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I am considering Durock ( 1/2″ ) as an underlayment over 1/2″ Wirsbo tubing and 1″ pine sleepers. Any concerns or advice on this application?
This is a new addition on a concrete slab. Construction todate: 2×8 floor joists on top of the slab and cavities insulated tightly with three layers of 2″ blueboard (~1 1/2″ air space between insulation and concrete & vented to the outside). 3/4″ Pelican board laid atop of the joists. 1″ sleepers screwed & glued to the oriented board & spaced 1 1/2″ apart for the Wirsbo tubing (See diagram). Now I want to apply a suitable underlayment that will allow for either wood, tile or carpeting in the future. That’s where I thought ½” Durock would work. My questions are:
1. Can I lay the Durock right over the sleepers? I would glue and screw to the sleepers. The gap between the sleepers is 1 1/2″ and the tubing is 1/2″ diameter. Will the integrity of the Durock be compromised?
2. Any advantages to filling the void between the sleepers and around the tubing with sand? Would this help hold and transfer heat to the Durock? Is sand too abrasive for the polymer wrap (for preventing oxygen diffusion) on the tubing? Would this alleviate concerns in Q#1?
Thanks in advance for your suggestions.
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Have I said something wrong?!? Is this such a bonehead idea that its not deserving of a comment? Is additional info needed?
Please... Go ahead I can take it - good or bad! Any advice is appreciated.
*I don't think you can take the truth.I read your post and I saw every argument for and against that I have ever seen on breaktime for the past year.What was the purpose of venting under the styrofoam to the outside or to anywhere? From where is it vented?Why didn't you simply install the hosing underneath your deck plywood BETWEEN the styrofoam and the deck?Why couldn't you lay one layer of high density styrofoam on the concrete and pour another layer on top with your hosing in it?Why didn't you post earlier in your project?Gabe
*I can appreciate that from your perspective this was poorly conceived. You are right. This originally started out as an addition with a conventional force air system. Except, when the project was under a GC, he had a half-@$$ plan for tying to the existing force air system (as well as other issues). At that point the job was framed and enclosed (i.e. the 3/4" Pelican board was down). Well the GC is gone. In consulting a HVAC/radiant heat contractor, he suggested the sleeper system of putting down the radiant tubes along with 3/4" underlayment ontop, if I was to take it on as a DIY project. That's where I am at today. Radiant heat was an after thought to this project. I am just trying to make the best of a compromised situation. I clearly understand why you would ask the questions that you have. I think I have answered them -- I have adopted a bastard child!After reading a number of posts regarding the pros and cons of wood underlayments in a radiant heat application, I wanted to consider other materials that would hold and distribute the heat more efficiently. Hence the thoughts about Durock and the use of sand. I can take the truth, thank you. Your thoughts on the Durock please. Gerry
*Hi Gerry,You answered my thoughts but you didn't fill in the information about the ventilation.I'm at a total loss as to why this would have been done.Also can you tell me the size of the room and what you're going to cover the floor with?Whats the spacing of the joists?Hang in there and I'll see if I can help you out.Gabe
*I don't have an answer for the ventilation. That was the handy work of the GC and framer. Ventilation holes (approx. 1 1/2" diameter) are present only at the end of those joist cavities located under the bays (see diagram). I can only venture that there may have been a concern for moisture from the concrete slab as it cured?? I suppose they could be capped closed. Interior room dimensions are ~25'x12'. The floor joists are at most 19" O.C. Two bays (floor to ceiling height) are cantilevered over the concrete slab. As shown in the diagram, the bays are located along the 25' length of the room. The home is built on a mountainside and is supported by four ~20+' concrete columns. The "addition" is immediately off of the basement's exposed wall (downhill side) and "wedged" between the newly created concrete slab, the living space above and the support columns.Floor covering planned is Berber carpeting with 1/4" rubber pad. But I would like to maintain flexibility in the design for tile or wood in the future.I'm sure I have created a visual nightmare, not to mention more questions.
*Hi Gerry,As it is I cannot open your attachments. I don't know the program you're using or if it's IBM compatible. But When I bring it up I only get a blank screen where a picture should be.Can you save the sketches as JPG or TIF?Gabe
*Previous attachment Word .doc. This one .jpg
*Hi Gerry,Gotcha!The existing house forms the canopy over the addition. Did the contractor frame the outside perimeter with standard wood studs and did he allow for deflection from up above or did he transfer some of the load to your new slab?As I understand the timimg, you are not doing any of the finished work yet?Is the joist framing "inside" the wall framing, in other words was it done after the outside walls were done?The reason I'm looking at this, is to find a "permanent" solution to your investment. If it were possible to write off the joists system or use them elsewhere, you could reuse 1 layer of styrofoam over the slab, and pour the radiant heating into a 3" pea stone slab over top.This way you would never have to worry about moisture or it's associated problems under your floor now or in the future when you change to ceramic tiles or wood.How far north are you located, is frost a problem in your area?Gabe
*2x6 framing was used on the exterior walls (2x4 partition along basement wall) with overhead load transferred via the shorter walls to the slab. The longer exterior wall is non-load bearing as it is under a 10" I-beam that runs atop the three concrete columns.The addition is enclosed with exterior walls insulated with f/g and electrical complete. Joist framing is inside framed walls except for the interior wall and bays (the portion of the exterior wall between the bays sits on the slab). I gave brief thought to ripping out the joists as well. However, the bays are supported by the joists. Home is located north of Denver, CO. Altitude is 7400' and we do have frost. Humidity is seldom a problem; typically 20-40% winter, 50-70% summer.
