Questions for Rod Gervais about his book, Build it Like the Pros

[naethoven]

IF THIS IS YOUR FIRST TIME ON THIS THREAD, READ THIS.

This thread is dedicated to people who have read Rod Gervias' book, Home Recording Studio Build it Like the Pros, and have more questions to go deeper or to gain clarification of something in the book. I know a lot of us on GS have read this book and constantly recommend it to others on the site. While I was reading it, I was wishing I could ask Rod some questions about things he covered that I wanted further information on. I figured there were a lot of us who would be interested in that, so I contacted him and he agreed to help us with this thread.

Please feel free to post questions you have specifically about things in the book here for Rod to answer. Since Rod does have a life outside of reading GS all day, he may not be able to respond every day. But post your questions and he'll do what he can to help us grow in our knowledge. When you post, please try to reference a page number from the book so the rest of us can follow what you're talking about. You may want to include Google Sketchup pics to get your point across. Also, please be respectful of Rod's time by doing your homework and reading what he wrote about your topic in the text before posting. And, be sure to reply with QUOTE when continuing a conversation about a particular question. A note: This is not the place to have your entire studio build thread. Please use this thread only for discussing questions directly about the book. What a unique opportunity it is to have direct contact with the author of the book!

If you do not yet have Rod's book, it can be purchased from Amazon.com for about $27 US$. Look for Home Recording Studio Build it Like the Pros, by Rod Gervais.

-Nathan Webb

[naethoven]

Hey Rod, here are my 1st questions:

p.56 You tell us to seal the gap btwn the footer of the outside wall and the concrete foundation with mineral wool followed with caulk. I understand you want density from the mineral wool. I am building in a garage and I am a little worried about the mineral wool soaking up moisture because this gap is on the outside wall and in direct contact with the elements. Should I do something different or go ahead with the mineral wool? Will it soak up moisture?


p. 67 Does this detail of adding mass btwn the joists of an existing ceiling apply EXACTLY the same to walls? ie: do you still need the backer rod on the walls or can you just cut it to fit and caulk the edges? What is the purpose of using a backer rod instead of cutting it to fit and caulking edges?


Thanks, thanks for doing this for us!

Nathan

[Rod Gervais]

Nathan,

you asked:

p.56 You tell us to seal the gap btwn the footer of the outside wall and the concrete foundation with mineral wool followed with caulk. I understand you want density from the mineral wool. I am building in a garage and I am a little worried about the mineral wool soaking up moisture because this gap is on the outside wall and in direct contact with the elements. Should I do something different or go ahead with the mineral wool? Will it soak up moisture?

If you are following my detail - you should never have a condition where you are directly in contact with the outside elements.

The building sheathing/siding should always cover the gap at the base of the wood frame - if this is not the case - then first you need to fix that problem.

Once the seal exists - (and it just has to be covered - not caulked) then the only change on kmosture level in the rockwool would be related to the outside humidity levels - which is not an issue for any insulation.

p. 67 Does this detail of adding mass btwn the joists of an existing ceiling apply EXACTLY the same to walls? ie: do you still need the backer rod on the walls or can you just cut it to fit and caulk the edges? What is the purpose of using a backer rod instead of cutting it to fit and caulking edges?

Yes it is exactly the same regardless of walls or decks above.

Backer rod is required to assure a 2 point contact for the caulk. Without this - the caulk has a 3 point contact - and will fail in it's length due to the forces acting upon it.

There should never be a case in any construction where caulk is installed without a backer rod.

If you have even seen caulk with small cracks running lengthwise in the joint - those cracks are caused by 3 point contact in the application. This is to be avoided like the proverbial plague.

Rod

[jacobq]

Hi Rod

What is the correct material to use in a brick veneer garage exterior wall to avoid the dreaded three leaf situation. And also keep the MAM(mass air mass) setup. This will be new construction.

