Insulating basement slab, no radiant
Hey all,
I live at about 5,000′ in the Rockies and am having a house built with some living quarters in the basement. Our humidity levels are very low. The space will be conditioned with insulation on the walls and forced air heating (sadly, no radiant.) We have an option to insulate the concrete slab floor and leave it bare or to install wall-to-wall carpet. I want to be able to walk around barefoot or in socks without my feet getting cold and would rather have the bare concrete floor which I’ll stain but I don’t know how much of difference the insulated floor will make (our builder says it would be equivalent to R7). The slab will be 8 or 9 feet below the surface of the ground. Does anyone have any experience in this area who can offer advice to a novice?
Thanks,
doo
Replies
Hey doohickey I am doing the same thing, but I am putting 3/4 T&G Advantech over this product http://www.cosella-dorken.com/products/foundation_residential/products/MS.php?navid=10 this appears to be the way to go, from what I have researched, since you are also insualting your basement slab, but not installing radiant heat.
Insulating the slab will reduce heat losses.
However, it will not make the slab WARM.
Concrete has a high specific heat (I think that is the right term), The amount heat required to warm a mass. For bare feet to feel warm on concrete the concret has to be above ambient temp.
I have an slabe that was insulated around the outside 2 ft, that is what was done 25 years ago.
And forced warm air with ducts under the slab. It does not really "heat" the slab, but it is warmer than similar insulated slab in the basement.
In the main floor I you can stand barefoot for a few minutes without being uncomfortable, In the basement only a few seconds.
Hey doohickey-
I'm faced with the same dilemma...planned for radiant in slab but wife wanted new heat source now so we put in a new forced air unit. I'm planning on putting the thickest foam t+g panels I can find under the slab and having registers at floor level. From researching radiant slabs I learned that a great amount of heat runs out of the side edges of a slab, so I figure I'll insulate there as well. As for bare feet on bare slab, I don't know. Might want to consider carpet or REAL linoleum over an osb-type subfloor designed for the purpose. I've seen them at Lowe's in 2x2 dimensions. Or dense 4x8 osb t+g might do the trick. Good luck!
I think Bill Hartman got it right.
Insulating a slab will reduce the heat loss through the slab, but will not make the slab warm. It is still going to reach equilibrium with the soil temperature beneath it, but a much slower rate, because of the insulation. With a radiant heat floor your heat source is in the floor and temperatures are usually in the 90 degree range the water flowing through the slab. The mass of the slab tends to hold this temp. and radiates it slowly in both directions (into the room and the earth), since both directions are cooler than the heated slab.
In some cases radiant floor heated slabs are only insulated around the edge and under the first 4' to 6' of the slab, and the earth beneath the uninsulated center of the slab is used as an additional heat sink. The diffrent heat capacities of the concrete and the earth are not as great that of an air to concrete interface. Heat is always going to "flow" to the coldest side of the equation and in the direction of the least resistance (heat capacity).
Bottom line is your concrete floor will reach earth temperature eventually, no matter how much insulation you put under it, unless you put heat in the slab. You want warm toes, put something between those 98.6 degrees feet and that 55 degree slab.
Dave
"It is still going to reach equilibrium with the soil temperature beneath it, but a much slower rate, because of the insulation."Actually, if the room is actively heated it won't reach soil tempature. There will be a tempature gradient, with the largest amount being across the insulation and another "across the air" between the heat source and the slab.I just ran a test with an CHEAP IR thermometer. First floor slab on grade with insulation only in the prermimater. And forced air ducts under it to distribute the air, but only marginally warm the slab.I have 3 areas, one carpeted, one with cushioned vinyl, and an unfinished bare concrete area.All measured 62-65 degrees. There was more variations between areas in the room due to closeness of refigerator, door or other heating/cooling sources. The carpet was warm to the barefeet because with the low specific heat and high R-value it quickly warmed up to "feet tempature". The vinyl was cool to the feet. Will I assume that it's specific heat was also low, it had a low R-value to the concrete mass.The concrete was definitely colder. It has a large heat mass and it is drawing heat out of the feet to warm that mass. Stand in one spot for a year ot two and it will start to feel much warmer.Not unlike 2nd story tile bathrooms. There they should be at "room temp", but are cold on feet because of the thermomass.Now my basement floor, with the same insulation, but no full time heat was in the 50's and really cold. As was a room that finished in it with vinyl over sheet foam over concrete. But again the heat is off in that area. Now that vinyl was cheap peal and stick so you have what I assume is higher specific heat and lower R-value to the plywood and underlayment below it. And at that temp it was very definitely COLD to the feet.
The only slabs I have checked thus far have been uninsulated, and with forced air heat. I consistantly get between 50 and 55 degrees in most areas. At the edge of slab near uninsulated frost walls the temp drops to around 40 to 45 degree. Those are delta Ts in the 20 to 30 degree range below ambiant air temperatures. I get the same temps on below grade poured walls with no insulation. Adding insulation inside seems to have helped, but IIRC it did not change the actual delta T very much.
