The architect's drawings and the structural engineer's calculation

The architect got to work. In January 2026 we spoke on the phone several times and he came up with the following drawings. Several changes were made during this process and I’ll explain them with the drawings as well as I can.

Drawing #1

The layout stayed largely the same, and at this stage of the build it wasn’t very relevant to me yet. I wanted to get the structural engineer sorted so I could start on the foundation, and for that mainly the size and building materials mattered.

Roof height

For a flat roof you can build up to a maximum of 3 metres relative to the surrounding ground level. We went right up to those 3 metres because it lets us create a nice overhang on the visible sides of the building. A 50 centimetre overhang doesn’t count towards your built-up area. Notably, the garage is 2650 millimetres high, so we can let the overhang extend over it too. Because the garage’s rainwater downpipe had to be moved anyway, we combined it with the garden office’s. One half of the garden office drains out by the garage and the other half will drain out at the back.

Size

After a lot of deliberation I decided to make the building smaller. We have raised beds to take up the height difference with the lawn. If the building stuck out further into the garden, it would create very odd shapes in those raised beds. On top of that, I didn’t think it looked good visually next to the house. The new plan is to use the maximum space within the raised bed. Effectively you then get a strip of gravel or soil of about 200 mm between the bed edge and the building, and maybe even less if the thickness of the cladding turns out bigger.

Neighbours’ heights

You can see that with both neighbours I’m dealing with a total of 4 different heights. At one height I could connect the roof by letting the roofing felt hang down, but in most places a kind of gutter will be fixed halfway up my wall to minimise rain getting into the ventilation strip.

Drawing #2

A site drawing that gives the structural engineer a lot of context. I dug trial holes on every side. There I looked at the foundations of the surrounding buildings and at what depth the sandy soil started. How wide and how deep are the foundations, and from what depth can we build on firm ground? The architect took these points over and added a few things, such as the height difference with the garden. The height difference is a very important piece of information for a structural engineer.

Drawings #3 and #4

These actually already show part of the structural engineer’s result. This is the roof plan, and the architect already knew steel would have to go in. I did note an open point for myself here, because with the rainwater drainage I don’t yet know how I want to lay the fall of the roof. That could mean the HEA beam ends up positioned differently if I use it for the fall, but I’ll see when I come to plan the walls and roof.

You can also see the overhang clearly in the second photo.

Drawing #5

Screens On V.B-1 you can see nicely how the screens are hidden behind the fascia boards.

Waterproofing The red lines on V.B-1 and V.A.-A indicate the waterproofing between the timber frame and the Ytong blocks that are placed all around. You want to keep moisture from outside out of your foundation and make sure the moisture that is there doesn’t find a way up. That’s how you keep moisture out of your timber structure. With my choice not to connect to the surrounding buildings anywhere, there’s a challenge here. We have to create a kind of gutter between the Ytong and the outer walls.

I have to say I got fairly scared when I learned about capillary action from Henrie. Moisture that moves upwards — think of holding a sugar cube just in your coffee and watching the coffee get sucked up. I now try to double-check this phenomenon at every step, because moisture problems in places I can barely reach don’t seem much fun to me!

Wall build-up The final wall build-up we have in mind is included here. It has been designed around the vapour-open principle: the most vapour-retarding layer (high SD value) on the warm side (inside), then decreasing towards the outside (low SD values).

Structural engineer

A structural engineer receives the drawings from an architect and then adds notes to them, which the architect in turn works into his drawings. You also get a report back with all the load calculations. The following practical points came out of it.

• The bed edge is wide enough (150 mm blocks)
• 800 mm frost footing with 120 mm slab was fine
• 6 mm diameter reinforcement mesh with 150 mm spacing is sufficient
• HEA 200 in the roof is fine

Then a light bulb went on. Henrie from Zelfbouw Cursussen had told me several times: ‘on smaller projects I often use 2x 4 mm reinforcement mesh’. On smaller structures this is often perfectly fine, and it has a big advantage. You can bend the mesh by hand and so let it hang into the frost footing at a 90-degree angle. That means you hardly need to tie anything and don’t have to buy or bend separate cages. I checked this with the structural engineer and it was fine.

The first real costs of the build have now been incurred!