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HELP!, roof/ceiling venting plan, is this an isolation disaster?

Member for

5 years 1 month
I am having a back garden practice/recording cabin built. Structure will be (from outside to inside)

Concrete base with DPM
timber frame (total area 4x5m)
OSB with 18 mm shiplap cladding
4x2in wooden studs
100mm RW3
2 layers of 15mm acoustic plasterboard.

Roof
OSB covered with EPDM

I was quite concerned when I saw how the roof has been put up with roof joists on top of walls and a huge ventilation gap from one side of room to other(see pic).

the builder intends to put 2 layers of 15mm acoustic plasterboard (as on internal walls) attached from below to the roof joists with 75mm of rockwool above.
Builder emphasises the importance of ventilation to avoid condensation (which I get) but my concern is that all that is between the inside and outside is the 2x15mm plasterboard and 75mm Rockwool (with an air gap open to the eaves)

. I am unsure if this setup will compromise the already modest isolation.

Structure today is as it appears in pic but work is due to continue in a few days. have attached a rudimentary sketchup image of the design. a pic of the roof from inside and one of outside as it is today.

Questions

Is this an acoustic disaster?

Is there anything I can do at this stage to improve the outlook if it is that bad, preferably without ripping off the roof or anything that drastic?

I feel foolish not having focussed on these details prior to construction but feel now that I need to make urgent decisions to avoid having wasted money on materials while having a massive open gap to the outside, Any advice would be very much appreciated.
many thanks
Jose

Comments

Member for

19 years 5 months

Kurt Foster Sun, 10/30/2016 - 16:36
ventilation in studios is usually accomplished by low velocity fans pushing air through a labyrinth of duct work. every bend in the duct attenuates the sound traveing each way. (in and out). the low velocity fan assure fan noise and the sound of air moving is kept to a minimum.

please keep in mind, i am not an acoustician. i just play one in the studio and on the interweb thingie.

Member for

5 years 1 month

Jose Luis Sun, 10/30/2016 - 17:21
Hi Kurt,
Thanks for your thoughts on ventilation. Is your suggestion used for roof ventilation? I thought what you describe was for the inside studio space, might be something for me to consider if it can be used to keep airflow in roof cavity.guessing something like that could be costly.
I have seen images of cabin type home studios which have flat (pent) roof like mine but I does not have open exposed spaces between the joists under the OSB roof. BTW my cabin is not like this one in size or style but just wonder how condensation is avoided without the kind of roof design I have (see my pics) unless as you say there is a HVAC system being used and no gap needed between ceiling and OSB board roof as ventilation is supplied by mechanical means.
Appreciate your thoughts Kurt,
The studio on the link just looks more sealed? How is this achieved while maintaining ventilation and preventing condensation?
Cheers.
Jose

[[url=http://[/URL]="http://www.soundpro…"]http://www.soundpro… teaching studio.html[/]="http://www.soundpro…"]http://www.soundpro… teaching studio.html[/]

Member for

12 years 11 months

dvdhawk Mon, 10/31/2016 - 10:32
I'm sure Brien will be the definitive answer on this.

But in the meantime I'm not seeing any picture, so we can't tell if you just mean the normal overhang you see in roof trusses. IF that's all we're talking about, I'd say your professional building contractor is on the right path. Construction methods can be very specific from one region to the next, because of your specific climate, he probably knows what works best in your area. The contractor's main objective is avoiding water damage and giving you a building that will last.

IF you're concerned about something other than this, you'll have to be more specific and/or provide drawings or photos.




Although it's counterintuitive to your energy-efficiency and sound-loss goals, the attic space absolutely has to breath outside air freely through the soffit and usually in conjunction with either a vent down the ridge of the roof, vents at the top of the gable-ends, or vents cut into the roof. Otherwise, you will have condensation problems that will lead to water damage and rot. People also often mistakenly cram insulation over the soffits too, which leads to warm spots in the roofing. And in the wintertime that results in a cycle of snow melting/freezing that causes ice buildup around the gutters and ice working under the shingles doing even more damage.

If there's any ductwork in the attic, insulated duct has probably been recommended. In the wintertime the attic will be cold (as it should be), so any ductwork in the attic should be well insulated to prevent heat-loss and condensation. Condensation occurs when something has drastic temperature differences on the inner and outer surface, so insulated ducts are beneficial in the summertime too, if it's used for air-conditioning.

