Flush joints for cladding or finishes

[Alex Whitcroft]

Hi all,

Does anyone (I'm looking at you Alastair!) know the load bearing capacity of the flush finish wedge joints used in V3 of the Wikihouse?

We need a flush finish joint to use under rainscreen cladding.  The V3 flush joint is perfect, except... we're not sure how strong it is.  It will be used in a similar situation, but holding bands of ply (rather than complete sheets) and will be holding up timber rain screen cladding.

Anyone know?

[Alastair]

Hi Alex!

Uh-oh. I'm being looked at. What kind of strong are you looking at them to be> The flush-finish wedges (which we've named 'supergrips', as compared to the normal 'grips') are intended not so much as a way to hold the external panels on (although they will do some work doing this), they basically grip the plywood sheating sideways, which means the chassis structure as a whole becomes tight. But these panels would be additionally held on by screws.*

On the 'bands of ply' (might need a drawing of this to help) thing, its also worth noting that the external plywood (or versaliner) panels are doing structural work, making the whole chassis into a structural 'box'. 

For rainscreens, our current intention is to get the chassis flush using the supergrips, then overlay Tyvek and screw battens on in the usual way. However, we're also experimenting with CNC 'comb' battens which are shaped to receive the cladding, so no measuring is required to fix the rainscreen.

Does that make any kind of sense? If not, please do attach a sketch  / sketchup model and we'll work it out!

Best

A

*More on this to follow, following some current work with engineers getting to a certified structure.

[Alex Whitcroft]

Alastair!

What kind of strong = was hoping we could get away without screwing fixings for the outer sheathing.

Sounds like that might be asking too much of those supergrips.  Sounds like we don't have the engineering thumbs up or thumbs down yet though.  It would be a real victory to be able to just use those supergrips without screws.

Not by Sketchup right now, but will send a sketch along shortly.  It basically this: With regular enough batons we don't actually need continuous external sheathing.  You can just rely on the batons to hold the house wrap in place.  There are some affordable fibre reinforced membranes which are designed specifically for this.  Cost and material saving, lighter weight structure, and a more vapour open exterior face to the envelope (which is better for the cold/temperate climate like the UK).  We were looking at a strip of wood top and bottom and then continuous vertical cladding batons (less assembly work as no counter batons and no horizontals to collect water) and some kind of horizontal "combs" (seems like you are thinking along those lines too).  Anyway... sketch to follow.

It's interesting that the exterior panels are structural too.  I would have thought that only one layer (ideally the inner one, double as the air barrier in the UK) was necessary.

I'm pretty flexible in terms where I work and what on over the next 2-3 months.  If there is WikiHouse - or related - stuffs that would be good to have an extra brain and set of hands on would be useful for me to come work out of Hub Westminster for a while?  Really keen to get more involved now that the US project I was working on when we last met has wound up.

Beardy A

[Alex Whitcroft]

Et voila... sketch...

That's just the v3.3 model tweaked to show the 'bands' of ply I was talking about.

So there are two parts to the question/uncertainty:

1. Will the supergrips be able to support timber rain screen cladding.

2. Will the system be structurally braced enough still now the outer sheathing is not continuous.

PS: Is the 200mm depth for the studs/fins the minimum required for the joints?  Or was it partially based on allowing for a moderate amount of insulation.  Ie: They could be narrower, structurally.

A