For example in my case beginning with the brick veneer.Following that is two 2x4 framed walls with insulation. The second wall being decoupled from the main stud framed wall. A layer of 5/8 drywall followed by a layer of 5/8 drywall applied with green glue.
If I use a styrofoam INSULATING board on the exterior framed wall between it and the bricks,will this create a three leaf system? If so what do recommend on the outer stud wall between it and the brick? Surely I cannot just leave it open with no barrier I would not think.

[Rod Gervais]

Originally Posted by jacobq

Hi Rod

What is the correct material to use in a brick veneer garage exterior wall to avoid the dreaded three leaf situation. And also keep the MAM(mass air mass) setup. This will be new construction.

For example in my case beginning with the brick veneer.Following that is two 2x4 framed walls with insulation. The second wall being decoupled from the main stud framed wall. A layer of 5/8 drywall followed by a layer of 5/8 drywall applied with green glue.
If I use a styrofoam INSULATING board on the exterior framed wall between it and the bricks,will this create a three leaf system? If so what do recommend on the outer stud wall between it and the brick? Surely I cannot just leave it open with no barrier I would not think.

OK - first off - if the brick is a veneer - then that means you have a structure to attach it to - which means a framed wall with structural sheathing........... styrofoam won't give you a sutructural attachment for the brick - and thus would never pass code for new construction.

So it's brick - followed by building paper - exterior structural sheathing - framing
(2x6 2' on center is better than 2x4 16"on center) with insulation in the cavity (fluffy is just fine) then say a 1" air space - framing with insulation in the bays (same with 2x6 as before) then your 2 layers of 5/8" with green glue.

Make certain that they do get some mortar into the space between the building paper and the brick to brace it with the wall so they act as one leaf.

If you want some added mass in the outer then add a couple more layers of OSB for the sheathing -

Perfectly caulked wall perimiters as well as the edges of the outer wall to each other and to the foundation.

That's a good 2 leaf system.........

[stuntbutt]

On page 128, Figure 7.5 shows an exchange chamber. I would like to know what sort of cfm of exchange would be appropriate in such a design. My room is approximately 1700 cubic feet and never has more than four people.

Thank you in advance,

John Katsafanas

[Rod Gervais]

Originally Posted by stuntbutt

On page 128, Figure 7.5 shows an exchange chamber. I would like to know what sort of cfm of exchange would be appropriate in such a design. My room is approximately 1700 cubic feet and never has more than four people.

Thank you in advance,

John Katsafanas

John,

I would lean towards roughly 150 cfm for a room 15' x 14' x 8' (1680 c.f.) and would want about 60 cfm of that to be fresh air to handle the needs of 4 people........


Rod

[naethoven]

Hey Rod!

Thanks for all the info.

I wanted to ask a few things about installing drywall btwn studs/trusses inside the wall/ceiling/floor. I apologize everyone, I am at work and do not have the book in front of me for a page number reference. I will edit and add it later.

I am designing to build in my detached 2 car garage. It is currently unfinished and stickbuilt. 1) How can I figure out how much weight I can add to my roof without overloading the stucture?

2) Ideally, I would want to add 2 layers of 5/8" drywall inside the ceiling, followed by 2 layers on the interior detached ceiling. If the roof cannot hold the weight, would it work as well to only add one layer to the inside of the roof and 3 to the inner ceiling? Same mass, still a 2 leaf sys., but mass is heavier on one side of the MAM.

3) The other issue I'm dealing with is when I begin to add the 1st layer to the roof btwn the trusses, nails (I guess holding the shingles) are sticking through the plywood roof about 1/2". There are probably close to 100 of them over the 24x24' building ceiling. How do I go about mounting the 1st layer? It will obviously poke holes in the drywall, but I can't exaclty break off all those nails. I don't know what to do about it if I don't add another layer on top. What do I do?

4) I use "A" weighting on my SPL meter to test indoor vs. outdoor levels for my build, right?


Thank you so much.
-Nathan

[Rod Gervais]

Originally Posted by naethoven

I am designing to build in my detached 2 car garage. It is currently unfinished and stickbuilt. 1) How can I figure out how much weight I can add to my roof without overloading the stucture?

Play it safe and invest 100 to perhaps 150 dollars and hire a structural engineer so there is no guesswork involved.

2) Ideally, I would want to add 2 layers of 5/8" drywall inside the ceiling, followed by 2 layers on the interior detached ceiling. If the roof cannot hold the weight, would it work as well to only add one layer to the inside of the roof and 3 to the inner ceiling? Same mass, still a 2 leaf sys., but mass is heavier on one side of the MAM.

As I am very fond of saying - we live with what we have..........

if this is how it has to be done then that is what ytou live with - it is not rational to worry about things you cannot change.

In an ideal world - go with 2 layers on each surface (which is still an uneven ratio due to the added deck shething on the roof) but if you must go with one and three - then so be it.

3) The other issue I'm dealing with is when I begin to add the 1st layer to the roof btwn the trusses, nails (I guess holding the shingles) are sticking through the plywood roof about 1/2". There are probably close to 100 of them over the 24x24' building ceiling. How do I go about mounting the 1st layer? It will obviously poke holes in the drywall, but I can't exaclty break off all those nails. I don't know what to do about it if I don't add another layer on top. What do I do?

Just put a layer of styrofoam insulation (either the blue or white board) between the inner drywall and the outer roof - the nails will penetrate this easily.

4) I use "A" weighting on my SPL meter to test indoor vs. outdoor levels for my build, right?

Use the "A" weighting regardless of in or outdoors.

That is unless you have a "C" weighting (which is considered a flat measurement) at which point I would opt for the "C" weighting.

Rod

[mwagener]

Rod

first let me say that your input and infinite advice here is very much appreciated, you have helped a lot of us to make less mistakes when building a studio. Your book is an absolute must for anybody thinking about building a studio.

I do have a question about the 3 leaf situation:
On the attached picture you can see the current roof construction. One side is open to the outside and will just be covered with metal flashing from the outside, which has holes in it, so not much insulation there.

The plan is to build a room inside a room which will not touch any of the existing construction except for the concrete floor. Would it be better to fill the roof cavity between the rafters with insulation and add a layer of drywall to the bottom of the rafters, then build the room with a ceiling with two layers drywall (plus green glue), or would that create a 3 leaf situation together with the roof itself.

We were thinking of just filling the space in between the rafters with insulation and then insert the rafters for the new room in between the existing rafters to also gain some height, so no drywall on the bottom of the existing rafters.

[nosebleedaudio]

How tall is the ceiling?
To me it would depend on how much space you plan on having between the next ceiling.
If you drilled a hole in the OSB would you see daylight?
This subject was touched on in another thread, depends on how much space, a few inches or a foot or two...
You want good isolation, as you know Michael, just saying it out loud... Things like thunder can produce some serious low end...
Depending on how much space you have to work with, a nice size space would be great, and also is a perfect place to run HVAC duct...just a thought...
Michael, if you were close I would love to pop in and check it out...
Looking good...

[mwagener]

The space inside the rafters goes from about a foot on one side to about 4 feet on the other, it's a slanted roof. The top of the stud frame is at 11' from the floor. Yes, I would see daylight if I drilled a hole in the OSB.

In the pictures, you are looking into the roof cavity from the side, when it was being built.

I am actually more concerned about sound getting out. We are in a pretty remote area, but since it's very quiet here I don't want to disturb the neighbors. As you know, those guitar amps can make quite a racket. The closest house is about 7 acres away. Thunder always makes for a great mood on rock recordings

Thinking of the 3 leaf system, would the extra sheet of drywall on the bottom of the rafters still improve the transmission loss? Would the roof and the planned dual; layer of drywall on the inside ceiling count as two layers? As far as I understand it, it would create two separate airspaces in between, correct?

And yes, the A/C ducts will have to squeeze into that space as well, we have to do that before we put any kind of ceiling on, it's not really accessible from above, too small.