From my non-professional understanding, your sound-loss efforts need to be concentrated on sealing any and all air gaps in the ceiling layer between the interior space and the attic. That goes for the edges, around any place wires might penetrate, ductwork, light fixtures, etc. ANYTHING that might be cut into the ceiling, then install the rock wool above that. Just bear in mind that any place that leaks air, will also leak sound.

Hopefully you can benefit from Brien's professional opinion before your contractor moves on.

Member for

12 years 4 months

kmetal Wed, 11/02/2016 - 15:06
Best thing you can do is pause the project. And then use some time to get your plans right. Theres absolutely no need to rush.

From your description it sounds like the builder going to hang drywall from the outer shell building framing's interior faces?

This is a huge error. For any substantial isolation you've got two options. Room inside a room, or using a RISC clip/channel, or resilient channel system.

From the description it sounds like the builder is putting up a standard shed type building. And then just addding a second layer of drywall.

What you want is an exterior frame with double layers or more of sheathing, and an inner frame/ shell physically decoupled from the outer one. Decoupling is acheived by one of the methods above. It's on the interior framing/clips/channel you add your layers of drywall to.

That's the first most important issue.

2nd- if possible use fluffy insulatiinnfor the cavities not rockwool. Assuming it's cheaper where your located as it is over here in the states. Fluffy insulation is cheaper and more effective at certain frequencies. Rockwool is a waste of money inside a wall cavity.

One way or anther the building has to breathe. With docoupled inner framing and sealed drywall standard ventilation wouldn't be as much as an issue with reguarded to isolation. Your inner frame will block a healthy 30-40 db at mid range frequencies, and your beefed up sealed outer frame could add another 15-20db. That's a very very broad generalized statement. The vent holes will be a breach in the sealing and isolation, but it's something you just will have to live with.

You want a ventilation system that has the smallest sqft of penetration possible.

What's the plan for hvac inside the studio??

Ideally you would incorporate the ventilation and air exchange for the outer shell with that.

I'm not an hvac expert. if possible you would incorporate your fresh air supply and stale air exhaust into the outer shell ventilation.

If you for instance used the outer shells space as an exhcange chamber you can control the humidity within it. Whether or not this is feasible depends on codes and space availability.

Either way I'd be aiming to keep the outer shell sealed up and exchange air between the studio and the attic space. With proper circulation and conditioning you can maintain proper humidity. One way or another you need a penetration thru to the outside so you can intake fresh air. You may be able to integrate the fresh air with the roof ventilation.

A lot of the new 'green' houses are using this sort of thing to take warm air rom the upper floors and pump it down to the lower floors to help be efficient when heating in the winter, doing the opposite in the summer.

This really depends on a lot of details so it's impossible to come up with any sort of design at this point. It's definately no area to rush.

You should pick up 'build it like the pros' by rod Gervias. It's the defacto book for home studio construction.

Member for

5 years 1 month

Jose Luis Thu, 11/10/2016 - 09:26
Hello everone who responded and big apologies for not responding sooner (unfortunately emails ended up in my junk mail).
I really appreciate all the advice everyone took the time to give.
I am in Brighton UK. It is clear that I have not given enough clear info about my build. I will do some sketches and post them (my sketchup skills are not that good yet).
probably best to restate the info together with my sketches rather than write out at this point.
Once again , many thanks, will be back asap
Jose

Member for

5 years 1 month

Jose Luis Sat, 11/12/2016 - 12:33
Hi folks, Thanks again to you helpful people forall your advice! have attached pics etc to clarify the build so far and what I am aiming for.

My initial question was about whether the cavity below the flat roof is a problem for sound leakage, as outlined by Dvdhawk ` your sound-loss efforts need to be concentrated on sealing any and all air gaps in the ceiling layer between the interior space and the attic` from this I understand that the general roof/soffitt vent structure is acceptable providing that the inner `cabin` below is well sealed from this upper airgap?

I understand that SPL readings should be done with a proper meter, unfortunately I cannot afford to buy one at present, failing that I have done some readings with a sound meter on my mobile phone, I know how inadequate this is for accuracy but for me at the moment it serves as a very approximate guide. At approx 1m distance from monitors playing a track quite a bit louder than my usual listening level I got a max reading of 80db with an average of 40db or less.

I do not plan to record a drum kit or have a full band playing, loudest instruments would be ocassional congas, vocals and acoustic guitar. I currently record in a bedroom at home so having more space and less interuptions would really improve my workflow, I have had no complaints from neighbours and want to keep it that way! As most in my situation I don't have unlimited funds to throw at this but need to try and achieve good enough results for my needs.

Regarding the question by Kmetal about ventilation, I know that HVAC is the best way to go but again I have a very modest budget (hoped for £12-13k but now expecting to go to £15k).

What I decided on is a Rytons passive acoustic vent. According to manufacturer's data (obviously in ideal conditions) when open it can reduce sound transmission by 43db and by 50db when closed. I know it is not ideal but am prepared to periodically pause work to allow airflow by opening vent and door/window. Unfortunately this is a compromise I am obliged to make due to budget.

I know I have made mistakes in my planning and construction, some of which are irreversible so I will need to move forward from where I am.

Mistakes (am sure there are many more than listed!)

I have already had installed the Rockwool in stud cavities.

I have already had it built as in pics.

I have already bought the vent.

Listening to the advice in response to my last post I understand that I should halt adding further plasterboarding inside then my next action should be.....

* remove plasterboard already up (including vent)

* install resilient channels on walls and ceiling

* put up the 2 layers of acoustic plasterboard (15mm each) attached to RC


Am I on the right track now and is this the most cost effective route to get acceptable results given where I am in the build now? Would genie clips/furring strips be better for my situation? Don't think budget will stretch to Green Glue.

Builder is away until next Friday so it would be ideal to get my plan clear and buy extra materials needed ready for him to continue the job without delay .there are some exterior jobs he could do if there is a delay such as finishing and painting the exterior cladding although the weather is against us now!

All advice and guidance has been very valuable to me, thanks again.

Jose
Attached files

Member for

6 years 8 months

OBrien Sat, 11/12/2016 - 12:42
Explain to us in some detail about this roof you are going to build. Developing a hermetically sealed environment is one thing...but you have to stop sound sound as close to the source as you can get. So rather than a gable roof with vents on the ends of the gable I would build one similiar to what your pictures reveal on the other structures which is termed a hip roof. You eliminate the large vent openings and simply add soffit vents which are required with either design, and install a hip ridge vent which is common practice.

Member for

5 years 1 month

Jose Luis Sat, 11/12/2016 - 13:27
Hello Brien,
Thank you very much for your prompt reply.
The roof is already up (please see pic) with EPDM covering already in place.
If a hip ridge vent you describe requires a roof pitched either side of a higher central ridge this would not be possible as an adaptation to my build as I am building subject to UK Permitted Development rules (no planning permission required) which prohibits total height more than 2.5m unless 3 or maybe 4 meters from boundary with neighbours. I chose that location as being furthest from neighbours while still leaving some garden space. Looks like I have to go with what I have.
Must admit the builder is able to build what I want but (like me) has little experience with this type of specialised build . I have been researching as much as I can and learning a great deal but inevitably am making many mistakes and incurring extra costs despite my best efforts.
I can upload more pics if needed but assuming I can't change the basis structure is the best advice to add resilient channels to ceiling and wall joists/studs and then 2 layers of plasterboard? Some PB has already gone up directly onto studs but not too late to remove then put back if RCs are best option, obviously any extra cost of materials and labor would be tough but will have to take the pain if it means the difference between being able to work problem free or having problems with neighbours. Currently have a 7pm curfew as that is my daughters bedtime! Hope to be able to work later than that in a new space.
If these pics are no help I can take more tomorrow (in daylight).
your advice is very much appreciated!
José
Attached files

Member for

6 years 8 months

OBrien Sat, 11/12/2016 - 13:58
I will tell you like I have told hundreds of men over 10 + years in my time of doing this on line. You are too far ahead of me for me to help you now. I will not say that you cannot recover but it is always better to plan your work and work your plan.

Many in this field that I am only a student of will say that you must access your needs first as to what your requirements are and build accordingly. They will also tell you that a ceiling and a wall are the same in respect to each must be designed and built to match one with the other in respect to sound containment and sound isolation properties.

To justify isolation clips and hat-track you would lean on the exterior ambient noise levels and your anticipated sound output from the room...anything beyond that is good money after bad my friend.

Member for

5 years 1 month

Jose Luis Sat, 11/12/2016 - 14:18
Hello Brien,
Again thank you for your wise advice.
I am sure many before me have made similar mistakes. Part of my eagerness to get the room built is simply to do it before other unforeseen financial demands take over. Another issue is that we live in a 2 bedroom house and my daughter needs her own bedroom (currently my studio!). Currently I sleep on the sofa downstairs and she with my wife upstairs!. None of this negates the good sense in your advice Brien, as you suggest there is no point throwing good money after bad, will just need to do the best I can with the understanding and money I have then live with the consequences.
Thanks to you and all others who have taken the time to pass on their thoughts.
José

Member for

5 years 1 month

Jose Luis Sun, 11/13/2016 - 09:05
Hi folks,




Thanks again to you helpful people for getting me on the right track! have attached pics etc to clarify the build so far and what I am aiming for. I hope they help clarify my situation.




