The original deck acted as a porch roof for a ground-level entry to the home, and had been waterproofed with an EPDM membrane laid over plywood sheathing.
Emanuel Silva The original deck acted as a porch roof for a ground-level entry to the home, and had been waterproofed with an EPDM membrane laid over plywood sheathing.

This article originally appeared on our sister site, PROFESSIONAL DECK BUILDER.

When I was asked last year to fix a leak on an elevated deck that doubled as a porch roof for a ground-level entry, I didn’t realize at the time that this seemingly simple repair job would turn out to become one of my most challenging remodeling projects.

Measuring about 17 feet by 12 feet, the 10-year-old deck included an L-shaped flight of stairs with a mid-flight landing. There were entrances into the house on both the upper and lower levels, and the builder had waterproofed the deck by first installing plywood sheathing over the joists followed by an EPDM rubber membrane. The decking was then fastened to 2-by sleepers laid over the membrane.

Water damage is clearly visible on the built-up support beam underneath the guard posts at the top of the stairs.
Emanuel Silva Water damage is clearly visible on the built-up support beam underneath the guard posts at the top of the stairs.

Finding the Leak

Viewed from below, water damage appeared to be concentrated underneath a pair of guard posts at the top of the stairs. So this is where I started my investigation, pulling the composite post sleeves off the 4x4 PT posts to check out the flashing. Here is where I uncovered my first surprise: Short 4x4 blocks had been added to the top of the posts to provide backing where the upper rails were fastened to the post sleeves. Apparently, the posts were too short when originally installed, and the builder hoped that the post sleeves would be strong enough to hold the assembly together. Not the cause of the leak, of course, but certainly a structural problem.

Shallow notches had been cut into the post bases to make room for the membrane flashing extended up from the roof deck. But with no counterflashing, it was possible that water running down between the posts and the post sleeves was causing the leakage visible underneath. I couldn’t be sure, because it looked like cracks had also opened up in the membrane around the post. Compounding the problem, the deck framing had very little pitch, because of the low headroom underneath the deck, so water didn’t drain off the membrane very quickly, if at all.

Whatever the cause, peeling the roof membrane back away from the posts revealed the extent of the water damage to both the plywood sheathing and framing underneath. I knew that I would have to remove the rest of the decking and the sleepers, strip off the rest of the membrane, and replace the damaged sheathing. That’s when I discovered significant rot damage in the triple support beam underneath the posts, which would have to be reframed.

The porch decking was fastened to sleepers laid across a membrane-covered plywood roof deck. The posts were flashed to the membrane, but there was no counterflashing.
Emanual Silva The porch decking was fastened to sleepers laid across a membrane-covered plywood roof deck. The posts were flashed to the membrane, but there was no counterflashing.
Water damage to the sheathing was evident after the waterproofing membrane was removed.
Emanual Silva Water damage to the sheathing was evident after the waterproofing membrane was removed.

As I peeled away the layers, more problems emerged. The roof-wall flashing membrane lapped over the weather-resistive barrier underneath the shingles, for example. This created a reverse lap that allowed water draining down the WRB behind the shingles to flow down behind the flashing too. The flashing membrane was also perforated with hundreds of staples. Because the homeowners also complained that water was leaking in around a couple of ground-level windows, I continued to strip shingles off the wall to find the problem. What started out as a deck repair had now expanded into a siding job, too.

Water had seeped down into the triple support beam below the posts, causing significant rot. Note all the dirt and debris that had collected underneath the decking between the sleepers.
Emanuel Silva Water had seeped down into the triple support beam below the posts, causing significant rot. Note all the dirt and debris that had collected underneath the decking between the sleepers.
The porch deck-to-wall flashing was reverse-lapped over the WRB underneath the wall shingles, creating a potential pathway for water to penetrate the structure.
Emanuel Silva The porch deck-to-wall flashing was reverse-lapped over the WRB underneath the wall shingles, creating a potential pathway for water to penetrate the structure.

Code Violations

Despite the post "extensions" hidden inside the post sleeves, the stair guard rails themselves were only 30 inches high and wouldn’t pass inspection. Worse, they had been notched around the 2-by framing, leaving only a 2x2 cross-section. They would have to be replaced.

An even bigger problem was the way the stair stringers were attached to the landing. With minimal bearing surface at the bottom of the stringers (less than 1 ½ inches, and at the toe rather than at the heel), there was no way my inspector would allow those stairs to remain. The entire landing would have to be reframed.

Shallow notches had been cut into this 4x4 post to allow room for the roof deck flashing membrane, while deeper notches were cut for the 2-by framing, critically weakening the post.
Emanuel Silva Shallow notches had been cut into this 4x4 post to allow room for the roof deck flashing membrane, while deeper notches were cut for the 2-by framing, critically weakening the post.
These stair stringers don't have adequate bearing on the landing. The landing will need to be enlarged, and the stringers replaced.
Emanuel Silva These stair stringers don't have adequate bearing on the landing. The landing will need to be enlarged, and the stringers replaced.

That’s when I discovered that the concrete piers supporting the stairs would have to be replaced, too. When I am working on an existing deck, I typically dig down to take a look at the condition of the piers and footings to make sure they are built and sized properly. In this case, the first pier I inspected only extended down less than half as far as the 48-inch depth required by local code, and rested on a large boulder. More digging revealed more boulders and more shallow piers. It looked like the boulders had been intentionally placed there when the foundation for the house was built, and that they had interfered with pier installation when the deck addition was built. To satisfy the inspector, the existing piers would have to come out of the ground and be replaced.

