London: Installing timber steps tier-by-tier
from sections that were constructed off-site.
This article follows on from Modern Timber Steps — A Garden Design and Build Project and focuses on the construction planning, build and installation of these modular timber steps in a London garden.
DIY GARDEN TIMBER PROJECTS
Although this article is about garden steps, there are many tips and techniques that can be applied to any garden timber project: decking, storage, benches, potting tables etc.
Designing The timber steps
In the previous article, I looked at the considerations that went into designing a set of steps for a London garden so that they were in harmony with the aesthetic and functional requirements of the property and client. In this post, I am going to look at the other half of the design process that focused on construction: how exactly, these steps should be built. Both aspects of a design are important, and there is little point in coming up with a great looking design that is impractical or uneconomic to build.
Materials
For this project, there was a reasonable quantity of good quality Siberian Larch boards available, left over from the main decking installation a couple of years before, and although we considered other materials (e.g. poured concrete or my favourite garden timber: Accoya) the cost saving achieved by using existing materials was significant. Although pressure-treated softwood could be used for a project like this, larch is a far more durable timber, especially when not in ground contact. Having a tighter grain, it is also less likely to suffer wear and tear than typical softwood.
- See my post: Accoya – the best new timber for garden design?
- Accoya prices: https://www.laver.co.uk/timber/sawn-carcassing-timber/accoya.html
Site Access
Another limitation was site access. Being such a small rear courtyard, there was limited space to undertake construction on site, so I realised early on that it would be advantageous to construct the steps as a series of modules (three tiers as it happened) then deliver these to site ready to install.
Geometry
The location where the steps were to go was irregular: nothing at right angles to anything else. The rear wall was not parallel to the house, not to the adjacent slatted fence. The client had indicated that they preferred the steps to be built in line with the fence, which meant it would meet the rear retaining wall at an angle. Provision had to be made, therefore, for the steps to be cut to fit on site. I planned for this by allowing boards to overhang at the back of the unit, so that it would be a simple matter of a few straight cuts with a circular saw when installing.
Important Considerations
The new steps will need to be built at least 5cm clear of the existing vertical slat fencing (seen here to the left of the existing steps) to provide flow of air to prevent rotting.
The base on which the new steps must sit is part decking and part concrete (visible here, directly below the existing temporary steps) The new steps are wider and deeper, so will hide the concrete.
The new steps will be constructed around a series of vertical legs which will sit on these surfaces. The legs will be made of Accoya, as this treated timber is effectively rot-proof. The legs will be bolted down to the concrete, but rest freely on the decking.
The concrete intrusion (to the left of the steps in this photo) will need to be spanned, and at least two of the new step legs will need to rest on it. These can be cut/added on site to ensure they are exactly the right length.
Obstacles
Two further issues were (1) That the steps would have to sit across two surface materials: a concrete section and adjacent timber deck. Also, (2) There was a concrete ‘step’ intruding in from the left-hand side (when looking out) which the new steps would need to span.
It would be necessary to design the steps with supporting legs that could be bolted down to the concrete pad to make the entire structure rigid. Some legs, however, would need to be cut to length on site to ensure they rested on the concrete step, as this could not be measured accurately enough in advance. The legs that would rest on the decking needed special consideration to minimise the chance of rot setting in on the decking boards they rested on.
Dimensions
The height of the steps was relatively easy to calculate, as there would be four risers (the last being the existing concrete back wall). As the back wall was 138cm tall, each riser would need to be 138/4 = 34.5cm tall. The top two steps were chosen to fit within the opening onto the top of the retaining wall, between the slatted fence and the metal post/handrail already in place (see photo). The top steps were therefore deigned to fit within this space, but slightly narrower to allow a 5-10cm air-gap on the left-hand side to reduce the risk of the slatted fence rotting.
Durability and maintenance
Rot begins on timber structures where water collects and boards fail to dry out thoroughly. By including a 4mm air gap between each side board and tread, the structure as a whole will be ventilated. The steps will be held clear of the ground by the legs. The most vulnerable location is where the legs rest on the ground, as they will potentially sit in water, hence my choice of Accoya for these elements as it is effectively rot-proof. Coating all surfaces of the timber (especially the larch end grain) with a high quality stain will make a huge difference to its longevity.
