The Marathon: Final Flashing

So this is it...the last two days of our marathon to finish the roof and get the scaffolding down. It's been a huge push - working 10-12 hour days and even with that, extending my trip by several days to get everything done. While i have loved being up on the roof (except when we re-framed the joists in the dead of an English winter) and seeing London from this unusually serene perch, I'm ready to finish and move on...

There are a lot of small things to finish before we can take the scaffolding down, but the last "big" item is to finish all the flashing around the dormer and along the edge - again, a tricky detail to span both types of roofing: traditional slates and modern membranes.

So I started up on the flat portion of the dormer by installing lengths of heavy lead - known as "code 4 lead" - to cover the edge of the flat roofing membrane that wraps up to face of the brick wall.

Where the roofing membrane meets the brick wall

Before inserting the lead, one has to cut away at one row of mortar joints, so there's a gap for the lead to go into - fortunately I had done this messy job several weeks ago, so installing the flashing here went relatively quickly. that is (of course!) except for the tricky bits, which were at the various corners towards the edge of the dormer. That proved time consuming, but I had it done in time for a late lunch.

Late morning of July 4th - the rows of lead flashing installed

This area is the trickiest - several corners and an overhang from the coping stone

It's not too clear, but the corner flashing pieces are installed

I then spent several hours working on some of the other tasks (see next post) but by the early evening I was able to start on the final flashing task, which involved installing the lead along the edge of the dormer. This flashing detail was worked out about a month or two ago when I was finishing the slates on the dormer. This is the tricky flashing detail I've mentioned several times: it has to span two very different types of roofing.

My sketchbook where I worked out the flashing details - the one in the center of this page is the final version for the edge detail of the dormer - a wooden drip edge wrapped in lead that works over the slates and the membrane.

 Because we had previously treated and painted the wood structure, I was able to start attaching the lead right away. To further enhance the durability of the detail (and because we had a lot of extra pieces), I decided to add a row of "soakers", which are folded sheets of stainless steel used to prevent water penetration at any 90 degree intersection of slates. These "soakers" helped seal the top of the wood and were then wrapped in the code 4 lead. The lead is held in place by a series of straps that are nailed into the wood, but are cleverly covered by the flashing - a great traditional detail used for hundreds of years.

This work was only completed the following day. The last tasks involved cleaning the roof for the last time, applying a protective patina coating on all the lead, and inserting a special caulk into the open joints where the lead is inserted into the brick. This caulk prevents water from going into the brickwork, and under the lead, while allowing for the naturally-occurring movement between the brick and lead without cracking.

In the early evening able to start the edge flashing - fitting the first pieces

The stainless steel "soakers" with the lead clips awaiting the final piece of lead flashing

The completed assembly - looking up

The completed assembly - looking down. Here you can see the all-important drip-edge taking shape

Morning of July 5th (final day) - preparing to flash the edge along the flat roof

Ready to install the roughly formed lead

Here you can see the stainless steel "soakers" ready for the lead

A detail view of how the clips will be covered by the final piece of lead

Flashing finished - cleaning the roof for the last time!

View of the finished roof & flashing - her you can see the detail where two roofing types come together, with the recently completed edge flashing in the distance

Final view of the upper roof - flashing completed, lead has it's patina coating, caulking done.

Just in case you think the roof is finished...

...it's not.

One might imagine that now with the slates done, the roof is finished...

...but unfortunately that's hardly the case.

There's still a long list of things that needs to be done before the roof work is officially finished, the scaffolding can come down, and I can go back to New York:

