Screws thru deck ledger flashing
Most or all the diagrams I’ve seen showing proper attachment of a deck ledger to a house (new construction) show flashing under the housewrap & siding and over the edge of the ledger. Some sketches also show spacers between the ledger and the flashed rim. One might argue that there also could be flashing that goes under the flashing over the top edge of the ledger and down over the bolt holes, to protect those spots from weather, unless the use of spacers obviates the need to do this. In theory, all of this should keep water from getting into the building shell and causing problems. But what about the attachment of the decking to the ledger? Assuming joists go out from the ledger, on hangars, should the decking be screwed only to the joists, with no screws through the flashing over the ledger? This would put the closest screws at least 2″ from the edge of the decking. Is that a problem with any types of decking? Or would screws thrugh the flashing not be a problem if there are spacers to provide an air gap between the ledger and the flashed rim? Comments?
Replies
Personally, I'm not terribly concerned with the possibility of water finding its way through the few holes in the horizontal portion of the flashing.
If it concerns you a bunch, pre-drill for those screws and shoot some silicone into the holes prior to screwing.
J. D. Reynolds
Home Improvements
Further to the matter of attaching decking to the ledger end of the joists, if the Z-flashing over the ledger is covered with the inside edge of the first deck piece, then there will be a tendency for dirt, debris from trees, etc. to collect between the edge of that first piece of decking and the flashing against the house. To promote free draining of rainwater off the flashing and flushing of dirt along with it, how about mounting the joist hangars so that the top edges of the joists are, say, 1/4" above the top edge of the Z-flashing, so that the inner edge of that first piece of decking is cantilevered 1"+ over the flashing, with the screws only into the joists. There really won't be any load on the edge of the decking over the ledger. Thoughts?
I assume you pitch your decks away from the house slightly.....
I usually install a small cant strip on top of the ledger( a rip of PT 2x, 1/4" or 3/8" tapered to 1/8") then set the Z flashing on top of it, or if you install Z flashing first,make allowances for the cant strip to be installed after, but before decking.....then fasten decking with 1 screw placed so as not to penetrate Z flashing, not hard with typical 5/4 x 6 decking......the cant strip will help shed wateraway from the ledger, and the debris with it. Iusually make thew Z flashing with at least a 2" leg on the ledger/joist, helps keep the water running in the right direction.
Geoff
Edited 4/27/2007 6:49 pm ET by Geoffrey
Are your joist tops flush with the top of the ledger or with the thick edge of the cant strip? Does your first decking piece end up slightly canted? Or are your joists higher than the ledger? And if the first decking inner edge rests on the inner (thick) edge of the cant piece, where is the space for water to flush away debris?
Dick,
Are your joist tops flush with the top of the ledger
yes
Does your first decking piece end up slightly canted?
yes, away from the building
And if the first decking inner edge rests on the inner (thick) edge of the cant piece, where is the space for water to flush away debris?
If you wish you can rip the bullnose edge off the edge of the decking that goes against the house,or not, either way is O.K.... because you have siding coming down and you have the decking pushed up against the flashing, the water will drip onto the decking and away from the house,... the flashing becomes just a "back-up" in a way.....remember the cant is just enought to shed water away from the building, not a ski-jump ramp....so it will have minimal or no effect on appearance.
Geoff
If the edge of the decking is pressed up against the vertical segment of flashing, both the rounded edge of the decking and the slight cant will result in an open V-shaped gap between the flashing and siding, providing a place for debris to collect. This won't cause a problem for composite decking, but it makes the periodic cleaning of the debris with a hose required that much more often and messier. Taking your approach one step further, one could trim the edge of the decking at an angle to avoid the gap between it and the flashing, but general recommendations on composite decking installation call for a gap at both edges for expansion, etc.
An earlier reply implied that nailing the decking to the ledger should be done to strengthen the joist-ledger connection. While the strengthening would occur, I have always believed that the joist-ledger connection should stand on its own structurally, without the need for reinforcement by the decking. If reinforcement of the joint were deemed needed, I would think that a metal connector would be more appropriate, such as a Simpson A35 or T strap tie.
Dick,
Taking your approach one step further, one could trim the edge of the decking at an angle to avoid the gap between it and the flashing,
As I indeed said in my previous post......
but general recommendations on composite decking installation call for a gap at both edges for expansion, etc.
since your only fastening the decking at one location on each joist (as I previously suggested) the expansion issue is minimal and moot. You should be more concerned with getting the right spacing to allow debris from trees to wash through the spacing and not get caught in between deck boards, rather than expansion issues, that's the least of your problems, especially in N.H., where you have pine trees(needles) to worry about.
As I said, your tucking this whole decking/flashing assembly under the siding,.....weather will fall onto the decking and drain away from the building. It's a lot simplier than you're making it out to be......usually the siding is brought down to with-in a 1/4" of the deck board,... depending on siding, you could sit it right on the decking.
Geoff
Sorry... I think you are overthinking this a bit... Non the less, if you are worried about it, do what JD said with the silicone. Same for the bolts that attach the ledger to the house, which to me, is more of a concern. Another method is to put the Z flashing on top of the deck boards - although it is not that attractive, but if painted the same as the siding isn't too bad.
The thing is that the deck boards being attached to both the joists AND the ledger helps hold that framing connection together tight. Same for the outboard end of the joists. Some BIs even require this. See attached pic.
I put the flashing over the top of the finished deck and under the siding. If you put the flashing over the joists and then install the decking on top of the joists and flashing it creates a trough for water and the decking acts as a dam.
I have never had any problem when I have done it that way.