Our heads were blown! Why?

Our heads were blown! 🤯 Why?

I recently had to design an abutment box gutter perfectly, with absolutely no mistakes or issues. There was to be no guesswork on this job! As a result our heads were blown. Read on to find out why.

This may not sound like the sexiest design job, but we thought we’d share some of our recent experience designing an abutment box gutter at the junction of where a sloping roof butts up to a wall that goes up past the roof.

Keeping it to the guidelines

To do this properly you have to design the gutter in accordance with BS EN 12056 Part 3, Gravity drainage systems inside buildings – Roof drainage, layout and calculation.

This super exciting design guide is cross referenced in the Building Regulations Approved Docs. You have consider things like rainfall intensity for certain parts of the country + capacity of the gutter + rainwater pipe sizes and outlet capacity. It didn’t pass first time, we had to adjust the design size of the gutter so there is greater capacity.

Accommodating for climate change

We also looked at worst case scenarios and made the gutter slightly bigger, so it’s designed to be future proof and accommodate some of the crazy heavy downpours that are now becoming the norm, possibly as a result of climate change.

Part of the design is also ensuring the material to provide the gutter is suitable. Traditionally for this sort of gutter you should use lead sheet, as a result we also had to consult the best practice recommendation from the Rolled Lead Sheet Manual design guide, produced by the Lead Sheet Training Academy. This double whammy of the British Standard and lead sheet guide meant we had a lot of information to get our heads round.

We ended up specifying code 8 lead which is the thickest and most expensive lead sheet available. Our reasoning was that the lead sheet can be laid in larger sheets before junctions and steps are required.

This means only two steps are needed for each gutter, which in turn, means less timber framing and lining is needed. As a result less overall materials should be needed, and a lot less labour. This results in a quicker and cheaper solution to the original problem.

We also had to introduce ventilated junctions at the gutter edges to reduce the chances of condensation occurring in the areas below the leadwork. Introducing the junctions ensures any condensation can be drawn off to prevent it decaying the timber and corroding the lead from the inside out.

We modelled this up in 3D which was a difficult process, but we know this will be super helpful to show the guys on site. This way, while they’re building the gutter and associated parts, our design intention is clearly understood.

We can’t have the gutter overflowing and leaking inside the building now can we!

Long and complex calculations

We spent an afternoon completing these calculations and the leadwork design. It was the first time we’ve ever had to do these calculations in over 25 years of working in the industry, so perhaps we had been lucky before.

As a result our heads were fully blown at the end!

Despite the complexity, this was a positive experience and a good opportunity to continue our professional development. We learned a lot of valuable information and skills we can apply to future jobs.