Residential home?

<blockquote><cite>Posted By: Doubting_Thomas</cite>FosterTom on a thread here has previously shown a method using OSB and polyurethane glue</blockquote>

Found it!

Photos about halfway down this page, note this was 2017 and I think some opinions will have changed on things like Icynene (not as good as it seemed at the time). Still, the general approach is still sound. There was mention of using flat metal strap over the joints instead/as well I seem to recall.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=14931

Posted By: MagpieI need to avoid all glued products because of the preservatives in glues as well!

Not all adhesives are created equally so I would spend some time investigating the polyurethane options since this is widely touted as 'non-toxic'. MVHR will also remove a lot of the off-gassing potential since the whole volume of air in the house is replaced every few hours.

There is also nail-laminated timber which some engineers are looking at reviving: https://www.thinkwood.com/mass-timber/nlt previous comments about brettstapel apply here.

Posted By: MagpieI’m not too keen on MVHR because of the risk of mould in the ducting, and outdoor pollution from woodburning stoves everyday (despite people having gas central heating). I know you can get filters but it gets a bit high maintenance. I prefer to open the windows if the outside air is clean

There is almost no risk of mould in the ducting, since (done right) the ducts are all warm as inside the thermal envelope so any condensation occurs inside the unit where it is drained away. Added to which, the physics of MVHR and moisture-content in warm vs cold air means you almost have the opposite problem - dry air.

The outdoor pollution aspect is precisely why I prefer MVHR. We live next door to neighbours who literally burnt tractor loads of waste, not just timber but old electrical goods etc. during lockdown. If we were stuck with opening windows in warm weather we'd have had to bring un-filtered air straight into the house. As it was, the filters did the hard work and removed the worst of the particulates. They were basically black from smoke at the last change.

Speaking of changing filters, it is really straightforward - swap out a paper rectangle every quarter. Less hassle than emptying the hoover!

Posted By: MagpieDoes all exposed internal timber have to be painted with fire retardant paint?

It depends on the amount you have on show and the size of the room. We were determined to 'see our investment' in the CLT and went for a semi-translucent coat to improve the rating everywhere. You can plasterboard over the top instead but we weren't keen on this. If you want to leave it completely un-treated, the Building Regs Approved Document B 1 states:

"4.4 Parts of walls in rooms may be of lower performance than stated in Table 4.1, but no worse than
class D-s3, d2. In any one room, the total area of lower performance wall lining should be less than
an area equivalent to half of the room’s floor area, up to a maximum of 20m2 of wall lining."

In reality that usually means covering some of it up with something.

Thank you for all your comments, which have been very enlightening.

Yes I have medical conditions which make me extremely sensitive to minute amounts of chemicals

My bete noir (apart from formaldehyde, mould and smoke) are isothiazolinones, which are the go-to EU preservative for water based products - paints, sealants, glues, nearly all DIY products unless solvent based. Of course solvents tend to be high voc.

Lime products are good - I have considered limecrete, but again the question of loans, insurance, and resale values

Everything also has to be low maintenance because supermarket laundry products on contractors’ clothes usually contain isothiazolinones, so I need to be able to maintain everything myself as much as possible

I would go for a single skin block construction with EWI. I don't know if EPS is acceptable from the point of view of VOCs but there is a lot less VOCs with EPS than other solid sheet insulation boards, also the EWI EPS being outside and covered with a render may not be an issue. But of course there are other EWI materials such as mineral wool.
The advantage with this type of construction would be mainstream construction methods whereby it's bread and butter stuff for local builders and lenders won't throw a wobbly because it is not a typical construction. Also IMO a block wall with EWI is much harder for a builder to muck up than a timber frame construction

Posted By: VictorianecoHow do you test for such allergies to such materials?

Contact allergy tests.

Posted By: GreenPaddyWould straw bale construction be a possibility, at least as a way to get the structure up, without man-made chemicals...but I guess you'll maybe have concerns about what it might have been sprayed with in the field? It "could" be a bit more DIYable, as it's a skill you could train to do, reasonably forgiving I'd have though, and one that is not readily available, so might as well DIY. Lime render inside and out?

DJH might have useful pointers, if you thought that could be a possibility?

