First, thanks in advance for any advice you can give.
Second, I’m building my own house and am planning radiant heat on the main floor (ave already placed PEX in the slab in basement). I was planning laying PEX in 1.5″ gypcrete or something similar? on top of my already in place 3/4 t&g OSB subfloor and then finish with hardwood.
My question arose when I was starting to build the stairs from the basement to the main floor and asked the hardwood supplier what thickness of hardwood is common, etc.
I was surprised when he said that i would have to install another deck of plywood over the top of the gypcrete for something to nail the floor to, and also said that some woods do better than others with radiant heat (warping, etc)
Is this correct and what other options do i have? I have loked at warmboard but am leery of the price, Wirsbo seems to not have the thermal mass i’d like. Could i install 1.5″ nailing strips 16″ oc inside the gypcrete?
Does glue down engineered wood seem like a good alternative and how does it compare to real wood?
The stairs have come to a halt until I can figure this out. I’ve searched around for an answer but haven’t come up with a best practice. Surely, I’m not the first to have run into this. Thanks again!
Replies
IMO, yes, the supplier has that correct. You won't nail to gyp, and gluedown to gyp is unpleasant and not something I'd recommend (I've done it). Sleepers is a possibility...some like that, but I've no experience with it.
You mentioned mass...gypcrete won't provide suitable mass. It's a medium solution...none of the benefit of a true high-mass system (concrete floor and walls with capacity to both store and moderate heat) and none of the benefit of a low-mass solution (quick response).
The suitability of different woods (or bamboo) will depend a lot on the wall/roof assemblies. If the house has fluctuations in humidity, then a glued solution, or wood on concrete, is not the best solution be/c of expansion/contraction. If interior humidity is stable year-round, then you have more options.
If I couldn't have the high mass system I do, then I'd go with a low mass, quick response solution such as the Wirsbo and nails.
Thanks, I didn't know that characteristic about gypcrete. Is there something better out there that does provide the thermal mass?
As far as my location, I'm in Idaho where humidity is usually quite low. I am planning SIPs for exterior walls and extra insulation in attic trusses. I am seriously hoping that this house turns out to be very energy efficient given this climate. Hot dry summers, long cold winters, not much in between.
I'd not even try for the thermal mass. If you used ICF walls, then yes. Also, mass is nice if you have giant south-facing windows that wil benefit from solar gain. But lacking that, and with SIPs, I'd go for a high-response system instead.1.5 inches of any product won't be enough to qualify as a high mass system. By contrast, I have a 5" slab and an 8" slab with 3"-8" thick concrete walls/roof. Now THAT'S a high mass assembly, and it behaves as such. With no-mass walls and roof, all 1.5" of gyp or lightweight concrete in a floor will do is piss you off when the heat doesn't show up immediately (figure a few hours till you really feel it after the t-stat kicks on). At the same time, it won't retain the heat for very long after the heat's off...maybe 4 hours, versus a couple days or so for my setup.Look into a low mass (Warmboard/Wirsbo/under subfloor) setup that'll provide heat immediately when it turns on, and stop when it's not needed. And make sure the t-stat's in a place where it'll allow for even heating (not in the sun, for example).My issue with gyp is that the surface sucks for gluedown unless you add a membrane, which adds cost. It's not very abrasive resistant. And it's neither high-mass nor low-mass, without the benefits of either. On the other hand, on an upper floor, it does provide fire resistance and soundproofing, so, like most products, some advantages and some disadvantages.
Thanks Cloudhidden, I appreciate your candid advice.
Anyone have any thoughts on under floor systems? This was the way i originally planned to do it until I had a radiant guy tell me that he wouldn't even sell me the parts for a project with that setup as it just plain doesn't work (I have a vaulted great room with big windows app 30'x30'{faces west}, everything else in roof trusses @ 8', entire main floor about 2400 sf)
Anyone using Wirsbo Quiktrak?
How about warmboard? I already have a subfloor down, so the extra strength and $ for this seems monotous. If that truly seems the best way to do it then thats what it'll be.
Remember this is Idaho and winter starts in October and last until April, so i need this thing to work!
