zombiescustoms
Well-known member
Can I use 2" Polyisocyanurate insulation, under my slab for radiant floor heat insulation?
Polyisocyanurate under slab??
- Thread starter zombiescustoms
- Start date
Someone asked a similar question recently and my knee-jerk reaction is no.
Of course you have to question it, but if you read the Wiki Article on Polyisocyanurate the uses it lists are not really high compression applications like the foam will experience under a concrete slab.
Of course you have to question it, but if you read the Wiki Article on Polyisocyanurate the uses it lists are not really high compression applications like the foam will experience under a concrete slab.
Use high density XPS (extruded polystyrene). It is designed to carry the load of the slab and can be in direct contact with soil and moisture without breaking down.
Polyiso isn't designed for that use and is primarily used in walls and some roofing structures. Check out the Polyisocyanurate Insulation Manufacturers Association (PIMA) website at http://www.pima.org and you will find they don't mention it being used in floors... only in walls and some roof designs.
Polyiso isn't designed for that use and is primarily used in walls and some roofing structures. Check out the Polyisocyanurate Insulation Manufacturers Association (PIMA) website at http://www.pima.org and you will find they don't mention it being used in floors... only in walls and some roof designs.
OP
zombiescustoms
Well-known member
Well I called DOW and the said no, because of the reaction of the foil and wet concrete, who carries 2 inch polystyrene? i have not seen it at the dopot or lowes and 84 lumber wants me to order a minimum of 96 sheets.
I had some left over from a job, its now under my sidewalk. Works fine.
The only thing is, it absorbs water. SO if you have a wet location I wouldn't use it. If its only wet in spring it should dry out.
tdkkart
Well-known member
You got Menards around you?? They carry the 2" pink poly. Our Lowes and HD do not carry it either.
OP
zombiescustoms
Well-known member
no Menards here in MD the best price I have found is over $1700 for 48 8x4 sheets, I'm starting to rethink this whole floor heat thing!
Look for some plumbing and HVAC companies. I got my polystyrene from a tile/plumbing/hvac place that sells retail, wholesale and does installs. Throw some lines out and ask around, someone will know someone who might know someone who knows something. 
hidollartoys
Well-known member
Price does not sound THAT bad. That stuff is expensive. These shops are expensive when done right.
That price is pretty bad. I paid less than $1k for 42 sheets at Menards (on sale). IIRC your shop is smaller than mine, so you need even fewer sheets and I'll actually be returning 3 sheets (was able to use my 'waste' to insulate the sides of the slab). Might want to check their site to see where the closest Menards is...might be worth a road trip.
OP
zombiescustoms
Well-known member
I just started my build and have decided to scrap the in-floor heat and use the money for a bend-pak lift.
nate379
Banned
http://www.insulfoam.com/images/stories/docs/6081_RT_IV.pdf
This is what is commonly used around here. It's around $20 for a 4x8 2" thick sheet.
I'd take in floor heat over a lift ANY day. I can put a lift down the road when I have the money. Floor heat... not easily done after the fact. I suppose it depends where you live of course. If you need to heat only 1-2 months a year, might not be worth it.
This is what is commonly used around here. It's around $20 for a 4x8 2" thick sheet.
I'd take in floor heat over a lift ANY day. I can put a lift down the road when I have the money. Floor heat... not easily done after the fact. I suppose it depends where you live of course. If you need to heat only 1-2 months a year, might not be worth it.
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OP
zombiescustoms
Well-known member
I'm in Maryland, and we average 35deg in the winter, it will have 6in insulation in the walls and ceiling, I'm going to use a pellet stove or wood stove to heat it.
HoosierBuddy
Well-known member
I bought my 2" high density polystyrene from the concrete company.
Radiant heat is the berries.
That being said...there are certainly cheaper ways to heat a garage.
Phil
Radiant heat is the berries.
That being said...there are certainly cheaper ways to heat a garage.
