How to make a new room airtight?
I am building a room 14’L x 8′ h x 42″ wide inside my warehouse and the temp is constant 70 degrees..
Am using one interior wall as the back wall of my room. So I am building three walls using 2×4 studs
And I have already solved the problem of air sealing the door. I am not going to insulate or put on interior sheet rock. Just sheet rock on the outside. What should I do to make the room air tight.? I thought about wrapping the whole room in plastic and glueing it down on each stud or joist it touches.
Then sheet rocking over that then painting with an elastomeric paint to seal the dry wall.
Obviously I am not a contractor, so if someone can help me figure out the best way to build out the walls to make them airtight that would be great. No other holes in the walls except for were the door is going to be. I need it air tight as I am going to be storing freshly silvered mirror without the protective backing to keep the silver from tarnishing.
Thanks in advance for sharing your expertise.
John West
http://Www.westdesign.net
California
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Replies
In making conventional buildings we distinguish between an air barrier and a vapor barrier. The former lets water vapor diffuse through, but prevents airflow. I'm not sure what the requirements are to prevent silver from tarnishing.
Just to be sure I understand correctly, the temperature of the whole building is already kept constant at 70 F, not just the new room?
What is the construction of the wall it is built against?
Wrapping the whole room in plastic is likely to work well, but I'm not sure I understand the application well enough to know if that is good enough or whether it's overkill.
John,
From the limited research I have just conducted, silver tarnishes due to the effects of atmospheric oxygen and atmospheric hydrogen sulfide. I assume that you are taking steps to alter the air in this room to reduce either the room's oxygen levels or hydrogen sulfide levels... and if you are doing that, I wonder: (a) Are there safety concerns? and (b) How are you doing that?
Leaving aside the questions that swirl around your planned industrial process, you can use polyethylene as an air barrier without any problems, as long as (a) there is no temperature differential on either side of the poly -- so that you have no condensation concerns, (b) you figure out a way to install the poly to minimize or eliminate penetrations by fasteners (this can be tough), (c) you prevent any injury to the poly during construction, and (d) you overlap the poly seams on framing lumber, and seal those overlaps with Tremco acoustical sealant.
You may find it easier to simply use the drywall as your air barrier, following the Airtight Drywall Approach. For more information on this topic, see Airtight Drywall.
Whether you use polyethylene or drywall as your air barrier, you need to seal the gap under the bottom plates (your options include sill seal, caulk, or an EPDM gasket), as well as the wall-to-ceiling seams and any penetrations, including wiring penetrations.
You may also want to consider using a thin layer of closed-cell spray foam as your air barrier.
Charlie,
Thanks for your input. The temp in the were house and the little room will be 70 degrees. No moisture problems from being to cold or warm on inside and out. The requirements to keep silver from tarnishing are to haven no oxygen and hydrogen sulfide levels. I have already solved the chemical portion of stopping the patina, just need to keep all air from going into room once I suck it out with a pump. The back wall is standard construction dry wall over studs then painted. I am aware of all the places, crevices, under bottom plate and have read about the air tight drywall system instituted in the eighths.
So you think if I just wrap the framing in poly, sealing all the overlaps and dry walling and doing a standard dry wall sealer, ova, then high quality paint would do it. I found a hardware system that will allow me to make the door airtight, so it is just the walls and ceiling I am concerned about. Let me know what you think of my plan and feel free to criticize, make suggestions. I read one article written by a co. That says the air Tight Drywall method does not work and the have a different material they sell that does. Did not read whole article but I bet the material costs buckhorn bucks. Thanks again for sharing your expertise.
John West
John,
If you are trying to pull a vacuum on this room using a pump, then you are talking about a whole different level of airtightness than what builders commonly talk about. Depending on what type of depressurization you're talking about, you may need to talk to an engineer about your plan.
Martin,
Your right about what makes silver tarnish and I have a solution for the chemical component. I just need to make sure that once I close the door and suck out the air it won't leak back in through the walls. Read an article by some co. Saying the airtight drywall method is ineffective and out of date and they have a special material mets etc that works better.mhave you ever heard this to be true. I saved the website so I could read it all later. If I do wrap it with poly and glue it down to each stud how do I seal the screw holes when attaching the drywall? Should I have them drive the deep and use some compound to fill the dent just flush with the sheet rock so as not to interfere with the tape and finish job? Let me know your final thoughts now that every thing is clear, I hope. Thanks for sharing your expertise. I just hade an idea for sealing drywall screws...I could pre drill the whole and use one of those plastic syringes and shove it into the whole to reach the poly and squirt out sealant but not enough the prevent a good flat tape job? A little over the top but the case of mirror cost about 3,600 so it would be worth it. What do you think? Thanks again.
John West
John,
You're right that the Airtight Drywall Approach can't be used to create a vacuum chamber. Talk to an engineer.
Making a vacuum chamber entails more challenges than making an airtight building. Suppose, for example, you reduce the air pressure to half of normal atmospheric pressure. That's probably not good enough to avoid tarnish, but might be enough to help a little. In that case, the pressure inside is 7.5 psi, vs. 15 atmospheric, so you have 7.5 psi pressure differences across the drywall. Can the drywall withstand that? It happens that Martin was kind enough to look up the load rating of drywall a while back, on this thread:
https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/25580/58-drywall-sufficient-support-r-60-cellulose-ceiling
It's rated for 2.4 lbs/sq foot (psf). Since there are 144 square inches in a square foot, the 7.5 psi we need to withstand is 1080 psf. So we are off by a factor of 450. It's way outside the realm of what a normal structure is designed to support. For example, in very snowy places, roof are designed for 50 to 100 psf snow load. Even the high end of that range is only 1/10th of what you'd need for evacuating just 50% of the air.
A vacuum chamber needs to be a very strong structure. There's a reason vacuum chambers, even small ones, are very expensive and look like submarines. For your 14'x8' wall, the total force with just 50% vacuum would be 60 tons. Perhaps you can pick up a surplus submarine and use that.
But more seriously, I would consider whether there are alternatives such as removing moisture and hydrogen sulfide without removing oxygen, or displacing the oxygen with nitrogen.