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perchking

Concrete overpour and radiant heating?

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We currently have a small 4 season lake cottage 28x32, in September we will be tearing it down, rebuilding and making it bigger.  I would like to keep the existing slab and add on both with a loft new kitchen and screened in porch.  I would like to have in-floor heating both on the existing slab and the new area that needs to be poured.  What are your thoughts of putting the tubing on top of the existing slab then doing a over-pour so I can have radiant heating throughout?  I haven't picked a contractor yet, however I did some searching online and it seems possible. 

 

Any experts out there?

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I am no expert, but I am guessing that you will be advised to put some insulation under it, and if you don't have insulation under the slab now, that may be an issue. I would also think that it would be better to keep your foundation/slab one piece for all. But again, i am not an expert in the least! We do have infloor heating in our cabin slab and it is very nice, and the off-peak/dual-fuel electric pricing makes it nice and affordable heat. Very nice on the feet in winter, and keeps the gas bill very low.

 

If you don't have off-peak/dual-fuel pricing then the electric may get very very expensive to run, especially without proper insulation missing from part of it.

 

Good luck.

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Definitely need an insulated slab or you'll bleed our money, however I would guess if it was initially built as a 4 season they should have insulated the slab initially.  If the existing slab is already insulated, i have heard people running their pex along the top of the slab and boxing up the floor with 1x2's and sheeting over it.  Results sounded pretty good.  Also not an expert.  

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That is what I was thinking Moon, just raising the existing slab another 2 inches or so potentially with product called gyp-crete or a thin or light weight concrete.  Sounds like staying away from gypcrete might be a good idea based on some recent searches..  The existing slab does have blueboard under it when it was poured.

 

 

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You really don't need much insulation under the ground slab, I like to use pole barn ins.[bubble wrap] or 1 inch r board [heat rises],gyp crete works but it is patented and can only be installed by certified and licensed factory contractors. they mix it on sight, it cant be mixed by youre local ready mix provider,as the formula is property of gyp crete.

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If you end up pouring your own make sure the pex is full of water otherwise it will try to float and you gyp crete will look like corrugated cardboard

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Usually they make ties or brackets that you can bolt it down with.  Doesn't take much just enough to hold it in place until everything sets.  Definitely worth filling first though for a pressure check at a minimum. 

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Thanks everyone, it looks like warmboard had a product that might fit the bill.  It might be a little spendy but it may be an option if I don't want to tear up the existing concrete...

 

 

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On 2017-03-28 at 7:50 AM, Moon Lake Refuge said:

Usually they make ties or brackets that you can bolt it down with.  Doesn't take much just enough to hold it in place until everything sets.  Definitely worth filling first though for a pressure check at a minimum. 

I had the fasteners they recommended but it still needs to be filled to prevent floating . I don't recall what spacing I used but was told later I did every thing correct except for the water .

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I could see it for a pressure test, but if you fasten the pex in enough spots there wouldn't be any floating.  Maybe expansion once filled but if it wasnt filled until the concrete set that shouldn't be a problem either.

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I thought that I had read somewhere that over pouring over old concrete is not the best thing to do as it may not bond and could crack?  :confused:

 

 

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How much is this going to save for all the work it takes to make it work with everything being level? Is the existing slab perfectly level to start with? there are times when it makes sense dollar wise and times where it might cost more to keep.

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i have no idea PF, I was simply asking if anyone did this before. I guess I will wait until I hire a general to give me my options. 

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23 hours ago, Moon Lake Refuge said:

I could see it for a pressure test, but if you fasten the pex in enough spots there wouldn't be any floating.  Maybe expansion once filled but if it wasnt filled until the concrete set that shouldn't be a problem either.

So are you saying what happened to me did not happen ? We not talking about a 4 inch concrete slab , it is a thin layer of gyp crete that covers the pex , it has the consistency of water when poured and sets up fast, it is self leveling and any movement in the pex shows up and cant be undone . Yes if it was fastened continuously it could not move but that would be ridiculous . As so this discussion !  

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30 minutes ago, Cheers said:

So are you saying what happened to me did not happen ? We not talking about a 4 inch concrete slab , it is a thin layer of gyp crete that covers the pex , it has the consistency of water when poured and sets up fast, it is self leveling and any movement in the pex shows up and cant be undone . Yes if it was fastened continuously it could not move but that would be ridiculous . As so this discussion !  

Ridiculous... but it would work.  Sorry to offend, guess I don't get quite so fired up about concrete.

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15 hours ago, perchking said:

i have no idea PF, I was simply asking if anyone did this before. I guess I will wait until I hire a general to give me my options. 

 

You'll probably run into plenty of "experts" among the experts, too...;)

 

Floor heat is nice, but definitely not the best option if you're looking for the best efficiency, since it is a slow recovery system.  If you were looking for efficiency and lowest cost, I would suggest looking into a mini-split heat pump to complement the gas furnace if you have off-peak available.

 

(Disclaimer: Not an expert either, but I have stayed at a Holiday Inn Express a few times.)

 

 

 

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On ‎3‎/‎27‎/‎2017 at 6:30 PM, trolloni said:

You really don't need much insulation under the ground slab, I like to use pole barn ins.[bubble wrap] or 1 inch r board [heat rises],gyp crete works but it is patented and can only be installed by certified and licensed factory contractors. they mix it on sight, it cant be mixed by youre local ready mix provider,as the formula is property of gyp crete.

no expert here, but heat doesn't rise. heat radiates in the direction of least resistance (R value).

warm air or water rises because it is less dense than colder air or water.  If you don't insulate you will be heating the ground under your cabin and the earth is a very large heat sink $$$. get some info from an expert in the radiant field as far as tube diameter, spacing, water temp, manifolds, length of runs, and so on. it varies on amount of windows (solar) ceiling height and room type (bed, bath, living area,  storage etc.). once you pour over the tubing you get to live with it. I did my own Home 15 years ago and got some good advise (wish I would have taken it all)

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22 hours ago, perchking said:

i have no idea PF, I was simply asking if anyone did this before. I guess I will wait until I hire a general to give me my options. 

