UKC

I'm building an insulated home board in the garden. The wall will be a timber framed floor on concrete piers with a gabled roof to house a 40° board and a 30° board.

I've sorted the floor and the piers. I'm now planning the roof. Looking at span tables for the roof it seems the building industry works to 0.5kN / 0.75kN / 1kN per m2. If my overall roof is about 20m2 this would total 10kN / 15kN / 20kN. This is the deadload that the rafters can support.

Obviously the wall and e.g. two climbers is going to be fine with 0.5kN per m2 but the forces generated by dynoing for example may mean I need more. I don't want to over engineer this thing and spend more than I need to.

If anyone is able to suggest the forces generated my climbing or if anyone has looked into this already if be grateful for some help!

Ta

Span tables:

https://www.timberbeamcalculator.co.uk/en-gb/span-table/rafters?load=1&...

I very much doubt that I could stick more than 2g holding the finishing jug of a dyno (equivalent to hanging the jug with another climber on your back). So depending exactly how much of a beast/lardarse you are, that should give you your peak live load at a point directly under a rafter.

You also need to consider how the load is distributed across the rafters - both how many rafters and where attached. If your board is attached at mid span, the deflection for a given load will be 1.6 times greater than for the same load uniformly distributed, which is what those tables assume.

Also, the roof design dead load is vertically down but worst case is you are swinging out on the jug, perpendicular to the rafter, so add a factor of 1 over cosine of your roof angle.

Amazing thanks for taking the time. I get what you are saying except for the last paragraph. Can you explain? That seems important.

That last point was just that weight acts straight down, so only part of that weight (cosine of roof angle) is acting to bend the rafter, whereas a swinging climber could be pulling straight out on the rafter.

But I have never built a board, never mind a building, so this is just armchair theorising on my part. My point is really that you need to be careful about comparing an evenly distributed total load on the roof with a point load from a climber swinging on a jug.

For example, if you use that table to select rafters for a 2m span at 450mm spacing, 0.5kN/sq.m dead load, then each rafter is designed to support 0.9 square metres with dead load 0.5kN/sq.m and 1.0kN/sq.m imposed (wind) load, giving about 1.3kN in total. That load is evenly distributed - you would get the same deflection with a load of 0.85kN at the midpoint. A swinging 85kg climber could perhaps generate twice that load.

Of course there are factors of safety in there that would probably see you right, but I think the main thing is just to distribute the load well from the board to multiple rafters or other supports. A good stiff joist along the top of the board would probably be sufficient.

And don't climb during a gale

IIRC the load figures you quote relate to snow and wind loads, the applicable figure for your region can be picked off a map that is downloadable (sorry, you'll have to google).

I'm struggling to visualise exactly what you're proposing. A long thin 3-walled shed with a simple double pitched roof and a climbing wall inside? Or no walls, just a roof on posts?

Unless your wall surface is articulated the floor carries most of the climbing load. Even the 40deg board if tied to the rafters acts to deform the roof and wallplates laterally and vertically. That does need consideration but there are various triangulation/sarking options which will easily deal with it.

Unless you do something really mad structurally once it's strong enough to withstand British weather it'll handle you climbing under it just fine.

jk