Sunday, 9 May 2010

Building for Kiwis

We planted three kiwis last year to grow over the outdoor table, to provide summer shade and winter fruit. They hardly grew, we gradually forgot about the prospect of fruit, and ended up using any old screen for shading erected over a bamboo frame, supported on both granite and wooden posts dug into the ground . By Spring, at least one of the wooden posts had started to rot - mould and fungi were starting to appear half way up, inevitable given the amount of water in the ground all winter. Also, by this Spring, the kiwis started to grow again, and they have almost reached head-high.

This issue of using wood close to the ground in building is a classic design fault common all over the world. In 1997 I worked with Movimondo in Guatemala where a part of their community development project involved showing locals how the use of around 70cm of stone footing for their homes would extend the life of the wooden walls, saving them the financial burden of rebuilding their homes every five to ten years.

Here in Portugal, and also in Scotland, I know that people generally believe it's sensible to sink a post deep into the ground, often bedded into cement for "extra strength". We are also advised to paint the end of the post in tar, or burn it first to prevent rottage. But Paulo has introduced the idea of using rocks as the principle footing to ensure the posts stay dry and last many times longer. Small metal bars, around 8mm diameter are inserted into the but of the post, and a similar hole drilled into the rock. This merely holds it in place - it is really wobbly and insecure at this stage. Temporary cross bracing to the ground keeps it from falling down.

Once a few posts are erected, a beam joins them together along the top, with simple lap joints with more metal bar to keep it together. This helps to secure the wobble a bit, but it really starts to get more secure when you link up the posts in both directions and add cross bracing. Rafters helped with stability too.

The posts are made from oak chopped from Donald's forest last year, and the central beam is from chestnut coppiced from around our watermill this winter, shown here. We have taken to removing all the bark to prevent the multitudes of bugs and creepy crawlies that live under there chomping away at the sap wood.

So we decided to build a whole new frame partially using the granite posts that we had but mostly from new oak posts. Photos say rest of the story...

Jon - roped in from Scotland, helps shape some new cross bracing for the central posts (that's him in the nifty hat:)

One of Paulo's lap joints

Chisling in for another

The chestnut beam is placed

Paulo's bird's nest view of us 3 trying to get our heads around more cross-bracing

Someone taking it easy (that'll be Charlie)

Bugui, Galician yoga teacher, going with the flow of debarking.


Rupert Wolfe Murray said...

They say all the best ideas are the simple ones

luís said...

Olá. Podes dar-me uma tradução de "cross bracing" e "rafters". Obrigado e bom trabalho!