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Separately supplied and conditioned room within a room

jimbox | Posted in General Questions on

This is kinda a weird question and I searched pretty hard but didn’t find much except a post about a very elaborate gun storage room which was focused on totally different stuff. Google returns a lot of acoustic studio advice which is not exactly relevant either.

I hope the medical stuff doesn’t break any Q&A rules, I included the bare minimum for context.

Unfortunately I have been diagnosed with something called Mast Cell Activation Syndrome (MCAS) and it severely affects my quality of life. Without going into details it’s one of reasons why doctors are thinking some people are very sensitive to things like mold, pollen, VOCs, etc, and others seem to tolerate them with gusto. For me even the mildest of exposures will trigger incapacitating, whole body pain plus other unpleasantness. I haven’t slept for more than 2 hours at a time in 3 years.

Previously I only had mild issues that didn’t cross my mind as medical stuff, until one day I was exposed to a large quantity of lab waste at work without proper ventilation or PPE (someone dropped a container). Now I cannot really work and am just trying to figure out how to spend my retirement savings in a way that will hopefully get me to a place where I can work again.

I currently live in a condo with really bad air quality; it’s downwind of a frequently used parking garage and is also really close by a busy gas station. And to top it off I’m pretty sure the ceiling is showing signs of moisture damage. I’ve had stuff in closets away from the bathroom grow mold, so something is up. I am living with my dad because I don’t have income and he says he has no problems living here, but he’s accumulated quite the laundry list of health problems since we moved in, so…

The number one treatment for MCAS is to reduce exposure to triggers. Obviously I plan to move, but the thought of ending up on a year lease in a place that’s only slightly better without some kind of longer term life raft plan seems a little depressing, and I can’t afford to repeat that process too many times. Also, despite having enough savings for rent, it’s very hard to find rentals that don’t require 3x income regardless of savings here.

I have an aunt who has offered up their porch that has since been converted to interior space, approximately 12′ x 20′ (guessing).

The house was built probably post-WW2, and the pre-existing porch roof is basically the old giant overhang (double height at the old exterior wall). I don’t know the how or if this roof is vented.

Then the added walls are 2×4 framed and sheathed with T1-11 grooved plywood siding(?) with unknown amounts of insulation. I believe the floor is tile over bare concrete slab.

It is in Bellevue, WA, climate zone 4C. I stayed there a few times when I was a kid, and I remember it being extremely cold at night during the winter, even with several space heaters running. Maybe 48-55F? I would keep the single pane sliding door open to the house and move my sleeping bag close to the opening.

How unrealistic would it be to build a room within this converted porch? I was thinking I could make it small, just enough room to safely fit a twin bed, a small computer desk, a portable dehumidifier, a portable air purifier, and heating/cooling (temperature extremes are a trigger).

I was thinking since bulk water is no concern, to build something like this:

Taped plywood (air control layer)
2×4/6 structural framing with some kind of tolerable cavity insulation
2 layers of 40mm(?) Gutex, or cork? with staggered joints

Roof – same idea as the walls but with appropriately sized structural framing, and maybe more insulation? And of course tape the plywood to the wall plywood.

Floor system – this I’m not really sure about. I think the walls would sit on the true floor since I don’t care so much about acoustic isolation. Then I guess stack 2 layers of staggered Gutex or cork on top of the tiled or bare slab and top it with Advantech or similar, taping that to the walls. Then undyed red rosin paper and some kind of floating hardwood floor

Electrical – uhm…put it close enough to the wall with existing outlets that I can just plug things in directly through a gasketed port? As I write this, it already sounds like a bad idea.

Ventilation – two through wall ERVs or a regular ERV to an insulated duct running through the exterior wall. Condensation issues along the duct?

Windows and doors – one good of each in terms of air infiltration. And the window sized for egress. Two windows if in the budget?

Having now written this out, it does sort of sound uhm, not exactly realistic. But as I sit here wondering if for the third year in a row I’m going to spend tonight repeatedly waking up to a vomit filled mouth because the wind shifted…

Problems I could guess about:
-permitting; in searching I only found info about permitting for commercial recording studios built inside homes, but nothing suggesting a recreational studio required a permit. But maybe that’s because nobody sleeps in their recording studios.
-might be a lot of work and money to not solve anything



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  1. DC_Contrarian_ | | #1

    Do you know what the contaminants are? Are they all things that can be filtered out? If so all you need is an enclosure that is tight enough that it can be kept at a slightly higher pressure than the surroundings with a fan, and a fan and filter. I'm thinking like an oxygen tent or an altitude tent, Google them.