*Hi Gerry,Your weather conditions are as they are here so frost is a major consideration.Your slab, is it a slab on grade or is it structural? (designed by an engineer and full of rebar)Is it insulated underneath around the perimeter?I'm worried about a few reg flags.Gabe
*The slab is structural - along with the room they're designed to assist in the load borne by the columns and stabilize the home under high wind conditions. 70 to 100 mph winds are not uncommon here; strong enough to get the bed swaying at night. The slab is approx. 6" thick at the basement and 5 feet thick at the bay end! Extensive rebar 3 feet into bedrock. No perimeter insulation.Is "reg" flags, red or regulatory?Gerry
*Sorry that it's taken me this long to reply but I'm having difficulty posting lately.Red flags.I'm worried about the lack of insulation around and under your slab.Your assembly has too many oddities.The 3 layers of insulation between your joists is a waste. The venting between the insulation and slab can't work.You're in a heavy frost area and no protection for your structural slab.The insulation between your living area and the exterior slab make it worst.Essentially you have an unprotected slab.Do you have any photos of the construction that you can email me?Gabe
*Photos of the construction emailed.
*Hi Gerry,Your photos re-enforce what I suspected.I assume that the columns are either drilled into or pinned into the granite.The structural slab should have some type of protection from the frost.With the precautions your contractor has taken to isolate the living quarters, he has left your slab out in the cold. Its as if you were to not build the walls around your addition and were to leave the slab exposed over the winter. Is there a possibility of water infiltration between the cracks in the granite and the concrete and freezing?If the contractor would have put insulation under the slab, around the perimeter this would not be a problem. Heat loss would further protect the slab.Heat rises from your radiant heat source and with 6" of styrofoam separating the two, the slab will be cold.If you would cast the tubing directly over the concrete you would loss some efficiency due to the slab not being insulated but by adding 2" on the outside face, you would minimize this loss and your slab would be protected from any frost heaving.Was the design site inspected by an engineer?Gabe
*Gabe,I have a better appreciation for your concern for the ventilation between the slab and insulation. There exists the v. good possibility of water infiltration where the slab meets the granite. It would seem to me that if little can be done to prevent the slab from freezing at this point, preventing water infiltration would be the next best recourse? For instance, protecting the slab exterior from water using blue board (&/or apply a waterproof coating?) and some mechanism or material for preventing water infilatration at the granite/slab interface. Would you agree?The site was supposedly inspected by the engineer that specified the slab design (though I never saw him on the site). I do have a copy of the letter given to the county building department stating that he "observed the reinforcing steel as it was drilled into bedrock...and for concrete reinforcement." No mention ever of insulation for the slab.Gerry
*Hi Gerry,I would highly recommend you have an engineer come to your site to give an opinion on the slab's exposure.I would also highly recommend that expose the exterior as much as possible and install 2" styrofoam and then backfill against it. If you can't get down because of the rock being too close to the surface, then you can lay the insulation on the flat for a portion.The idea is to use the ground temperature to protect your slab. The best way to do this is to lay insulation against and away from the perimeter. Your living quarters will protect from the top, you just have to protect from the sides now.Believe me you have more than enough insulation on the inside, you can use one layer of it on the outside and have no effect on the radiant heat.Chat later Gabe.With regards to trying to prevent water from infiltrating, that would be a loss cause and besides you wouldn't know if you were successful or not until it was too late.
*Gabe,Thanks for the good advice on the slab.Any suggestions for an underlayment over the PEX tubing in this situation? 3/4" ply, Gyp-crete, light-weight concrete, or other? that would offer the most flexibility down the road for floor coverings?Gerry
*Hi Gerry,Stay with the 3/4" ply for now. Its the least expensive option and easy to add to later on.At one time, I didn't recommend cork floating floor over radiant heat, but in discussions with my supplier in Portugal, I'm informed that they not only approve of cork floating floors over radiant heat but encourage it.The reason is that because of corks thermal resistance and it being a warm floor, the heating system does not have to be turned on as early in the season to warm the floor.I don't know, I'm going to have to check into it more before I recommend it in North America.Chat later,Gabe
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I am considering Durock ( 1/2" ) as an underlayment over 1/2" Wirsbo tubing and 1" pine sleepers. Any concerns or advice on this application?
This is a new addition on a concrete slab. Construction todate: 2x8 floor joists on top of the slab and cavities insulated tightly with three layers of 2" blueboard (~1 1/2" air space between insulation and concrete & vented to the outside). 3/4" Pelican board laid atop of the joists. 1" sleepers screwed & glued to the oriented board & spaced 1 1/2" apart for the Wirsbo tubing (See diagram). Now I want to apply a suitable underlayment that will allow for either wood, tile or carpeting in the future. That's where I thought ½" Durock would work. My questions are:
1. Can I lay the Durock right over the sleepers? I would glue and screw to the sleepers. The gap between the sleepers is 1 1/2" and the tubing is 1/2" diameter. Will the integrity of the Durock be compromised?
2. Any advantages to filling the void between the sleepers and around the tubing with sand? Would this help hold and transfer heat to the Durock? Is sand too abrasive for the polymer wrap (for preventing oxygen diffusion) on the tubing? Would this alleviate concerns in Q#1?
Thanks in advance for your suggestions.