Building a straw bale house on the western side of Islay

[saveasteading]

35 minutes ago, sgt_woulds said:

I haven’t seen any logical arguments presented to preclude its use in a properly considered and constructed building in his location.

That's the fascination of this discussion.

I have the same opinion in reverse...show me that it won't be a disaster.

So many of us think it's a bad idea and advise against. 

@Selinais thinking again.  @sgt_woulds is sold on straw.

 

I look forward to hearing of any straw builds as I'm prepared to be convinced.

 

Out.

 

[ProDave]

I worked on a straw bale house build near me.  But the straw bales were for insulation not structure.  It was basically a larsen truss style timber frame with the gap between the inner and outer sections of the larsen truss matching the bale size and the bales were stacked up in there forming the wall insulation.

 

Issues I recall, they were very lucky to get a dry enough spell once the straw was cut for it to dry and then be baled.  they had trouble finding anyone with a working small square baler, most farms bale as very big round or square bales now.  And then renting a barn to store the bales under cover until they were ready to build them in.

 

Imho all it did was add complication and cost and made the finished walls very thick.  Just so the builder had a cosy notion he had a "natural" material.  He could have achieved the same building performance at lower cost and with thinner walls using some variation on mineral wool like Frametherm,

[joe90]

Although I considered straw years ago a think the likes of frametherm or cellulose are a better option nowadays and more acceptable by insurance and mortgage companies. 

[SteamyTea]

45 minutes ago, saveasteading said:

look forward to hearing of any straw builds as I'm prepared to be convinced

Was it @Nick Thomas that built his shed out of weeds and twigs last summer?

[joe90]

17 minutes ago, SteamyTea said:

Was it @Nick Thomas that built his shed out of weeds and twigs last summer?

No it was straw!!! 🙄

[saveasteading]

1 hour ago, SteamyTea said:

built his shed out of weeds

Yes I've been following that, but it's a shed, so fair enough. Different for a house.

 Another thought: 600mm thick, or whatever,  bales in walls will increase the gross area or decrease the nett area. 

[SteamyTea]

20 minutes ago, saveasteading said:

bales in walls will increase the gross area or decrease the nett area

There is a point, and it varies with other material properties, where increasing the outside area because of thicker insulation, actually increases the losses.

Might just be for pipes though, corners make thermal modelling tricky, why I use the simplified method of adding the wall thickness area to the exposed area.  Makes sense to me.  So take a simple wall that is 5 metres wide, 5 metres high and 0.25 metres thick, normally the exposed area would be 25 m², but because of 'edges and corners' it is actually 30 m².

It over estimates the losses, on thicker walls, but that is the better way than underestimating.

Shared edges/corners can have a reduction, so half wall thickness.

Edited Monday at 12:38 by SteamyTea

[joe90]

1 hour ago, saveasteading said:

bales in walls will increase the gross area or decrease the nett area. 

The same goes for any type of build, I was told with a large cavity and brick and block the rooms would be smaller, however I planned/decided on room sizes first. Mine was 400mm thick walls all included, bales only need lime render on both faces so not hugely different. A brick and block with 300mm cavity (which someone on this forum did) gave a 500mm thick wall.

[Iceverge]

1 hour ago, SteamyTea said:

There is a point, and it varies with other material properties, where increasing the outside area because of thicker insulation, actually increases the losses.

Might just be for pipes though, corners make thermal modelling tricky, why I use the simplified method of adding the wall thickness area to the exposed area.  Makes sense to me.  So take a simple wall that is 5 metres wide, 5 metres high and 0.25 metres thick, normally the exposed area would be 25 m², but because of 'edges and corners' it is actually 30 m².

It over estimates the losses, on thicker walls, but that is the better way than underestimating.

Shared edges/corners can have a reduction, so half wall thickness.

 

 

Similar to passivhaus. It uses external surface area which tends to overestimate heat loss. 

 

It's one of the reasons that smaller houses struggle to meet the standard. 

 

Back to straw. 

 

I can see almost zero people advocating for structural straw bale houses but rather as an infill for a timber frame as insulation. 

 

The issues isn't the straw. Straw is fine. I've already linked lots of examples. It's the bales. They were designed to be able to package, transport and store a useful farm material and are full of compromise for any other purpose. 

 

Building a house out of them makes little more sense than making a house out of these just because they're made from polystyrene. 

 

 

 

 

 

Edited Monday at 13:56 by Iceverge

[saveasteading]

1 hour ago, SteamyTea said:

actually increases the losses.

Surely not. The heat loss starts at the internal face. Extra thickness is effectively added to the outside face and does not increase effective areas of losses.

