Construction Help

Hi, I have read the FAQ and help sections and have found alot of useful information although a little confusing at times. I now have a concrete bae 16ft by 9 ft to build upon a soundproofed room. From reading the site 2 leafs are better than one which I can understand from the graphs. The part that confuses me is the definition of an "air gap". I had originally planned on making (from outside to inside) a wall with wood cladding, vaporshield plaster board and acoustic sound board screwed into the timber studs which will be 2x3", filling between the 2x3" frame roof insulation but so it doesnt pertrude the frame itself. Then an air gap of 2" to another timber frame with more roof insulation attached, then having rc channel on the inner side (the actual iside of room) mounting more plasterboard, acoustic sound board and possibly another medium to the rc channel. Would filling the gaps between the stud frames lower the t&l, not the air gap of 2" (I can draw a diagram if needed). Also I read that screwing into the timber can greatly decrease the t&l of the structure but it also says not to use 2 rc channels in the walls as this also has a negative effect. I hope this made sense but if any diagrams are needed I can draw them as it did confuse my dad when I explain it to him asI'm not very good at explaining. Thanks Nick

How are you calculating your 2" air gap? It is supposed to be measured from the back of the outside wall (the one closest to the inside of the room) to the back of the first layer of drywall (or whatever) on the inside wall. In other words, it's not the gap between the two frames but the gap between what you hang ON the frames. It sounds like you're on the right track with the possible exception of the "sound board." I believe it's been determined here that you get more for your money with plain drywall. You also want to make sure that the two walls never touch in any way (with the possible exception of the insulation between the studs). Since you already have a slab, the walls will share a floor but that should be the only place. The inside structure should be strong enough to stand on it's own. len

I was using the 2" gap as between the wooden frame themselves and the total gap would be about 8". The soundboard my dad and I were both wrong on we thought it was solid board it is infact just slabs of insulation. We were thinking of putting this inbetween each individual frame if you get me like you would a normal wall but leaving a 2" gap between the actualy walls (if that makes sense) would this be ok or would this decrease the t&l loss.

Nick Garland wrote:

I was using the 2" gap as between the wooden frame themselves and the total gap would be about 8".

More like 7"... 2x3 lumber is 1 1/2" x 2 1/2" nominal. 2 1/2" + 2" + 2 1/2" = 7". Personally, I wouldn't mess with 2x3s -- I'd use 2x4s.

The soundboard my dad and I were both wrong on we thought it was solid board it is infact just slabs of insulation. We were thinking of putting this inbetween each individual frame if you get me like you would a normal wall but leaving a 2" gap between the actualy walls (if that makes sense) would this be ok or would this decrease the t&l loss.

Are you describing a four leaf wall assembly?? :shock: Also, it's not "t&l loss"... It's just "TL" which is short for "Transmission Loss." Also, if you're using separate frames, you don't need (and don't want) resilient channel ("RC"). I might humbly suggest you read and study more here before you build anything. You're getting some concepts but I fear you're missing some very important pieces of the puzzle that could really cost you. Not to discourage you from asking questions -- we're always happy to answer -- but it takes days, weeks sometimes to even start to get it. That was surely the case for me fifteen months ago! :idea: --Keith :mrgreen:

Thats where the problem is the more I read on here the more I get confused as I read on here to use resilliant channel and originally I wasnt planning to due to the double leaf wall, so I was unsure on this. Now I know not to like I originally had intended. As for the quad leaf thats was Im asking about. Is placing roof insulation in the 600mm gap between the uprights on each wall classed as part of the "air gap" or would this turn it into a quad leaf wall? (Hope this made sense the 3rd time round Im useless at explaining) Thanks for the help Nick

As a general guideline, any insulation that is less than say 8 or so pcf would be considered "air" and not a leaf. If it gets any denser than that, the answer gets cloudy. len

...and, really, if it's closed cell foam, you can't blow air through it, and therefore it's considered a "mass" and not "air" in the mass-air-mass equation. Believe me, I do understand and sympathize about the confusion. It takes a lot of study to get this stuff down. Have you bought Rod's book yet? If not, buy it today. You'll be so glad you did. --Keith :mrgreen: