Redoing siding and rethinking indoor swimming pool wall insulation. Need advice on moisture management and choice of insulation.
I am planning to replace siding on the entire house, and while I am clear on the route I want to take with adding a layer of continuous Roxul on the main side of the house (built in 60s, already replaced fiberglass with Roxul batts when I redid drywall), we have an indoor pool in an attached building that was built in ’93. I am controlling RH rather well, since we have an automatic pool cover that is closed anytime the pool is not used, and I have a dehumidifier that only runs when the pool is open. The size of the pool is 20X40, so a lot of evaporation when open, and the RH goes up to about 70% during that hour or so we use it each day, but then in the next couple of hours, the dehumidifier knocks it down back into the 50s.
The current wall cross-section detail is attached.
I am considering removing the siding and 1/2 CDX sheathing and replacing the fiberglass with a flash layer of closed-cell and Roxul for the rest of the cavity. Then, I would wrap the Zip-R sheathing and siding with a rainscreen behind it.
Why do that? My concern is that moisture was not managed well before, like in the rest of the house, so when I open that wall, I may find what I found in the rest of the house – crumbled vapor barrier (plastic) and fiberglass batts gray from dust and mold. Would be nice to have tighter air infiltration control so I need to heat the building less in the winter.
I am not very good at understanding vapor drive with natatoriums, so that is one area I would like to get educated on.
Any advice, direction, or places to look for info would be appreciated.
I am in Boston MA.
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The way I see it you have a wall with at least an R10 value that seems to be working now. An R10 wall will stop over 90% of the heat flow. If you change something you have no guarantee the new wall will not rot. The new wall will not save much energy. The new wall will cost a lot of money. I see a lot of risk and almost no reward.
Walta
So, if I am not touching anything within the walls and only removing the siding, would liquid-applied WRB make sense to make the structure much more air-tight? Or maybe 2" of XPS with seams taped, then rainscreen, then siding?
"An R10 wall will stop over 90% of the heat flow."
You see formulations like this all the time, particularly from foam salesmen. It just grates on me.
A wall with zero insulation allows infinite heat flow. 90% of infinity is infinity.
It's asking the wrong question. Yes, there's always diminishing returns to additional insulation. Add insulation until it no longer makes sense to do so.
I believe the starting point for this math is R2 as it is a given as the sheeting and drywall give you that.
Yes, everything is relative if you decide R10 is the base and don’t show the lower numbers the chart looks pretty different. The line is pretty flat much after R25.
Walta
I totally forgot about that chart. I recall seeing it a long time ago. The big question is how good or bad the current state of the studs and sheathing is, at least on the pool house. On the main house, I know the first floor is a disaster since it has Masonite siding that is like a sponge.
The house was owned by a couple who did zero maintenance. The pool was mostly uncovered (since they broke the pool cover), and the dehumidification system was also non-operational for many years (and to make matters worse, they were renting out the pool to the public). Interior walls are clear cedar planks and I can see there was a lot of condensation allowed. So I have to find location where I can open up the wall and see the condition of everything inside.
But from what I am seeing in the comments so far, if everything is fine inside, I should be thinking about a smart membrane on the outside of the sheathing with a drying to outside configuration, followed by a rainscreen and white cedar shiplap.
It works now the more you change the greater the risk. Most liquid water barriers will also be vapor barriers that make them risky for your damp location.
Understand you have happened apron a recipe for a wall that works for you under very harsh conditions.
Any change you make no matter how well intended could turn the wall into a moldy rotting mess.
Reducing the air leakage and increasing the R value seems like a good idea until you consider the air and heat leaking thru your walls is keeping them warm enough to prevent condensation and carries the moisture safely out of the wall.
If what you had worked but the siding is weather try to find and use the same materials. If you are replacing the siding because what you have now made it fail then that is a different story.
Walta
Not sure if this is helpful for your specific circumstances, but Joe Lstiburek has a pretty good article about indoor pools here:
https://buildingscience.com/documents/insights/bsi-055-in-the-deep-end#02
If you're removing the siding anyway to replace, and not opposed to also removing & replacing the sheathing... You might consider re-sheathing with Zip for a bombproof air barrier, then doing all your insulation on the exterior. Remove any insulation on the interior. If you have a bombproof air barrier at the sheathing, and enough insulation on the exterior, there shouldn't be any way for warm wet air to dump its water on a cold surface, and there's no interior insulation to potentially get saturated.
I did this recently on a project with a large indoor pool at 8,000' elevation, CZ6. We did 6" of exterior Rockwool on the walls (preferred over foam since it doesn't limit drying), with wood or stone siding over a rainscreen. The roof was an "inverted roof," so low-slope roof with just enough polyiso on top of the sheathing to taper to drainage, roofing membrane, 8" XPS, gravel on top.
I did read Joe's article bit after I posted. I think my next step is to find a location or two to open up and see what the state of the framing, insulation, etc., is.