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ketchgould
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# Posted: 18 Mar 2021 10:50am
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I am planning a cabin in northern Wisconsin and want to use it year round on weekends for the next 12 years. I will build 600 square feet right away but will add on over the next 12 years to build a retirement place. I would love a cozy warm floor and was curious how efficient, warm and responsive a radiant joist built foundation is?
How would you assemble a joist foundation to optimize the assembly?
I like the simplicity, efficiency and green nature of the FPSF slab but wonder what the costs would be to keep the slab heated at 60 degrees all winter when I only plan to be up on weekends. Also, when I want to add on to the 600sf build, how hard will that be with concrete?
The retirement home seems to favor concrete but the weekend use cabin seems to favor joists in my mind.
Lastly, I want to get something built as soon as possible and would continue to improve and grow the space over the years. I would probably use the cabin for two or three winters without a boiler to heat the floor anyways, just relying on the wood stove I already own.
What would you do?
Can the joist floor be cozy warm?
Thanks
Christian
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snobdds
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# Posted: 18 Mar 2021 11:00am
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It seems like your biggest constraint is time. You know what to do for your retirement home needs, and that is a traditional foundation like a slab with radiant.
You only get to do this once, so build what you want right off the bat. Make the foundation big enough that you can expand later on.
If you start taking short cuts to have benefits now, you will regret it later.
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ketchgould
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# Posted: 18 Mar 2021 11:14am
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Right now money is the biggest constraint. The slab is almost cost neutral with the joist foundation for construction costs.
Is the slab expensive to keep heating with a propane boiler all winter long at the required temps?
What would a FPSF slab be like unheated for the first few years on winter Wisconsin weekends?
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snobdds
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# Posted: 18 Mar 2021 11:31am
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I have no experience with heating via propane or the heating difference between a slab and joist in a radiant package.
Common sense says radiant heat either by slab or joist is not a good plan on a weekend cabin. Radiant needs time to warm up and mass to keep it warm for long periods of time. Good for a permanent home, but not a cabin. That is why you really don't see those techniques being used much by weekend cabineners. This is where your stove comes in and you will rely upon much more than the radiant heat until you retire. I understand planning for the future though.
If the costs are the same, always go slab and insulate under the concrete for the most efficient way to heat.
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ICC
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# Posted: 18 Mar 2021 12:26pm
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I have a friend here with a concrete slab foundation. Our winters are not like WI but it freezes every night December thru March.
When we poured the slab 10 years ago we laid the tubes for a radiant system. It took one year including a winter before the house was all dried in. It took another year before it was heated and being lived in. The radiant system was not placed into service until two years ago. Everything was fine.
The system must be filled with potable type antifreeze when placed into service. No plain water, no ethylene glycol antifreeze. Leave it empty but with the lines capped.
If you are thinking you would like to have radiant heat at some time in the future I would set it up like that and pour an insulated slab.
Quoting: ketchgould Also, when I want to add on to the 600sf build, how hard will that be with concrete?
Building an addition to a structure on a concrete slab is done all the time.
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ICC
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# Posted: 18 Mar 2021 12:28pm
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As snobdds mentioned radiant and weekend use really do not go together well.
Antifreeze in the radiant system will be necessary for insurance coverage.
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Nate R
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# Posted: 18 Mar 2021 01:20pm
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Quoting: ketchgould What would a FPSF slab be like unheated for the first few years on winter Wisconsin weekends?
I'm not sure yet, give me another year and I'll have some answers for you. 
Quoting: snobdds This is where your stove comes in and you will rely upon much more than the radiant heat until you retire. I understand planning for the future though.
I think so too...if you're starting with 600 SF, lay the radiant tube in an insulated slab, figure out how you'd do other later additional zones, and add/use all that stuff later. For now, I'd think you'd be OK running with a wood stove.
Not sure about radiant on joists, etc...... If you want to start ASAP though, better make sure you can find a concrete guy who's got availability this year......Lots of areas are SWAMPED with work.
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gcrank1
Member
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# Posted: 18 Mar 2021 01:22pm
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I would think that a lower temp, maybe 50*? would be considerably cheaper to keep it 'idled' and building the initial as its own loop c/w valves to expand to future build would allow best options.
Can you design with passive solar to heat an interior 'heat sink wall' as well as slab? That should really cut the lp expense.
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Nate R
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# Posted: 18 Mar 2021 01:31pm
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OTOH, as gcrank1 points out, Idling the radiant (and maybe just cranking the wood stove on weekends for additional temp?) might not be too bad.
Slabs DO have the advantage of ground heat.
My relative has a place on an UNINSULATED slab. Unheated, it's never been colder than 25 inside that he knows of. (And that was at -20 outside!)
