PROSOCO Liquid Flashing

Another technique I picked up from Hammer & Hand was the use of liquid flashing in place of traditional housewrap.

There are some advantages to liquid flashing: it’s relatively straighforward to apply – which is not entirely the case with housewrap which needs to be carefully shingled, especially so around window openings.

Liquid flashing also serves as an air barrier which is not the case for housewrap. Peel and stick membranes can block water and air however they’re expensive and I’d think difficult to apply without experience.

The product Hammer & Hand uses is made by Prosoco – a Portland based company. It’s well adapted for the Pacific Northwest as it can be applied in a damp environment and moisture helps it cure.

Initially I had the product shipped down from Small Planet Supply in Washington state but then found a local distributor: Atlas Supply in SE Portland.

It comes in sausage tubes which require a special caulking gun – not the usual Home Depot/Lowes product range at all. It’s an excellent caulking system: high capacity tubes, the nozzle doesn’t dry up and clog so easily. Best of all there is no bulky tube to dispose of later. Just the thin compressed skin. Here’s a photo of the reusable nozzle and the used skin.

Prosoco Flashing Products

R-Guard Joint & Seam Filler: fiber-re-enforced for filling gaps (Pink color)

R-Guard FastFlash: for filling nail holes, flashing rough openings, and sealing sheathing penetrations. (Red color)

R-Guard Cat 5: elastomeric weatherproofing membrane for exterior sheathing (Orange color)

Application Techniques

Prosoco has a comprehensive guide to using their flashing products:

Hammer & Hand also provide a bunch of videos that explain how to apply these products. This video demonstrates the R-Guard Joint & Seam Filler

My Experience

I used R-Guard Joint and Seam Filler wherever there was a gap between two plywood sheets, also between the framing, the concrete slab and the slab insulation foam. I also used it to fill in any large holes or imperfections in the plywood outer layer.

I used R-Guard FastFlash to fill in nail holes, to cover where two plywood sheets butt up to each other with little or no gap, and to flash the window and door rough openings.

I used R-Guard Cat 5 to cover the roof and walls.

Some comments:

  • It’s more efficient to keep two caulking guns loaded – one with Pink Joint & Seam filler, the other with Red FastFlash. Initially I only used one gun and found myself continually swapping between the two products which wastes both product and time.
  • The most efficient way to work is to setup your ladder, then apply both Joint & Seam filler, and the FastFlash to that section of wall. Then move the ladder and do the next section. Finally, once both products have cured, then roll on the Cat 5 liquid membrane on the roof and walls.
  • I think it worth covering all knots in plywood sheathing with Red FastFlash. It’s extra product and work, however if you don’t do this then when you roll on the Cat-5 membrane there will be gaps left around the edges of some knots.
  • Protect adjacent surfaces with plastic before rolling on the Orange Cat 5. It sticks tenaciously and probably don’t come off whatever it lands on.
  • The product literature suggests these products can be applied in a damp environment however there are limits to this. The Joint and Seam and FastFlash fillers can be applied to damp surfaces but it requires more force on the plastic spreader tool to get it to adhere compared to a dry surface. They skin over quite quickly so you only need a half-day or ideally a full 24 hours of rain-free conditions.
  • The Cat 5 liquid flashing is another story. The surface is better dry as it’s only rolled on. It’s hard to get enough force on the roller to get it to adhere well to damp surfaces. I found that the Cat 5 membrane was not well adhered on one section of roof sheathing that had been quite damp when I rolled it on. You also need at least 2-3 days of no rain in cool winter temperatures, to allow the Cat 5 membrane to skin over and partly cure. It could be different in summer. The first time I applied Cat 5 to the roof it rained 3 hours later. This turned the surface into a spongy crater-like mess. Worse there was a wind-storm and a bunch of leaves and seeds from a nearby cedar tree embedded themselves in the membrane. I ended up spending hours picking out debris from the membrane, Finally I applied a second coat. This time when there was 4 days of clear weather forecast.

