This article was written after owner building the HEY House. We've posted it on our website because the experience was invaluable to our practice and might be useful to others.
Here is our retrospective account of building some of the structure, step by step in photos.
Our first task was to excavate the pool.
The pool was positioned away from the side boundary wall, as we were worried about cave ins. The roots in the sub-soil along the wall base thankfully held the ground together, but elsewhere we were not so lucky.
The areas that did cave in required sacrificial formwork to be installed to hold the shell profile.
As with most conventional pools, the steel reinforcement gets bent up from straight bars and shaped entirely by hand. Once plumbing services were laid and the pool earthed, the concrete was 'shot-creted' or sprayed to form the shell.
The site for HEY House was flat, so there was not much we needed to excavate to get started building the slab. We only needed to scrape the surface and establish a level ground at the top of footings.
Once the pool was poured and backfilled we covered it over with formwork so we could retain the space during the build.
It's very common for engineers to specify metal screw piers to strengthen the footing structure, particularly on sandy sites that are susceptible to cave-ins.
As the name suggests, the piers are like giant corkscrews, with a helix at one end and handle at the other, that get rotated into the ground using a helical drive head. Once the pier reaches the desired bearing pressure it then gets tied in to the steel reinforcement along the footing.
Fortunately, we only needed to screw pier underneath the edge of slab along the swimming pool, and the piers went in rather effortlessly.
When we show footings on our drawings, they are like a perfect rectangular box in the ground with a constant width and height, dimensioned off grid.
Unfortunately those precise lines are near impossible to achieve when building in sand!
The concreters did their best to markout the footings off grid, but once they started to excavate, cave-ins became unavoidable
Because of the sandy ground conditions, it was vital that the prescribed bearing pressure was reached at the base of footing prior to pouring. The simple method of watering in the ground was adapted, until the bearing pressure could be verified by the geotechnical engineer.
The reinforcement 'cages' were then made up onsite and laid into position on bar chairs. Once inspected by the structural engineer the footings were then poured with concrete.
From herein, things got more way more challenging!
Our goal of maintaining material integrity meant the trades needed to be organised and aware of their workflow, and be cautious of particular details that required early rough-in.
For instance, the lighting and power had to be routed through the slab and up walls, as there was no plasterboard or frame. The positioning of steel reinforcement and risers also had to be spot on, as the polished concrete slab through-out the ground floor meant there was nowhere to hide any mistakes.
Once the services we in place, we then graded the base of the slab with road base, compacted it, and laid plastic membrane for moisture control.
The slab edges were formed up, reinforcement laid, and once signed off by the structural engineer, the slab poured using a mix that contained black oxide additive to tint the finished concrete.
loaD BEARING MASONRY
Brick laying is a skilled craft, particularly when the wall being worked on cannot be rendered and needs retain a clean face finish with visible mortar joints.
We invested in a brick saw that was onsite for the duration of the build. Even though we thought the design 'worked block modules', there was so much cutting!
Because the walls were over 3m in height, we had to work in 2 stages, and only lay unfilled up 1.6m in height.
The mortar mix had a anti-efflorescent additive, which affected its workability onsite.
The issue of clean-out blocks was raised with the structural engineer, and fortunately avoided in scenarios where the wall was double-sided and without a cavity.
The bricklayer insisted on 'raked joints' as he said it looked better, giving the block more dimension and shadow. We followed his advice (contrary to the manufacturers recommendations).
All exposed faces of the masonry walls needed to be brick cleaned and sealed prior to formwork.
The slab soffits throughout the majority of the ground floor were to remain visible, with bulkheads limited to covering up services.
The approach meant we generally required new formwork ply, and had to ensure the deck kept as pristine as possible.
The sheets were set-out in a half bond pattern, so that when stripped, the joints made purposeful.
Suspended slab design and construction is more challenging than slab on ground, and generally requires a specialist crew of steel fixers. Unlike slabs on ground, precision is vital, but is fortunately attainable doe to the stability of the formwork base.
The steel fixer marked out with chalk every strand of steel in the bottom layer of the slab. Then plumber and electrician marked out and installed collars and junction boxes at penetrations.
Because of the lighting that was to be mounted on the slab soffit, the electrician had to route electrical conduits through the center-layer of reinforcement.
Finally, the top layer of reinforcement was added and signed off by the structural engineer with a site visit, then poured.
stud wall frame & trusses
Once stripped, our carpenters joined the team onsite and began setout and construction of the stud walls and trussed roof framing.
Conventionally detailed, the frame was fast to build and permitted services to be routed through as needed.
The trusses were prefabricated and stood up in position ready for the roofing contractor.
Large spanning openings featured parallel chord trusses, an innovative suggestion by the structural engineer that permitted a flush wall return and floor to ceiling window detail.
roof & CLADDING
Once the timber frame was approved by the structural engineer, the roofer laid the steel roof battens and insulation blanket.
The roof sheeting we used had a clip system of fastening, with limited need to puncture the surface.
Box gutters were used with internal downpipes, so as to maintain clean lines along the exterior parapets.
We chose to use Lysaght Enseam as the wall cladding which required a flat parapet that extended to the outer edge of the cladding creating a continuous picture frame.