    1. jimbox | | #2

      Yeah I thought about that route too. Probably the better option to try first. I don't think the goal is to get to 100% reduction as that's likely impossible.

      Filtration would be a decent idea but I think the outside air supply would be ideal because portable filters can themselves be a source of issues. I read somewhere but I can't remember now that they can actually increase the concentration of certain types of things (not particulates, it was something else, I can't remember. I read it on some science blog. I'll have to go look for it).

      Thanks for the idea I'll look into those tents. My guess is it would really depend on the materials the tents were made out of. I can deal with some better than others depending on if they've been aired out. Brand new clothes are always a lottery.

    2. jimbox | | #4

      I don't think this is a reputable source but it says:

      "The humidity inside the Higher Peak sleep canopy was 48% compared to 70% inside the Hypoxico Deluxe Bed Tent and 64% in the Colorado Altitude Walk-in Tent."

      The canopy is more like a hood that your head and neck lay in. So it sounds like humidity's a concern with these designs.

  2. mr_reference_Hugh | | #3

    Hello jimbox,

    My biggest concern, believe it or not, is your very first statement: "This is kinda a weird question". It is NOT weird, it’s really important. I don't have the heath issues you describe but they are real and you need a workable solution. You have a limited budget and a lot of other constraints.

    I think that the first step in this journey is to build up you confidence and assert that this is a valid technical "building" issue that is gaining importance and recognition every day. The Building Biology Institute has apparently existed for 33 years. Also, everyone who ever builds anything needs to be budget conscious, except maybe billionaires. You are not alone. It is totally normal.

    There is a possibility to spin this on its head and look at this as a great opportunity. A person with this type of health condition could build a small "bubble" as you propose (I hope it is ok to call it a bubble) by doing some basic research (see a link below). You could then work from inside that bubble online to study the cr@p out of this topic. You could eventually become a paid consultant to others. That Building Biology Institute (link above) apparently offers certification programs, which is a concrete example of how you can study the topic and get recognized for the studies you complete. There must be other similar institutions around.

    Checkout this super well-organized website from a certified consultant

    That second site basically walks through every major aspect of choosing materials.

    You do basically want to build a "bubble" inside a house. Did you know that in commercial construction there are all kinds of different business requirements where there is a need for a "room within...a building" that has control layers to control infiltration of outside air? This type of requirement is totally normal.

    When you think of building an airtight room, this is completely aligned with the notion of building an air-tight house. Building an airtight room on a covered porch is basically the same thing, but you will have less "load" or forces (no snow, wind, etc.) on the roof of your room.

    In terms of permitting, you technically need a permit for everything. But the reality is that many many people just skip that part. On this aspect, I would just be cautious that if you build something in someone else’s house, be sure that that you respect building codes and don't cause problems with the home insurance policy that the person might have in place already.

    I will put a separate post to address your more specific questions.

    1. jimbox | | #5

      Thank you!!! I think I am kind of conditioned by years of funny looks at the doctor, to be honest. I pretty much cried when one specialist was like "yeah you're not crazy, I see more and more people like you each year."

  3. Expert Member
    BILL WICHERS | | #6

    Humidity is a common issue if you put a person in a sealed off space, since the person will release some moisture, and that will drive up humidity levels in a sealed, small space. Your case is different, so I don't think that applies here.

    My first though would be to run a slight positive pressure in the room (which means all the air leaks OUT, not IN, so you can control what comes in), and bring that air in through a HEPA filter, which will get most particulate contaminents. If you need chemical filtration too, you might also need an activated carbon filter. Anything beyond those two filter types gets very complicated. What you're now doing is bringing ALL air into the room through your filters, and the slight positive pressure means ALL the air leaks are leaking OUT, so no air leaks bring any contaiminents INto the room. This would be relatively easy to setup in any regular room without needing any fancy construction, so I'd recommend trying this first before spending a lot of money.

    If you want to build out a room in a porch, all the normal construction rules apply. The only difference is the underside of the porch floor is probably open to the outdoors, so you'll need to seal that off somehow (which could be plywood under the joists, but there are many ways to do it), similar to what you'd do if you were building over a vented crawlspace. If you are also going to run positive pressure in the room, which is the only way to really be sure you don't have anything getting in that isn't filtered, you need to be a little more careful with moisture drive into the walls than you would in a normal structure.


