I have a new construction house with radiant on the main floor done in a "plywood and plates" fashion. There is also radiant in the basement slab (ICF Basement) Currently with only the main floor loop on, the basement stays warmer than the main floor by 2-3 degrees. I assume insulating the first floor joists/basement ceiling is the answer. But what is the best way? I have seen radiant barrier foil used. I have seen the bubble style foil used. Both with air spaces. I am assuming that foil faced fiberglass Batts would work in a similar fashion and provide some further insulation and double as a sound deadener, is that correct?? What's the best way? PS I intend to finish the basement ceiling with exposed fastner metal roofing panels (eventually).

Presumably, if you have separate heating zones and thermostats for each of these living spaces and adequate thermal isolation between these living spaces, you should be able to have whatever temp you desire in each living space. Do you always want to heat this basement? Is there something else also generating heat in this basement?

I suspect the issue you have is the result of having a higher performance hydronic floor emitter in the basement and a lower performance hydronic floor emitter on the main floor and not having adequate thermal isolation between the two living spaces. What does your design call out for the flow rates and supply temps for each of these heating zones? It may well be that you simply need to provide more flow rate and temp to the hydronic floor emitter that serves the living space that is not providing the higher temp you desire.

If the basement emitter is truly not being used and only the main floor emitter is being used as you indicated, and the basement is still warmer than the main floor, you definitely need to improve the thermal isolation by increasing the insulation below the main floor emitter. In this case, much of the upward heat that this emitter should be providing to the main floor is actually going downward into the basement. I don’t recommend or think radiant barrier foil or bubble wrap will get the job done. You really need to add a significant amount of R-value below this emitter and I would be thinking polyiso rigid insulation or fiberglass batts if you have the space. How much R-value is currently above this emitter (i.e., above the PEX tube)? Typically, you would want to have at least 10 times this R-value below this emitter.

Posted By loghomebuilder on 09 Nov 2018 01:47 AM
I have a new construction house with radiant on the main floor done in a "plywood and plates" fashion. There is also radiant in the basement slab (ICF Basement) Currently with only the main floor loop on, the basement stays warmer than the main floor by 2-3 degrees. I assume insulating the first floor joists/basement ceiling is the answer. But what is the best way? I have seen radiant barrier foil used. I have seen the bubble style foil used. Both with air spaces. I am assuming that foil faced fiberglass Batts would work in a similar fashion and provide some further insulation and double as a sound deadener, is that correct?? What's the best way? PS I intend to finish the basement ceiling with exposed fastner metal roofing panels (eventually).

There is really no point to radiant barrier under a low temp plated system. Aluminized bubble-pack is about R2 unless given at least an inch of air space on BOTH sides material, and may not have sufficient fire ratings to be left exposed to the basement. What you want is fiber insulation snugged right up to the tubing and heat spreader plates.

The fire ratings of batt facers aren't good enough to leave them exposed to the basement- they are a fire-spread hazard. Going with unfaced fiberglass can have an ongoing airborne suspended glass fragments issue if left exposed. Rock wool R15s (or 3" thick fire & sound isolation rock wool) doesn't have that issue, and is probably going to be enough R.

If you've been really taken in by the radiant barrier concept (complete with pictures of space shuttle launches :-) ), take a 48" wide roll of aluminized fabric type radiant barrier and carefully cut it into three 16" wide rolls. There is enough width to side-staple it on the under side of fiberglass batts to keep them in place with 16" o.c. joists, and it will keep the tiny glass shards out of the basement air. Aluminized fabric type radiant barrier almost always has sufficient fire ratings to be left exposed in a basement. The low emissivity of the aluminum facing the basement air (or cavity above the eventual ceiling gypsum) buys you that bit of additional thermal performance too, not that you're likely to need it. R11 is usually sufficient zone isolation for plates staple-ups unless it's a thick pile rug on the floor above. Cheap contractor roll R11s or R13s with kraft facers are fine and easy to install, as long as there is a fire-rated material between the facer & basement.

"radiant on the main floor done in a "plywood and plates" fashion"

"snugged right up to the tubing and heat spreader plates."

I think he used strips of plywood on top of subfloor with plates and tubing between/On top.

Posted By ChrisJ on 09 Nov 2018 06:52 PM
"radiant on the main floor done in a "plywood and plates" fashion"

"snugged right up to the tubing and heat spreader plates."

I think he used strips of plywood on top of subfloor with plates and tubing between/On top.

