# Riser Construction



## fax6202 (Apr 5, 2012)

I have read all that I can find in the forums about construction of risers and the only thing that I have come up with is to use roofing felt on the concrete floor to protect the lumber. I know that i could always use PT lumber but I would rather not. Does anyone have any suggestions/recommendations on what to protect the lumber from the bare concrete. Thanks.


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## bpape (Sep 14, 2006)

You need something between the cold, wet concrete and the wood, Felt is cheap. Just also remember to insulate the riser rully and use seomething like 2 layers of 3/4" MDF for the top plate to keep it rom resonating.


Bryan


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## ALMFamily (Oct 19, 2011)

Not sure what you are looking to spend, but I have found a couple things that you might be able to use.

The first is a Dri-Core underlayment that creates a gap with an air pocket to allow air flow through to help get rid of any moisture. You can then build the riser on top of it. This might be fairly costly - in the few hundred dollar neighborhood. More info can be found here.

The second is something called a U-Boat that can be found here. Now, their purpose is sound isolation but they may work for you to suspend your riser. I have not priced them out so I cannot provide you that though.

Hope that helps!


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## fax6202 (Apr 5, 2012)

are there any materials that you would recommend? I am fine with not using felt, i want to make sure there is no moisture problems in the future


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## fax6202 (Apr 5, 2012)

I like the idea of U-boats. If they can serve as an acoustic improvement and moisture control that would be great. Does anyone have information on their performance concerning moisture prevention?


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## ALMFamily (Oct 19, 2011)

I have only seen one person that had considered using them - it was in this thread. Bryan might be able to anwer your question, or I might suggest contacting the vendor and asking them.


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## fax6202 (Apr 5, 2012)

Thank you.


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## ALMFamily (Oct 19, 2011)

You bet - good luck! :T


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## Anthony (Oct 5, 2006)

The U boats are common, I didn't use anything on my last one, but the concrete floor had vinyl tiles on the concrete, so there was a moisture break to the wood.

In construction, the common practice is the plastic / spongy roll between the wood and the concrete. Hard core foam also works and dri-core gets good reviews although I haven't worked with it.

The U boats are your best bet for full de-coupling though.

As for resonance, keep with 16" centers to support the plywood top. Install blocking between them to further stiffen and prevent resonance. Finally, on the second layer on top, stagger the seams.

Other things to consider: Add the smurf tube or other conduit to allow for electrical runs (if you want a data jack, control port, audio dock, whatever). Also, if you use plywood for the top, you can have a small overhang, which looks nice once carpeted. Only with plywood, though. MDF is too weak on the edges to support a lip like that.

Good luck!


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## fax6202 (Apr 5, 2012)

So the U boats would be ok for moisture? also, to be honest I am not doing a whole lot as far as acoustics. I will have a decent system but i havent used green glue or double drywalled, bass trap etc. So since that is the case would i be wasting my time with the U-boats or does every little bit matter. If i do use the U-boats how would i fit them on the outside/plates of my framed riser, as they would get in the way of carpeting/fabric/trim.


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## Anthony (Oct 5, 2006)

That last part I'm not sure of, but they are fine for a thermal/moisture break. Direct contact makes the wood wick up the moisture and then stays wet all the time. This is when rot sets in. 

If you have them under the "joist" part of the riser, you may not need them on the face plate. Hopefully someone who has used those can chime in, though.


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## fax6202 (Apr 5, 2012)

Thanks. I think on the joist would be ok as long as they are spaced evenly and can be very close to the plates...just not actually on them. Baseboard will take care of the gap. And the more that i think about it I would like to work in some acoustics into the room considering it is a complete dedicated HT


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