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[Dusk Bennett]

I am documenting my stupidity in a public forum in hopes that it will be found for future generations. Some folks are destined in life to serve as an example to others as to what NOT to do. _I have never been that guy_. I'm too smart for that. I'm well educated, have experience in construction, and was well researched when I made the decision to convert my garage into an actual room.

Last week, after 11 long months I finally finished the wiring of my gear and added AC to my room. The room is ready to start work, or so I thought. On Friday I discovered a silent disaster just waiting to pounce.

Some context.

A year ago I planned my buildout from beginning to end. I thought I did a brilliant job too. I bid the project out to several contractors and brought in the guy I felt the best with, designed the room, had a hand in its construction and even did all the finish work on my own. It is beautiful.

Through rainstorms and a few minor screw ups we sealed the lid on Dec 25th of last year. The room was really thought out for STC value. Raised floor, 2x6 24" OC staggered stud walls, 5/8 drywall on RC1 and RC2 (which was it's own battle since the installers had the mistaken notion to hit the studs and NOT the RC), 65 tubes of elastomeric caulking, and 10+ cans of Good Stuff. This room was AIRTIGHT and well soundproofed! In fact it was so tight for the first 6 weeks you could cut the air with a knife because of the sweating wood and paint. After a few weeks of letting the room breathe though I had a nice space to work in. The noise control was really nice too.

Of course the one thing I overlooked was attic ventilation. My contractor advised that at one point I cut a vent into the attic but I figured I had time to bid that out now that the project was done. Plus more holes equals more noise leakage, right?

Well I finally got around to hiring a contractor to install AC last week and in the process we cut into the lid to create attic access. The minute I looked up at the roof sheeting I was mortified. I had levels of mold so high that would make some Katrina survivors shudder. The consensus was that it's cheaper to tear off the roof, disinfect, paint and reinsulate the attic rather than try to remediate the mold (because it's grown into hard to reach spots). As you would imagine in L.A. dollars this is going to be quite an expensive mistake to recover from.

My reason for posting my stupidity is obvious. I gained so much information from this newsgroup (and others) about how to properly soundproof a room but I never stopped to consider ventilation. You can build an airtight space without much effort, but you shouldn't. It is better to sacrifice a few STC points and know that your cavities are well ventilated rather than button your areas up so tight that condensation occurs in invisible areas. Terrariums like this are homes for mold to breed. Codes exist for this reason, I just didn't realize this at the time.

So there you go, my mistake which will cost me thousands and drag out my project for at least another month or two, should serve as an example to others I hope. STC's can come at a price!

[franman]

... Codes exist for this reason..

EXACTLY.. This is why we don't do a residential renovation without the assistance of an architect who understands vapor barriers, dew points and all this stuff... I always say that "I'm responsible for almost everything on this project, but... if there's something that I'm not an expert in, then let's get somebody else to be responsible for that". (Of course, I end up having to become 'an expert' in many new areas every year... it's hard to find good help!)

On a recent project we had a large (volume) of space above the studio rooms in a new-building-construction. There was a lot of talk amongst the design team about thermal conditioning in the 'interstitial space'... It turns out (as Dusk has experienced) to be quite important. We ended up installing two additional air handlers to temper the interstitial space and had extensive discussions about the dew points at various barriers to be sure we weren't setting up a mildew factory. (It has all worked out well so far, BTW.. right Dave??)

In the end, if properly implemented, ventilation of interstitial spaces does not need to be a serious compromise in your sound isolation. Avoid direct holes through multiple layers of the shell (don't put your attic vent directly above the A/C inlet into the studio ceiling, etc.).

Moral of the story is Dusk is right on about this. You do need to consult with an architectural or mechanical engineer when you turn a non-occupied space into an occupied one. It's penny wise and dime foolish to not do this. DIY'ers... knock yourself out on the studio design and detailing... pick our brains about this stuff if you like... BUT GET ASSISTANCE with your building envelope, codes, etc. They do exist for a reason.  

Thanks Dusk!

FM