Radiant over existing concrete in newer home
Last Post 20 Apr 2018 09:27 PM by DB10. 20 Replies.
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18 Apr 2018 05:29 PM
Hi all, Unfortunately I received some bad advice when I built approx. 9 years ago and didn't do anything other than a standard basement floor for an exposed ranch. Working on a large basement build-out now and coming to the hard realization that there is now great way to heat this in WI. My challenge is one of height based on the plan and exising doors, steps etc. (I know, not suprising) I can get away with 1.5 inches total including .25 or less for plank vinyl. The question...how much insulation is minimum to add any value in separation? Beyond this, any suggestions for making this happen? I thought about Prodex .25 insulation roll and then Gypsum but the cost is crazy at $3+ per sf. Open to any/all ideas as I am very much stuck! Thanks!
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18 Apr 2018 07:27 PM
The R-value claims for Prodex .25 are ludicrous (outrageous?) in your application. They're only close to valid if there is a substantial air gap both below and above the product. If it's in contact with both the slab and the layer above (zero gap depth both sides) it's worth about R1.25, not R17.

Roth panels are about as good as you're going to be able to do given your 1.5" total stackup limitations. They come in both 3/4" and 1" thicknesses, and are designed to embed the radiant tubing in channels in the foam. A 3/4" Roth panel with and 5/8" plywood sheathing as a sub-floor would be about the limit. Check the fastener depth requirements for the flooring, and be sure to mark the subfloor to not puncture the tubing.

http://www.roth-usa.com/products_radiant_panelsystem.cfm

With 3/8" tubing the 3/8" Roth panel has ;ess than R2 between the tubing and slab at the thinnest spot, so it will be fairly lossy at the slab edges close to grade in a walk-out basement. Hopefully there is exterior slab edge insulation? Further back from the outdoors at-grade edge the R-value and thermal mass of the soil helps out a bit. In an ideal world you'd want R10 or better between the slab & subsoil, but you don't.

There may be issues getting enough heat out of the floor to fully heat the space at sub-zero temps - have you run the heat load numbers? Radiant ceilings &/or a few low temp panel radiators (possibly as a second stage) can usually make up the difference.
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19 Apr 2018 02:37 PM
Thanks for the response! Not sure on insulation at foundation but guessing not. As I said, very little thought was put into basement. I am guessing that the floor temps are likely near their lowpoint at this point of year. Center is 63 degrees, edges below grade 60ish, edges exposed areas 57 degree. Perhaps this means something for those with more knowledge of calculations. Does this help explain my situation?
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19 Apr 2018 05:53 PM
Sorry, chat board rookie. Adding an important detail. the area to finish is almost 1700 sf. The roth panel system that was mentioned appears to be over $6 per foot, making this almost $11k just for the panels. I was thinking about making my own with a router or ??? There has to be some way to do this that isn't $11k just for the floor panels? Thanks again!
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19 Apr 2018 05:53 PM
Sorry, chat board rookie. Adding an important detail. the area to finish is almost 1700 sf. The roth panel system that was mentioned appears to be over $6 per foot, making this almost $11k just for the panels. I was thinking about making my own with a router or ??? There has to be some way to do this that isn't $11k just for the floor panels? Thanks again!
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19 Apr 2018 05:53 PM
Sorry, chat board rookie. Adding an important detail. the area to finish is almost 1700 sf. The roth panel system that was mentioned appears to be over $6 per foot, making this almost $11k just for the panels. I was thinking about making my own with a router or ??? There has to be some way to do this that isn't $11k just for the floor panels? Thanks again!
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19 Apr 2018 05:53 PM
I am always saddened to hear these stories. Some under slab insulation and couple hundred dollars of PEX embedded in the slab would have made this a very comfortable and low cost heating system. Anyhow, I think you should abandon the thought of using HR for this basement floor now. Perhaps just insulate above the slab to maximum extent that you can and then use another approach for heating the basement.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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19 Apr 2018 05:54 PM
Sorry, chat board rookie. Adding an important detail. the area to finish is almost 1700 sf. The roth panel system that was mentioned appears to be over $6 per foot, making this almost $11k just for the panels. I was thinking about making my own with a router or ??? There has to be some way to do this that isn't $11k just for the floor panels? Thanks again!
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19 Apr 2018 06:58 PM
Greetings all
OK so in basements we have used the RHT floor panel system, The basement needs to be a dry basement, no water issues.
There are 2 ways to deal with the application best is 1/2 pressure treated plywood on top of slab. Our panels then lay on top pf press ply and are staples together. While this is not a great insulation value it will work fine.
For price estimates we see the typical application of our floor panel system running about $3.00 square foot Pipe, manifolds, heat plates, and you purchasing 3/4 " plywood locally ripping to 6" strips. You then fasten this to the 1/2" underlay and you have the sandwich. You can add a 1/4" barrier foam" foam under the 1/2" plywood for moisture block and a bit more r value. cost then is 1/2" ply plus $3.00 square foot. We provide a loop layout with purchase.
Good luck out there
Dan
www.blueridgecompany.com
Dan <br>BlueRidgeCompany.com
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19 Apr 2018 07:32 PM
Posted By sailawayrb on 19 Apr 2018 05:53 PM
I am always saddened to hear these stories. Some under slab insulation and couple hundred dollars of PEX embedded in the slab would have made this a very comfortable and low cost heating system. Anyhow, I think you should abandon the thought of using HR for this basement floor now. Perhaps just insulate above the slab to maximum extent that you can and then use another approach for heating the basement.