With above-the-subfloor radiant, snug the fluffy stuff up to be in full contact with the subfloor.

yes my floor structure is joists- 3/4" osb - 3/4" plywood strips with pex and alum plates - 3/4" hardwoods. Main floor has a zone and basement slab is on a separate zone. I have not turned the basement on yet because we aren't living there yet. I will try to add a picture. I'm not sure I'm understanding you guys right... Sound like those radiant barriers are more gimmick than function - correct?? So an r 11 or r 13 batt insulation should be good so long as it's fire rated?? Just confirming I have it right. Would a foil faced batt perform better than none faced?? Would it be ok to have an air space between the insulation and the plywood subfloor above? My plan was to let gravity hold the insulation in place against the ceiling of the basement.

Radiant barriers do function and have applications, but this is not one of them. Yes, R11 or R13 batts will get the job done well. As Dana indicated, be sure to properly contain any fiberglass and meet the fire requirements. You still might need to set the flow rates and temps to have system perform well.

The performance difference between foil faced vs. unfaced, vs kraft faced batts is "in the noise." The density of the fiberglass and quality of the installation are much bigger factors. Leaving an air space between the insulation and subfloor is a thermal bypass path, reducing the effectiveness of the insulation. Snug it up to the subfloor, so that the air-retardency of the fiber can inhibit lateral air flows. (Some radiant installers cut pieces of 15" somewhat springy steel wires to hold up batts between 14.5" wide spaces between 16" o.c. joists.)

He didn’t answer the question, but if he plans on continuously heating the basement, he doesn’t need to do all that great an insulation job here. He only needs to get enough insulation and R-value under the PEX to generate adequate thermal isolation between the two living spaces as any heat loss from this ceiling into the basement isn’t a bad thing. If he doesn’t plan to heat the basement, we would use over-lapping rigid polyiso of various thicknesses to entirely fill and seal each bay cavity and we would not even consider using fiberglass batts so as to maximize the emitter performance and to minimize heat loss. But it never hurts to properly install whatever insulation you elect to use...

as well as all you have said -which i agree with
could it be the basement has a lot better insulated walls -no air leakage and drafts than main living area -so is upstairs a lot larger ?
simple to test actual floor temp of both areas -if similar. then you need to stop the leaks in living area or up the input to heat the bigger area.
certainly any poor insulation of basement ceiling will allow it to be stealing heat form living space--does the basement have a thermostat on that circuit?

Posted By scottishjohn on 17 Nov 2018 10:41 AM
as well as all you have said -which i agree with
could it be the basement has a lot better insulated walls -no air leakage and drafts than main living area -so is upstairs a lot larger ?
simple to test actual floor temp of both areas -if similar. then you need to stop the leaks in living area or up the input to heat the bigger area.
certainly any poor insulation of basement ceiling will allow it to be stealing heat form living space--does the basement have a thermostat on that circuit?

I'm sure the basement is better insulated and is a smaller area, upstairs I have 25 foot vaulted ceilings. There is a thermostat in the basement but it doesn't ever kick on as the temps get higher than it's set from the heat from above. Kinda related to my question... But I'm wondering if my understanding of radiant barriers is incorrect. There needs to be an air gap on both sides of the radiant barrier?? I thought that in a roof rafter installation say, a foil faced polyiso with an air gap between the polyiso and roof sheathing would really the benefits of the radiant barrier. Is that incorrect??

Posted By scottishjohn on 17 Nov 2018 10:41 AM
as well as all you have said -which i agree with
could it be the basement has a lot better insulated walls -no air leakage and drafts than main living area -so is upstairs a lot larger ?
simple to test actual floor temp of both areas -if similar. then you need to stop the leaks in living area or up the input to heat the bigger area.
certainly any poor insulation of basement ceiling will allow it to be stealing heat form living space--does the basement have a thermostat on that circuit?

I'm sure the basement is better insulated and is a smaller area, upstairs I have 25 foot vaulted ceilings. There is a thermostat in the basement but it doesn't ever kick on as the temps get higher than it's set from the heat from above. Kinda related to my question... But I'm wondering if my understanding of radiant barriers is incorrect. There needs to be an air gap on both sides of the radiant barrier?? I thought that in a roof rafter installation say, a foil faced polyiso with an air gap between the polyiso and roof sheathing would reap the benefits of the radiant barrier. Is that incorrect??

Yes, like Dana indicated, you would need at least an inch of air space of each side of the radiant barrier to obtain any significant performance benefit. However, your relatively low temp above-floor hydronic radiant emitter is actually mostly conductive and convective heating and the radiant barrier approach won't provide the R-value you need to achieve adequate thermal isolation of these two living spaces. How much R-value you should actually use depends on whether you plan to heat the basement full time or only occasionally.

Thank you very much for clarifying.

I do plan to heat the basement full time. I'll look into some options. Thanks!