Now I have to find my IR gun and repeat the whole thing agian, since you added the carpet, vinyl , and refrigerator factors :-(
Load calculations on my FILs home showed that the basement floor and poured walls (all uninsulated) contributed more to the heat loss than any other wall and window combination used in the construction of that house. With a single zone GSHP and the T-stat located on the first floor, that means anyone occupying the basement durring the winter months is going to get cold before the T-stat calls for heat.
Dave
My house is at ground level on the front and 1/2 of the 2 sides. Ground slopes up by 4ft at the back and the back wall is 12ft to support the garage on the uphill side.And the front is about 25% glass. And the first floor has the kitchen, LR and DR. But all of that faces way from the stree. From the street all you see is the garage, which is 1/2 story above the 2nd story.Despite that all of the living space is on the first floor and all of the glass and that it has 50% a ground level when I built in 79 all of the HVAC contractors kept saying - "we will stick a couple of registers in the ceiling for the BASEMENT". Even after correcting them I still had to talk to about 10 different ones before I found one that would cover the "basement". Ended up with 2 systems.Also I was had of GSHP, but don't think that they where called that then. But no one around here knew anything about them. A few said that "heard of something" but really did not know anything about them.
If you insulate the slab so its loss is slower than the heat gain from active heating in the area, it will eventually reach room temperature at least for the portion near the surface. So this depends on loss, insulation levels, and the heat to the area.it may take quite a while for this to occur after initial season start-up, and setbacks will ruin this ability.all that said, a "room temp" slab still feels cool or chilly to the touch, and will still draw heat from your body. But it is more comfortable than an "earth temp" slab.I am biased, but I always tell people if you pour concrete without insulation and without pipe in it, you're crazy. Someone might want to heat that slab someday, pipe is cheap, and insulation is good whether the slab is heated or not. I would pipe the slab for radiant and cap it off. Worst case, you're out 0.50-1.00 a square foot. Best case, you just avoided a retrofit nightmare down the road.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob, I want to pipe the basement slab and hook it up when I can afford it. You mention .80-1.00 per SF, but I am getting bids for $3200 to lay the pex and cap it for 1000 SF of basement slab.
It doesn't look that hard to lay the pex. Is it worth saving the 2k to do it myself, and are the amateur mistakes easy for someone to list and prevent before I begin?
Do you suggest laying the pex right on the 2" foam insulation before the pour? I will do my research, and this is part of it.
Thanks, Jim in Michigan
well, you spend the time on your knees probably, tying tubing to wire mesh, it's not that hard but it's not a walk on the beach either. That said, of all the tasks in radiant, I consider tubing in a slab the most DIY friendly. The numbers I gave were material only, btw.Keep your loops to 250 or less, to stay safe. In a basement, 12" o.c. should be just fine.You can lay it right on the foam, but if wire mesh is going in, you can tie to that and lift it slightly, for slightly better performance.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I put the PEX in my 24x36 garage slab a couple years ago. Put some extra time into making sure the gravel was extra level so the 2" of EPS would be well supported and not crack, laid wire mesh on that.
Tied 3 loops ~250' each to the mesh. Some rebar around the perimeter and at the front where cars drive in.
A few hours to cut & fit the foam into place. Mesh went down quickly. Placed the tubing by myself in an afternoon (a helper would have made this an easy couple hour job). 6 mil poly vapor barrier was on the gravel under the foam.
Some people make or buy a manifold to tie the tubing together, and some will pressurize the system to make sure it doesn't have or develop a leak. I just tied the 6 ends of tubing to a board, and used some foam pipe insulation to protect the tube where it comes out of the concrete (usual recommendation is to use pvc conduit sweeps).
So far, that's where it sits. Don't know when/if I'll actually hook it up to a heat source, but I figured it's a lot easier to put the tubing in when the concrete's wet.
Don
Insulate the slab regardless.
Why not an insulated slab AND carpet? Gives you a better shot at comfort.
Thanks everyone for all your input! I guess what we'll do -- now that the slab has been poured with no insulation whatsoever (arrggghhh!) -- is to lay down some sort of insulation on top of the slab (someone suggested Delta-FL) and then put padding and an airy carpet over it.
How's that sound?
doo
Already poured?
You need a thermal break. Dricore is one option, 1 inch of foamboard with a subfloor on top is another. Heck, if you want the radiant option back, you could lay down a subfloor tubing system over the foam.
Edited 12/19/2005 9:27 pm ET by csnow
thick socks.
Treat every person you meet like you will know them the rest of your life - you just might!
"thick socks."
Just goes to show, there is a solution for every budget.
Bill Hartman had a good explaination as to why slabs feel cold. I'll add my two cents worth of things we have done.
First are you sure the basement won't flood at some point.
If that's not a concern then I would put down 3/4 inch of foam sheating and tapcon a plywood floor over the top (no furring strips required). Stagger the seams so the joints in the foam don't line up with joints in the plywood. We also cut strips of sheet metal and placed it under the seams between the foam board and plywood to distribute the weight over both sides of the joint. On Another project we splined ends of the sheets, long edge was T&G. We used a finish grade of plywood and poly varnished the surface after installation. The screws were layed out on a grid pattern for appearance and painted black before installation. This sounds like a lot of work but we did a 1200 sq. ft. basement in a weekend and produced a, warm quiet floor that the kids could play on all day long. With some thought you could also add radient heat as well.