Stainless steel screws and fixings have been used throughout, with most screws dipped in petroleum jelly before insertion as this aids with future removal if required. The structure has been designed to be relatively easy to dismantle on-site (e.g. by using stainless steel toggle catches to hold the layers together), especially the top two steps which can be removed to get inside the lower step for cleaning/maintenance if needed.
Clean looks
Stainless steel deck-tite/tongue-tite/lost-tite (various trade names!), T-star screws were used for most of the construction as these leave only tiny surface holes which can easily be filled if desired. When complete, no screw heads will be visible in the external surface, just small ‘nail holes’. All the main fixing screws between the structure and the base and rear wall will be inside the structure, so invisible in normal use.
Construction plan – overview
As far as possible in a project like this, I plan out each step of the build in my head before beginning, thinking through how everything will fit together, and what cuts, clamps and fixings I will need. I usually sketch out my ideas (on the computer or on paper) so I can keep track of all the considerations and measurements. This first diagram was intended to make sure I had all of the site dimensions and quirks taken into account:
This construction plan included the basic dimensions and clearances. I also used it to begin calculating the quantity of timber required, as the client only had a limited number of larch boards.
Several key measurements needed to be kept front and centre:
- Tread (step depth) 38cm
- Riser (step height) 34.5cm (1/4 the total flight height)
- Width of top two steps: 89cm (to accommodate air gap to left and post to right)
With the larch boards being 1.80cm long, it might be tempting to think of cutting them into two 90cm boards. This is rarely a good option. Firstly, because the saw blade will use up 2mm, and secondly, because there is usually some variation in boards length (some might be a few mm short) and thirdly, the ends of supplied timber are rarely perfectly square and free of imperfections, so might well need squaring up or trimming a few mm off. So, knowing this, I aimed to get 2 x 89.0cm pieces out of each plank.
Note, that the legs of each step are designed to rest on legs of the step below, so that vertical loads are transferred to the ground.
At this stage I asked the client to confirm the dimensions on site, and approve the design. Once they had checked and agreed, I was able to begin building the steps.
Construction
It might seem counter-intuitive, but I began building the steps from the top down, i.e. starting with the top step first. The logic of this was that the top step is the smallest, and would enable me to practice my construction technique. Any mistakes would risk only a minimum amount of timber going to waste.
Top Step
Here is a construction diagram I made before cutting any timber. The client requested that no end grain was visible on any of the visible faces. To achieve this, I planned to have a mitre join on the visible corner (front-right) of each step (see diagram below). With these details decided, cutting sizes for the side pieces could thus be determined.
The client requested that the side boards should all be the same height, and that the air-gap between each board was consistent throughout the structure. This would mean ripping down the boards (cutting them lengthways) so that there were three equal boards vertically per step, with three spacer gaps. I decided to use 4mm hardboard spacers. This was not only a pragmatic choice (I already had some 4mm hardboard offcuts), but was necessary to accommodate expansion and contraction of the boards throughout the season. Once agreed with the client, the board width could be calculated by dividing the riser height by three (345 / 3 = 115mm), then subtracting 4mm for the gap, giving a board width of 111mm (11.1cm).
The larch boards are excellent quality: fine-grained, straight and almost free of knots. The available larch boards were all 155mm wide, so cutting them down to 111mm produced a high proportion of waste — something I try and avoid wherever possible. In this case there was no option, but I have kept these 42mm slats and will use them in another project.
The top step consists of three rectangular ‘rings’ of 111mm boards stacked on top of each other and separated by a hardboard spacer. To ensure each ‘ring’ was square and all three rings were identical, I assembled them around an internal template: a piece of 15mm MDF which I cut to the exact size of the internal dimensions of the step. The corners were screwed together with loss-head decking screws. These go in really easily using a t-star bit, and pull up tight, leaving only a tiny hole, which could easily be filled, but are practically invisible once stained.
Legs were then fixed into each corner. I used Accoya, as it is strong and rot-proof. Approximately 45x45mm in cross-section, I cut them to length and screwed them inside each corner, which tied the three layers together, producing a strong box. For the top step, the legs were cut deliberately undersized, so that they provide a 15mm rebate on the bottom. The legs on the step below will protrude 15mm above, so that they will lock together — a bit like a lego brick — preventing the steps from sliding across each other.