I apologize if that came out wrong. The idea might very well be the best route to go. It's just that over the past 25 years or so I have seen many attempts to save a dollar that cost a buck and a half to do lol. 

 

Here are my two cents. If you have a slab and you want to pour on top of it while keeping the same footprint that sounds pretty doable and could probably save some money if you don't have to change drain lines, run water, heat runs, electrical etc into the slab.

 

If you intend to tie into the existing slab and run zones of pex across the joint and have the new and old floors end up at the same elevation it still can be done. Some contractors will not want to mess with tying into and raising the elevation of the slabs and will prefer to start from scratch especially if you as the homeowner want them to warranty the finished product. 

The critical thing would be to use enough rebar drilled into the old slab and have enough compaction and sufficient footings to make sure the slabs stay where they are without settling. That would make all kinds of problems with the pex. 

 

Hopefully that response came across better.

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1 hour ago, PurpleFloyd said:

I apologize if that came out wrong. The idea might very well be the best route to go. It's just that over the past 25 years or so I have seen many attempts to save a dollar that cost a buck and a half to do lol. 

 

Here are my two cents. If you have a slab and you want to pour on top of it while keeping the same footprint that sounds pretty doable and could probably save some money if you don't have to change drain lines, run water, heat runs, electrical etc into the slab.

 

If you intend to tie into the existing slab and run zones of pex across the joint and have the new and old floors end up at the same elevation it still can be done. Some contractors will not want to mess with tying into and raising the elevation of the slabs and will prefer to start from scratch especially if you as the homeowner want them to warranty the finished product. 

The critical thing would be to use enough rebar drilled into the old slab and have enough compaction and sufficient footings to make sure the slabs stay where they are without settling. That would make all kinds of problems with the pex. 

 

Hopefully that response came across better.

I appreciate the response, I take nothing personally and didn't mean to be snippy in my reply. There are a lot of great comments on here and I will keep you posted on what I decide. Thanks again. 

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On 3/27/2017 at 8:17 AM, perchking said:

We currently have a small 4 season lake cottage 28x32, in September we will be tearing it down, rebuilding and making it bigger.  I would like to keep the existing slab and add on both with a loft new kitchen and screened in porch.  I would like to have in-floor heating both on the existing slab and the new area that needs to be poured.  What are your thoughts of putting the tubing on top of the existing slab then doing a over-pour so I can have radiant heating throughout?  I haven't picked a contractor yet, however I did some searching online and it seems possible. 

 

Any experts out there?

 

No expert here either but I've talked to a couple. 

 

Would your new, expanded slab be conducive to making the addition another zone or zones?  You could maybe run that expansion off different lines from the manifold above the slab so you don't have to route and pour over seams.

 

Definitely insulate below with GOOD insulation.  As mentioned, heat doesn't really rise the way we think it does; it moves to the cold and the earth will soak it up.

 

Heating your loop would be cheapest with a natural gas fired boiler, propane second.  Geothermal is expensive to put in so your payback on a new system is long.  Air source heat pumps are great until it gets really cold.  In the end, radiant in floor is the most efficient way to heat, but yes, it's slow to respond.  But if your toes are warm, you will be too.

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Do you have footings? You haven't said. My garage isn't heated but when it was torn down and rebuilt bigger the cement contractor said the old slab would be fine under there, solid footing, etc. Well guess where the new slab formed it's first crack, right along the edge of old slab, it's not big but I notice it.  We also just had a sidewalk replaced from settling and not poured correctly the first time last year and contractor poured over that and that turned out perfect.  Just my expirences.

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4 hours ago, Wanderer said:

 In the end, radiant in floor is the most efficient way to heat, but yes, it's slow to respond.  But if your toes are warm, you will be too.

 

 

What I've seen is in-floor heat is great in the winter when it's cold day and night - not so good when you have large temperature swings from night to day in the spring and fall.

 

If you think you might run into problems installing pex in the floor, it can also be done in a wall - and probably at less cost.

 

 

58ddd3f758da6_radiantwallheat.gif.40bf5c31f03a182f64c51b9259ede67b.gif

 

 

 

 

 

 

 

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spring and fall I have to lower the  water temp so the system doesn't over shoot the set temp in the morning when the outdoor temp rises in the morning. basically  have two operating temps one for spring and fall and one for mid winter.

this makes the house really comfortable. Its not as simple as other systems but when I wake up in the middle of the night to pee and step on the tile floor, it makes me smile every time.

 

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9 hours ago, swamptiger said:

 

If you think you might run into problems installing pex in the floor, it can also be done in a wall - and probably at less cost.

 

 

There may also be some overhead options that will fit the bill.

 

http://www.sshcinc.com/basement/basement_ceiling_radiant_heating.htm

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11 hours ago, magicstix said:

Do you have footings? You haven't said. My garage isn't heated but when it was torn down and rebuilt bigger the cement contractor said the old slab would be fine under there, solid footing, etc. Well guess where the new slab formed it's first crack, right along the edge of old slab, it's not big but I notice it.  We also just had a sidewalk replaced from settling and not poured correctly the first time last year and contractor poured over that and that turned out perfect.  Just my expirences.

I do have footings, we may just pull the entire thing up and start from scratch.  I am worried about the settling that others are talking about. 

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