That's right- skip the radiant floor idea. That ship has pretty much sailed if you're on a budget.

A 3/4" layer of EPS under a 5/8" t & g plywood subfloor TapConned to the slab (taking care not to over-torque the tapcons near the edges creating ridges at the seams) with the seams of the plywood overlapping those of the EPS by at least a foot will work. Putting plywood directly on a bare slab is risking mold issues at your subsoil temperatures & summertime outdoor dew point temperature. The ~R3 EPS provides at least a modicum of under-foot comfort at the cold edges during winter, and is enough of a thermal break to keep the subfloor from developing mold/rot during the humid summer season when the outdoor dew points dwell for weeks at a time above the slab temperature.

Radiant ceilings &/or low temp panel radiators can still heat the place comfortably, albeit without the cozy bare-feet on warm floor level of comfort that you get with radiant floor.

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20 Apr 2018 12:54 AM
Thanks for the responses! I am on a budget simply because of the size. That said, is there a "reasonable" solution that will function without spending $8 per sf? In other words, something that will be functional if not at ultimate efficiency? If I give on the $$, would 1/2 or 3/4 foam plus 3/8 pex and gypsum overpour work? What about 3/8 pex routed into 3/4 foam with 5/8 plywood over that? 57 degree for the coldest part of the floor at end of winter didn't seem shocking although I have no basis for comparison.

I agree with the radiator panel idea as a next option. I thought ceiling fans could help to keep the insulated floor more comfortable as part of "plan B" if it goes that way.

Thanks again!
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20 Apr 2018 01:05 AM
I presented a solution in floor.
total material cost 4.50 sq ft. total thickness 1.25 "
1/2" treated ply base, 3/4" RHT floor panel on top, combined material about 4.500 sq ft. Pipe, heat transfer plates, floor panel system, manifold.
labor about 500 sq ft day 2 persons.
Dan
Dan <br>BlueRidgeCompany.com
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20 Apr 2018 01:23 AM
Thanks, Dan! Not looking past your suggestion at all, sorry it seemed that way. Was on your website a few times and was planning to call you to discuss. Just looking for other ideas as well. Will try you tomorrow or Monday.
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20 Apr 2018 02:35 AM
β€œIn other words, something that will be functional if not at ultimate efficiency?”

Good HR floor emitters typically deliver 90-95% of the heat that they receive to the living space. If you go the plywood route, you will likely only deliver 50ish % of the heat to the living space... So for every utility heating fuel dollar that you spend, 50 cents will go to heating the ground below your house. I guess if you consider that functional and not ultimate efficiency, go for it and good luck!
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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20 Apr 2018 04:08 AM
Well well well,
Ok I will bite.
please place this in your calculator,
1/2" inch of plywood is about R.63 3/4 ply .94 our floor system would then be 25% .63 R value (1/2 only areas ) Under pipes trough and 75% 1.57 Areas of floor that are 3/4 " ply on top of 1/2" ply. Plus our heat transfer plates do not make direct contact with the 1/2" ply under, there is a 1/8" air gap under the pex pipe. Source http://www.coloradoenergy.org/procorner/stuff/r-values.htm
I know, not much but the emitter is on the surface. If you place a laminate or engineered wood on top what do we have moving in the room VS down in to the slab.
Then we ask what function will the waste that loads in to the slab provide, what is lost once the flywheel effect in the slab is is in place, the slab has some radiant saturation.
I doubt your 50% downward heat loss guesstimate is even remotely close to reality.
There is a large diminishing return on R value past the first R1 or R 2 . Not to say I do not support Insulation, yes more is much better. 2" rigid would have been best for sure. perfect world.
Perhaps in a perfect world Trump would be selling pencils on the corner (check the lead). But we work with what we have.
Dan
Dan <br>BlueRidgeCompany.com
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20 Apr 2018 10:35 AM
Again, I appreciate the responses. I understand that my comment on functional without ultimate efficiency is based on lack of detailed knowledge, I grasp the concepts but I am not an engineer. I guess my question is as follows: Do the temps I provided (let's assume they are annual low points for discussion sake) of 57f at exposed edges, 60ish at below grade edges, and 63 in mid floor tell you anything about the challenge and/or need for insulation? I understand that without any thermal break the energy put into the existing floor would be significant.

It is easy to start-out with "I can't give up the height" because doing so makes things difficult in many ways. That said, as I am learning about more options I think I will take a closer look at what I can afford to give-up.
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20 Apr 2018 12:46 PM
You twwoo at it again.... The ground is an insulator and works even better with no ground water R.25 per inch. Also adding in ground insulation on the outside lower walls if possible would help the house as whole and also this project. In the summer the ground will heat up and you are maintaining that temp through winter. The basement is currently not a freezer so it isn't going to take that much energy to make it a comfortable living space.

It is apparent the OP doesn't want forced air to heat the basement and Dan's option is valid way of doing it. I have heard of many houses that do in slab radiant with no insulation. In Dan's option there is also the response time advantage of not having to heat the whole slab floor so it could be heated up when its planned to be used. I am guessing turning it up an hour before use would work.
"Never argue with an idiot. They will only bring you down to their level and beat you with experience." George Carlins
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20 Apr 2018 02:53 PM
Provided the temperature below and above the floor is less than the water temp in the PEX tube (which would be the case), it is only the R-value below and above the PEX tube that matters. If you have the same R-value above and below the PEX tube (1 /2” inch plywood, 6” wood, etc.) you only get 50% upward heat transmission. So what exactly will you put above the PEX tube that will be LESS than the R-value of what is below the PEX tube? I suspect you will be challenged to get even 50% upward heat transmission...and I would be happy to PE stamp this too once you sort it out.

Radiant panels would be a far better solution as Dana recommended.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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20 Apr 2018 04:39 PM
OK,
So Roth panel, great product I agree but reality is where the pipe is on a 7/8" panel you have 3/16" foam at best insulation between the pipe and the concrete. The pipe at that location represents a concentrated heat point downward and upward only due to the insulation on the foam side walls. Do not get me wrong I like Roth panel product but there is this weak link as well.
Roth Panel $6.50 + sq ft (on line price + freight) Add to that cost pipe and manifolds. Still faced with a solution for the final surface but now with some limitation. Cant use traditional nail down floor. You can with our RHT panel.
Can not tile over with out first understanding how wonder board will be attached and how a soft substrate will preform with the tile structure. Rht floor panel, screw wonder board to sleepers, stable tile base.
As I pointed out RHT Floor panel price point is about 1/2 even with the 1/2" pt ply under layment.
so a 1,000 sq ft roth panel with pipe and manifold runs about $7,100.00 (panel $6.5 sq ft, pex .35' manifold $250.) I am sure you can shop this for better but not by much.
RHT floor panel about $3.00 sq ft. treated 1/2" ply under layment add .55 sq ft so we have $3,550.00 for the same sq footage, and a stable sub floor. I think your R values though not as good as the R4.5 possible on the foam will provide similar performance.
That $3500 saved covers most of the cost of a quality engineered flooring on top.
Dan


Dan <br>BlueRidgeCompany.com
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20 Apr 2018 04:44 PM
Seriously, you DON'T want to do radiant floors on a walk-out basement in place as cool as WI without at least some real insulation under the PEX. For a basement slab that's fully below the 100 year frost depth it wouldn't be quite as bad, assuming VERY well drained dry and sandy soil, not clay. If the soil is dry and all of the near-grade slab edge /stem wall is insulated to at least R10 all the way down to the footing it won't be terrible either but would still be a lot lossier than radiant ceilings or panel rads.

Given the described basement radiant ceilings or flat panel radiators are going to be dramatically more efficient, still cheap to install (compared to WarmBoard or Roth), quite comfortable, and do not use "...forced air..." (which nobody here has suggested.)

Getting to the optimum solution starts with a careful Manual-J heat load calculation of the space. Efficiency might not matter very much if it's a tiny load, but I suspect it's not really a tiny load. But without some numbers to work with it's all just a bunch of arm-waving speculation.

BTW: The wind chill effects of ceiling fans make humans LESS comfortable during the heating season, even if it raises the floor temp a couple of degrees.
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