Plastic needed for radiant slab on grade?

GW

going to pour a slab mid next week for a basement job. The builder asked if we should put some plastic down, any comments? Thanks.

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Chris_82

Insulation?

Generally the contractor should or it has been reccomended to lay down what is know as contractors cloth. It's this very heavy duty nylon reinforced plastic sheeting that can not be found at your local store. It is a pleasure to walk on as well. Then depending upon budget, what type of insulation on grade, the pink stuff or the 2" blue stuff, I like the blue stuff 2" and around the primeter as well. then the tubing or if your in a race with the contractor, the wire mesh, or whatever works out so that you can keep a carefull eye on sharp corners and burrs etc. Ty wrap, plastic is preffered, but some use the wire, personally this makes me nervous to use wire. Many like the mesh or wire reiforcment down first to ty the tubing onto? Is this making any sense? I like to see a box around the area where the tubing comes up from underneath, we used to like to see individual zones in insulation, but now a box that later gets filled in with grout or cement at a later date. It seemed that we had more problems with the vertical penitrations than the horizontal sections in the below grade box. Mostly others hitting the tube as it comes out of the slab.

ALH_4

off the subject, but...

Anyone else notice you get a worse sunburn from that short wavelength reflection off the blue foam than the longer wavelength off the pink foam?

GW

yes

2" on the vert and 1" on the flat. It's just the poly I was wondering about.

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GW

Now that you mention it, no, i never noticed!

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ALH_4

beyond the pale

With my pale skin, I'm like the canary in the coal mine.

Constantin

I would...

... put down 6 mil of PE with taped seams on top of the insulation.

Depending on the part of the country you're in, I'd also install some 4" perf pipe at the footer level to collect any radon. Terminate it in solid 4" somewhere convenient in case radon does ever become an issue, it'll save thousands. I didn't install a lot of pipe (the crushed gravel below the slab insulation works very well for permeating the gas), just made sure that every section below the slab had some pipe in it (we have running footers traversing the basement).

The PE may or may not be necessary if you are insulating below the slab. I believe that building science corp. does not think it's necessary unless Radon is an issue. However, I'd check out their site and documentation for more inspiration.

kevin coppinger_4

not to be difficult...

but I would put the polyethylene down 1st then insulate on top of the poly w/ blue board both floor and perimeter...it will keep out the moisture from the foam board. Seems like a minor thing but I do belive it is important to do it that way....kpc
-Actually weather you do radiant or not you should put down the poly to keep the moisture away from thing in the slab.

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Chris_82

Andrew?

When is your web site going to get done, so far it looks nice.

Troy_3

poly

I've always recommended 6mil. poly on top of the insulation. I assumed you always install vapor barrier on the warm side of the insulation. I could make a case to go either way but I think it was a Dow guy at an RPA session years ago that said vapor always on the warm side. Opinions? Does anyone else recall this comment?

jp_2

but, in this case

aren't you trying to stop moisture from below, coming from the soil/rain/snowmelt. I'd agree with poly,insulation,slab.

[Deleted User]

Vapor barrier...

Do youhave a shallow water table that cold wick away paid for energy? Even if only seasonal?

Had a job once for a former employer who had no cajones and would not require things like insulation or vapor barriers. We did a RFH system on a slab on grade home next to an empty irrigation canal. In the spring, when the canal filled up, the guys gas bills doubled, and the comfort factor went way down...

If in doubt, put it down. Cheap insurance.

ME