Low-E Slab Shield - heatboy

heatboy

I'm now officially hooked on this stuff. Easy to work with, great R value for it's thickness and, most importantly, I am now in control of insulating the slabs. 3/8" has an insulating value of 2.5 The concrete guys love this stuff also. Final grade doesn't have to be perfect and there is no cracking of the insulation as with polystyrene. Another thing about Slab Shield is the 3/8" has a crush rating of 10K lbs. psf. and the 1/2" is 7K psf. They also have duct wrap, house wrap and other goodies.

hb

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hr

I'm shocked! First Cheese now you. Wheels wouldn't have any thing to do with this revolution now would he.

hot rod

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heatboy

Teamwork

No, hr. He supplied it, but we discussed all of the available materials and options before this was decided on. Insul-tarp was near the top of the list, but their reluctance to confirm any kind of insulating value for their product makes me nervous. That, and the rep for Insul-tarp here is a complete idiot ;-)

hb

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John Ruhnke1

What thickness would make R-10?

HeatBoy,

Why do you like Low E slab shield? I use Dow Blue Board 2" = r-10 or it is r5 per inch. 3/8 times 4 = 12/8 or 1.5" thats a savings of 1/2 an inch. Do they make it in differant sizes or would I use four layers to get r-10. How is it with termites? I know in some areas they don't like dow blue board because of termites. What about cost compared to Dow Blue Board?

JR

heatboy

At what point.............

> HeatBoy,

>

> Why do you like Low E slab shield? I

> use Dow Blue Board 2" = r-10 or it is r5 per

> inch. 3/8 times 4 = 12/8 or 1.5" thats a savings

> of 1/2 an inch. Do they make it in differant

> sizes or would I use four layers to get r-10. How

> is it with termites? I know in some areas they

> don't like dow blue board because of termites.

> What about cost compared to Dow Blue Board?

>

> JR



is there a diminishing return for insulation. I firmly believe the every slab should be insulated. But how much? I think we can agree that all insulation does is slow down the rate of heat transfer and that the soil under the slab will eventually catch up and start to create a heat sink. At that point, what is the difference between R 2.5 and R 10. I know of slabs with no insulation that work just fine. Maybe keeping slab temps as low as possible via reset controls is more important than insulation values? Don't know. I have more questions than answers.

Things like Slab Shield and Insul-tarp are much easier to get to a jobsite, to work with and, as I said above, the concrete guys like it and final grade is not as critical, which helps a great deal when it comes to "gettin' along".

hb

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heatboy

At what point.............

is there a diminishing return for insulation. I firmly believe the every slab should be insulated. But how much? I think we can agree that all insulation does is slow down the rate of heat transfer and that the soil under the slab will eventually catch up and start to create a heat sink. At that point, what is the difference between R 2.5 and R 10. I know of slabs with no insulation that work just fine. Maybe keeping slab temps as low as possible via reset controls is more important than insulation values? Don't know. I have more questions than answers.

Things like Slab Shield and Insul-tarp are much easier to get to a jobsite, to work with and, as I said above, the concrete guys like it and final grade is not as critical, which helps a great deal when it comes to "gettin' along".

hb

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hr

Exactly right HB. At some point in the heating season the temperature under an insulated slab will be exactly that of an un-insulated slab, regardless of the R-value. Insulation merely slows the process, it cannot stop the heat flow. Years ago Larry Drake experimented with this at Infloor. In Minnosota conditions he found right around 30 days the temperatures under both applications equalized. So many factors, almost impossible to model downward heat flow thru the soil, geo engineers tell. Soil type, moisture, temperatures, etc etc.

Having worked with foamboards for years, I will gladly trade some R value for installation and integrity of the foam after considering the handeling, foot traffic, and pest issues.

A big issue controlling the downward heat flow is the R-value on top of the slab.

hot rod

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Art Pittaway_2

Insulation under slab

isn't installed to prevent the transfer of heat...because we all know it can't. But, it should direct that flow where you want it to go to. That is where the discussion on responce time comes up. No insulation and you raise the temp of a ton of ground 3 degrees or with insulation you raise 400 lbs of concrete 3 degrees and let the ground catch up later.