[yarrick19]

Hi Rod,

I have a question about Helmholtz slot resonators. In your book on page 179 you state, "Helmholtz traps are a type of membrane trap that does not rely on sealed spring cavities".

In doing some other research, I see that other sources say the cavity must be sealed. For example, the SAE Institute says "...the cavity behind must be sealed to an airtight container..." (Source)

So, when building a Helmholtz slot resonator, does the cavity need to be sealed or not?

Thanks!

[Rod Gervais]

Originally Posted by yarrick19

Hi Rod,

I have a question about Helmholtz slot resonators. In your book on page 179 you state, "Helmholtz traps are a type of membrane trap that does not rely on sealed spring cavities".

In doing some other research, I see that other sources say the cavity must be sealed. For example, the SAE Institute says "...the cavity behind must be sealed to an airtight container..." (Source)

So, when building a Helmholtz slot resonator, does the cavity need to be sealed or not?

Thanks!

A panel trap is a spring sealed cavity - which means that the entire cavity is sealed. all 6 sides of the trap.

A Hemholtz trap has an unsealed face - and thus is not a sealed cavity trap - however - that does not mean that it would work if it were installed without a sealed wall behind it......... that is an altogether different thing.

SAE is correct - as is my book - the cavity behind must be sealed.

[nosebleedaudio]

Originally Posted by mwagener

The space inside the rafters goes from about a foot on one side to about 4 feet on the other, it's a slanted roof. The top of the stud frame is at 11' from the floor. Yes, I would see daylight if I drilled a hole in the OSB.

In the pictures, you are looking into the roof cavity from the side, when it was being built.

I am actually more concerned about sound getting out. We are in a pretty remote area, but since it's very quiet here I don't want to disturb the neighbors. As you know, those guitar amps can make quite a racket. The closest house is about 7 acres away. Thunder always makes for a great mood on rock recordings

Thinking of the 3 leaf system, would the extra sheet of drywall on the bottom of the rafters still improve the transmission loss? Would the roof and the planned dual; layer of drywall on the inside ceiling count as two layers? As far as I understand it, it would create two separate airspaces in between, correct?

And yes, the A/C ducts will have to squeeze into that space as well, we have to do that before we put any kind of ceiling on, it's not really accessible from above, too small.

OK, makes more sense now...
Michael, there is some great info on the BBC sites regarding 1,2 & 3 leaf walls, with specs, showing down to 50hz...
The bigger the space the better, as you know.. but if the space is more in the 12" and more it would become less of a problem.
All the wall designs I've seen (2 & 3 leaf) have a small space between them, 2 to 4 inches, I have not seen one that had a foot space and showed the specs for it...
So my point is, I have no data to support my comment....Its just logical..

What's the full dimension of the slab? Never mind, 53 by 22, just saw it on the 0ther thread..

[yarrick19]

Originally Posted by Rod Gervais

A panel trap is a spring sealed cavity - which means that the entire cavity is sealed. all 6 sides of the trap.

A Hemholtz trap has an unsealed face - and thus is not a sealed cavity trap - however - that does not mean that it would work if it were installed without a sealed wall behind it......... that is an altogether different thing.

SAE is correct - as is my book - the cavity behind must be sealed.

Thanks for the clarification!

[jacobq]

Originally Posted by mwagener

Rod

first let me say that your input and infinite advice here is very much appreciated, you have helped a lot of us to make less mistakes when building a studio. Your book is an absolute must for anybody thinking about building a studio.

I do have a question about the 3 leaf situation:
On the attached picture you can see the current roof construction. One side is open to the outside and will just be covered with metal flashing from the outside, which has holes in it, so not much insulation there.

The plan is to build a room inside a room which will not touch any of the existing construction except for the concrete floor. Would it be better to fill the roof cavity between the rafters with insulation and add a layer of drywall to the bottom of the rafters, then build the room with a ceiling with two layers drywall (plus green glue), or would that create a 3 leaf situation together with the roof itself.

We were thinking of just filling the space in between the rafters with insulation and then insert the rafters for the new room in between the existing rafters to also gain some height, so no drywall on the bottom of the existing rafters.

