The coolness factor of a deck/patio that you can walk out onto and having living space underneath cannot be denied. When houses are built on/in hills it can be a very efficient way to maximize the usable space while minimizing concrete.
These deck/patio areas are considered “flat roofs.” Everyone hears the word “level” when I say flat and that is not true. Flat roofs are any roof with a less than 4-12 pitch. They all have slope, some more than others. The tricky thing about flat roofs is that they don’t really get to take advantage of gravity to bring the moisture down and away. The water is flowing down the slope of the surface just much slower and if there are any low areas of areas of ponding water will sit and work on any vulnerable areas until there is a leak.
Case in point:
With this decking system we can look into the past a little and see that as the contractors installed the framing and sheathing everything was nice and sloped and smooth. Then the roofing was installed and part of the roofing at the lowest edge a 90° edge metal was installed. This created a little high area, right alond the edge that wouldn’t let water drain effectively but over all it was sloped and the standing water could be managed. Almost done right? Oh, wait! We still need a railing!
If the rail has not been thought about until this point in the deck’s construction it is screwed (in more ways than one!). There is no good way to install deck posts that won’t damage or hamper another part of the roof surface. With the deck surface needing a rail and a nice (mostly flat) roof surface to the edge the contractor chose to go right through the surface of the roof with fasteners. This is a terrible installation for structural stability (toe-nailed fasteners are not very reliable against lateral/horizontal forces).
Now, right at the edge of the roof slope, where remember we had those areas of ponding, the roofing membrane was filled full of holes to mount the wooden posts. The poor home owners tried to caulk this post-to-roofing transition, but it was too late.
Inside the thermal camera did not see any smoking guns (sometimes it can be hard when temperature inside and outside is very close to the same), the moisture meter was able to confirm current ongoing leakage in this system under the edges and especially where the rail posts where installed.
The top sides of the windows are always a good place to check for leakage. Even if it is not active the tannins in the water from soaking through wood framing alow you to see the “tea” colored stains.
By failing to plan for the finishes and rail this deck was doomed to fail. These decks can be done much better, but it takes an experienced contractor who knows what the issues are going to be 5 steps ahead!
As always if you have any questions or would like some help diagnosing an issue just give me a call or email:
Jim Allhiser 503.508.4321
Your favorite Salem Home Inspector.