[Strawbale] Fwd: Repair work on danish strawbale house

[Dave Howorth]

On Tue, 2011-10-04 at 15:24 -0400, RT wrote:
> ...from the GSBN List, my thought being that there should be some Danes on  
> this Euro SB List who are more familiar with Denmark-specific SB issues  
> than those of us here in the Colonies.

I'm not Danish but can perhaps provide some pointers, hopefully others
with more direct knowledge will add to them.

On Oct 2, 2011, at 2:59 PM, Michael M. Jörgensen wrote:
> > a major rainfall on 2nd July, the largest in Denmark in more than
> > 100 years, which flooded our fine house,

Sorry to hear that.

> > Do we have to use welded chicken net/wire ? we did the last time,
> > but we have also heard of a method of using straw mats, example:  
> > http://www.hiss-reet.de/produkte/naturbaustoffe/unterputzgewebe.html
> > My thoughts are that the bales and the mats are the same material,
> > and using the mats to close the gaps over wooden joints etc. ought
> > to ensure a wall that does not work in different ways.

Reed mats or hessian sacking are commonly used for this purpose.

> > Will this ensure a rendered wall without cracks and tears or should
> > we stay with the chicken nets?
> >
> > If we end up using the chicken nets ? should we then cover all bale
> > surfaces with the nets? Or only the wooden joint parts?

When using lime render, it is usual to just use the mats over smooth
areas such as timber to provide a key and a continuous surface. The lime
adheres well to the straw bales themselves.

I believe that all over wire mesh is commonly used when using cement
render and in seismically active areas.

When traditional timber buildings were built, with lath or reed panels
and lime render, wire mesh was not yet invented!

> > We intend to build the new walls in bales, but start with a not-
> > water-absorbing material for the first 50-60 cm from the base ? no
> > reason to invite disaster a second time. Should the joint of the two
> > materials be separated by a water repellent material like to avoid
> > ascending moisture or will that force any moisture in the bottom
> > strawbale to stay there thus causing problems in the bottom
> > strawbale. The direct reason for this question lies in the
> > construction of the last wall, which was mounted on a wooden bench
> > of 2 by 4 inch beams parallel to the house deck and elevated about
> > 30 cm above ground and actually fully ventilated from below given
> > the bench construction (should have been a bit further up, as we
> > realize now, but no one knew at the time). That construction ensured
> > that no water could accumulate in the bottom strawbale. It there any
> > technical advice on this?

I guess your Danish building law will dictate that you have a damp-proof
course at the base of your wall? That will provide substantial
protection. It won't do any harm to have another damp-proof course at
the top of the wall - this could just be a course of engineering brick
if you are using a brick wall construction.

You are still correct that you should ensure good drainage from the
bales, so you need to make sure that water doesn't collect on top of the
wall. A wooden ladder base plate with porous insulation is a good
transition. The water needs to drain either within a cavity wall or be
directed outside the wall.

For reading about straw bale construction details in northern European
conditions I can suggest:

Barbara Jones - Building with Straw Bales

Gernot Minke & Friedemann Mahlke - Building with Straw

For additional techniques to use with lime render:

Holmes & Wingate - Building with Lime

Cheers, Dave