'Commercial' radiant questions

ScottSecor

We were just invited to bid on an unusual project (for us anyway). Commercial Architect has designed a home for his son and asked us to bid on the radiant heat and boiler install. Home will be approximately 7500 square feet of living space Including finished basement). East facing wall will will view the NYC skyline from approximately twenty-five miles away. Basement and first floor will have nine foot ceilings, second floor will have twenty foot ceilings. Entire house has just been framed with steel I beams and girders. Steel decking is on site and going to be installed within a week. Basement walls will be poured poured concrete.

I have not visited the jobsite yet. I gather it is on top of a pretty substantial hill if they can see NYC from there. My guess is about 500 feet above sea level.

Homeowner wants commercial look, so they will have radiant heated polished cement floors on all three levels. Some areas of the radiant floors will be covered with area rugs.
Ceilings will be exposed (painted) steel corrugated decking (that supports cement slab/roof above). First and second floor walls will be regular 2x6 steel studs with sheetrock interiors. Exterior siding will be some sort of steel. Not sure of the roofing materials (yet).

With regard to the first and second floors, they want us to install the radiant tubing immediately after the steel deck is installed. Once our tubing is installed and pressure tested, they will pour (pump) the concrete on top of our tubing. I recommended chairs for the wire mesh and we'll tie to that. Once the concrete is cured they will have the walls framed and roof installed.

With regard to the basement slab, I suggested 2" rigid foam first, with chairs for the wire mesh that we can tie our tubing to.

Here are the questions I have (for now).
1. How can they insulate under the concrete slabs for the first and second floors if they want to see the bottom of the steel deck from the room below? For that matter, they will also see the steel beams and conduit I suppose for electric lights. I am concerned that the radiant heat will just as easily radiate downward as it does upward. This is especially concerning of the second floor.
2. What is the preferred method these days for the basement slab. Vapor barrier under or above 2" rigid foam? Pour on top of foam/vapor barrier or cover with a layer of crushed stone first? Any suggestions are welcome.
3. The rooms with the twenty foot ceilings also happen to have enormous window walls. I mentioned that these rooms will likely need ancillary heat. They already planned on installing multiple commercial rooftop units and two residential warm air furnaces in the basement for additional heating, and cooling. The HVAC and straight up plumbing will be done by others.

Please share your thoughts.
Thanks,
Scott

hot_rod

I assume they are pouring on a span deck type steel product? You would need insulation on top somehow, 2" ideally. So his floor elevations would need to consider that.

I did a custom home much like that, about 1/3 the size. The entire home was poured on span deck, but not exposed from below, so they spray foamed the underside. All the manifolds were below, se we had to make sleeves to get the pex down through the steel deck, in oval shaped holes.

Edge insulation detail is also a challenge on steel framed, steel deck floors. You want 2- 4" insulation around the slab pour, but that ends up under the framed exterior wall somehow, unless a siding detail hides it?.

They could spray foam below and spray paint flat black If they can't or won't give you the 2" above.

Ideally the architect would detail all this to get fair bids? And your liability is covered.

GGross

Insulating under that radiant slab is key, whether they spray foam under the decking or insulate above, that thermal break is going to keep your heat headed to the correct area. If they are concerned about losing the steel decking look, they could consider installing "fake" decking under it, something that looks the same as the real deal but is not providing any structural support, ideally they just give you a couple inches above the decking. I would guess that money is not a big roadblock here.


Be prepared for a wild ride, we are blessed to have many homes like this in my area and these jobs tend to become a cluster real quick, but are very satisfying projects to be involved with

ScottSecor

As part of my proposal, I suggested fastening 2" rigid foam to the underside of the basement ceiling and the first floor ceiling, then covering the bottom of the foam with another "false" layer of steel decking (light gauge?) from below. I am aware that that the better rigid foam can certainly take some weight without compressing too much, but I would think the roughly 1.25" void under the foam if installed from above before the pour is a recipe for disaster?

With regard to the slab for the basement, how do you guys feel about the vapor barrier location (above or below the slab)?

I appreciate the feedback and will be adding these items to my proposal to cover myself and for transparency. I prefer to prevent surprises!

mattmia2

hot_rod said:

I assume they are pouring on a span deck type steel product? You would need insulation on top somehow, 2" ideally. So his floor elevations would need to consider that.

I wonder if the solution is to use the radiant as a base heat level that goes up and down to conditioned spaces and keeps the slab warm but have the warm air heating pick up enough of the load that it ends up regulating the temp in the areas, the slab becomes both a radiant floor and ceiling.

I hope everyone is well aware of this but the basement slab with the vapor barrier and foam will act very differently than an ordinary pour, it won't have the soil to absorb moisture from the concrete(the crushed stone could help with that if you go that route). It needs to be a concrete contractor with experience with this.