My unheated, uninsulated garage this year got down to 13 (briefly) inside when it was -9 outside, and had been cold for a few days.
My shed, that's on wood skids, up off the ground, stayed about the same as ambient all winter. -4 outside? -4 inside. In summer, it heats up more than ambient from sun.
I'm HOPING my insulated slab cabin won't drop below 30 or so when unheated, with a carefully insulated building on top that's a dark color. We'll see.....
Point is, heating a slab to 50 degree air temp or so might not be too bad.....Taking it from 25-30 to 50 instead of say from outside of 0 to inside of 50 (like joists), may be a bit cheaper.
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ICC
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# Posted: 18 Mar 2021 01:33pm
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Quoting: gcrank1 I would think that a lower temp, maybe 50*? would be considerably cheaper to keep it 'idled'
The lower temperature would be safe and less expensive for periods when it was not occupied. A considerable savings. However, radiant floor heat is slower to warm up the interior when one does decide to use the space for a weekend or whatever. The floor is heated to 75 F, maybe 80 F depending on a number of factors. That will take longer if the interior temperature needs to be elevated from 50 instead of 60. If it was possible to set the system up with a thermostat that allows remote control then it could be adjusted days ahead. That of course requires an internet connection working all the time.
Radiant and occasional occupancy is not a good idea IMO. A waste of energy.
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Nate R
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# Posted: 18 Mar 2021 02:59pm
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Quoting: ICC That will take longer if the interior temperature needs to be elevated from 50 instead of 60.
Absolutely....Which is why I think one could keep it at 50 and run the wood stove he mentioned on the weekends to elevate room temps.
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Steve_S
Member
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# Posted: 18 Mar 2021 03:59pm - Edited by: Steve_S
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Forbidden
You don't have permission to access this resource.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.
Try to post a detailed response and the above appears??? okay....
Response attached as PDF File. won't take a TXT ?
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ICC
Member
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# Posted: 18 Mar 2021 05:03pm
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File Upload Rules
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The sum of the sizes of all the files that you are uploading at once, should not be larger than 1048576 Kb. Otherwise your message can be denied at all.
There are many security issues related to the files uploaded on our forums. Each case is individual, and if you think you can not attach files because of some bad hitch in the system, which doesn't fit in the rules described above, please report our administrative stuff.
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Steve_S
Member
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# Posted: 18 Mar 2021 05:52pm
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Been registered since 2014. Have large postings of my build with images PDF's and more including links to materials & products.
I wrote the message out and it would not post and that is the message I got. Then tried using simple TXT and it won't take TXT so saved it as PDF and it took it.
Condescension not accepted. Retry !
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ICC
Member
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# Posted: 18 Mar 2021 06:18pm - Edited by: ICC
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I've had ocassions when this system would not take something I had typed in a word processor and pasted here. Hard to understand what happens at times.
I copied and pasted that 18 Mar 2021 17:03 post of mine from the forum uploads rules. I had no idea if you were aware that TXT was not on the accepted list. There was no condescension intended from me if that jab was directed my way.
I've been registered since 25 Mar 2013
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CabinBuilder
Admin
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# Posted: 18 Mar 2021 09:31pm
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There are some limitations posting text when using certain special characters.
Sorry.
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ketchgould
Member
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# Posted: 21 Mar 2021 10:17am
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Great ideas. Nate I am curious how your slab will feel in a year or so too. I had not thought of the earth warming the slab some.
Does anyone have any idea what the propane monthly costs would be to heat something like a 2 car garage sized slab at idle 50 degrees and ten days a month at 70?
Is a guess that this would be $60 or less each month? I haven't worked with propane so much so I really do not know the efficiency.
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ketchgould
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# Posted: 21 Mar 2021 10:22am
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Steve, great information and links - Thanks.
What do you think the weekenders propane consumption is for a month with the schedule you describe?
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gcrank1
Member
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# Posted: 21 Mar 2021 01:43pm - Edited by: gcrank1
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Compared to my dead cold uninsulated wood floor Im thinking your slab floor left at a constant 50* (which might be holding the room too?) would feel pretty good to walk into as is, then just supplement the room with wood or lp furnace heat while there might work well?
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Steve_S
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# Posted: 23 Mar 2021 06:21am
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Energy use is not easy to figure because there are dependencies. How square footage is the building, how well is the building insulated, how well is the pad insulated, what are the temp swings to expect and more.
If the building is well insulated & retains heat then the system will obviously run less than if the building has poor insulation. A Garage is one of the hardest buildings, because of the doors not being great for insulation and usually the building is not well insulated compared to a house.
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