Hi Micheal
I was waiting on the edge of my seat for Rods suggestion on this question. What solution did you end up going with?

I have the same issue on a much smaller scale.

[mwagener]

Well, since I am trying to keep the sound inside I feel that I should put as much insulation in the roof as I can and then put one layer of 5/8 drywall under the rafters. The roof is just one big open hole otherwise and the drywall is mass and can be completely closed off at the sides. I will lose some height for the tracking room, the remaining height inside will be about 10', but I guess the soundproofing is more important.

We have some time until the A/CD is installed (pipes go into the same roof, before it can be closed off) so I'll do some more research.

[Rod Gervais]

Originally Posted by mwagener

Well, since I am trying to keep the sound inside I feel that I should put as much insulation in the roof as I can and then put one layer of 5/8 drywall under the rafters. The roof is just one big open hole otherwise and the drywall is mass and can be completely closed off at the sides. I will lose some height for the tracking room, the remaining height inside will be about 10', but I guess the soundproofing is more important.

We have some time until the A/CD is installed (pipes go into the same roof, before it can be closed off) so I'll do some more research.

Michael,

sorry about that - i thought I had everything here covered - apparently I was mistaken.

Add whatever you can to the existing roof - and then make up the difference below.

You can overcome 3 leaf situations - it just costs you additional mass on the innermost face of your assembly -

Remember - we deal with what we can - and we live with what we must.

If you keep that in mind everything will wind up fine in the end.

(We have 3 leaf conditions in Power Station - and yet we have great isolation there.)

Rod

[mwagener]

Originally Posted by Rod Gervais

Michael,

sorry about that - i thought I had everything here covered - apparently I was mistaken.

Add whatever you can to the existing roof - and then make up the difference below.

You can overcome 3 leaf situations - it just costs you additional mass on the innermost face of your assembly -

Remember - we deal with what we can - and we live with what we must.

If you keep that in mind everything will wind up fine in the end.

(We have 3 leaf conditions in Power Station - and yet we have great isolation there.)

Rod

No problem, I know you're busy. Thank you for the advice.

Then I will go with what I described above. The "inner room" will have two layers of 5/8" DW all around with GG in between and to the sides we have a 6" air gap between inner and outer wall, that should be sufficient.

[torquemada]

Hi Rod I have some questions about wall construction :

First I live in Peru where all houses are made of concrete, so my main question is what are the differences between a concrete wall/air/insulation/drywall/green glue/drywall and a double frame wall with an STC of 63 like it`s said on your book. Which one is better?

And my second question is how much isolation does an STC 63 gives, is it enough so I don`t disturb the neighbourghs at night playing drums?

I plan to build a home studio at the 3rd floor of my house I bought your book and it has been really helpful, but I need to read it one more time, to understand everything better.

Eddie

[chad bush]

Just tryin to get the ball rolling on the basement studio I am wondering what type of insulation to use in the stud spaces is there a special make or is it just any type of fibreglass. And that type of caulk should be used. I am sorry if this is a lame question just searching for examples and cant seem to find them. Any help would be appreciated. does not nessesarily have to be from Rod ThANKS

[pangurini]

Dear Rod,

We are planning on building a Helmholtz Resonator in our control room, floor to ceiling as described in your book. The diagram on page 181, figure 9.15, shows 1x6 slats and 1/2 inch gaps.

The text then says that "figure 9.15a is a 3D view of this slot resonator in the room corner." However, diagram 9.15a caption says "1x8 slats with 1/8 inch" gaps.

Are they effectively the same? Does the formula for calculating still work in the corner where there is technically more volume behind the resonator and triangular space?

And finally, you note that the use of alternating 4,6, and 8 inch slats, page 180, but there is no explanation if there is an advantage to different size slats (in the same unit)?

Thanks for such an amazing book and resource.

[Rod Gervais]

pangurini

We are planning on building a Helmholtz Resonator in our control room, floor to ceiling as described in your book. The diagram on page 181, figure 9.15, shows 1x6 slats and 1/2 inch gaps.