• The Ridge tiles need to be installed along the sloping edge of each roof plane. These tiles are triangular shaped and cover the gaps where the roof planes meet (at one of the dreaded corners) with a bed or mortar. The tiles are placed on the mortar which holds everything together and seals all the openings. (You can see one of these ridge tiles sitting on the edge in the picture above.)
• The eaves, which are plywood, need to be be protected from the rain so they don't rot away. They can either painted (which would mean they would have to be re-painted every few years), or - preferably - covered by a waterproof sheet (so they won't fade or need repainting).
• The gutters need to replaced because we took the old ones out in order to remove the roof joists back in January as part of the structural work. Besides being in the way, the old gutters were metal and rusting away - it was only a matter of time before they started falling off...
• There's a small area of re-pointing to be completed in the brick party wall over the flat roof.
• The flashing needs to be completed along the brick wall - primarily where the flat roof is.
• Once the flashing is completely finished, I need to apply a special waterproof caulk in the open joints where the lead is inserted into the brick. The caulk is formulated to bond between the brick and lead, but allows each to expand and contract properly - this avoids the problems associated with water getting into cracked mortar, which is the traditional way to seal the joint.
• Our neighbors' TV antennas, which are cluttered along the face of the dormer, will need to be relocated.
• And now on to the dormer - the first element of the dormer that needs to be done is all of the final exterior trim-work and facing. The plan is to do this with wood and then paint it (beacuse it will be easily accessible for repainting)
• Once the dormer is trimmed out, the wood needs to be treated for exposure to the rain & damp weather with a protective coating for the wood. Once that's dry (2 days later), all joists and screw holes need to be patched with an exterior filler. After drying and sanding, the wood is ready to be primed, and then finally painted with 3 coats of black exterior paint.
• Once the dormer is painted and finished, the final flashing/cap can be installed over the top edge. this will prevent water from coming in along the edge of the dormer where the slates stop. The trick with this is that the detail needs to span both types of roofing: traditional slates and modern membranes, yet look the same for visual consistency.
• The vents for the boiler, kitchen exhaust and bathroom exhaust need to be cut through the brick wall in the rear and the vents need to be installed. This has to be done before the scaffolding comes down because otherwise there is no way to install the vents and patch the holes. The plumbers will do the boiler vents and I'll take care of the others.
• The hole from the old boiler vent needs to be patched (once the plumbers take it down) - otherwise we'll have a 4" hole on the side of the building!
• The windows need to scraped and painted (not replaced) because in a few years we would like to replace the windows with efficient double-glazed windows. 
• Paint the exterior stone sills and other decorative stone elements that frame the windows. These are probably the most distinctive features of our building's facade.
• The floor of the Juliette balcony needs to be poured in concrete. To do this, the wood form-work must be made, followed by the placement of steel reinforcing bars, followed by the brackets that hold the railing posts. Once all of that is done...then you can pour the concrete...
• Once the balcony is poured and dry, the balcony railing can be installed.
• Finally...the scaffolding needs to be cleared of all the debris that's piled up since November, and then it can be taken down by the scaffolding company!

"Flashing" the Roof

No, it's not what you think... Flashing in the building world is fairly mundane - not a trench-coat in sight... Anyway - flashing is a waterproofing element that typically prevents water from seeping in between the joint of a roof and a wall. It's actually quite tricky because water is a rather mischievous thing and is the scourge of buildings, builders and architects everywhere. In a brick building with a sloped roof the flashing is even trickier because one has to put it at an angle and then cut openings in a step-like pattern in between the bricks for a single sheet of lead to be inserted into. That lead wraps over another element that is typically coming from the roof itself and when they are combined, water can't get in (almost like a yin/yang arrangement). It's a very meticulous and time-consuming process and if you're slightly off with your measurements & cuts it won't fit (as I found out the hard way) It's probably easier to explain with the photos:

May 3rd - The step-like openings between the bricks and the ends of the waterproof membranes

Before cutting the steps into the lower half of the wall (a dirty, messy job)

A piece of flashing (known as "Code 4") that is being cut after the measurements made

The lead flashing in place to verify the cuts are correct (if it's slightly off, it won't work as I discovered)

Bending the lead into the correct shape (playing with lead is kinda fun)

The finished piece of lead flashing

The lead put into place overlapping membranes and the "soakers". Soakers are small 10" pieces of bent stainless steel (shaped like an "L") that site between the slates and prevent water from getting in. The edges of the lead are tucked into the brick openings and wedged into place.

May 4th - The flashing at the bottom with the "soakers" and membrane exposed above

Now that area has its flashing

May 5th & 6th - Around the corner and almost at the top. Here, a chemical patina has been applied which prevents the lead from discoloring and staining the slates.