Straw bale construction

mynewshoes

Hi,

I am wondering if anyone has come across any literature in relation to straw bale construction WITHOUT a rendered finish? I am looking at the rain-screen on a breather membrane possibility.

Obviously there are Regs to consider as the render satisfies a lot of the fire issues, the post construction method with bale infill will create undesirable vertical cavities, however these can be stopped.

Or has anyone any opinions as to the feasibility of such construction.
I am considering building myself a design studio/ office and can not find any literature to support or hinder my proposal.

Thanks

sydthebeat

two issues:

1. the condensation point will be on the cold face of the bale. the rain screen by its nature will create a cavity. this cavity HAS to be ventilated to prevent real risk of mould and fungal problems.

2. insurance for this build will be very hard to come by

mynewshoes

Thanks sydthebest,

Ya, I intend to seal internally with a vapour control layer and provide a ventilated cavity behind the rainscreen closed with wire mesh.

I think insurance will probably be impossible but its a construction experiment for myself and should build it for approx 5k, finished.

Might meet the building control officer and have a chat, see what he thinks.

sydthebeat

you must have great faith in BCO's

in my eperience they are barely up to speed with standard construction methods, and anyway you can argue your build is exempt from building regulations if under 25 sqm and meets some other requirements.

sinnerboy

mynewshoes wrote: »

Obviously there are Regs to consider as the render satisfies a lot of the fire issues

Well - not really. External walls that are located close to boundary walls have to be fire resistant - ( TGD B4 refers) . not simply have a low surface spread of flame which is all render will give you wrt fire.

mynewshoes

Ya true, sorry I meant a lot in relation to my build, its a green field site away from boundaries.
sydthebest made a good point regarding the exemption as the experimental build will be approx. 22sqm- I will have to do some research into this.

shane6977

You might find this useful:

Building with Straw Bales: A Practical Guide for the UK and Ireland by Barbera Jones.

Saw it referenced on a BRE Information Paper, haven't read it so don't know if it deals with walls without render finish.

Would be interested to hear how your experiment progresses, maybe you could post some photos up here from time to time once you get going?

BTW the BRE paper is reference IP 15/11 if you want to look it up, costs about £10-12 from the BRE bookshop

mynewshoes

Thanks Shane6977,

I have actually just bought that book, it has lots of good info re vapour barriers and condensation but as with most info I have come across nothing on render-less construction.

Ya, I intend to keep a good photo and written record of the design and construction process. I will try to do a blog maybe but need to figure all that out.

I will also discuss with local planning office and building control officer and post the comments- that might be helpful.

hiromoto

There's a book called Serious straw bale by Paul Lacinski and Michael Bergeron that covers all aspects of building with bales, I'd be slightly wary of Barbara Jones book, no offence to her she is such an enthusiast she neglects to mention the things that can go wrong. I live in a lime rendered straw bale house, three years old and so far so good. Any reason you don't want to use render? Ben Law (the woodsman on Grand Designs) clad his bale walls with timber outside and clay render inside, not sure what happened between the cladding and bales.

Noel.G

The S-House in Austria is an office and exhibition building which is built to passive house standard.

The walls are wooden plate construction, straw bales with clay plaster and timber cladding. There is a typical wall detail on the following paper;

S-house – sustainable building demonstrated by a passive house made of renewable resources

Also if you take a look at the S-house website I'm sure you'll find some more information.

BryanF

Biggest issue I see with straw is its requirement to be in compression. I did a course with Barbra jones and one of the main contentious issues between the purists and the bunch of arch's on the course was the load bearing v non-load bearing approach.

hiromoto

I definitely wouldn't be keen on load bearing in our climate but the OP said they're using post construction with bale infill so it's not an issue.

BryanF

So then the issue becomes ensuring compression of every inch of straw. I've seen first hand even on an exceptional project where one section was no compacted cause interstitial condensation to occur . I should point point out I like straw bale construction but see a product like modcell the best alternative to loading bearing the bales

hiromoto

Surely even on compressed walls there is a dew point somewhere in the wall if the wall is breathing. Warm moist air inside and -1 outside.

BryanF

Exactly where its not compacted at such a due point location, the wall will not disperse the moisture ie 'breath ability' is hampered by lack of straw compression

hiromoto

Explain to me what happens that same water vapor in a compressed wall?

BryanF

compressing the bales allowed water vapour to be absorbed or released (or as some call it :'breathe') where as if the bales were not adequately compressed that vapour would condense causing mould etc.

hiromoto

My point is that even in a compressed wall the same amount of vapor will enter and as it moves out through the wall will condense. Granted if there are gaps in the bales these will be damp spots. I screwed a row of vertical ribs (2x1) to the outside of the frame, stacked the bales up snugly inside then more ribs inside and tied them together through the courses. I'm confident there was no gaps prior to rendering, but I wouldn't call this a compressed wall as such.

mynewshoes

hiromoto,

I have designed a frame that will be used to create some compression from the top down and also the bales will be packed between the vertical posts, so like you the condensation risk in relation to the compaction is not a worry with me. I am beginning to change my mind from my OP and might go with clay render. It will work out cheaper and may avoid some other condensation issues.

Have you built your straw bale home in Ireland? Any issues with planning and/ or building control?

Anyone have issues with straw bale construction that were not apparent?
I know the "standard" construction process very well.

BryanF

In theory you just need to provide wall uvalues and show structural compliance.
IMO it's all about the design and working with planners so they understand the need for increased eaves and footings to protect the walls. I heard mixed insurance requirements but there's a great YouTube clip from ecocell showing fire resistance of strawbale

hiromoto

Yes in Ireland and planning was straightforward after pre planning consultation.
Beware of mice, after only a period of about two weeks between stacking walls and rendering I was infested. Once I got rid of them and got render on it was OK. The rodent issue is one reason I would prefer render as there will be a gap between the straw and cladding perfect for mice.

mynewshoes

Ya, I think I will go the render route. How does lime render work out cost wise?
Is clay render suitable for the Irish climate?

Heard there is an issue with cracking with both options.