Here’s the structure after applying the Joint & Seam Filler and the FastFlash

Here’s the structure after the Cat 5 liquid membrane is applied:

Foundation Drainage and Waterproofing continued

TREMproof 250GC waterproof coating has already been applied to the 2-foot deep slab edges, then 2 inches of XPS foam glued on using Dow EnerFoam.
Now it was time to complete the slab drainage and protect and finish the above-ground part of the slab

Footing Drain

Providing a footing drain was probably not required as it’s only a 2 foot deep edge-thickened slab, however I already had a dry well available that had previously been used hold rainwater from the back half of the garage roof.

The sequence was:

I used 3-inch perforated ABS drainage pipe sloped at 1/8-inch/foot around the perimeter.

  • Dig and correctly slope the trench
  • Geotextile fabric to help keep the drain clear of silt
  • 2-inches of 3/4-in clear gravel
  • 3-inch perforated ABS drain pipe
  • Adjust drain slope then cover in 2-inches of gravel
  • Wrap the remaining width of geotextile over the top of the gravel burrito style to slow down silt infiltration
3-inch perforated pipe bedded in gravel

I then used Dow EnerFoam to glue drainboard to the foam. The drainboard extends one foot from the top of the XPS insulation, down to the perforated drain pipe

I then filled in the trench to just below the top of the drainboard using soil and more gravel.

Drainboard glued to the XPS using Dow Enerfoam

Finishing the Exposed XPS

The XPS needed to be covered and protected. Perhaps the best product available is Finex produced by a Canadian company. It contains little or no wood fibers and it’s rated for exposure to soil. However there is no Oregon distribution and the cost of shipping it down was too high for such a small project.

Hammer & Hand have used coated Hardiepanel in some of their projects so that’s what I did.

First cut the panels into foot-wide strips (for my foundation 8-inches above grade, 4 below), then apply one coat of Tamoseal on the front surface and four edges using a mason’s brush. Mason’s Supply in SE Portland has all the materials. The older guy at Mason’s took time to write down the mixing rations for the Tamoseal and the bonding acrylic for my application. The customer service there is excellent.

I then glued these coated panels to the XPS using Dow Enerfoam. I used Tamlyn flashing strips to protect the panel edges at joins and corners. Parr Lumber on SE Stark St in Gresham stocks this trim (my local Parr Lumber branch on MLK does not). There’s a display of the trim types on the left of the counter as you go in so easy to select what you need.

I then coated the mounted panels with a second coat of Tamoseal.

Tamoseal-coated HardiePanels attached to the XPS foam. (Tamlyn flashing strip visible on the right.)

I then applied two coats of Drylok (probably overkill).

Then two coats of paint.

Finally I installed metal Z-flashing over the top of the XPS to protect it and keep the rain off. I’ve found the easiest place to buy this is Lakeside Lumber in Tualatin. There have an excellent selection graded by 1/4 and 1/2inch.
I applied a bead of Prosoco FastFlash to the back top of the flashing, placed it in position then nailed in every 1-2 feet using stainless steel shingle nails. The flashed over the top seam using FastFlash. Do not flash the bottom; water needs to be able to freely drain out.

I then covered the bottom 4 inches of the hardiepanels using 1/4-inch clear gravel. I did this rather than use soil as I want water to drain away from the hardiepanels as quickly as possible given this product is not rated for ground contact.

Framing and Window Rough-Ins

Platform Framing

The platform is built – 2x6s on hangers. The bathroom is on the left, kitchen on the right. The bed slides under the cavity to the left. The right will be used for plumbing, and electrical runs.

Cavity reserved for the hot water tank

The floor is left open in the corner of the kitchen for the hot water tank which will slide in under the kitchen counter and rest on the concrete slab.

Window Rough-Ins

I added beveled siding strips onto the window sills to provide a drainage slope to the exterior. The window rough-in had already been flashed with Prosoco Gap & Crack Filler. I layed out three stripes of Prosoco FastFlash and then tacked in the siding.

As this reduced the rough-in vertical dimension by 1/4-inch I updated the window supplier (Western Pacific) with the new rough-in size.

Door and Window Specification

The door and window products were specified on the architect’s plans: Simpson french doors and Marvin windows. The Marvin windows are well constructed and weather-tight – important given the likely exposure to weather due to the short roof overhangs of the “English Cottage” style. On the overhand Marvin doors would have been expensive and Simpson was a good balance of cost and quality. Velux was specified for the two skylights.

