Ignore this post. It is a repeat which reposted when I used the back button on my browser.

azstoneconsulting, I was reading the comments you made regarding counterbalance island bracketts on their web site and you mention that MIA recommends marine quality plywood, although it is an overkill. I called the local Lowe's and talked to the manager, they can special order marine quality 5/8" for $73.53 and special order 5/8" ACX plywood for $48.88. The cost difference is not enormous, do you think it would be better to use the marine quality? I know nothing about marine quality and have not even seen it, is is harder to cut? Does it give? Sometimes more expensive is not better for the situation. After all that I have been through regarding this counter top, I want to make sure I never have to do it again!

The correct term is roofing "underlayment" commonly used under asphalt or slate roofing shingles. It can be made of permeable asphalt-saturated cellulose (felt made from recycled cotton rags is no longer available nor is coal tar) or it can be made of impermeable synthetic materials. In a cold climate the lower part of the roof at the eaves and at the valleys is covered with self-adhering flexible flashing (Grace Ice & Water Shield or its imitators) and the rest is covered with an underlayment. I am in MA and typically from here and to the north the entire roof is covered with I&WS. Building paper underlayment has several standards and you are not likely to get much asphalt in the material if you specify #15 (no longer called 15# since it doesn't weight 15# per 100 s.f. "square"). A better spec is #30 which is less than 30# but heavier than #15. There are many superior products available but the the biggest problem with today's asphalt-saturated paper is that it is made from the residue from oil refining and the quality of the asphalt has dropped as oil refining techniques improve to meet the challenge of lower fuel prices. There will inevitably be a point where it is no longer an acceptable material for use as roofing underlayment. IMO that happened many years ago. If you are comparing bids, the bidders should have been told what the underlayment will be and what quality standards must be met. Leaving it up to the roofer is unwise. In order to control the quality of the project you must control the design shown on the bid documents. Where is the project located? Here is a discussion of asphalt-saturated roofing underlayment.

I'm assuming the cork will be UNDER the heat mats...and then the heat mats will have the hardwood OVER TOP? Cork is rated for in-floor radiant heat....but I always worry about putting electric heat mats DIRECTLY over a product that will CATCH FIRE! Yes. Electric heat mats have a long and glorious history of "shorting out" (although I must admit they are getting much much better) which can cause a spark. Cork doesn't like to burn but it CAN burn and it WILL burn if something is hot enough and allowed to sit long enough (like a sparking electrical wire sitting underneath hardwood). For that reason, I have always said that cork should be encased in concrete if heat mats are being used on top. I always err on the side of caution with fire ratings. The next thing you MUST do is to find out if the FELT material is rated for in-floor electric heat (many are not because they are made up of mixed fibres like PLASTIC = they can melt). And then, finally please check to make sure your engineered hardwoods are rated for ELECTRIC in-floor radiant heat. Many are NOT. Many ONLY ALLOWED the hydronic heating system (water/oil/gel filled tubing). I'm sorry to say but the BIGGEST problem isn't the cork or the hardwood or the felt. It is the ELECTRIC heat-mat system. More than 30% of flooring products on the market do NOT allow use with ELECTRIC heat-mat systems. The heat produced is often TOO HOT and the wires themselves are too delicate for use under many floors (delicate wires break = sparking = fire hazard). Ignore the heat-mat company's advertise. Investigate the OTHER materials used below/above the mats. I think you will be surprised what you find (or don't find...many do not allow this type of install). Personally if it were me, I would work with 1/4" cork and upgrade the wall heaters with lovely little baseboards that are efficient. The cork + new heating baseboards = wonderfully efficient. Save the $10K from the heat-mats and invest a little bit into upgrading the baseboard heaters. Cork will do the rest - both thermal and acoustic insulation all in one product. Skip the electric heat mats.