Currently I'm in Boise, but most of my carpentry has been in the colder parts of Wyoming where radiant heat is in almost every new mountain home. A week doesn't go by that I don't miss working in the mountains! It's also strange to me that even in $m custom homes it's almost unheard of to have radiant heat anywhere in Boise. Air ducts should only be used for air cond. :-)
A past employer was/is a warmboard supplier and it does work well, but not for the prices they are currently charging! We essentially threw out any remaining refference material and wrote off warmboard as a serious product. If you can get a good price be sure and request an installation manual since there are a lot of quirks. Oh yeah, you wouldn't be using it as decking so scratch what I said about the manual.
Gypcrete works very well if you aren't looking to be a thermostat fiddler. It's the method of choice for much of Colorado/Wyoming. Gypcrete shrinks a bunch so even if you have nailers every 16" you'll have to cover it with decking strength plywood since you'll essentially have a free span between the nailers.
Didn't you mention in the orginal post that you currently have hardwood floors installed? Would your framing handle the extra weight of gypcrete?
Since the space under your main floor is heated it's not critical if some of the heat on the main floor is lost as would happen with a groved pannel without a heat reflector (essentially warmboard without the reflector). This is something that can be acheived quite easily with ply strips for straight shots and a core-box bit in a router for curves. Personally, this is the route I'd choose since it's light, inexpensive, provides good nailing for a wood floor, and doesn't require anything exotic. It's been used a great deal with good results.
Whatever method you choose, don't skimp on the number of pex loops or your tube pattern.
Best of luck,
Don
Thanks Don, Actually I'm in eastern Idaho about 5 miles from the Wyoming border. Yes, beautiful location and we have a great view of the Tetons. We do not plan to ever sell this house and are planning it as such. i want this radiant stuff to work correctly!
I've seen on other boards about making your own warmboard w/o the reflective barrier. But does it really work well or am i better off in the long run going with the Wirsbo of even the Warmboard? What do you think of the staple up from underneath?
No, i do not already have flooring down, only the OSB deck (which is covered for the winter until my SIPs and roof are on hopefully early spring. I used TJIs for the floor joists and was very open with the supplier as to my inentions with the gypcrete. He thought that the extra weight would be fine given my design.
I've seen on other boards about making your own warmboard w/o the reflective barrier. But does it really work well or am i better off in the long run going with the Wirsbo of even the Warmboard?
Situations with an unheated crawlspace is where the reflective liners are most valuable since they keep more of the heat within the heated building envelope.
Using pex without a reflective liner won't work better, but in your case it would work well at a lower installed cost. That's money that could be used for additional insulation.
Without the reflective liner some heat that would go upstairs will be warming the area below, which doesn't have a detrimental effect as long as the BTUs going into the upper floors is sufficient.
The more insulation you can get the less the heating system has to work and the less important getting the "perfect" pex arangement is. The super-insulated houses we built in Wyoming had very even heat distributions inside and were thus very comfortable. They also only required relatively small heat sources for the radiant system.
You mentioned that the ceilings in the great room are vaulted. Hopefully you've devised a way to get as much insulation up there as possible. It's often easy to built a vaulted ceiling way too thin for a decent R value.
Also, spray in foam is fantastic in vaulted ceilings since it eliminates all air movement, eliminates the need for rafter venting and provides a superior R value. Highly recommended. Thicknesses allowing R50 (10") would be good and R60 (12") would be great.
What do you think of the staple up from underneath?
I've never heard of it being used on new construction, only retrofitting an existing floor. Probably not a good idea.
I used TJIs for the floor joists and was very open with the supplier as to my intentions with the gypcrete. He thought that the extra weight would be fine given my design.
Don't get me wrong, gypcrete works very well and also helps deaden sound transmission through the floor. If you are at all worried about your system working well then I'd say go with Gypcrete since it is so popular and is a known commodity. You'll love the comfort of the room and shouldn't have any regrets.
If you use nailers/sleepers in the gypcrete to attach ply for the flooring, after the gypcrete has fully dried and shrunk I would skim the area between the nailers with a floor leveler to fully support the plywood.
Cheers,
Don
Hardwoodinstaller.com is a good wood floor forum, and they sell a wide range of flooring. If you look at the specs for the flooring, it tells which ones are suitable for radiant heat.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt