Building Blox: Week 11 – Roof steel ridge beams and design work

What we did:

  • Roof design
  • Roof steel beams installed.

With the brickwork completed up to the top of the roof, this week the steel ‘ridge beams’ which make up the roof structure could go in. A slight issue was that the roof design hadn’t quite been finalised, but as with most other parts of the build, the contractor wanted to race ahead and get this done, and rightly so to keep all the cogs turning.

Let's build a roof

Back in week 9 I showed you how traditional truss roofs work, with much of the structure pre-fabricated offsite and simply secured into place onsite. However, I had opted for a vaulted ceiling in which the top floor extends up to the inside of the roof, so there is no attic space.

Here’s how you build one…

Roof section drawing

Roof section drawing

After the brickwork is completed, steel ridge beams are laid on top of high-density concrete padstones, at the highest points. This is where the top of the roof will be. Here’s a little video of us putting the beams into place this week using a new bit of machinery, controlled by a pretty over-exuberant driver!

On to the chippies

No I’m not talking about a Friday fish & chips treat… #dadjoke

Next week the carpenters AKA ‘chippies’ will be onsite to make up the roof – here’s what they’ll be doing.

Following the ridge beam installation, pieces of timber, known as rafters (see the diagram above), are secured diagonally between the ‘web’ of the steel beams and a ring of timber which goes around the top of the walls, known as a roof plate. Incidentally, this roof plate running across the top of the brickwork helps hold the walls together.* The rafters lie perpendicular to both the ridge beam and wall between which they sit. Once this is done all the way around the perimeter, the basic structure is completed.

*(In a future post I’ll discuss why much of the traditional UK building isn’t great, but meets our needs)

Roof plate on top of blockwork

Roof plate on top of blockwork

In my design (pic below to remind you), there is a main section of roof across all 3 houses, but also another smaller gable at the front of each house. As such there are 2 perpendicular roof ridges, requiring 2 pieces of steel beams bolted together. Similar to the main section of roof, rafters are also placed here to complete this part of the roof structure.

Proposed 3D front elevation

Proposed 3D front elevation

As you can see, the sections of roof will intersect at some point and there will be nowhere for the rafters to be secured to. The answer is to lay ‘valley beams’ – large pieces of timber laid diagonally at 45 degrees to the rafters, from the steel to a corner of the building. You can see these in the diagram above. The rafters can now be secured between this and the steel beam.

More details on the roof fabrication next week, after all I’m learning as well!

Working with designers

In a less than ideal sequence of events, the final roof design work was being done whilst the roof steel was being installed, but drawing on their experience I was confident the contractors could proceed without issue.

What I’ve found when working with engineers, architects, etc. who are designing structures, is that they may often over-specify or over-engineer elements. Perhaps it’s down to the high-stakes litigious climate which business is done in, or simply because they want to ensure safety, but the impact is to drive up costs and time spent checking minor details.

An example here is that huge 63mm wide pieces of timber were specified for the roof by the engineer, however everyone in the trade is used to using 47mm ones. 63mm is not widely available so we must go up to more expensive 75mm ones to ensure compliance, and to make things worse, must ‘down-tools’ until we have sign off that this is acceptable. After that I’ll then spend time chasing up for written confirmation.

Mezzanine floor dream dies

I mentioned a couple of weeks back that given we have so much space in this vaulted ceiling, perhaps I could fit another small section of floor in where the roof is at its highest point. However, after much time on the CAD software, and ultimately pacing around the site, there wasn’t quite enough space to make it useful space. I also had to remind myself these houses weren’t for me so costs need to be kept to a minimum…

They may have looked something like this though…

Mezzanine idea

Mezzanine idea

Next week we should see the main structure of the back side of the roof go in, which will give me a solid lesson in design and carpentry!

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