The builder recommended Western Pacific in NW Portland as the supplier. They are a large organized building materials supplier located in NW Portland. I scheduled meetings with Western Pacific’s window and door people and ordered the doors, windows, and skylights. The skylights came within a week, the windows and doors around 3-4 weeks. I provided the door lock to Western Pacific and they drilled for the lock-set and hung and fitted the doors in their shop before delivery. (On installation, the door alignment with the frame was pretty much spot on.)

Innie or Outie windows?

The following Green Building Advisor article discusses the pros/cons and installation methods for Innie and Outie windows. I flip-flopped back and forth on the method several times.

Advantages of Innie Windows:

  • The window frame is set back inside the exterior insulation layer so it’s in a warmer location, less risk of condensation on the interior glass
  • The window is recessed away from rain and wind
  • The architect suggested that the innie windows create deeper and more interesting shadow lines on the building facade

The advantages of Outie Windows:

  • Most American homes are built with Outie windows so it looks normal
  • The main house has Outie windows (there’s no exterior insulation so the shallow wall depth means outie/innie choice doesn’t exist). The ADU details are supposed to match the main house as it’s in a Historical District.
  • It creates a deep interior sill that provides useful interior space in such a small structure
  • The French Doors are outswinging so they will be Outies by default. So Outie windows will align with the plane of the doors.

So I went with Outie windows. As the rough framing had already been completed by the time I made this decision, this narrowed my installation options.

Main house windows: the ADU “Outie” windows will match these where the window is set level with the back of the siding

Door and Window Installation

With the electrical rough-in date approaching I needed to get the doors and windows installed to make the structure weather-proof. The builder scheduled a day for his crew to come on-site and do the installation.

Building window and door bucks

The window and door openings were not framed with bucks to extend out past the exterior insulation layer as I only made the decision between innie/outie windows after the structural framing was complete. So the first task was to build frames to extend out the door and window openings.

The builder had his crew build the window bucks as a complete frame that was then screwed onto the structure as one piece. This allowed for an easier and higher-quality build than tacking separate pieces of frame directly to the structure.

I flashed the bucks to the sheathing using Prosoco Gap and Crack filler and Fast Flash.

Tremco ExoAir Trio

From the Hammer & Hands blogs I picked up on a new system for mounting and sealing windows and doors based around a Tremco product.

ExoAir Trio is a self-expanding joint sealing tape that is used in place of traditional spray-foam sealant to weatherproof windows and doors. It was my the first time to try this technique and the builder hadn’t used it before. We ended up using a combination of traditional shimming , Tremco ExoAir tape, and spray foam to install the windows. Now that I know how it works, I would be able to much more easily use this Tremco product for any future window installs.

Here’s the Hammer & Hand video demonstrating how to set a window using Tremco tape and Shim Screws.

My observation is that this is a significantly easier method for aligning and installing window frames vs traditional methods and that it provides a significantly better weather and air seal than using spray foam.

Installation of the living room window

Installation of the doors

The builder recommended a metal sill pan under the door sill and the window guy at Western Pacific agreed. It’s cheap compared to the cost of a door, it’s good insurance against water leaks through onto the floor, and although not required by code in Portland, it’s mandatory in a bunch of other states.


Based on this experience my suggestions are:

