Staple Up (Tar Paper)

Craig

I have a signed deal to intall a new boiler with staple up radiant on the main level. We showed up to start work and while drilling discovered that the underlayment below the hard wood floors is tar paper. We have heard that heating the floors though the subfloor and tar paper may cause the Tar to Off Gas and produce an odor. IS THIS A CONCERN ???
The house is 1923 with origional floors and TAR.
We plan on staple up without plates (140 degrees) backed with a bubble foil and fiberglass insulation.
How do I find out more info on this subject

Alan(CaliforniaRadiant)Forbes

I've never

tried it, but there have been enough warnings about tar paper here on The Wall that I always check for it and decline to do it if it's present. I'm told that even with plates (~100*) it can be a problem.

It would be nice to hear from someone who's actually installed a system that has tar paper and what's happened.

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Mike T., Swampeast MO

Are you ABSOLUTELY certain

that it's tar paper? Not "red-rosin" building paper possibly looking sort of black from coal burning?

That stuff makes it into some really strange places--to the point you would swear the structure burned at one time. It's worst in structures that used free-standing coal stoves or gravity warm air.

I don't believe that the rosin paper is a problem, but tar paper? Even from 1923 I'd be kind of wary.

hr

It may be a problem

I suspect what you have is asphalt impregnated felt paper, often called tar paper. I have had one problem on a staple up on a 1950 vintage home with this paper. There is a temperature where that paper will start outgassing. The question has been, and still is, what's the number.

I'm not sure there is an exact number. I suppose it could depend on who and how that product was produced. If in fact you are doing a direct staple to sub floor, not suspended tube, you may in fact reach the off gassing tempertaure. I suspect the temperature needed to cause the off gassing is probably hotter than the wood associations recommend for continious temperature in contact with wood anyways.

Personally I think 150 should be the limit for DIRECT contact with wood, but I can't at this time substanciate that number. Plywood and OSB manufactures throw that number around for a confort range under CONTINOUS conditions 24/7, which a floor heat application would be subject to on design days, or weeks.

I have suggested to others that they take a sample piece of the underlayment paper and heat it up in an old electric fry pan with an accurate thermometer, maybe an infared. Then you would be able to see first hand where the paper starts to "squirm" and off gas.

Other than that it's buyer beware

The job I mentioned above was my brother in laws own home. He cranked the boiler to 190 one weekend and opened all the doors and windows and let er off gas for a day. That was 8 years ago and the job has been fine since then. Don't know that I would recommend that for you customers tho

I think using plates on a reset control with a not to excees temperature programed in would be one safe way to approch the job. You may need supplemental BB or panel radiators to meet the load on a design day, however. An accurate heat loss calc would help point the way. Hopoe this helps

hot rod

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