Phil
That was my thinking. I ended up over budget on the building due to zoning restrictions (hoped I'd have a enough left over for a lift) so it won't get the lift or the rest of the heating system until next year (may be able to swing the rest of the heating system if I can pick up some side work and/or sell some excess Jeep parts), but the key for me was to at least have the insulation and PEX in place since you can't really go back and do it later cleanly/cheaply. I had a furnace in my old garage and it was great...until you needed to get down on the floor. One of my buddies in WI had extended his garage and put in the in-floor heat and I had one of my Jeeps up there for a while and it was a joy to get down on the floor in there.
nate379
Banned
Yeah. Over are my days of laying the floor freezing my **** off. It's either crank the heat to 90* and sweat your nuts off when working standing up or leave it at 70* and wear Carhardts while laying down.
Not so bad with a lift, but cold feet all day aren't fun either.
Not so bad with a lift, but cold feet all day aren't fun either.
boiler7904
Well-known member
The other thing to consider is that most of your heat transfer out of the building slab is at the perimeter where the top few inches of the foundation is exposed. You might be able to get away with just putting down a 4' strip under the slab at the perimeter of the building and a lining the interior face of the foundation walls themselves from the bottom of the slab to the top of the footing. Putting insulation under the slab usually isn't done around the Chicago area due to cost. You reach a point of diminishing returns where the extra insulation won't help stop the transfer of heat enough to justify the cost.
Going on your order for 48 sheets at 32 sf per sheet, you have a building in the neighborhood of 1,500 sf. Heat isn't really going anywhere in the middle of a slab that large. The soil underneath it is going to stay a pretty constant temperature in the mid 50s year round.
Going on your order for 48 sheets at 32 sf per sheet, you have a building in the neighborhood of 1,500 sf. Heat isn't really going anywhere in the middle of a slab that large. The soil underneath it is going to stay a pretty constant temperature in the mid 50s year round.
fordsteel
Well-known member
You can just insulate the edge 4 feet of your slab and the edges with 2" exp polly
and just put a 6mill vapor barrier under the entire area
this is a great alternative if you will be heating the space all the time.
the center open area will heat the earth under the slab. this heat is not lost tho but stored in the thermal mass. this is very favorable in places that have many power outages. because with the amount of heat stored in the ground you can make it about 2.5 to 3 days in the building before it freezes up.
the down side to this is that is your heat is kicked down at times or turned off. it takes a much longer time to bring the space up to temp.
I just did a radiant slab for my new garage this weekend 36x50. I insulated the whole thing with a product called "the Barrier" I hear good things about it I would never use exp polly myself. the barrier cost me $149 per 4' x 60' roll it is thinner then exp poly and dose not crack to **** when you work on it. also has a higher R value then exp polly so it dose not need to be as thick.
this is what it looks like its 3mil plastic then 3/8" urethane based foam and then another 3 mill of plastic and it peel and sticks to the roll next to it
and just put a 6mill vapor barrier under the entire area
this is a great alternative if you will be heating the space all the time.
the center open area will heat the earth under the slab. this heat is not lost tho but stored in the thermal mass. this is very favorable in places that have many power outages. because with the amount of heat stored in the ground you can make it about 2.5 to 3 days in the building before it freezes up.
the down side to this is that is your heat is kicked down at times or turned off. it takes a much longer time to bring the space up to temp.
I just did a radiant slab for my new garage this weekend 36x50. I insulated the whole thing with a product called "the Barrier" I hear good things about it I would never use exp polly myself. the barrier cost me $149 per 4' x 60' roll it is thinner then exp poly and dose not crack to **** when you work on it. also has a higher R value then exp polly so it dose not need to be as thick.
this is what it looks like its 3mil plastic then 3/8" urethane based foam and then another 3 mill of plastic and it peel and sticks to the roll next to it
tcianci
Well-known member
I have seen Polyiso soak up water on a failed roof. So even if it can take the compressive forces, the insulating value goes to nothing if its soaked however the chances of it getting soaked under the floor are slim so I think the compressive strength would be the limiting factor.