  • The Tremco tape can be ordered in 3 different thickness, each thickness being rated for a different sized gap between the window frame and the rough-opening: 3/16” – 3/8” gap, 1/4” – 9/16” gap, and 3/8” – 3/4” gap.
    I had a range of gap sizes so I went with the smallest thickness tape. As it turned out this was a very tight fit (too tight) around the door, good fit for the small kitchen window and the sides of the large window, and way too small for the bottom and top gaps on the large window.
    It only comes in lots of 3 rolls and it’s expense to order a bunch of different sizes for a one-off project like mine.
    So my suggestion is when sizing your windows/doors and rough-openings, try to keep the gaps top/bottom/sides consistent so you can use just one variant of Tremco tape.
    If you end up with a large gap as I did on the large living room window then you can always use spray-foam after the window is installed to complete the gap sealing.
  • Don’t shim in the traditional way by pushing shims all the way through the opening. You need to ditch that method completely. It only creates a path for water and air penetration through the frame which is exactly what you are avoiding by using this Tremco product. Also you don’t have time to mess around shimming once the tape is in place and starting to expand. Instead use the shim technique demonstrated in the Hammer & Hand video above where the bottom sill is shimmed part-way through the foam layer only and the shims are set perfectly level before you apply the tape or install the window.
  • It’s really important to cut the tape longer than each frame dimension and to bunch up the tape at the ends of the sill as shown in the video. On those corners where I did not cram enough tape into the corner, the tape started pulling back from the corner once it started expanding, This left a couple of corners with a large gap in the expanded foam tape that I then needed to spray-foam to seal.
  • Make sure the white side of the tape goes to the interior. It’s a partial vapor barrier and you want to direct any water outwards, not inwards.
  • Use shim screws to fasten the window to the framing and to adjust the horizontal left/right position. (You will have already got the vertical top/bottom alignment correct by using the correct thickness shims on the bottom sill before applying the tape.)
  • It took over a week for the tape to fully expand and close some of the wider gaps – perhaps due to the cooler weather.

Shim Screws

You can buy Shim Screws from Conservation Technologies:

I chose to drive them flush with the frame surface and leave them exposed as they have an attractive stainless steel head although you could always fill, sand, and paint over.

Platform Framing and Internal Walls

The kitchen and bathroom are located on a raised platform providing 2 feet of utility space under the kitchen and space to stow a Queen sized bed under the bathroom.

My builder constructed the floor framing first and tied this in to the wall studs. The framing is supported down the center where the bathroom/kitchen wall will go by a 2 foot high wall built on a pressure-treated 4×4 resting on a rubber membrane.

A space was left in the kitchen corner for the hot water cylinder. The kitchen units will be built in such a way that the tank can be removed and replaced during the life of the kitchen.

There were are couple of options for the floor/wall sequence. i) Install the internal wall framing then lay down plywood sheathing (3/4″) between the walls. ii) Install the floor sheathing in one continuous run and then build the walls on top of the floor sheathing.
The builder recommended ii) floor sheathing first – there are several advantages – better isolation of the bathroom and kitchen from the utility space and bed storage area below. Better floor strength.

I was wondering how the internal walls would tie in with the rafters. One part of the bathroom wall aligned with a rafter so that was easy. Where they didn’t align he installed blocking between the rafters and the attached the top plate to that. Because of the angled roof it was easier to install one stud at a time rather than build as a complete wall on the flat and then raise into place.

Bed cavity and shelf for media equipment/TV etc on the right; closet on the left protrudes back into the shower space.

Overall internal framing

Pocket Door

I’m using a pocket door between the bathroom and kitchen; no space to swing a door.

Johnson Hardware vs. Hafele

Initially I went with a door frame and track provided by my door/window supplier – based on a Johnson Hardware 1500 frame and mechanism. $267 for the frame, track, slider mechanism, and 2-foot wide door panel.
However the metal bracing was lightweight and the framing had a lot of flex. Furthermore Hammer & Hand have a guide to installing pocket doors and they explicitly say:

Do not use Johnson Pocket Door Kit 1500, 1500HD, 1500SC, 2511, or 2000

Instead they recommend using Johnson Pocket Door Kit 2710 or 2711. They don’t give any reasons however I’d think it’s about durability.

My other concern was about maintenance of the track. All of the Johnson Hardware frames would require the wall be taken apart to replace a damaged track. Presumably the tracks would be good for a couple of decades or more of life, however, that didn’t seem acceptable to me.

After more research I settled on a Hafele frame and track. The framing is made of a sturdy wood/metal composite and the track slots into the cavity with no hidden screws at all allowing the track to be removed and replaced without cutting into the wall.