    1. jimbox | | #8

      Sorry, I think my original message was not clear. I'll go back and edit it.

      The porch isn't exposed to the exterior anymore, but I have doubts about how well insulated it is. It is 100% enclosed by 2x4 walls sided with T1-11 grooved plywood and has two french doors and two windows. I believe there is also electrical running through these walls.

      The new enclosed room's floor I believe is just tile over the old bare concrete porch slab.

      The positive pressure approach in the existing converted porch sounds promising, I'll have to look into it. Would the positive pressure environment be easy to maintain even when it's very windy? Usually there are steady ~20-25mph winds at least every other day from October to March.

      1. Expert Member
        BILL WICHERS | | #10

        It's not hard to maintain positive pressure in a room that is reasonably well sealed -- even a simple muffin fan can usually do it. You're not trying to pressurize things like some kind of pressure capsule, all you need is enough positive pressure to make the leaks leak "out". You can even monitor this with a differential manometer -- as long as the "inside" pressure is always higher than the "outside" pressure, you're good to go. You only need fractions of an inch of water worth of pressure here.

        BTW, Magnehelic makes very good manometers for measuring this sort of thing, and they aren't very expensive if purchased used.


  4. mr_reference_Hugh | | #7

    OMG. Trust yourself. It can be difficult when you have Doctors looking at you funny. I hope that you start to surround yourself with people (even it is just online) that fully understand this topic in extreme detail. Of course, you need to avoid the trolls online who will be more than happy to invest effort in denigrating anything that does not relate to their ridiculous extreme views.

    This type of condition is going to affect more an more people.

    I was following the "Build Show" hosted by Matt Risinger on YouTube. He is a high-end builder, and Youtuber, who focusses on high-performing, airtight homes. He is pretty mainstream and even he covers these topics. Listen to this this video.

    The builder walks through what he is doing for his client. You will see how some people with these environmental sensitivies have big bucks to spend to build something I would consider a major dream home.

    Even me, who has none of these health issues, did research on all my building products used on the interior to consider the chemical emissions that could cause my family issues sometime in the future. Our home was made airtight to control air quality. My air exchanger only has a MERV 8 filter but there are other air exchangers that can have much higher rated filters.

    Also, government are actively studying new home air quality. Check this out.

    Again, this reply is to first convince you that this topic of environmental sensitivities is mainstream. It may not be apparent in your immediate environment but you can start to study this in an informal fashion by reading credible sources online, but then look for a certification you might want to pursue - if you can shift your attitude towards this condition.

    Again, I will post soon to address you specific questions.

    1. jimbox | | #11

      Thanks again for your replies. I am pretty familiar with Risinger's channel yeah. I'd be interested to hear your feedback on a room-within-a-room enclosure. My gut says the safest bet is to treat it like a completely new building and not try to integrate any of the existing walls, floor, or roof; i.e. put new floor joists down attached to 4" posts or something. I was thinking of adapting Risinger's shed plans to this enclosure.

      1. mr_reference_Hugh | | #12

        I did not want to interrupt Bill’s thread. I will get back with a reply.

        I want to formulate a good reply so I hope to respond by Monday morning.

      2. mr_reference_Hugh | | #13

        Jimbox, would you be willing toprovide a bit more info about the space in the cover porch?

        I was just thinkink whether, for example, you could draw a very quick sketch to show the layout of the porch, like where the windows and doors are located? (I am certainly not expecting it to be to scale.) It could be hand drawn and you just take a picture and upload it here as an attachment. The location of doors/windows could impact how you could use the space and would then impact how you choose the materials for your space. If you have any info other than the location of doors and windows about the layout, throw it into the sketch. Let me know if this is feasible.

        1. jimbox | | #14

          Sure. Please excuse the messy dimensioning (solidworks professor rolling in their grave right now).

          I don't know if the walls are 2x6 or 2x4. I would guess 2x6 based on height. Interior and exterior sheathing/siding is T1-11 grooved plywood with paint. Don't know what kind of paint.

          I did it up in sketchup and quickly realised that if I were to try and build something insulated (or even uninsulated) and maintain a 3' pathway around it, the interior room becomes laughably small. I then thought about using the original interior sliding door to count as one of the 3' pathways, and I don't think it gets much better (maybe 4' width if building an insulated enclosure).

          I'm wondering at this point if a big old tent made out of Intello or similar is a better option.