GGross

Generally from the bottom up, Vapor Barrier->Insulation->Tubing

With the steel decking, I see why you would be concerned, and yes that would certainly cause some structural issues! The other option I suppose you could consider, a light poor to fill those pockets, then insulate, then slab floor. I am not sure if that works at this point it is purely spitballing.

ScottSecor

@mattmia2 I get what your saying and mentioned that with the warm air system for design conditions. As of this moment, I think the radiant will take care of the heat until it drops to approximately twenty five degrees. Design for this area is about 12 or 14 degrees.

We always use or demand the masons use a decent amount of tamped crushed stone on slab on grade pours. My own house we used about eight inches total, tamped between loads. It's been five or six years so far and no issues.

I will propose these ideas to the architect. I have worked with many of them over the years and have come to realize that many of them do not listen to a word we contractors say. In this case the architect is all ears, he's a pleasure to work with.

Alan (California Radiant) Forbes

Ideally the architect would detail all this to get fair bids? And your liability is covered.

I always say, "This is what I see on other jobs." as I don't want to specify anything not directly specific to my trade. Structural requirements, slab thicknesses, slab composition...........even insulation. They should all be left to the engineers and architects with us being suggesters.

mattmia2

As I think about this more, I wonder if you can be very intentional in how it is designed about the upper slabs heat both spaces and are sized accordingly and the lower slab makes up the difference. It would have to be very careful and intentional and should be well documented that it works that way by the engineer but I think it could work.

PC7060

What’s about 2” of closed cell foam over the decking, then tubing and top coat. 

The compressive strength of 15-25PSI should be fine for the floors.  The point load regions will take some detailing. 

Really the architect and the PE should detail this out in the drawing package. 

hot_rod

On that metal rib steel decking I think the concrete needs to go into the channels that the ribs form for strength. I don't think you could foamboard the top?

ScottSecor

I agree with hot rod.  I always assumed the steel 'corrugated' decking had to be filled with concrete for strength.  The architect suggested 4" thick on the high points (roughly 5.25" on the low points).  I have never needed to do the psf calculations for steel decking.   

PC7060

hot_rod said:

On that metal rib steel decking I think the concrete needs to go into the channels that the ribs form for strength. I don't think you could foamboard the top?

Good point.  Didn’t consider that metal requires the concrete to complete the assembly. 

mattmia2

Yeah, it is some sort of a reinforced concrete assembly, it isn't just a shelf that holds the concrete. A 3 layer system with concrete, insulation, then masonry with the radiant tubing is an option.

mattmia2 said:

As I think about this more, I wonder if you can be very intentional in how it is designed about the upper slabs heat both spaces and are sized accordingly and the lower slab makes up the difference. It would have to be very careful and intentional and should be well documented that it works that way by the engineer but I think it could work.

This sounds like the building my office is in where someone in the late 70's said all the heat loss is at the outside, we only put radiation around the perimeter then we have thermostats that turn the cold air supply on and off. looked good on pa[per, clearly designed by someone who never actually built something.

Rich_49

Just perform your heat loss for all floors and use R value of zero but state that area below is heated . see how it shakes out first then start making suggestions and decisions .

As far as the basement , I really like using Barrier X5 , with a 6" gravel base below the R value is 10.3 . 240 or 256 sf rolls with adhesive and it's permeability to moisture because it has an integral vapor barrier is ZERO . https://www.thebarrier.com/pdf/brochure.pdf

Paul Pollets

You're likely to have the pex on 6" centers for some of the rooms. How would that be accomplished? I'd be using the radiant software to examine the "what ifs". Or use the Uponor design services. Viega may also be of assistance.

SgtMaj

Schluter Bekotec radiant barrier or something similar would be my go to product for your installation. Concrete floor first, radiant barrier then pour a concrete slurry over the top after installation of barrier and piping.

JohnNY

ScottSecor said:

I gather it is on top of a pretty substantial hill if they can see NYC from there.

Hi Scott,
We work in lots of homes in West Orange and Montclair that have Manhattan views. I'd guess the home is in one of those towns.

leonz

In my speaking and seeing this plumbing job as a layperson and hopefully not out of turn,
this seems like a perfect installation for a Mills top fed gravity hot water or Mills top fed one pipe steam heating system with flat panel radiators.

The yes votes for a top fed gravity hot water would be:

1. no circulators
2. no in floor piping
3. no possible leaks in the floor
4. slow even heat
5. a poured floor that will act as a heat sink
6. suspended ceilings for hot water feeder pipes to panel radiators and cool water return pipe runs to the cool water return drop pipe
7. 170-180 degree fahrenheit water flow for convection heating
8. a system that will not require bleeding of air
9. very small elevation to allow faster heating of all floors and basement with the drop pipe gravity flow
of hot water
10. simplicity in the design as the entire home would have one thermostat and much less wiring and no
circulators
11. greater first cost but lower cost of operation over the system life span as the plumbing is simpler
as all that would be required is treating the water with a corrosion inhibitor using non toxic
antifreeze.