Hafele Slido Pocket Door

I bought the:

  • Hafele frameset from The Builders Supply in Austin, TX
    “HAF_94272000 Hafele 942.72.000 Pocket Door Frame Set, Slido” for $309.
    (this kit comes with a track – no need to purchase the track separately)
  • Soft-close slider set from Cabinet Parts
    “Slido Classic 40-P Fitting Set with 1 Side Smuso Soft-Close HAF-940.43.000” for $133.
Rough-In Framing Guide

Installation Gallery

Plumbing Rough-In

Plumbing rough-in needs to happen before electrical and mechanical rough-in as drainage requires specific placement and gradients whereas electrical and mechanical have more routing flexibility.

Grohe Sense Guard

As the hot water cylinder will be buried away in the dead-corner of the kitchen cabinets I wanted to be able to detect water leaks and automatically shutoff the water. I went with Grohe’s Sense Guard system. I needed two of these for the City Water and Rainwater supplies. There are a bunch of valves so each unit can be bypassed and maintained.

Once installed and connected to WiFi and my phone app I’m able to receive notifications of water leaks, remotely turn water service on and off, and track water usage in gallons, water temperature and pressure.

Supply lines

Bathroom, shower, and kitchen hot and cold lines were installed as home-runs to manifolds using 1/2-inch PEX.
The toilet, laundry and outdoor faucet were run as 1/2-inch purple PEX to a rainwater manifold.
Each homerun line can be individually isolated with a valve located at the manifold.


The back wall of the bathroom is framed out an additional 6-inches. This provides space for an in-wall tank for the wall-hung toilet and for routing shower lines without intruding into the insulated 3.5-inch framing cavity.

Baseplate for the 6-inch plumbing cavity

Toto provides a detailed framing plan for their wall-hung toilets.

There is an electrical outlet installed to left of the toilet for a Toto bidet toilet seat.


The toilet and shower are vented through the roof. The roof penetration was sealed using a Roflex 30 gasket from 475 High Performance Building Supply and this was then sealed with Prosocco liquid membrane.
The basin, kitchen, and laundry drains are vented using Air Admittance Valves as there was not enough room to run vents through walls.

Outdoors Faucet

I used Aquor’s “House Hydrant” connected to the rainwater manifold for the outdoor faucet. Aquor is based in Washington state.

Non-Vented “hot” Roof Assembly

The roof was designed as an unvented “hot” roof. A 4-inch box is built on top of the roof sheathing, filled with foam and a final 3/4-inch roof deck screwed down on top to provide a nailing plane for the shingles. It’s air-tight so any moisture that gets in will rely on inward/outward drying.

First I built a framed 4-inch high box around the outside of the roof. I used cutting jigs and a circular saw to cut 1-1/2-inch notches in the gable ends for lookouts. The eave-pieces were cut sloped top and bottom. so they install vertical.

Next I built 4-inch high boxes for the skylights. Prosoco Fast-flash was used to seal between the sheathing and the boxes. The whole roof box was then sealed on the inside and outside using Prosoco Cat5 liquid flashing.

DensGlass extends the fire-break from the sheathing up to the top of the roof assembly.

I lined the bottom of the roof box with wrap to isolate the liquid flashed sheathing from the rigid insulation. The reason was I’d read some people have reported squeaking noises from roofs with rigid foam as solar heat causes the foam to expand and contract against the sheathing. I suspect it’s not necessary but it should reduce any abrasion of the flashing membrane during daily heat/cool cycles.

Next a layer of 2-inch XPS foam was installed and taped.
The gable-end lookouts (2x4s on the flat) were screwed down over the first layer of insulation back at the first rafter. The eliminates thermal bridging from the lookouts to the roof sheathing. I could get by with lookouts on the flat as the overhangs are short. (For substantial overhangs it would have been necessary to use 2x4s vertically.)
The second layer of foam was then applied and taped down.
I decided against using Rockwool for the roof insulation as I was concerned about it’s compressiblility when the top roof deck is screwed down. The XPS foam is sufficiently dense that it provides a solid base for the top roof deck.
I believe Rockwool could be used for the roof assembly, now that I have some experience working with rockwool for the exterior walls. It would take a little more fiddling around to get the deck screwed down true and level but it should work okay.

Next the eave rafter tails were cut and screwed on to the 4-inch high roof assembly box. It’s not possible to use the actual structural rafters as i) they are too low down given there’s a 4-inch roof assembly built on top of the roof sheathing and ii) the structure is built as a smooth box with the rafters cut smooth with the sheathing so that the exterior insulation can wrap completely around.