The text then says that "figure 9.15a is a 3D view of this slot resonator in the room corner." However, diagram 9.15a caption says "1x8 slats with 1/8 inch" gaps.

Are they effectively the same? Does the formula for calculating still work in the corner where there is technically more volume behind the resonator and triangular space?

No they are not the same - but that doesn't matter anyway - because you are going to have to calculate for whatever you need in the end.

The formular works - but base it on the spread of the deepest point to the shallowest point - it tends to work more broadband in the corners than to target a specific frequency.

And finally, you note that the use of alternating 4,6, and 8 inch slats, page 180, but there is no explanation if there is an advantage to different size slats (in the same unit)?

Ah....... something I didn't mess up - lol. Look at Figure 9.14 for your explanation.


Thanks for such an amazing book and resource.

Thanks to you for the complement.

Sincerely,

Rod

[Rod Gervais]

Originally Posted by chad bush

Just tryin to get the ball rolling on the basement studio I am wondering what type of insulation to use in the stud spaces is there a special make or is it just any type of fibreglass. And that type of caulk should be used. I am sorry if this is a lame question just searching for examples and cant seem to find them. Any help would be appreciated. does not nessesarily have to be from Rod ThANKS

Chad,

fluffy insulation works fine inside of a wall.

Any caulk that does not harden will get the job done.

Silicone will work - as will most of the butyl caulks.

Rod

[Rod Gervais]

Originally Posted by torquemada

Hi Rod I have some questions about wall construction :

First I live in Peru where all houses are made of concrete, so my main question is what are the differences between a concrete wall/air/insulation/drywall/green glue/drywall and a double frame wall with an STC of 63 like it`s said on your book. Which one is better?

And my second question is how much isolation does an STC 63 gives, is it enough so I don`t disturb the neighbourghs at night playing drums?

I plan to build a home studio at the 3rd floor of my house I bought your book and it has been really helpful, but I need to read it one more time, to understand everything better.

Eddie

Eddie,

As I explain in the book - "The higher the STC rating, the better the sound isolation value of the assembly will be. However, STC ratings were really designed and intended for the frequencies dealing with human speech not for music. There is no standard (that I know of) that is specifically designed for recording studios. So although we will deal with STC for initially choosing an assembly to start with, we will leave it behind as we try to deal with isolating the frequencies below those that the STC ratings deal with."

But - the concrete walls will typically be better at isolating low frequencies than framed walls.

No - a typicall STC 63 wall is not going to get the job done. Although it will help.

The problem is (again) going to be low frequency in nature.

You need a lot of mass and decoupling to do what you want.

Rod

[naethoven]

Hey Rod, thanks for all the responses on this thread.
On p. 67 where you detail the technique for adding mass between studs or ceiling joists, you are using 5/8" gypsum, with a 1/4" space on each side, and 3/8" backer rod. In my situation, I am able to get a lot of 1/2" gypsum for really cheap, so I'm using that instead of 5/8".

My question is, since my gypsum is smaller, do I need to go with a smaller backer rod (to get the depth of the backer rod vs thickness of drywall right) and therefore have a smaller gap on each side of the drywall. For instance, would I leave an 1/8" gap and use 1/4" backer rod?

Also, I've already done my first few pieces, and a day or two after I did them I noticed some of the caulk was peeling away from the gypsum. Can you tell me what I did wrong? At this point I was using 1/2" drywall with a 1/4" gap and 3/8" backer rod. I have some pics here of my method (for your approval) and the caulk that is peeling away.

Thanks, Nathan

[naethoven]

speed bump

[naethoven]

Yoo-hoo?


Any thoughts?

[mark.james]

After reading chapter 2 regarding modes, I was wondering if having an A-frame type ceiling would reduce the occurance of "modes". Also, I would like to build my room (which will be in an existing detached garage) with one of the popular room ratios, but am not sure how to calculate this with an A-Frame type of ceiling.

Mark