The yes votes for a Mills top fed steam heat would be:

1. low pressure steam heat controlled with a TRV on each radiator
2. use of a double drop header to make dryer steam that would travel faster to panel radiators using
smaller header pipes
3. suspended ceilings for concealing steam header pipes
4. dryer steam to radiators to allow them to more slowly shed heat into the living spaces just as a top
fed gravity hot water system would deliver slow even heat.
5. no water flowing in the top fed steam piping
6. poured floors that would act as heat sinks
7. no piping in floor slabs that could possibly leak
8. greater first cost but lower cost of operation over the system life span as long as the system is taken
care of properly, making sure the low water cut offs work, making sure the air vents are working, the
water feeder is working and the pig tail is not plugged and the boiler is drained of sludge as needed



I have not included everything of course, and I probably missed some things with these lists other than detailing the additional parts needed for both systems; but I thought I would throw it out against the wall to see if it sticks.

ScottSecor

@leonz the owners of this project prefer a hidden heating system. In reality, the radiant system will be hidden inside the three slabs (one for each floor). I suspect the radiant system will take care of the heating needs by itself on all but the coldest winter days. On these days the rooftop heaters and/or the basement warm air furnace will be utilized alongside with the radiant system.

If I had the funds to build a house like this on top of a hill that had similar NYC views I suspect I would design it differently. I don't have that kind of money and likely never will. However, if I do start buying lottery tickets and hit the jackpot someday I think I too would go all radiant heat. I much prefer a hidden heating system if at all possible. I would not want any part of warm air heat if it were my house.

In some other rather expensive homes that we designed and installed the heating systems from scratch we installed radiant floors and ceilings in some areas to overcome the load. Oftentimes, this was in brownstones with massive walls of glass on back of the house on the first and second floors. These systems work quite well overall, as a matter of fact we just visited one recently for annual maintenance that we did over fifteen years ago.

Update: @leonz I just noticed you updated your post with much more details. Both systems you describe have merit. However, there are some fundamental items that might not work for this system. Some key items that you may not be aware of:
1. East facing wall will (faces NYC) be almost all glass on first and second floors. Not practical to install "wall mounted" heat emitters or piping on this wall.
2. Customer does not want any sort of traditional chimney. Nor do they want to add a large chase for high temperature breaching.
3. Customer wants high efficiency condensing boiler for heating and dhw (large indirect). Ideally the low temperature radiant heating system will be operating in condensing mode most of the time.
4. I did not ask the customer directly, but I suspect they want the ability to adjust the heat in certain areas of the home. Based on the preliminary drawings that show a thermostat in almost every room, I think this is the case. The customer is also the type that will likely want to control or view the temperature in each of the many zones on his phone at any given time.

mattmia2

ScottSecor said:

4. I did not ask the customer directly, but I suspect they want the ability to adjust the heat in certain areas of the home. Based on the preliminary drawings that show a thermostat in almost every room, I think this is the case. The customer is also the type that will likely want to control or view the temperature in each of the many zones on his phone at any given time.

I think you need to be very careful here to set the expectation that radiant will not change temp quickly if they decide to constantly fiddle with these thermostats.

leonz

I can see many, many problems with this, and I would
not want to be anywhere near it especially if the wind
starts howling since there is no shelter belt of trees.

GroundUp

I've done a number of these types of systems, with all 3 methods of insulation listed above. Obviously spraying foam or cellulose below is going to be the best from a performance perspective, but unless this is some sort of ribbed steel decking I've never seen before, it does not require concrete in the ribs to create a system. The standard steel decking with the 1-3/4" ribs is a support system in itself with proper beam support below, and concrete in the ribs or not, it will support the load of the concrete with proper engineering. The majority of these I've done have utilized 2 layers of 2" XPS laid in opposing directions, with a 3-5" pour on top. The ribs below the foam are void, and I personally do not care for that, but somebody well above my pay grade signed off on it and some of these buildings have been occupied for over a decade now. We did a 22 story condo building in Minneapolis a couple years ago with the same type of system, but with 3" of closed cell spray foam directly over the decking and then 1/2" pex on 6" centers stapled to the foam, with a grid of #5 rebar on chairs above that, and a 4" pour. If I were going to build such a building for myself, that's how I would do it.

Tim_D

In commercial construction these slabs are typically two part. A structural slab is poured on the Q deck with insulation above and then finished with a topping slab with the tubing embedded. Also, sounds like a possible candidate for radiant cooling?

hot_rod

The embossed pattern on the various metal decking was to help the concrete adhere to the panel, and become one composite, the metal and the concrete.
The deeper the channels, which do need to be filled and adhered to the concrete, that is why the dimples are in the grooves, the longer the spans allowed.