This project would be rolling in no time.

Gordy

I’d glue, and nail to the 2x10. Screwing would be over kill. Not sure if a paslode framing nail gun would fit in between joists once lvl is in. You want to make sure you are not shooting at an angle. With 3 1/4” nails. You would probably have to nail from joist bay with out the lvl going through the 2x10 into the lvl using a nail gun. Then work progressively each joist.

If you hold the lvl to the top of the joist it will beef up your sub deck spans from joist to joist then cut lvl blocks at the sill plate to get the additional bearing.

hot_rod

Sukhoi29SU said:

@hot_rod

Thanks for response. You’re talking a bit over my head on some of the concrete stuff. I won’t be pouring the concrete myself but hope to find someone that knows what the hell they are doing. If I was to show them your notes I imagine they’d have a better idea.



If I plan on a 2.5” pour. Are you thinking this would not be able to be finished , stained / polished and used for final floor?



The guy who is helping with the plans changed his mind on sistering the 2x8’s and advised to sister the joists with Versa lam 7.25 x 1.75. Not familiar with Versa lam but he thinks it will do the trick. I hope it will. 2.5 in of concrete will be 30lb dead load by itself, plus 3/4 osb.

There is one thing that all concrete can be guaranteed to do... crack.

All sorts of things can cause it to crack from the mix, installation, movement, conditions during pour, how it cures, etc, etc.

The main goal is to control as many of the variable as possible and be prepared to accept some cracks. With radiant you get the added challenge of heating and expansion, so external restraint steps can be taken, allowing some expansion around the edges.

Saw cuts try and stop or direct cracking in addition to preventing, but with tube in a thin slab that too will be tricky, I've heard 1/3 of the slab thickness for the cut, that gets you close to the tube.

Really, really pay attention to fastening the tube tightly, a floater in a thin pour is bad news. Tube too close to the surface is a guaranteed crack.

There are different types of cracks some less noticeable. Road mapping is the pencil thin type probably least noticeable. Shrinkage cracks tend to open a bit, most offensive. Some cracks travel across the slab others start and stop. The very worse is a crack that shifts.

Overworking a colored slab can cause blistering, I have some of that in my office, too much power troweling to try and get it glass smooth. I put the color in the truck when they delivered so a crack is colored Not thinking that the aggregate doesn't get colored, so I still see some grey down in the cracks.

I doubt you will find anyone willing to put a no crack clause in a written contract.

Sukhoi29SU

@hot_rod @Gordy thanks again. Fully expecting to get some cracks- they’ll add character. Just hoping to minimize them by taking the right precautionary steps- and you guys have been a big help.

Rather than stapling the pex tubing right to the subfloor, I’ve read about a roll out wire material that lays out across the floor that the pex can be stapled to.


Are there any products I should be definitely considering for this? A local guy trying to gain my business is telling me pex tubing is more expensive than copper tubing and wants to sell me all the pex, but the guy selling me the boiler says whenever you pour concrete put pex in it even if you don’t plan on radiant because you might want radiant later. He says the pex tubing is so cheap you might as well.

Local guy says I need special oxygen barrier pex tubing but boiler manufacturer says he’s never used it and it’s never been needed on his indoor boilers- and it was more a player for utilizing outdoor boilers.

Local guy is trying to sell me redi-foam. Boiler guy says any 2” of blue board will be more than sufficient.

Seems that hydronics isn’t very popular quite yet in the States so the industry is marked up quite a bit and some people probably just pay the high dollar thinking that’s what it must cost. But it seems to me if I can get the pex tubing relatively cheap and throw down some blue board to make sure the concrete is insulated properly - there shouldn’t be a really huge cost with this radiant project? I know I’ll be spending some bucks on the concrete for this project for sure...

RetrosPex

Sukhol: I re-read most of this post. You are getting good advice from Gordy and others on the framing aspects of this project. This is definitely an involved project. If it isn't too late to comment on some aspects:

