Do you mean a foot of soil ABOVE the matting? Don't you think the weeds will still grow above the matting?
In my experience weeds grow in the upper layer of the soil. If you want to suppress weeds in a new raised bed, then newspaper or cardboard would be better, as the will rot. Weeds growing above weed matting will put their roots down through it, and become extremely difficult to pull out. I have used weed mat under shredded bark for paths and ended up with a matted mess of weeds and had to roll the whole lot up and burn it. My paths now have newspaper under bark chips. I can pull the weeds out.

If you're talking about weed barrier fabric, that is laid on top of the soil and you cut holes in it where you want plants, and then usually mulched over for appearance's sake, I HATE the stuff. For a number of reasons: (WARNING: Ranting ahead!)
-Once you've got holes in it for the plants, the weeds come through, too.
-Weeds will grow in mulch, then sink their roots down through the fabric, making holes in it for more weeds. Crab grass is really good at this.
-The mulch breaks down and becomes soil, which the weeds will be even happier with. Putting soil over the fabric from the get-go will just speed up this process.
-Some ornamentals will try to spread roots on top of the fabric, and inevitably, they can NOT sink their roots through, and start to die. Just yesterday, a friend mentioned to me that her hydrangeas were all doing this. And in the beds at our new place, some old clumps of iris had tried valiently to spread over the top of the fabric, succeeding only because they managed to send roots through the foot+ of mulch the the previous owner put there. Not pretty.
-Plants' growth and spreading is limited by the size of the hole in the fabric, so you have to divide more often or enlarge the hole.
-Over time, the fabric breaks down and falls apart, making it nearly impossible to remove.
-Even intact, it's nearly impossible to remove once you have plants in a bed, or the mulch breaks down and becomes soil.
-With the fabric, I can't keep changing my mind about where I want plants - the holes are there and making more holes defeats the purpose. And I love to change my mind.
-It's not cheap.
-It's a pain to install.

Bottom line: it might work for a short time, but then it requires as much, if not more, maintenance than a bed without it would. Therefore, I mulch with more traditional mulches that break down and improve the soil and are often free (newspaper, cardboard, wood chips, shredded leaves, grass clippings, etc.), and weed as needed. Not mulching directly over the irises, of course. But between the clumps and in paths, it sure cuts down the weeding in those areas!

Sorry to be so negative about the stuff, but I really do despise it. The new place we just bought has lots of established perennial beds - ALL landscape fabricked several years ago, and now they are a mess, with over a foot of mulch and soil on top of the fabric, weeds growing like mad, and I can't get it out without destroying the beds completely. And in the meantime, I can't plant anything in those beds because the fabric is almost too deep now to dig down to put a new hole in for a plant without a backhoe.

*End rant*

Diana

Wow! Thanks for your replies.
I was thinking of laying down matting...then put about a pile of dirt like a raised bed( 2 foot) , then rhizomes. Not the mat/hole method.
I also have landscaped areas in the yard of house we bought, that I will have to tear out the matting to rebuild/replant beds! I am saving that for next year!
Thanks again
Rae Ann