My brand new sunroom is elevated above ground by posts set on concrete piers. There is about 18†of clearance between the ground and bottom of the floor joists. The 2X8 joists have been closed from the bottom with ½â€ plywood and filled with fiberglas insulation bats. The subfloor facing the room is ¾â€ plywood which at present is laid in loosly to be able to get to the joist area for electrical and plumbing installation.
This area (crawl space?) under the sunroom is against 2 walls of my house with the other 2 walls being open to the outside. I plan put a lattice skirt to cover the opening on both sides – preferrably removable so I can get under there if I need to. I lived on Long Island NY.
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From the finished inside of the room, I lifted up several sections of the top plywood. The insulation, joists and plywood bottom are damp. I think that moisture from the ground and surrounding air is going up into the joist cavities and staying there. Even though it has been exceptionally rainy, this does not seem good to me. A little moisture now could = much mildew, mold, insects and rot years later. <!—-> <!—->
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Question(s):
1. I know that in a closed in crawl space it is important to install 6mil vinyl on ground for moisture control – but in a relatively OPEN situation like mine is a vinyl vapor retarder still recommended?
2. I think the moisture is due to condensation. What is the best way to relieve this condition?
3. Is it possible that the bottom 1/2″ plywood bottom was a mistake and should be removed?
4. What is the best way to insulated the joists and remove all possibility of moisture build-up and its consequences.
Thank you very much for your assistance. It is a pressing issue as my contractor is finishing up and I feel I am very fortunate to see a potential problem before it becomes on for real.
jh
Replies
What I did on our enclosed porch was cover the bottom with framed panels made with a layer of hardware cloth and a layer of landscape fabric atop that. The hardware cloth keeps the vermin out, the fabric keeps out the bugs, and the whole thing "breathes" so that there will be no condensation buildup.
Hey DanH,
Hardware cloth and landscape fabric wrapped around a wood frame and attached to underside of joists? BRILLIANT!
So you are definitely suggesting REMOVING the existing solid plywood panels under the joists?
Would you keep the fiberglas insulation between fabric panel and sub-floor? Some other insulation type?
Leave the perimiter open or close it?
Thanks!
jh
FG insulation is what I used, because it was cheap and easy to deal with.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz
How is the grading under and around your porch addition?
Gentle slope away from house.
I thing the above suggestion to use wire and landscape fabric is a good one. You need it to breath. You could use Typar housewrap in place of the landscape fabric, but the LS FAB might be more cost effective since Typar only comes in large rolls.
If you Google for the "perm rating" of plywood you will see it doesn't breath much. The lower the perm rating, the less something breaths.
Assuming that the project is graded so that there is perfect drainage with no pockets under the porch I'd say cover the ground with black 6 mil poly and then pea gravel over that. You are going to need something to keep the weeds from growing under there anyway, and this will help keep the ground moisture from coming up through the floor.
BTW - you know that the insulation is supposed to be up against the subfloor, right?
Matt,
Thanks for your input here.
Right now my insulation bats are lying on the plywood that is covering my joist from the underside. It is an inch or so away from the upper sub-floor.
What about just cutting large holes into the plywood bottom cover - allowing air to circulate?
Why black poly and do you make this recommendation even though the area is open to the outside?
Is it ultimately better to close off outside air altogether.
Thanks again.
jh
Edited 8/4/2009 9:36 am ET by Jerry67
If you cut holes, cover them with wire to keep critters out. Critters LOVE to nest in fiberglass.
As I stood before the gates I realized that I never want to be as certain about anything as were the people who built this place. --Rabbi Sheila Peltz, on her visit to Auschwitz