I thought about the possibility but I wouldn't recommend it. There's a lot of unique issues that would be made a lot more complicated by severe allergies such as it sounds like Magpie has. I think PiH's idea of blockwork with EPS externally is likely to be a lot more practical solution, and it seems to me that employing builders is likely to lead to less contact with VOCs and other 'substances' than DIY of any kind.

Or just a cavity wall construction rather than single skin and external wall insulation.

I know the latter has its advantages but I would suggest that most builders are more comfortable with cavity wall than single skin.

More food for thought.

If buying a “log cabin” it would have to be untreated - there are a few around. Larch is a good option for me

Does anyone know of eco blocks that are structural - not cinder or slag waste

Polystyrene insulation is not really an option - there seem to be a few natural eco options, although I would like to avoid those treated with flame retardant or chemicals

One interesting option is an untreated softwood timber frame, with hempcrete walls/insulation - either as blocks or cast on site

Posted By: jfbOr just a cavity wall construction rather than single skin and external wall insulation.

I know the latter has its advantages but I would suggest that most builders are more comfortable with cavity wall than single skin.

The problem with cavity wall is that there is a lot of opportunity for builders to make a thermal mess of the cavity, single skin block and EWI is easier to get right (and easier to see the workmanship in progress).

Posted By: MagpiePolystyrene insulation is not really an option - there seem to be a few natural eco options, although I would like to avoid those treated with flame retardant or chemicals

Rockwool can be used for external insulation and shouldn't have the chemicals of polystyrene and is non-combustible without added chemicals

Posted By: MagpieAre there any eco loadbearing alternatives to the usual concrete blocks?

There are lots of systems. It depends what you mean by 'eco' and how exactly you want to use them.

Posted By: Mike1

Posted By: MagpieAre there any eco loadbearing alternatives to the usual concrete blocks?

Naturally dried clay bricks. Or, built in-situ, cob or rammed earth.

Also see https://www.bre.co.uk/filelibrary/pdf/projects/low_impact_materials/IP16_11.pdf

None of these are mainstream building techniques which will cause problems downstream with resale, loans etc.

Posted By: MagpieAre there any eco loadbearing alternatives to the usual concrete blocks?

The main building block over here is Porotherm, a fired clay honeycombed block that is load bearing. They are available in the UK and there are other brands available. I have just had an extension put up, single story flat(ish) tiled roof and the construction is 250mm Porotherm blocks and 200mm external insulation.
I am not sure if Porotherm are more eco than concrete but certainly lighter and easier to work with.

Posted By: Doubting_ThomasThe online IBO Bauteilkatalog has a couple of standard build-ups (AWm-05 Perforated brick), which google translate can help to decipher:

https://translate.google.com/translate?hl=en&sl=de&u=https://www.baubook.at/phbtk/&prev=search&pto=aue

Plus a solid brick option (AWm-04b) with hemp fibre insulation, that I imagine might translate across as a means of insulating with more benign materials.

Thanks for that link. I hadn't seen it before, although google translate does make it a bit weird to operate. I also notice there is now a version of the book specifically for renovations "Details for Passive Houses: Renovation: A Catalogue of Ecologically Rated Constructions for Renovation (Ecological Refurbishment)" that may be interesting for some people. There are also some interesting door details, including balcony doors.

It's interesting to note that AWm-05a (using EPS) is rated as slightly ecologically better than AWm-05b (using mineral wool) but looking in my 2008 paper copy of the book I don't see how they arrive at that - it seems to show EPS being worse on a number of measures.

The main difference in the ecological rating of either version of AWm-04 and AWm-05 is the difference between using fired clay bricks (Porotherm) and unfired clay bricks. EPS and hemp seem to score almost the same ecologically.

Posted By: WillInAberdeenI think the carbon intensity of electricity has dramatically decreased since 2008, so the balance has swung away from minimising energy usage for heating (the original passive house approach) and has swung towards minimising embodied carbon in building materials.

I agree with that. That's the opposite way the AWm-05 assessment seems to have changed though. EPS is now good and mineral wool is bad but previously it was the other way around. It's a puzzle and it's too late to solve it tonight.