Bristol Green House i-beam construction


Tyre walls
Straw bale walls
I-beam roof
Living roof
Clay/Lime render


I-beam roof construction.

A timber I-beam or I-joist uses one sixth the wood of a conventional joist for the same strength. They are made of wood composites so can be made of younger, more sustainably sourced woods and they’re lighter and easier to cut.

When I asked about sourcing them at my local timber merchants they all stroked their chins, drew in their breath and told me that I-beams were rubbish. When I pushed them further they revealed they had never even seen them. The idea was first developed in the 1940's, but only now are they becoming common. So what has held them back?


They are bloody pricey. As with many green products they are more expensive than the more damaging mass market alternative.

The i-beams I used were made in Finland, but there are ones made in Scotland. Note that all the different makes of i-beam have different load bearing specs.

Around the edge of the roof we used Kertos, also known as Timberstrands - these are effectively very thick plywood beams. They're heavy like timber beams but made out of younger wood glued in layers.

Below; what happens when you get millimetres and metres mixed up.