# insulating sunroom on deck floor



## ratherbefishing

A few years ago, we built a new deck and had a Champion aluminum and glass sunroom installed over part of it. The installers did a last minute inulation job and put faced R-13 batts between the joists. Joists are 2x10, floor is 5/4 boards, thinset, 1/2" Wonderboard and ceramic tile. The floor is always cool or cold to the touch. I figure I can replace the R-13 with R-30, or add unfaced below the R-13.

What would be the best thing to staple/nail to the bottom of the joists to protect the batts and prevent wind wash? I have part of a roll of housewrap. But I wasn't sure about making a vapor sandwich. Maybe slit or perforate the Tyvek?


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## joecaption

I'd use what's commonly called chicken wire. It's sold in the fencing area.
Wondering how that tiles holding up since the subflooring was done wrong.


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## ratherbefishing

No problem so far with the tiles. Trying to keep the wind away from the insulation.


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## Gary in WA

As you said deck- it is exposed to the outside air? Chicken wire will let the air through but stop the rodents (bigger ones at least).
Housewrap will stop the air but not insects and small rodents-- slashing it does nothing if for a vapor barrier because it is vapor permeable. It could be an air barrier, if done properly. 

I would add the f.g. (I can't believe I said that...http://www.diychatroom.com/f98/biggest-loser-fiberglass-insulation-90438/), then some foamboard on the joist bottoms, covered by plywood.

Gary


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## ratherbefishing

Yup. It's on a deck. Open on 3 sides, about 5 feet above the ground. Filling the joists with insulation, and enclosing with plywood sounds like the warmest way to do it. But I wasn't sure about moisture. The floor seems impermeable to me. FG has kraft paper facing up, towards the inside of the room. But the R-13 they used doesn't fill the joist cavities. I have a partial roll of Tyvek left over. Also have a 1/2 bundle of faced R-30 that I need to use for something. Plywood isn't that expensive; or I could use Celotex (The rest of the house has it under the siding)


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## Gary in WA

A good one; http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces/

Gary


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## ratherbefishing

Thanks, Gary. That Building Science doc took a couple of readings to digest. It looks like my sunroom/deck situation is most like a house on open piers. The spray foam option isn't going to happen right now. What do you think about adding unfaced R-19 FG to the existing R-13, then covering with blackboard? Quietbrace is available at the local Orange Box. It is rated R-1.3 and has a vapor perm of 5-15. It seems like the high perm may prevent any moisture problems.


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## cbaur88

ratherbefishing said:


> Thanks, Gary. That Building Science doc took a couple of readings to digest. It looks like my sunroom/deck situation is most like a house on open piers. The spray foam option isn't going to happen right now. What do you think about adding unfaced R-19 FG to the existing R-13, then covering with blackboard? Quietbrace is available at the local Orange Box. It is rated R-1.3 and has a vapor perm of 5-15. It seems like the high perm may prevent any moisture problems.


Spray foam obviously would work best but I totally hear with it not happening right now it's very expensive even the DIY kits are costly.

I think adding the unfaced R-19 will obviously give you better R-Value and would work best if you covered with as you mentioned with blackboard or some type of rigid foam with a high perm rating to avoid moisture issues. I say only if it's covered because I think fiberglass works best when not exposed to flowing air so air sealing that bottom and taping the seams will be the key avoiding any air drafts coming up through to the fiberglass and through the underside of the floor. Good Luck :thumbsup:


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## ratherbefishing

Thanks for the encouragement, cbaur. I got the pink stuff up this afternoon. Blackboard is stacked up, waiting until tomorrow. I was never sure what those "narrow crown" air staplers were good for. Now I wish I had one.


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## Gary in WA

Sorry I didn't get back right away. Foam board and plywood as I said in post #4.

Your Celotex is vapor open allowing moisture in during the summer when cooling with AC and would grow mold; http://www.inspectapedia.com/sickhouse/Fiberboard_Mold.htm It has minimal insulating R-value unable the change the dew-point in the cavity, your f.g. would get wet, degrading it’s R-value by 60-70%; http://www.nrc-cnrc.gc.ca/eng/ibp/irc/bsi/90-controlling-heat.html

Pp.7 on *“Mixed climates”* here; http://www.buildingscience.com/documents/reports/rr-0412-insulations-sheathings-and-vapor-retarders

Use the foil-faced foam board to stop moisture on the crawl side, as the BSC article said, figs. 6, and 7, read them again…..this will stop any moisture from condensing inside the cavity. Remove the paper facing as you are border-line in a “warm/humid climate zone 3/2; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec001_par001.htm

Gary


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## Medi0gre

You need a air space. The floor will heat the air space. I use those 4' pink foam insulation stops, stapled to the floor sheathing then install insul batts. More insulation Will not help the cold floor with no airspace. Sheath and tyvek. Skirt if you can.


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