The assembled step (without any tread) was sanded on the visible parts, and then stained on all surfaces. I used Barrettine Premier Wood Preserver (Black) which is an oil based, low odour stain and preservative in one. The photo below shows the mitred front corner nicely:
Middle Step
The middle step was a very similar construction, except being deeper, it had longer planks on two sides. Here it is, part-way through construction, with the top step being stacked on top to check it fits. Notice how the boards on the sides of the two steps line up to produce consistently spaced gaps:
This mid-layer step will have six legs: one in each corner, plus two which line up with the front two legs of the top step above it. The back four legs will stick up 15mm, where they will support the recessed legs in the step above, carrying the weight downwards, ultimately onto the ground. In the picture above, one front leg appears to be in place, but it is not attached. The two front legs will be cut flush so that the treads will cover them when fitted. You can see how the rear interlocking legs work in this close up photo of the back corner. The upper step (black stained wood) sits over the lower step leg (unstained wood)
Notice, that to get a consistent projection distance at the top, I used a piece of MDF as a spacer under the leg.
By this point, the steps are becoming quite heavy, and I can only just move them one at a time on my own. This was part of the reason for constructing them in modules.
Bottom Step
The bottom step was the most complicated, but by this point I had worked out all the tricks necessary and construction went smoothly, even though the whole structure was considerably wider the table I was building it on.
Many considerations go into the bottom step:
Here, all three layers are being checked for fit prior to staining the bottom step.
Adding the Treads
Now it was time to attach treads to each of the steps. It was only at this moment that I realised that the treads of the top two steps would have exposed end grain. I came up with a solution, which was to bond small fillets to the end of each tread so the end-grain was covered with side-grain. However, this presented a challenge for the front edge, requiring me to cut in a mitred end fillet. These were glued and clamped overnight. The end result was a pleasing attention to detail.
The treads were made using two full width boards (~155mm). This left a small 50mm infill towards the back of each tread. This was justified on the basis of aesthetics (wider boards look more generous) and strength (the full-width boards would take the foot-fall, while the narrow rear board was almost impossible to put any weight on).
The back tread of the top step was left full width, but not attached, as it would overshoot to meet the angled retaining wall. The plan was to scribe it to the back wall and cut it on site.
I gave the top and bottom edge of the treads a small 45 degree chamfer to create a shadow line beneath them and make the edges less likely to splinter-off during use.
Finishing
The whole structure was given one coat of stain on all sides, inside and out. The visible faces and treads were then sanded and given a second coat.
Here are the top steps being given their final, pre-delivery stain in my greenhouse. Due to careful planning I managed to waste very little material, so saved a dozen boards which will be stored in case of repairs or additional work in the future (you can see them in the back-corner, above)
And here is the lower unit, with an overnight fan heater helping it dry. Tomorrow I pick up the hire van and drive the units to London.
Installation
Having carried the base unit in from the van, it fitted almost perfectly. Using several thin plastic shims, the whole thing was levelled and checked. Then the end of the return step had to be cut so it could meet the angled retaining wall.
Once cut, the base unit was fixed to the concrete base using several stainless-steel angle-brackets. I had brought spare Accoya legs, which were fixed to the back on the left-hand boards so they rested on the concrete step, supporting that side properly. It had been decided that the surrounding decking was going to be coated with the same preservative stain, not only to match the steps, but also to prolong its life. As such, before permanently fixing down the first step, we lifted it and thoroughly stained/preservative-treated the deck beneath it.
By 6pm all three tiers were installed. I used stainless steel toggle catches to hold each tier securely to the one beneath it. The whole structure was solid, tight and secure, yet will be easy to dismantle if necessary (e.g. for repair or cleaning.)
Over the next couple of days the client gave the steps and surrounding decking a full coat of preservative-stain, and organised lighting.
The end result speaks for itself, looking great, and being very practical in use. Despite them being ‘double height’ steps, their wide treads make them much more secure under foot than the narrow-tread temporary steps they have replaced.