 

The heat loss  programs may say otherwise but be wrong. As I've said before, I've met some of the BRE people,  and discussed Sbem and BREeam  and they didn't understand much about reality, or want to discuss problems.

[sgt_woulds]

18 minutes ago, Iceverge said:

 

Back to straw. 

 

I can see almost zero people advocating for structural straw bale houses but rather as an infill for a timber frame as insulation. 

 

I'm not advocating either method, I don't write them off either.  I think using them for infill is a better idea - the blown straw you linked to is a case in point.

 

 

18 minutes ago, Iceverge said:

 

The issues isn't the straw. Straw is fine. I've already linked lots of examples. It's the bales. They were designed to be able to package, transport and store a useful farm material and are full of compromise for any other purpose. 

 

They are also designed to be stacked for storage and thus to take loads.  The amount of loading and the timeframe in which it will maintain structural integrity is for a structural engineer to confirm, but can also be gleaned from empirical evidence of existing strawbale structures.  There are many issues with straw bale construction as ProDave has rightly pointed out, but has anyone got evidence of a structural failure that wasn't due to poor design or construction?

 

 

18 minutes ago, Iceverge said:

 

Building a house out of them makes little more sense than making a house out of these just because they're made from polystyrene. 

 

 

 

 

 

 

 

A house shouldn't be made out of them because they are polystyrene! 

 

 

Strawbales should be thought of like SIPs and the building designed accordingly.   You could argue that SIPs are rubbish for a number of reasons, (I wish I'd built my extension from anything other than SIPs - a story for another day) but I don't think anyone here would argue that they are inherently structurally inferior to 'traditional' methods without some sort of evidence.

 

 

 

 

 

[Onoff]

5 hours ago, sgt_woulds said:

Who said anything about using it as an outer weather shield? This isn't the 3 little pigs 🙂

 

As the OP only mentions straw and not stone then I assume them. 

[SteamyTea]

I think the OP @Selina has run away.

[sgt_woulds]

The OP also said they planned to clad in stone; in any circumstance, they wouldn't leave the straw exposed to the weather. 

 

I wouldn't be confident about using lime render in that exposure zone without expert advice, but that come back to my point about designing for the conditions.

 

As an example, our woodfibre insulation can be used behind a close-slatted rain screen or roofing without a weatherproof membrane in most circumstances - but in high exposure zones, we always specify a membrane for belt and braces.

 

Similar consideration should be given when designing with any material.  You wouldn't clad the building in EPS without protection for the same reason.

[Iceverge]

1 hour ago, sgt_woulds said:

A house shouldn't be made out of them because they are polystyrene! 

 

 

Don't tell anyone who made their house from ICF......

[SteamyTea]

On 08/11/2024 at 19:45, joe90 said:

If you have any data on how dangerous natural products are

Just teasing a bit here.

 

https://scitechdaily.com/eco-friendly-fibers-may-pose-a-greater-threat-to-the-planet-than-plastics-concerning-study-reveals/

[Jilly]

Interesting that worms might be the canary in the coal mine, as it were.

[scottishjohn]

On 06/11/2024 at 18:03, Selina said:

I intend to clad it in rock keeping with the home blending into the environment. And being more traditional in appearance

how will you accomplish this 

the weight of even small stones like i did my firepond  will be  large and i do not think they will stay on if you intend to stick them to the straw bales 

 then there is the problem of finding enough stones of suitable thick ness for a large area 

 i used approx 2 tons of granite  pieces  + 2tons of sand + 12 bags cement to fix them  and that is not to a full wall height as you will have with a house and it is very time consuming and can only be done when it is dry  and need covering  for at least   2days to make sure the mortar does not get washed  by rain 

 so for full nouse you will be taking 4 times that amount 

 

I used them as i have a very large volume of them on site from previous quarrying and granite set making  in the past 

 the only way i see it wroking is if you clad outside first with exterior ply and attch a mesh to it to give something for the mortar to stick to 

 

 yes you could buy stone cladding panels ,but not cheap and they would require a solid frame work to fix them to 

I have no problem with straw as insulation  where you are  it will be good if thick enough  ,but  not as the outer wall which will still need wood for window and door openings .

Edited Tuesday at 07:52 by scottishjohn

[joe90]

But lime render turns into limestone so no need for stone facing 🤷‍♂️

[SteamyTea]

21 minutes ago, joe90 said:

lime render turns into limestone

Not really.

The chemical formula may similar, but the processing is different i.e. limestone is compressed in a high CO₂ atmosphere for at least 500 million years (Precambrian era. So not mixed up by a builder.

The Egyptians used clays and gypsum before the Romans were using lime mixes. They pyramids are still there, and there is a lot of evidence to suggest that they are not carved stone, but castings.

That is more to do with local geography than material properties though.