The eave overhang is short and the roof slope is working with us so lookouts were not needed. The rafters are screwed into the side of the structure. The gable-ends provide good rigidity to the whole eave structure. If the overhangs were significantly larger then obviously some stronger structure would have been needed.
I didn’t worry about getting all the rafter ends the correct length. Just build them longer than needed, then cut with a circular saw using a string line and a cutting jig.

I then installed the sub-fascias (cut down from 2x6s) and built the bird-boxes at the gable/eave ends.

The top roof deck was then installed over the roof assembly and insulation. (3/4-inch ply – fire-rated on the north-side due to proximity to the property-line).

I used Heco Topix screws to secure the ply through 4 inches of foam through the sheathing and into the interior rafters. These screws are a brilliant design. There are two groups of threads set at the same pitch. This allows any 3/4-inch strapping or ply sheet to be fastened through thick insulation so that the screw head self-countersinks without compressing the insulation. The screw can be tweaked in and out to really dial in the level of compression and get the roof deck super flat.
Heco Topix screws are available from from Small Planet Supply and come in a variety of lengths to suit your insulation thickness.

Installing these screws through thick insulation requires very accurate measurement and marking of the rafter locations on the roof – accurate to within 1/8 – 1/4-inch to make sure you hit the rafter right in the center.
I made a jig to help ensure they went in true. Out of 200 or so screws only 3 missed the rafter – due to a measurement error.

Video of installing the screws. The rafter locations are marked on the ply.
After screwing down the entire roof deck I then went back and retweaked all the screws to get the deck super flat.

I then ran a router around the ply perimeter to get a constant 3/4-inch overhang that will cap the fascia.

Finally I liquid-flashed all the plywood seams and also around the junction of the underside of the ply deck and the sub-fascia to make the roof assembly air-tight, then applied Cat5 on the roof deck to water-proof it.


The ADU Feed comes off the house 200Amp disconnect panel and passes through a privately owned meter so that ADU power usage can be sub-billed. The line runs through the basement ceiling and then underground conduit to the ADU.

Two conduits were also run underground from the house to the ADU for data lines.

In the photo below – left to right: (1) 100 Amp power (2) Extra conduit from house for data (3) Data conduit (4&5) Extra conduit running to the ADU rear for future solar/storage.
There is also an outdoor power outlet to power a future ONT (Optical Network Terminal) should fiber internet be run to the ADU at some point.
The ADU panel is directly behind this wall.

Circuits were run through a 1.5″ wiring chase above the door to avoid having to drill a large number of holes through all the rafters. The heat pump cable-set and data cables were also run through the same chase.

Service disconnects for the AC and water heater heat pump were added to the rear of the ADU. Above them is the required power outlet for servicing the heat pump.

A media/comms box was mounted below the power panel to serve as a hub for internet connection, cable, and a modem. It’s possible to pull data cables through conduit from the house to this box.

An in-wall media box was mounted behind the TV location complete with recessed power outlet and conduit to channel AV cables within the wall.
Another media box was mounted behind the bathroom mirror location to service a future smart mirror.
The in-wall boxes were sourced from:

A recess was framed in the shower for an “Electric Mirror” lighted and heated in-shower mirror. The low-voltage converter box was located under the platform and is controlled by a light switch next to the shower cubicle. Electric Mirror is located in Everett WA.

As space is very limited in the ADU, my plan is to locate as many services in the ceiling as possible to reduce clutter on shelves. So I ran speaker cable for ceiling mounted speakers in the living room and bathroom. There is a CAT8 ethernet cable run in the ceiling for a ceiling mounted WiFi access point. I ran cable to connect Amazon Echo devices in the living room and bathroom ceilings – once again removing the need for a clutter of devices sitting on shelves. Get them all out of the way and put them in the ceiling.

These various data cables are just left under the insulation and will be drywalled over. I have carefully made a note of their exact locations. Then once the ceiling surface is finished and painted I will use a hole saw to cut through the ceiling, locate the cables and wire up the various devices: WiFi, speakers, Amazon Echos. This will greatly simplify the ceiling drywalling and finishing.