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Last fall I had a small deck built to replace three masonry stoops that were falling apart. The sheathing behind the stoops was not flashed and was rotting.

The contractor did a good job as far as I could tell and, frankly, I don't know any better. As part of the job he replaced the rotted sheathing.

He put the tar paper membrane between the house and the ledger beam like this:

Tar paper membrane

He told me this was sufficient to prevent moisture from getting in.

After he was done, a few weeks later we had some major rains. The water leaked into the basement house right under one of the patio doors. This I think was a known problem before - the gutter in the back only had one downspout and used to overflow right over that door. So I added a down spot and caulked the gaps around the door - this problem went away as far as I can tell.

Recently we had a major snow storm in NJ. I did not shovel the deck. A few days later the weather warmed up a lot, snow began to melt, and I noticed a leak in another spot. This one seemed bad enough that it got into the house and formed a small wet spot on the floor indoors!

Since I asked the contractor to use screws on the part of the deck around the hot tub, I took a few planks out around the spot where the leak was. I found that the tar paper membrane was soaking wet on the inside of the ledger beam, the side against the house. The spot was right under the hot tub electrical conduit. The conduit was not previously caulked off by the electrician.

Going with the theory that the water found its way into the house along the conduit, I used some spray foam around it to seal it off. I put the planks back on.

Here is my question: is the flashing with a tar paper membrane sufficient? Was the contractor required to install a Z bar with a drip edge under the siding and over the ledger beam (I learned about this after the deck was done?

I do not think retrofitting the z bar would be that difficult since the planks are attached with the screws. It is something I could do myself, in theory, or with the help of a friend. The reason I am asking is to decide whether the contractor should come back and retrofit at his expense as part of labor warranty or not.

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  • Water intrusion into areas where wood will stay wet for long periods of time will result in eventual decay of the wood. You really do want to have flashing that fits up under the lower run of the siding and extends over any wood members that are part of the house and diverts any water away from areas where water gets down into cracks. You want the diversion to be toward areas that are open to the air and can eventually dry out.
    – Michael Karas ♦
    Mar 23, 2017 at 12:58
  • @MichaelKaras I get that and I may very well do it myself. Was the contractor responsible for installing the extra flashing or is it recommended feature?
    – Oleg Dulin
    Mar 23, 2017 at 14:04
  • Well if you hired the contractor as basically a handy man with no formal building plans then it is a kind of a toss up as to what should and should not be done by whom beyond the scope of localized building codes and what an inspector may or may not have approved. It the project was "formalized" by plans and building code enforcement then it may be more clear at where the responsibility lies.
    – Michael Karas ♦
    Mar 23, 2017 at 14:16
  • @MichaelKaras right, he was basically a handyman with no formal plans and the local code says nothing about z bars beyond a membrane between the ledger beam and the house. I think I will call him and offer him an extra job to come back and retrofit.
    – Oleg Dulin
    Mar 23, 2017 at 14:18
  • So, in the end, I worked it out with the contractor. I have more work planned for him this summer, and he agreed to retrofit Z-flashing as part of it. He did that last weekend. It hasn't rained hard enough to test it fully, but I hosed the deck down, and it feels bone dry on the inside of the house.
    – Oleg Dulin
    Apr 13, 2017 at 13:14

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