Radiant Ceiling between joists?

aschwa

Hi all-

I'm interested in doing a hydronic radiant retrofit on my ground floor. I don't want to lose any ceiling height, and I have a slab foundation.

Any way to do this? Baseboard radiators (anything visible whatsoever) is not an option.

For instance, is it possible to install hydronic radiant ceilings by installing the tubing between the joists and therefore not have to lower the ceilings?

Thanks,

Andrew

Rich_49

Did this type of install 4 years go in an 1870's home . Original ceilings and woodwork had to remain . Carefully cut / ground all plaster oozing through the lath , installed Uponor joist Trak plates 8" on center over aluminum flashing , secured using peanut screws , 3" spray foam directly over the installation . 10' ceilings and the place stays nice and warm .

Time consuming but worth it to keep all the original stuff looking good

ChrisJ

Rich said:

Did this type of install 4 years go in an 1870's home . Original ceilings and woodwork had to remain . Carefully cut / ground all plaster oozing through the lath , installed Uponor joist Trak plates 8" on center over aluminum flashing , secured using peanut screws , 3" spray foam directly over the installation . 10' ceilings and the place stays nice and warm .

Time consuming but worth it to keep all the original stuff looking good

Rich,
I'm not following.
You cut and ground the keyways off of the plaster?

Zman

If you could afford just 3/4", this one would save a whole lot of labor.

Rich_49

Leveled them out or made them uniform would have been more accurate Chris . Probably could have gone farther due to the coffered ceilings below .

ChrisJ

Rich said:

Leveled them out or made them uniform would have been more accurate Chris . Probably could have gone farther due to the coffered ceilings below .

Scary work and very risky. One wrong move and................

Rich_49

We did make it through . Deep Energy retrofit on a 142 year old house is an experience to say the least . Radiant ceilings , walls , some QuikTrak , Joist Trak below sub floor , embedded , overpour . Like a showplace for many different types of radiant . Happy to say all if it works very well today .

SWEI

We just love projects like this. Really rewarding when you make it work and keep the original finishes.

aschwa

I'm not completely following. I don't have coffered ceilings. In that case, your solution wouldn't work, right Rich?

Gordy

Rich is referring to old plaster with wooden lath. The brown coat is burned in so the plaster ozes through the gaps in the wood lath. This keyed bond holds the plaster to the lath. Now what is your ceiling detail?

aschwa

Haven't opened up the ceilings yet, but here's what we expect:
joists are 2x12 for most rooms, 16" center-to-center

8 foot ceilings, drywall covering the joists.

Does that answer your question?

Rich_49

Drywall makes it an easy retrofit . Nice and flat between the joists or at least it should be . Will you be removing the drywall from below ? If so you could look into Sunboard's Sunfoam panels , they fasten right to the bottom of the joists and tubing goes right in , Drywall contractor can see the tubes so there is no reason for him to nail into them . R13 in the cavities plus the board is all you'll need . You'll really need to perform a heat loss to determine water temp , BTU / sf requirement and all that no matter what you do .

http://www.sunboardpanel.com/Products.html

aschwa

Those ceilings will be open from both above and below. I'll be installing radiant floors on the second floor throughout the house, so the joists will be accessible from above as well.

Rich, would your Sunboard solution involve me losing a bit of ceiling height?

Rich_49

Yes, any radiant ceiling would . Unless you utilize a detail similar to what I described above . XLath , Sunboard , Joist Trak with strips , all will lower finish ceiling height . But ceilings don't require cutting doors and much other necessary stuff . 1 1/2" on the ceiling hurts alot less than an 1 1/2 on the floor

aschwa

I read in a couple of places that radiant ceilings over a slab floor are a bad idea. (For instance, see here)

Why is that? Do you agree?

We're in the SF Bay area.

SWEI

That summary is good, so yes -- I would agree.

More importantly for a retrofit, radiant floor heat in an uninsulated slab is kind of a deal-killer. More so in a really cold climate, but still not a good thing even in the mild climate of the SFBA.

Ceilings...

aschwa

If I'd need to raise the floors if I insulate my slab anyway, then I might as well do radiant floors instead of radiant ceilings. Sound right?

SWEI

Why do you need to insulate the slab? Are you planning on carpet, hardwood, or something else?

aschwa

California Energy Code says that heated slabs must be insulated.

Hardwood floors.

SWEI

aschwa said:

If I'd need to raise the floors if I insulate my slab anyway, then I might as well do radiant floors instead of radiant ceilings. Sound right?

Your logic escapes me. We suggested heating the ceilings. You said you were insulating the slab anyway.

aschwa

Sorry. I misunderstood your question. Let me clarify.

My understanding from you is that heating the ceilings will require raising the floors in order to insulate the slab.

The point I was making is: If I'm raising the floors anyway, then I might as well raise them some more and do radiant floors instead of radiant ceilings.