1. The concrete over the floor is dictating a lot of the project. You may like the idea of concrete finished floors, or what-ever. but that approach is going to limit all of your options, forever. There isn't any changing your mind later, once all the shoring, sistering, etc is done. By the way, I've done TONS of work like that myself, in Eastern Iowa. I just sistered some floor joists in my current home to beef up a short load bearing span under some 30' long Douglas fir exposed roof beams. If you are committed to the idea of sistering, consider getting some steel cut, and pre-drilled for bolts. If you intend to run PEX tubing through the finished joists, make sure they pre-drill holes for the PEX in advance. Read up on flitch beams to get an idea of the span carrying capability. A piece of steel sandwiched in the middle of other layers is very effective, and is much thinner than any LVL. For that matter, you might want to also look into steel joists. The problem with sistering is having room to do the work you need to do. Gordy refers to this when he talks about not nailing at an angle, etc. By the way you don't have to sister; you can put joists in the middle of the cavity and cut the spacing in half. But then you are really making it tough to do anything in there. By the way, I assume you have right angle drills, etc? Palm nailers (air driven) work great in tight spaces too. They are cheap.
2. When we refer to underfloor, we are talking about those aluminum plates you snap PEX tubing into, and fasten it to the underside of the plywood floor. I like the heavy extruded plates for their higher emission. About $8 each, 4' long. If you consider this option you don't have to do any sistering unless there is some other load demanding it. Put any kind of floor you like on top, that your floor system will support.

3. I'd personally consider using WarmBoard on the floor above. I think early posts talked about this. They will lay out the whole project, and generate a CAD file and ship you all the components you need. If I had not been in a hurry, it would be in my current addition project, 880 sf on first floor. The entire surface is covered with aluminum, and the PEX snaps into the grooves cut in the plywood sheets. It is extremely effective. You can put any floor you like on top. You would have to be able to accommodate the extra thickness, meaning headers and such might have to be re-framed higher. WarmBoard is in MN, I believe.

About insulation: a good heavy vapor barrier, some good rigid blue board, 25 psi, tape the seams with a high quality tape. Use the plastic staples to staple the pex to the board. Pour cement. (Basement) I'm getting ready to do 1300 sf of crawlspace floor, and I've decided to try using the AMVIC foam boards that have the nubs built right into it so you can snap the pex into the board, and pour right over it. A bit more expensive, but very fast, and effective. They come in smaller sheets, so easy to maneuver.

PEX: yes, you need oxygen barrier. Don't believe anyone who tells you different. I'm a fan of Wirsbo Pex A and expansion fittings. If Wirsbo is used, it would be HePex. You can also use Pex-AL-Pex. The aluminum inside is your oxygen barrier. Much harder to work with, but when you bend it, it stays bent. That is handy. Any tubing will be harder to work with if it is cold, so store it some place warm before you get ready to use it.

I'm sure I'm repeating things others have said, but I didn't want to miss anything.

Are you around Beloit by any chance?

hot_rod

The key to best slab performance and operating cost is the under slab insulation. Seems like 2" or more is becoming the norm. Some local codes may require more. I have seen pics of 4" on some jobs.

In a slab pour of 3-1/2" or more thickness you can, and should lift the tube into the pour. Wire mesh or rebar grid supported on "chairs" or strip chairs is one way to assure most of the tube is encased in concrete.

With a thin slab you are pretty much obligated to fastening the tube to subfloor or whatever you are pouring over, to assure that 1-1/8 or more of coverage. Concrete experts suggest 3 times the aggregate size over the tube. Common redimix uses a 3/4 minus size rock, you can request other size. Pea gravel mix around here is considered a 3/8 stone. Commonly used in concrete countertops also.

There are a number of products to make tube installations quick and simple.
Rehau has a velcro tube that sticks down to mats which self stick to the subfloor or concrete.
There are foam and plastic panel products of various thickness to allow you to snap tube between foam posts, quick, simple, perfectly straight layouts. It comes at a cost of course.

One concern with those foam and plastic snap in products is #1 the tube is at the bottom of the pour, and #2 you kinda insulate the tube away from the concrete where the all the posts and tube contact. Ideally the tube should be surrounded by nothing but concrete for best performance.
Concrete its your friend for moving heat energy, foam or plastic posts, not as much

For a thin pour, typical blueboard, or whatever color you prefer, and use foam staples to attach the tube to the foam, inexpensive and effective. 6X6 mesh could be put over the tube for some re-enforcement, but I think the fiber mixes do a better job and is much easier to negotiate.
I've also seen chicken wire used to fasten tube down A redneck method of sorts.

Sukhoi29SU

> @RetrosPex said:
>
> Are you around Beloit by any chance?

I am minutes from Beloit. Are you?

RetrosPex

No. Eastern Iowa. But I go through Beloit about every 3 weeks.