Dave Yates (PAH)

Just thinking that water tables present close to a slab might dictate the need for higher R-values. We always install, or have made the GC responsible to install, a network of perf pipe (typically 4") to ensure complete drainage of under-slab areas. We hit a spring when we built our home, so we raised the entire structure an additional 2', which made my concrete footers 30" thick! I've got 1,200 ft. of perf pipe that collects to a 6" main. In extremely heavy rains, that has run almost full bore! But thinking outloud, what if the water table did rise to within 4 or 6 inches of the slab and is drained away - wouldn't the heat transfer accelerate as the moisture and water approached the slab? Other tan that, I'd be inclined to agree with your idea that the ground can or will attain near surface floor temps - with the exception of perimeter areas at or only slightly below grade.

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hr

I would guess, Dave if the water table approches 4-6" of the bottom of a slab, and is drained or pumped away it is draining away substancial btus from the slab, and the ground beneath it! That would be something that I would
look to address around the outside of the building somehow. Maybe a sump pit and drain field, outside the building, deeper than the slab level by a few feet that would collect that water before it got under a slab. If not maybe radiant floor heat is not a good match for this application.

I'd consider collecting this heated ground water in a pit, throw in some copper coils and preheat your DHW with it, becaused they have payed for those btus that are draining or being pumped away capture some btus before they all get away

I remember an entire subdivision built around a golf course in a low lying area of Park City. The key here was to convince your neighbors into installing their "bigger is better" sump pumps a foot deper than yours. This way they footed the electric bill to lower the adjacent neighbors water table Wonder how deep those sumps are these days!

hot rod

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heatboy

If the water table..........

is that high, insulation of any resistance will be of little use, methinks. Radiant would probably not be a good choice for heating that potential swimming pool ;-). My point was, when you weigh all of the issues surrounding slab insulation, I believe the trade-off in resistance is more than made up with all of the beneficial aspects of these types of insulation.

hb

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heatboy

Concrete pours

How many of you are on site when the concrete is poured? Do you add money in the project for stand around time? I usually stop by the site before the actual pour just to check manifold pressures, but I don't normally hang around. I always ask if someone wants to pay my fee for being there, but seldom does it happen. I have never had any issues during the actual pour, so being there, to me, is not beneficial. What do you guys do and how do you handle any fees for it?

hb

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hr

I like to be there for the pour. I don't make all of them, however, as scheduleing around the weather for them is always the factor. I do leave a few repair kits with the concrete crew if I can't be at the pour.

I do take my concrete boots and help with pours. I think the concrete guys appreciate another hand, and it puts them in your corner concerning radiant. The general contractor or homeowner appreciates the willingness to help also. Some concrete guys will whine about pouring over radiant and the insulation, mesh, etc. ete, but not if you are at the pour:)

I generally buy lunch for them or refreshments, it's good pr and helps spread my name as the radiant guy. I've gotton more than one job from concrete contractor leads.

I don't charge extra, it's all in the overhead calculations

hot rod

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heatboy

Adding the time in the overhead.

hr,

Do you figure full rate or a partial rate for this? On this pour, if I added my charge for being there, it would have added another $600 for the half day the pour took.

hb

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Riles

Insole test

Yes, it is very forgiving versus the hard polystyrene. I just worked on a job this Saturday for a slab job.
Believe it or not, I was floor conditioning my Master Bedroom in a retro install using Wirsbo's Quik Trak and didn't want to pull up all the sub floor to insulate. So I experimented with Low-E. I like the density versus the other "Bubble Type". I stapled down the Low-E then screwed the Quik Trak down. It was a little tricky as it does give some so I had to make sure not to over screw any corner. I then put a floating wood floor down and it is remarkable firm.
Finally, did you first cut out some insoles for your shoes for the ultimate test discussed after this year's R.P.A.? Let's hope not.

Riles

Big Labor Savings

This type of product is much quicker and easier to work with. It comes in rolls. Just roll out and cut. VERY FAST. Easier to transport. Big labor savings, important whether you do it or the G.C. coordinates it being installed as the area is being prepared. Only down side is the Wirsbo "Fish Hook Type" Staples are designed for 1" Polystyrene. So with this type product we have stuck with wire mesh.