My initial question was about whether the cavity below the flat roof is a problem for sound leakage, as outlined by Dvdhawk ` your sound-loss efforts need to be concentrated on sealing any and all air gaps in the ceiling layer between the interior space and the attic` from this I understand that the general roof/soffitt vent structure is acceptable providing that the inner `cabin` below is well sealed from this upper airgap.







I understand that SPL readings should be done with a proper meter, unfortunately I cannot afford to buy one at present, failing that I have done some readings with a sound meter on my mobile phone, I know how inadequate this is for accuracy but for me at the moment it serves as a very approximate guide.




At approx 1m distance from monitors playing a track quite a bit louder than my usual listening level I got a max reading of 80db with an average of 40db or less.




I do not plan to record a drum kit or have a full band playing, loudest instruments would be ocassional congas, vocals and acoustic guitar. I currently record in a bedroom at home so having more space and less interuptions would really improve my workflow, I have had no complaints from neighbours and want to keep it that way! As most in my situation I don't have unlimited funds to throw at this but need to try and achieve good enough results for my needs.




Regarding the question by Kmetal about ventilation, I know that HVAC is the best way to go but again I have a very modest budget (hoped for £12-13k but now expecting to go to £15k).




What I decided on is a Rytons passive acoustic vent. According to manufacturer's data (obviously in ideal conditions) when open it can reduce sound transmission by 43db and by 50db when closed. I know it is not ideal but am prepared to periodically pause work to allow airflow by opening vent and door/window. Unfortunately this is a compromise I am obliged to make due to budget.




I know I have made mistakes in my planning and construction, some of which are irreversible so I will need to move forward from where I am.




Mistakes (am sure there are more than listed!)




I have already had installed the Rockwool in stud cavities.




I have already had it built as in pics.




I have already bought the vent.




Listening to the advice in response to my last post I understand that I should halt adding further plasterboarding inside then my next action should be.....




* remove plasterboard already up (including vent)




* install resilient channels on walls and ceiling (with care to follow installation




instructions)




* put up the 2 layers of acoustic plasterboard (15mm each)




Am I on the right track now and is this the most cost effective route to get acceptable results given where I am in the build now? Would genie clips/furring strips be better for my situation? Don't think budget will stretch to Green Glue.


Builder is away until next Friday so it would be ideal to get my plan clear and buy extra materials needed ready for him to continue the job without delay .there are some exterior jobs he could do if there is a delay such as finishing and painting the exterior cladding although the weather is against us now!



All advice and guidance has been very valuable to me, thanks again.


Jose

---------------------------------------------------------------------------------------



13.11.16



hello again,



am considering all the valuable advice received. I have been thinking hard about the options still available to me to mitigate some of the irreversible mistakes I have already made. Quite a rough night of self-created despair!!

One option I am considering which could go some way to reducing sound transmission in and out of the cabin is to install resilient bars on walls studs and ceiling joists then attach to this the 2 layers of 15mm acoustic plasterboard I have already purchased.

If I do this I have realised one issue that I am uncertain how to address.

there are roof joists running from one side to the other from longest side to the opposite side. The builder then put up a supporting beam perpendicular to the joists to offer further support to the roof (he admitted an errir he had made with joists and offered this as a solution which I accepted-my responsability!)

. If this were not there the RC installation seems straightforward to me but as this supporting beam runs below the parallel joists and protrudes downwards into the room I am unsure how to deal with it as it is fixed directly to the joists above. If this is not dampened then presumably it would transmit vibration to the joists above and on to the OSB above (and also from outside to inside via the same route).

One thought I had is...

1) to also apply RC to its 3 accessible sides then box it in with 2 layers of plasterboard attached to the RC. I cannot see how to give it the similar layer of rockwool that will be applied to the walls and ceiling though.

The other thought I had which to me does not seem to match the rest of the build is


2) to box it in without the RC on it and put rockwool between the beam and the plasterboaed covering it thus making a kind of baffled beam.

any thoughts or suggestions are greatly valued.

many thanks.
Attached files
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