Ventaling under 3 season addition
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Ventaling under a 3(4) season addition.
I’m looking for some advise about reducing the moisture under a 3(4) season addition.
Two years ago I had a contractor build a 14’x16’ addition. This was built on two sets of concrete piers and LVL beams . One is about 8’ and the other 15’, parallel to the house. From the ground to the bottom of the 2×10 floor joist is about 2’ were it attaches to the house and the far end (16’) is about 4’. It was build over dirt. The builder also built a 2×4 skirt wall from the bottom of the rim joist to the ground on all three sides. This is covered with ½ plywood and 1†insulating foam board and whole thing is vinyl sided, right to the ground. There are two 18â€x24†vents on each side and a one small access door. The floor is insulated with R30 faced fiberglass between the joist. The paper side is up or toward the heated living space. Nail to the bottom of the joist are 1†insulated foam panels. I guess this was to keep the fiberglase in place!. There are no pipes or heating vents in the floor only electrical wires.
After the first year and reading Fine Homebuilding, I added two layers of 6 mil poly to the ground and sealed the perimeters and around each post with caulk. I also sealed up the vents. After a mouth, I noticed a big reduction in moisture in the crawls space. Now this spring I notice water puddling on the top side of the poly.
I’m about to ripe out the three 2×4 skirt walls and replace the whole thing with lattice, and leave the poly on the ground. Its not going to look as finished as it does now, but I think it will solve any moisture problems. I’m also considering using vented vinyl instead of lattice for looks. I might be able to get the same color to match the vinly siding.
Does anyone have any suggestions, Thanks
Replies
Do you know the source of the water? It's possible its coming from condensation that has developed in the insulated cavity, and when spring came it dripped out. The foam is probably creating a second and probably better moisture that the Kraft race insulation. I would suggest that you remove a sheet of the foam and check the condition of the fiberglass. Removing the skirt may only give the moisture you saw on the poly a way to evaporate, but may not solve the real problem. (If I've read this right you're assuming the moisture is coming from the ground.)
Woody
I'm not sure of the source of water. I don't think is coming from the ground! I'm assuming it is condensation from the air. When the temperature and humidity change rather quirky, the differences between inside an out. At this time I don't know the condition of the fiberglass insulation. I will check into it this weekend. The skirt wall does not have insulation, just form board under the vinyl. By removing the skirt walls, I was think it would provide as must air circulation as possible. I have seen other 3 season additions that are comply opened underneath. My thoughts are that the negative effects would be maybe a colder floor in the winter and a less finish exterior look. The only heat in this room is a zero clearance gas fireplace. We plan on using it for the first time this coming winter as much as possible. Thanks, Bob
I doubt that putting in more ventilation will help much if the porch above is air conditioned. The trouble you're experiencing is likely due to the lack of insulation on top of the ground and inside the walls of that space. I imagine that if you were to insulate the ground and walls with XPS that the problem would largely go away (along with the heat flux in and out of that space). For a comprehensive explanation, look no further than buildingscience.com and delve into the homeowner resources. Cheers!
Edited 7/8/2005 9:50 am ET by Constantin