[sgt_woulds]

Yes, but Egypt tends to have less rain - although I suppose the Pyramids and other buildings probably get sandblasted regularly!

 

Lime render may stand up to extreme weathering - but I'd take the advice of an expert - there don't appear to be any on here at the moment...

 

These walls will likely be seeing horizontal wind-driven rain on a regular basis - if a stone rain screen can be made to work it will probably require less maintenance than a Lime render.  

 

Scottish John - I've not heard of this being done with bales, but the situation will be similar to using a brick or stone face with a ventilated cavity on a timber frame building.  Will need to be signed off by a structural engineer. 

 

I'm sure I read an article in a (very) old magazine where the owner used a drystone wall over rendered bales for a shed/study.  Can't remember if/how it was tied in, but it's not beyond the wit of man.  I wouldn't want to try it though - would be Mouse City...

 

On a separate front, a rubble foundation would not only be cheaper and easier to self-build but might also reduce the embodied carbon count enough to justify using a more conventional structure/insulation without so much environmental guilt.

 

To annoy the FUD brigade - this is quite often employed with Earth Bag construction which the OP could consider as a more weatherproof construction method, with suitable internal insulation 🙂

 

 

 

 

 

 

 

 

 

[Iceverge]

The only way I would consider straw bales as suitable for building a maintainable and mortgageable house would be as an infill to a timber frame.

 

Here's my idea.

 

Dig a standard strip foundation and build rising walls with 150mm blocks. 

 

Add a chunk of EPS perimeter insulation inboard and on the ground and pour a concrete slab as per normal. 

 

Build a 140*38mm stud frame on the 150mm rising blockwork at 450mm centres with 11mm OSB sheathing. Include ply gussets say 340mm long  to connect later to an inner stud. Roof the  house conventionally to ensure construction could continue inside in the dry. Add a sole and top plate for the inner stud too. 

 

 

 

Insert the bales "on end" in between the studs and push them tight against the outer sheathing. Use ratchet straps to compress them slightly and to compress any smaller segments that are needed at the top of the wall to take up any slack. 

 

Add the inner stud in a bay by bay fashion toe nailing it to the plates and screwing to the gussets. Take out the ratchet straps to allow the bales expand into the gaps. 

 

Finally add a good membrane inboard for airtighess and 38*50 horizontal battens to create a service cavity. 

 

Plasterboard and skim. 

 

Should have a U value of about 0.16W/m²K. 

 

With the double stud and large perimeter upstand it would have a very good thermal bridging characteristics and apart from the bales everything should be off the shelf from a merchant which is vitally important building in a more remote area. 

 

 

 

 

 

 

 

 

[Nick Thomas]

Hah, thanks for the highlight @SteamyTea.

 

@Selina there are at least a couple of straw bale builds on the Isle of Skye, which I would recommend you look up and try to chat to the owners about. They'll have plenty to say about how to do it in Scottish islands conditions, what works, what won't, etc. There was this little bothy in 2017 - https://strawworks.co.uk/projects/commercial/skye-strawbale-bothy/ - and I know a straw bale house got a lime render coat over there this summer. I wasn't involved but maybe it's "Vinca Petersen" ? Worth chatting with both projects if you haven't already.

 

Site conditions matter a lot - wind-blown rain is definitely the enemy, but if you have a sheltered site it can be mitigate significantly. You also want a roof structure that will protect the walls (big overhang, generally) without being vulnerable to being ripped off by the wind (so maybe a full hip sort of thing).

 

Lime render might or might not be suitable - I wouldn't rule it out *just* because you're on Islay. St Astier do NHLs and have some recommendations based on site conditions that you could look at. You can also harl a straw bale lime rendered wall, which might be more practical than the stone facing? Or a full timber / brick / block / stone / anything facade, which will definitely stand up to the rain. Just be sure to coat the straw with a coat of lime render to discourage rodents. I have one straw bale wall I built against a pre-existing brick wall which goes:

 

brick : ~50mm air gap : vapour-permeable membrane : lime render : straw

 

It's only been a year, but I've had no indications of issues with water, condensation, rodents, etc, so far.

 

On structural straw bales vs. non-structural, honestly, having done the former, I would absolutely have a timber frame and then just infill with the straw, if I were to go again. You end up using so much wood anyway, for the roofplate and baseplate and window and door posts, etc, that some more uprights just aren't a big deal, while making everything else easier - it'd let you get the roof on before bringing any straw onsite, which will help to keep it dry during construction, and should keep things from getting wonky as you build. Straw SIPs are also fine.

 

It's basically a technology / labour tradeoff, with structural straw bales being lowest technology but highest labour. So much labour. It *works*, but the technology to get the same result with less labour also exists, and it's fine to make use of it.