          1. mr_reference_Hugh | | #15

            Nice sketch. I was expecting something hand drawn.

            So basically your confirmed what I was thinking about… the size of the room if there is 3 feet all around.

            Question: is there a specific reason you would not want to created a hole in one of the wall to actually see what the assembly is made of?

            I will look at more at the drawings tomorrow. I find this super interesting. Thank you for this exchange. I appreciate it.

        2. jimbox | | #16

          I'm not opposed to investigating what the current assembly is made of but it's low on the list of things to take care of after medical stuff for now because driving over would take me a few days to recover from fatigue wise.

          1. mr_reference_Hugh | | #17

            Hello Jimbox,

            We agree that you can't realistically build a room that is separated from the outside walls.

            You mentioned that it is cold, but there are good changes that the air leakage from the doors is a big contributing factor.

            You could create an air sealed room by building a new wall assembly that is right up against the current structural exterior walls. The only issue that I see, and it is important, is the likelyhood that the current exterior wall assemblies have a vapour barrier in them under the drywall (or other wall finishings).

            Option #1 - If there were NO vapour barrier, you could build a new non-structural wall assembly in front of the existing exterior walls, plus one new wall beside the door that comes out from the house. In would only build the ceiling as high as you need and you could place your ERV/HVR and other air supply equipment on top of the room (take basic measures to ensure to minimize sound transfer from the equipment).

            This should actually save you some money - in theory because you only need to have one really well sealed air-barrier on the inside of the room. Of course, you could have another air barrier over the existing drywall but I never like to slap two layer together.

            Option #2 - If you DO FIND a vapour barrier, then you need to decide whether you could afford to have someone to remove the existing drywall and vapour barrier. Once you do that, one of 2 things happens.
            a) You find insulation and an intact exterior sheeting, which means you can proceed with your build.
            b) you find a problem like rot or leaks or other stuff that happens to many houses. Opening walls is always interesting. To control the risk, you could proceed with removal of materials in a very controlled manner (section by section). If you find something, you the pause the work briefly and determine whether you want to continue. In case you do find something, you would want to figure out ahead of time who would be paying to repair for pre-existing damage that you find in the wall assemblies.

            With either option 1 or 2, you would get to make use of
            > The existing windows
            > The existing electrical (unless it is not up to code)

            IMO, it is difficult to plan without knowing whether you have a vapour barrier in those wall.

            If you want to know the best materials to use for your construction, then I would refer to the website I already shared adn that mdhomeowner also shared.

            I would fully insulate the new walls, make sure they 100% air tight, install a vapour barrier where it is appropriate.

            Does this make sense? I beleive that knowing if there is a vapour barrier is pretty important if you were to build a space for yourself in the enclosed porch.

          2. mr_reference_Hugh | | #18

            Jimbox, I would strongly suggest posting a new different question in the GBA Q&A.

            In your text, just explain the your original question has led to a new question. You can attach the plans you shared and any new information that you have gathered. You could explain that you want to convert an existing covered porch to an air-tight room. You could name the condition that is affecting you and provide a link like this one:

            Explain that you need to use the types of mateirals on this site.

            Anyway, just a suggestion. You and I are talking on this thread but with a new question and posting additional info you will likely get solid input from others.

        3. jimbox | | #19

          Thanks for all your comments, I will definitely post another thread after I get some more info on the existing walls/roof/floor

        4. jimbox | | #20

          quick question: let's say I don't know what's inside the existing walls. Would building 1" away from them be sufficient that they won't interact hygrothermally? This would also have sound reduction benefits.

          1. mr_reference_Hugh | | #21

            The only concern I would have is creating a fire safety issue with the way you describe it. However, i wonder if you could just put strapping on to of the existing walls. You leave a good sized gap at the top and bottom of the strapping. This would allow air to come up from the the bottom and rise up to the top. This would allow for venting between your new wall and the existing walls.

            I feel really unsure about this on several fronts. I really think a new thread with a new question would be a good idea.

            Like I said initially, the condition affecting you is widespread. Modifying an existing space is done all the time. It’s about framing the question right and getting input from some of the people who know the code well and have lots of experience.

    2. jimbox | | #22

      I made a new thread. Still planning to renovate the porch, but it's more of a longer term project than I thought.

  5. mdhomeowner | | #9

    I have found to be a very good source of information about minimizing chemical toxins in a home. You may find it to be a good resource.

    Here is the article about insulation:

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