I need some help…..
I have a cantalevered section of our breakfast area where the underside needs to be weather proofed. The old section of 1/2 plywood that was acting as the soffit rotted out. There was a deck that was installed that prevented access to the area. I am in the process of rebuilding the deck and I need to replce the soffit section with something that will hold up to moisture and humidity.
My initial plan was to use 1/2″ MDO that is primed and paited with exterior paint. I was also going to cut in soffit vents and insulate the joist bays with R19 fiberglass insulation. One problem I run into is the new deck will effectively close off a lot of circulation underneath the deck in that area. This was due to new footing guidelines with my county (a very long story I posted a few weeks ago). The picture shows the cross section of the new joist system I am using.
My concern is with humidity rotting away a section of 1/2 MDO over time. One thought I had was to use 3/4″ exterior plywood primed and painted. Or, using a vapor/water membrane over the MDO or plywood. Air circulation may become an issue since the joists and beams are only about 4″ off the ground.
Any thoughts on how to prevent the soffit from rotting out again?
Edited 7/6/2008 9:21 am ET by Mike126
Replies
Sounds like a good spot for Hardipanel.
When you say soffit, you are talking about bottom side of your cantilevered bump out correct?
What was the cause for the old soffit rotting out? Think you need to address this situation first. My thoughts are, even if you use something like a hardi panel, if you've got that much moisture in that area, you are eventually going to have problems in other areas ( band joist, floor joists, etc.).
I dont know what cutting in soffit vents in would do? Where are they going to vent to?
Things I would pay special attention to would be flashing on the ledger boards. You say you only have 4" of clearance between the ground and your framing (joist & beams). Can you haul some of that dirt away to give yourself more space. Be sure to also slope the dirt away from the house.
Correct it is the underside of the cantilevered floor.
What originally caused the problem was the deck was butted up against the house and not able to drain. The water collected at the deck and the house where the bumpout is. It rotted the facia board as well as the soffit panel under the floor. I even had some joist rot.
My new deck design will leave at least a 1/2" space around the bumpout section. That framing cannot be attached to the rim joist of the bumpout. I was going to replace the facia as well since the deck will be about 2" - 3 " lower than the house floor level.
I had thought that installing vents would at least let the interior breath and prevent moisture build up since the floor above is a different temperature. That may not be a correct assumption though.
I'm concerned that once I get the deck in I don't want to have to worry about rot in that area.
Edited 7/6/2008 1:02 pm ET by Mike126
I have used aluminum soffit panels with good success.
Edited 7/6/2008 3:41 pm ET by frammer52
adding soffit vents in a location like that near the ground will let moisture INTO the framing and underfloor insulation. I'd bet it would be detrimental.at least the way it was, you stopped it at the soffitAny of the above materials would satisfy me there
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I looked into AZEK 4' x 8' sheets. Do you think installing this without vents would work ok?
As someone else mentioned, the most important thing is to properly flash the area so moisture can't get in from above. But in your situation you may have trouble with water splashing from the ground. Placing loose gravel along the drip line to minimize splashing may be worthwhile.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
Dan - One issue I might have with the flashing is getting is tucked into the subfloor under the doorway. I was thinking of using a waterproof membrane that glues in place to wrap the rim joist and then put a facia board on top of that to dress it up.
Whatever works, but likely the old stuff wouldn't have rotted if it had been properly flashed.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
Not necessarily. Just being that close to the ground with moisture keeping it humid could have caused the rot. Didn't need to have been wet water.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Guys - Here's what I'm planning on doing based on everyone's advice.
1. Remove the bump-out trim and flash around the slider and windows. I have to do this anyway as it is rotting at the bottom. I bought some adhesive back flashing membrane from my local lumber supply yard. I will extend the flashing all the way down to the bottom of the rim joists using felt paper.
2. Replace the bottom (soffit) panel with a piece of Kleer 3/8" PVC panel.
3. Replace the facia panels with Kleer 3/8" PVC. I will allow the facia to overhang the rim joist to carry the water away from the soffit panel . All seams will be caulked.
4. Regrade the area under the bump out and put in a couple of inches of gravel. Also regrade the area where the first set of joists are to try and get more ventilation.
5. Leave a 1/2" gap at the deck around the bumpout to allow for water drainage.
6. Slope the deck 1/8" per foot away for the house and use the maximum gap with the deck boards based on the manufacturer spec.
Once the deck is in, access to this area would require removing a large section of the deck. While not completely out of question it would be somewhat costly and time consuming. Not something I'd want to plan for... :) I hope this will work.
Sounds like you don't understand flashing. If you have an exposed fascia the flashing should lap OVER that, not run behind it.Think like a raindrop.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
Dan - What I was trying to prevent is water getting into the rim joist. So by flashing behind the fascia I was hoping to effectively seal the rim joist.
Other than the slider threshold, I'm not sure how I would flash where the fascia and deck meet. Unless you are saying I would not need to and just leave a sufficient gap between the fascia and deck to allow for drainage.
Would I be creating an issue by putting a membrane on the rim joist?
I'm talking about flashing between fascia and siding. Flashing should be behind the siding and over the top edge of the fascia.
It is an ironic habit of human beings to run faster when we have lost our way. --Rollo May
Dan - I attached some photos of the area that I'm talking about. What I was trying to create was the flashing that should have been done with the previous owner/builder installed the slider. There is none. The water got into the subfloor on the left side of the slider and went through the space behind the fascia and rim joist. That area was shimed out to provide the right amoung of reveal for the verticle trim pieces. You can see the water stain on the left side of the rim joist.
On the right side it looks like the same thing happened. The panel under the overhang rotten on the right side. The rim joist on the right side was also in very bad shape and I replaced that. All the verticle trim will be replaced along with reinstalling the lower sections of the fascia.
One question.... for the panel under the overhang, it there any reason to vent it? I was going to use a piece of PVC panel for that area so I don't have to worry as much about it rotting out.
Thanks for the feedback....
I looked at your drawing and all I can add to what others said (those who realized you were talking about the underside of a bumpout (floor) and not a roof overhang!) is to increase ventilation--maybe a bigger space between the deck joists and the bumpout. Make sure any water getting on the deck isn't flowing toward the house and make sure ground is sloping away from house. That's about all I can think of.
Danno - Sorry for the poor reference of the soffit. I'm planning on sloping the deck 1/8" per foot away from the house. I'll put some gravel under the overhang area and a few feet out to keep the drainage and splashing to a minimum. I was also probably going to gap the decking a little on the wider side to have it ventilate as much as possible.
Hardisoffit.