Constructing the Veranda, duckboards and gutter

We have chosen for the "open deck" construction, a slatted wooden deck that lets water run through. This is very much like the outer veranda of a shinden building, also called sunoko.
The wooden surfaces in the garden are all connected and placed in a Z-shape very much like ochi-en and nure-en.

These are two of the drawings we used to design the details of the veranda and to determine the amount of material required like wooden beams, planks and screws.
Determining the carrying beams. Calculate the required amount of planks and screws.

The wood we used is Bangkirai (Shorea Atrivernosa Sym.).

Bangkirai is relatively easy to work with using proper preparation and tools. It is also one of the most long-lasting woods in the market and can be used outdoors untreated and without any major preparation. It can last outdoors from 20 to 30 years without much care except for moss growth.

Here the new wood still in its original color. The next photo shows what the color will look like after having been untreated for a years or so. The surface gets a silver-gray patina because the sunlight draws the pigments out of the wood. This is the color that we want it to be in a Japanese garden.
To retain the natural color of the wood you need to apply a high quality penetrating oil stain annually
Drilling some 1300 pre-drilled screw-holes and as many shoulder holes and turning in all of them is not a sinecure and for sure requires the use of electrical or pneumatic tools. This is our most important tool-set.

Because we used (Philips, cross-head) RVS (stainless steel) wood screws (5 x 50 mm, #10 x 2) and drilled 4,2 mm holes, it is no problem to remove these screws.

Minimum 3 mm (1/8") spacing between the boards is recommended. We used a 5 mm (0.2") drill as or measure.

See What did not work well for the lessons learned regarding the screws we used.
Wooden platforms or decks are akin to a viewing terrace in their effect.

Most of the surface that is covered by the veranda and duckboards was originally paved and came with the house. Because of this we decided to go for the easy way of construction. Meaning that we used the existing pavement as a base rather than placing the whole of the veranda on poles which is normal practice.

Here you see how this ended up in the "quick and easy" way. Consequence of this is that after ten years we had to raise it after having been subsided some 10 cm. And again for this we use the same pavers, now stacking them.
A platform, being raised, always has open sides. Because our veranda platform is very low, that is only the height of the carrying beams and somewhat extra, the open sides are only just visible. Most part of the outer edges has a granite gutter that shields most of the open side.
The carrying beams are 69 x 60 mm and lay on the pavement. The gravel has the same height as the pavers and hence the platform is raised about 6 cm above the gravel level.

After some 10 years the level of the garden has lowered by about 10 cm (4 inch). Early 2009 we decided to up-lift and level the veranda and duckboards and as a result to also take along the gutter.

As we had recently had an "earth-leakage" in the Lighting and garden electricity-system (part of Infrastructure design and component selection) this was no luxury as such, as this was the problem area where all the cabling and connections reside.

To lower the weight and make room for these activities we removed about 1/3 of the veranda and duckboard planks (see Veranda duckboards and gutter).
As we used stainless steal screws, most of them came out well. Higher and levelling most of the veranda could be done by adding extra tiles of the type that where already used under it.
Where the tiles where taken out we covered the ground with plastic sheets.

Here you see the border with the Ginshanada, gravel area.
Prior to up-lifting the veranda and duckboards we had to add loads of sand to fill gaps and holes and to get to the required level.
We decided to use 25 kg bags with sand. These are more easy to carry and this makes it easier to divide the work, as we needed much more sand than that required for the walkways.

The following section gives an impression of the veranda in 2008 and how we constructed it.
We only have very few photos from the early days but could add a few after some structural maintenance activities.

This is the main veranda that has a size of 4 by 6 meter (13 by 20 feet). It is made of profiled Bangkirai wood (Shorea).
The stone-lined gutters, mikawamizu, are filled with gravel.
The gravel we used is called "Ardenner split" as it originates from the Belgium Ardennes. The color is in line with the paving colors you saw before.

The color of the granite edges was chosen such that the combination gives a nice but natural effect.

Details that we used for the construction of the gutters mostly came from the book by Bring and Wayembergh [3].
The granite edges are layed level on a foundation of sand.

To ensure that the gutter is waterproof we made it with a strip of neoprene of the type that is also used on flat roof surfaces. It was actually used on our roof.
To get a hollow gutter shape the ditch was dug so that the granite pole bottom lays just a few centimetres higher than the bottom of the ditch. Then the neoprene was put under the granite as shown on the photo. The inside neoprene goes up against the wooden carrier poles.
This is how the gutter looks prior to filling it up with gravel.

First we need to double check that the drainage will function correctly.
Here we filled the gutter with water to see if it had the right height and the correct level to ensure positive drainage to the waterfront.
The inside gutter neoprene goes up against the wooden carrier poles thus forming the hollow gutter that takes care of positive drainage to the waterfront.

The gravel we used is called "Ardenner split" as it originates from the Belgium Ardennes. The color is in line with the paving colors you saw before.
This home-made bamboo mat serves two purposes.
It hides the water-switch and pipes (see: Watering supply and irrigation or sprinkler-system) for the eye and it also shield it from the sun. The material is all plastic and most plastics do not like sun-light.
Small changes of ground level in areas of flat ground, like behind our house, can be very attractive, having the same ornamental value as terraces. If the terrace height is more than fifteen centimeters, steps will be necessary.

What did not work well

Here we document what went wrong with regard to the Veranda and Duckboards.

  1. Well made decking is very attractive in its own right, but it may become slippery with algae. This needs to be frequently removed e.g. with a wire-brush when dry, or a power hose when wet. In the maintenance chapter we will elaborate on this.
  2. Although we used (cross-head) RVS wood screws (5 x 50 mm, #10 x 2 ) and drilled 4,2 mm holes, it is no problem to remove these screws.
However one less positive quality of these screws is that the head is relatively weak and comes off in some cases. Also the cross-head can easily be damaged making it impossible to get it out again.

Only recently we found a stronger alternative. It uses a 6-corner bit rather than a cross-head.
Even more important, it has a reinforced "shoulder" just under the head. Also it has a drill-shape tip (end ?) that lowers the resistance on insertion (could even be self-drilling but I did not try that ! ).

For screw conversion see the related Links.

Links related to veranda and duckboards

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