The piers supporting the landing were too shallow, thanks to boulders that had been buried under the slab where they were located.
Emanual Silva The piers supporting the landing were too shallow, thanks to boulders that had been buried under the slab where they were located.
The original piers had been pinned to the boulders with rebar, making removal difficult.
Emanual Silva The original piers had been pinned to the boulders with rebar, making removal difficult.

This was probably the worst part of the project, since I had to do the job by hand. My helper and I were finally able to dig and pour proper footings, but not before a lot of grunt work, and in the end, we still had to leave one of the largest boulders in the hole. It was just too heavy to lift without a machine.

Weatherproofing and Waterproofing

When I repair a deck like this that is at least partially enclosed by walls, I like to extend the weatherproofing up the wall at least a couple of feet by installing a self-adhering rubberized membrane. That's because rain falling off the roof onto the deck will splash back onto the siding, while in the winter snow often gets piled up against the walls. Wind-driven rain is always a concern, too. So on this project, I stripped the shingles back to the bottom of the window flanges so that I could properly detail the walls from that point down to the roof deck.

The author sealed the roof flashing boots to the posts with Siga Wigluv, a high-performance, water-resistant tape.
Emanual Silva The author sealed the roof flashing boots to the posts with Siga Wigluv, a high-performance, water-resistant tape.
Emanual Silva The deck with its new EPDM membrane. The posts have also been wrapped with the same SAF flashing used on the walls.

Then I installed the new EPDM roof membrane, carefully detailing the flashing around the posts to make sure they wouldn't leak in the future. Molded one-piece EPDM boots are available to fit over 4x4 and 6x6 posts, but usually I just fold my own, using scrap pieces of membrane. Afterward, I liberally apply black lap sealant to the joints for an added level of protection.

Building New, but on an Existing Footprint

Once we formed and poured the new piers, framing the new landing platform was fairly straightforward. I upgraded the support posts from 4x4s to 6x6s, used appropriate metal hardware for the column bases and post-to-beam connections, and reinforced the guard post connections with plenty of blocking.

An overhead frame that defines the stair layout was used to ensure that the new support posts and landing were accurately located on top of the piers.
Emanuel Silva An overhead frame that defines the stair layout was used to ensure that the new support posts and landing were accurately located on top of the piers.

To make sure the stairs and landing were exactly square to the existing deck, I built an overhead frame to help with the layout. To avoid triggering a permit review, I had to use the existing layout for all four footings, so I started by leveling two boards out from each corner of the deck, then squared the ends where they intersected over the platform, using a plumb bob to make sure they landed over the corner footings. It took a bit of tweaking to square the landing to itself and the deck.

The lower stair stringers are pocket-screwed to a 2x10 that's wedge-bolted to the concrete-slab landing. Solid blocking reinforces the guard-post connection.
Emanual Silva The lower stair stringers are pocket-screwed to a 2x10 that's wedge-bolted to the concrete-slab landing. Solid blocking reinforces the guard-post connection.
The landing and upper and lower stairs have been reframed and are ready for tread and riser installation.
Emanual Silva The landing and upper and lower stairs have been reframed and are ready for tread and riser installation.

Having the frame above, I was able to locate each post along with each footing by dropping a plumb bob down to each one. There was really no other way to make this work. The platform ended up lining up with the deck perfectly along with being square. In my experience, taking the time to make jigs and templates always makes the job easier.

My inspector also likes the fact that I make it a practice to treat all end cuts and notches with preservative. This step is required by code (the IRC references the AWPA’s Standard M4), but he tells me most builders skip this step. In fact, my lumberyard explains that it doesn't typically keep preservative in stock because it doesn't sell enough of it, so I usually have to special-order it. There are several types of approved copper-based preservatives, but I prefer Copper Care’s Tenino Copper Naphthenate.

To accomodate the multiple flashing layers that were used to waterproof the 4x4 guard posts, the author installed composite post sleeves sized to fit 5x5 posts.
Emanual Silva To accomodate the multiple flashing layers that were used to waterproof the 4x4 guard posts, the author installed composite post sleeves sized to fit 5x5 posts.
While the new deck looks similar to the old one, the dry area underneath was enclosed with screening.
Emanual Silva While the new deck looks similar to the old one, the dry area underneath was enclosed with screening.

From this point on, thankfully, the job became fairly straightforward. To reduce the mold and mildew that was visible on the old PVC deck boards, my clients chose to install capped composite decking, which I fastened to the sleepers with hidden fasteners. Because I wrapped the 4x4 posts with waterproofing membrane, I decided to use 5x5 post sleeves to account for the extra thickness. Even so, I still had to trim away a bit of the core at the base of the sleeves so that they would slide down easily over the flashing boots and overlapping membrane. I did this by fitting my recip saw with a fine-tooth 12-inch blade and having my helper carefully hold the sleeves down on the work table with a protective cloth while I slowly cut each side.

The rebuilt porch and stairway occupies essentially the same footprint as the original, with similar details and finishes. But now that the deck above would stay perfectly dry, my clients asked me to screen in the area below, a nice finishing touch that added useful outdoor living space to the project.