Hot Rod is right about foam. Another common practice is to buy little plastic chairs that hold your tubing off the foam. I poured numerous slabs in Dubuque, and we often used steel wire panels held up off the foam with chairs, and then zip tied the PEX to the wire. Have also seen guys use cheap scrap 1/2" to 1" PVC tubing cut into short lengths, and zip tied to the tubing.

For my crawlspace, I plan to put down a layer of 1.5" 25 psi foam, and then go over top it with either another layer, or the Amvic panels I mentioned. Might do the scrap tubing idea. In all cases, I used fiber in the mix. I've got slabs poured 25 years ago with fiber that are still nearly perfect.

Sukhoi29SU

What a great forum here with tons of knowledge- I appreciate everyone’s time commenting and helping out. Lot of time and $ going into this project and I want to make sure it’s done correctly so I don’t have a lost cause buried in concrete.

RetrosPex

It is a great forum. There are some forums where people treat you like a fool because you don't know something. This forum is very helpful. A lot is at stake, like you said.

Sukhoi29SU

Entire slab has been removed and I have temporary support up with beams. As you can tell this has become quite the project... I’ve dug down along the perimeter wall as you can see in pic. As far as perimeter insulation, do I need to go all the way down to the horizontal portion of the footing to set the insulation on? Or will a couple feet down suffice? I am hesitant to dig too far to mess with undisturbed earth down there...

Sukhoi29SU

I would think you’d just need to go down past where your horizontal insulation is ...

Voyager

Sukhoi29SU said:

I would think you’d just need to go down past where your horizontal insulation is ...

That should suffice. I would try not to disturb the soil under the footing or within a 45 degree angle extending downward from the inner and outer edge of the bottom of the footing.

Sukhoi29SU

Thanks, I dug down about three feet but never hit a horizontal ledge as depicted in the attached photo. With a beveled edge on the insulation, I’ll need to ensure that the insulation is sitting on something solid beneath it (compacted soil, perhaps) so the concrete doesn’t push the insulation down too far when it is poured. Perhaps I can dig down a couple feet, put a layer of brick on the inside of foundation wall, and then set the insulation down on top of that to line the perimeter.

Gordy

pl 300 foam glue at desired location.

RetrosPex

Sukhoi: Is that tall cement wall the left side underground? The other side being a walkout? If so, I'd be focused on applying rigid foam to that wall, and putting rigid insulation on the dirt floor. I don't see any advantage to putting foam down to the footings. In my case, my house is a crawlspace, so I have 4' of wall that is sitting on the footings, with the dirt at the top of the footing. In my case, I will put the insulation on that 4' part. In your case, you would insulate about it, and cap with your heated slab. Personally, I'd run perimeter drain around that inside, to a sump jar, and also do radon mitigation at the same time.

Seeing your framing, I'd put underfloor plates in there, with 1/2" PEX rather than pour on top of your floor upstairs if you are still thinking along those lines. Forget all that sistering.
FWIW.

Sukhoi29SU

Yes sir, it’s a walkout lower level. The left side of those pics is underground with the footing near the dirt on the ground,, then the foundation wall steps down towards the north (right) where the walkout is.

I was sort of sold on the concrete floors throughout the entire project for a couple reasons : thermal mass - more effective / efficient radiant heat, , ease of pex tubing install right on the subfloor of main level,, sound proofing, ‘solid’ floor feel vs squeaky subfloors , and four kids that can destroy virtually any floor with the exception of concrete. My wife likes the idea for ease of cleaning, as well as not having to deal with multiple different types of flooring - tile in the kitchen, hardwood in living room, etc. And finished concrete is a really nice look if it’s done correctly.

When the kids move out, I figured we could always install a floating engineered hardwood over the concrete if we wanted to.

RetrosPex

Sukhoi: your thoughts/comments are all valid, of course. And in the end, it is your house to live in and enjoy. Or not. Concrete floors are certainly interesting. From the limited experience I've had with them, they need to be periodically sealed. Although not the same thing, I've seen many many terrazzo floors, and they require more maintenance than a person might think at first blush.

My advice in a case like this is to sit down and make up a budget for what this is really going to cost you. All the sistering, the cement, hydronics, etc. You might be surprised. You may not care, and may choose to just plow ahead.

I grew up in a family of 6 kids, a foreign student, and big dogs. We never managed to damage any of our floors. Want a tough floor? Maple. They make gym floors from it, and bowling alleys.

I'd also look at radiant ceilings, as an option to floor heat.

You have a very cool project. Proceed with your eyes, ears, and mind wide open.