Does that make more sense?

aschwa

In other words, my options are radiant ceilings with raised floors or radiant floors with raised floors.

Either way, my floors would have to be raised.

SWEI

If you heat the ceilings and install carpet with even a small R-value, I would not bother insulating the floors in that climate. If you're doing laminate floors, most of those have a bit of rubber/foam underneath that provides at least some amount of thermal isolation.

Are you on NG or LPG there? Possible modifications to the above advice depending on fuel costs.

aschwa

How about hardwood?

We're on nat gas.

Rich_49

Aschwa ,

California is not the only one that requires heated slabs to be insulated . Long before there was a California Mother Nature required this to work also . It's the alw , the laws of physics . I do not completely agree with the paper you referenced . At this point in time , most states are adopting and beginning to enforce IECC 2012 -2015 , whichever they are looking at and how far behind the times they are . These codes require slab insulation PERIOD . Heated or not . Believe it or not a cold slab will suck heat away from the interior space even in a forced air house , HOT goes to COLD . You could add perimeter insulation outside and down 2 feet and call it a day .

What would your assembly detail for hardwood on top of a slab look like ?

SWEI

Thought this was a retrofit?

aschwa

It is. Whole house remodel.

Gordy

As @SWEI said do the radiant ceiling use what ever floor coverings call it a day. As mentioned before raising the floor detail involves more work than lowering the ceiling detail. The uninsulated slab is not as SWEI stated in your climate going to be a deal breaker.

How ever for those that happen to come across this thread later. In a more severe winter climate I would recommend insulating the slab at the very least the perimeter. Radiant floor, or ceiling. As Rich said it will suck the heat energy out of an envelope.

Radiant heat will work even in an uninsulated slab the cost is considerable energy consumption which is why we insulate for the environment, and the wallet so ROI is narrowed to an exceptable time table.

As an owner of radiant ceilings, and floors I can testify that you won't be sorry. I always enjoyed Tom Tesmar when he frequented the RPA web site.

aschwa

Here's what I'm thinking based on this forum's input:
- Radiant ceilings on the first floor over an uninsulated slab. I'll use xLath and the 8' ceilings will drop 3/4".
- Radiant floors on the second floor. Probably go with gypcrete.

Does this sound right?

hot_rod

Sounds good. I think several million Californians live on un-insulated concrete slabs, cover it as Kurt mentioned with some minimal r-value covering and move on.

I like gyp applications for a nice consistent floor surface temperature. I'd call them a medium mass system. They add great sound and fire barrier to the structure also, and is a nice leveling feature. Gyp was originally designed for hotel floors for those reasons.

Make sure to accommodate the stair riser calculation if you add that 1-1/2" to the upper floor.

Gyp does add some dead weight to the floors, are they solid now? If they bounce as you walk across them from undersized joists, the gyp will add even more load.

Seal each and every hole in the floor before you pour gyp or it will end up downstairs!

aschwa

There's actually existing concrete (not gypcrete) from a 1960s era hydronic floor system on the second floor that was deactivated ~15 years ago. The concrete will be demolished and the weight of the gypcrete will be less than the existing concrete, so I think I'm good there.

Tom_133

Aschwa,

Are your bedrooms on the gypcrete or are they downstairs? If they are upstairs they should be zoned so they can be at a lower room temp. I have run into a lot of people who after the concrete or Gypcrete was poured found the slow temperature swings did not allow them to be comfortable in bedrooms. If you have them zoned separately, or just the bedrooms on their own zone than you should be fine, just a word of caution. I'm sure you already thought of it.

aschwa

They are indeed upstairs on the gypcrete. I will make sure to zone them separately.

Your post seems to imply that if the bedrooms were on the first floor with the radiant ceilings, then you wouldn't be worried. Why is that?

hot_rod

I'm not a huge fan of radiant floors in bedrooms.

Once the bed and furnishings are loaded in there is often not much "available floor space" left to cover the load. Any furniture that goes down to the floor or has a skirting like some beds, limits radiant floor considerably.

Fast responding panel rads ar my favorite for bedrooms. They are often the least destructive heat emitter to add in a reno project. A TRV or setback type TRV is an ideal control.

aschwa

@hot rod : You prefer panel radiators over ceiling radiators for bedrooms?

Gordy

@aschwa since it has not been mentioned. Do understand that you need to insulate the ceiling radiant detail from the floor radiant detail above.

aschwa

Yes absolutely

hot_rod

aschwa said:

@hot rod : You prefer panel radiators over ceiling radiators for bedrooms?

I like panel rads because they are low mass, low water content. As such they warm up within minutes, and ramp down quickly. They also tuck in against the wall nicely maybe 3" total off the wall, not as imposing in the room.

A wide range of sizes, shapes, colors are available.

Now for a historic home, or if you like the looks of cast iron radiators, it's in the eye of the beholder.