KELLHAMMER
Well-known member
I think more insulation makes for a more efficient system. A slab with no insulation will retain less heat and the heater will cycle more. My garage is 2 spaces and 2 zones over 1500 sf. I used 2 inch rigid Dow foam. Not polyiso. Under the entire slab. The edges got a 1 inch board of the same stuff. The walls are R-19 the ceiling is R-30. I run it at 55 in the dead of winter and you can walk around in a tee shirt. The system is quiet and theres no fumes or pollutants. I leave it on, since shutting it down requires a day to bring it up to temp from dead cold. I used to use a garage with a wood stove it would that a hour to get the space up to temp and it was about 500 sf it was a real pain. Not including the insulation my system cost 2800 installed. Thats for radiant piping, an 80 amp modulating elect boiler, 2 circ. pumps and all the controls. Which I installed on my own. The building has 2nd floor. Which I planned to heat separately. But it gets warm just from the heat rising from the garages below there ended being no need for it. Granted, the 2nd floor is just more of a storage area / hangout space but sufficient More than one expert told me I would have problems and the quotes I got to do their system system, installed, were anywhere for 15k to 20k. So far the system has been in for 5 years and it added 100 dollars a month to my elec bill for Dec thru Feb.
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5wndwcpe
Well-known member
I had ordered mine at Home Depot. It was 48" x 96" x 2" and I had to buy it in a lot of 48 pieces, as that is what comes in a unit.
Steve in Mi
Well-known member
Insulating the floor is a good idea for comfort. HOW YOU HEAT THE SPACE IS AN ENTIRELY DIFFERENT AND SEPARATE ISSUE. oops! cap lock mode mishap.
hi guys. i'm late to the party, but i am about to build a 22x44 workshop and plan to install solar thermal collectors on the roof to heat the shop in the winter and a pool in the summer. insulation is very important for me since the amount of solar energy is somewhat more limited.
from my research...the most important area, as already mentioned by some is the foundation. and it is best insulated from the outside. if you have not started your build, cantilever the wall framing so you can get at least 2" of xps around the perimeter.
if your shop is completed, you can insulate the footings as far down as possible...or go 2 feet down AND THEN go 2-3 feet HORIZONTAL from there and you will get the most bang for your buck.
i am planning on r-32 walls and r60+ attic.
here are a couple of links...one on a CHEAP way to insulate walls if you are doing a new build and one on heating/insulating a concrete foundation and slab
poke around this site and you will find lots of great info on radiant slabs http://www.radiantsolar.com/index.php
this site is primarily about solar heating, but along with that goes efficient building so the sizing of heating systems can be smaller. any cost in associated in making the building more efficient will pay back for the rest of its life and that says nothing about what the resulting comfort is worth to our weary (or not so weary bones!)
http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm
from my research...the most important area, as already mentioned by some is the foundation. and it is best insulated from the outside. if you have not started your build, cantilever the wall framing so you can get at least 2" of xps around the perimeter.
if your shop is completed, you can insulate the footings as far down as possible...or go 2 feet down AND THEN go 2-3 feet HORIZONTAL from there and you will get the most bang for your buck.
i am planning on r-32 walls and r60+ attic.
here are a couple of links...one on a CHEAP way to insulate walls if you are doing a new build and one on heating/insulating a concrete foundation and slab
poke around this site and you will find lots of great info on radiant slabs http://www.radiantsolar.com/index.php
this site is primarily about solar heating, but along with that goes efficient building so the sizing of heating systems can be smaller. any cost in associated in making the building more efficient will pay back for the rest of its life and that says nothing about what the resulting comfort is worth to our weary (or not so weary bones!)
http://www.builditsolar.com/Projects/SolarHomes/LarsenTruss/LarsenTruss.htm