breathable wall insulation

[sue gazzard]

Help please. I am trying to get quotes for removal of cement render from my early 16thc non-listed timber frame/wattle/daub/straw building followed by insulation with some kind of breathable material & then lime render. I'd assumed using sheeps wool. However builders keep telling me there will not be space unless we lose the existing infill of daub/straw, which of course I don't want to do! I'm tearing my hair out - no-one will quote unless I specify exactly what to use. I can't be the first to have faced this dimella - positive input please! Thanks/rgds Sue

 

[Nemesis]

I think that possibly they are correct - there won't be space to add much insulation.

http://www.tonygraham.co.uk/house_repair/wattle_daub/WD-5_5.html

http://www.buildingconservation.com/articles/wattleanddaub/wattleanddaub.htm

If you really do require extra, then possibly interior framing and insulation is a way forward, although you may lose a great deal of wobble and attractiveness.

Wattle and daub has its own insulation value though.

It may be possible to add stuff to the lime render to add a little more insulation value, we have had discussions here in the past about this, but you don't want to do anything which may cut down on the breathability and put the timber frame at risk. Also you don't want to do things which may bring into play building regs and building control...

 

[sue gazzard]

Thanks for that, particularly the two very helpful links. Couple of quick questions: does the price I've seen quoted on the site include lath and breathable membrane or is that literally the cost of the lime render? What's really to choose between expanded metal, stainless steel and chestnut? I don't have bottomless pockets & whilst wanting to do my best for my building I sense that I am going to have to make some choices to keep things affordable. What do I compromise on? Sorry that's four questions...

 

[Gervase]

Ordinary galvanised EML doesn't work well with lime, and will inevitably rust. Stainless steel is very expensive, and doesn't take a render coat as well as traditional laths or withies. If the choice were mine I'd go for sawn chestnut laths - a fraction the price of riven oak, great to render onto and also helping provide a tad more insulation than a metal mesh.

 

[skier-hughes]

Gervase,
What in your opinon is the best lath material?

I do't have too much to replace, so cost isn't going to be a major issue.

Should I find out what I have now and copy?

 

[Gervase]

Wood is best - riven oak gives a superb key for render or plaster, but sawn oak or chestnut come a close second. If someone else is paying, go for riven oak; if you're paying, sawn chestnut is fine.
If you want to go by the book, conservation-wise, copy what you've got already. That said, I've seen lathing made from split hazel that has suffered terribly from worm and decay, whereas oak and chestnut are much more durable.

 

[skier-hughes]

I'm paying, but as I said cost isn't too much of an issue because the area is relatively small. I'll carefully remove a decnt piece and get my father in law to see if he can identify it.
Cheers,
Graham

 

[Nemesis]

I suspect hazel was popular as it's easy to grow and coppice - the shoots can be used as they are if cut young enough. With chestnut and oak that's not so simple.

Hazel provided a crop too.

My experience of cutting our own coppiced hazel for use as bean poles is that it's very short lived indeed outside. Of course in theory buried in a wall it should be sound and dry, but houses aren't always like that. It was, though, easy to work for wattle.

 

[Gervase]

Sweet chestnut and oak can be coppiced, but with a 15-20 and 18-35-year cycle respectively (compared with the seven-year rotation for hazel), it calls for a far-sighted forester in this day and age. You also get a heck of a lot more hazel to the acre, with up to 800 stools to the acre, compared with just 80 for oak. It is pretty ropey as a building material, though. I've seen wattle and daub where the wattle has just about crumbled away, leaving the daub to supply the structural strength.

 

[Nemesis]

We don't have chestnut, but have coppiced an oak which is growing very slowly, wheas the hazels we have are rampant. Too rampant at times, and very keen to seed!

They make wonderfully decorative and rustic looking bean poles, and I suppose in the past the ability to weave the stuff for wattles was useful. I suspect the wattle and daub was never really designed to last for centuries, especially in more humble dwellings, bit like thatch - a building would use the best timber for the frame, the rest would be patched as required.

 

[Penners]

hazel ...is pretty ropey as a building material.

The following is not a weak attempt at a pun.

In our first oak framed cottage project (some 30 years ago), there were many surviving panels of the original wattle and daub. The withies upon which the mud/dung was daubed were tied together into a lattice with what were obviously thin lengths of green wood, used as a kind of rope. The CO at the time told me that these "ropes" would have been very young hazel twigs. Does that make sense? After some 500 years they still looked in pretty good condition - would the daub mixture have preserved them? Or do you think he was wrong?

 

[Nemesis]

He was correct. If the wall was kept sound and dry these would last.

Hazel was also used for thatching with ling. That may be why it grows in abundance around us.

It's very rapid growing and readily available in most places, very easy to bend. Like willow.

http://www.exmoor-nationalpark.gov.uk/filex_09.pdf

 

[Penners]

What's ling? In Scandinavia they have something called a lingonberry. Any connection?

 

[Nemesis]

Heather!

http://www.forestharvest.org.uk/species.php?name=Heather,%20ling

 

[Penners]

Aha! Ta.

 

[middi]

If someone "must" use " render" to re-clad the external of timber frame buildings then lime plaster on timber laths is the next best thing to feather lapped boards. Cladding external of timber frame buildings became a natural progression from limewashed exposed timbers infilled with wattle and daub panels, especially in the south east.

In reality any render on a traditionally timber frame building will craze and crack quite quickly allowing excess water. This normally accumulate mainly on the sole plates and even rich lime renders impeads the fast evaporation which is required, especially on this part of the building where most of the deteriorations starts.

Feather boards are better suited than any renders. Leaving these sole timbers, or any timbers, totally exposed ( as originally intended) does no harm at all.

With the aid of " modern" breathing papers on counterbattens, where air gaps are created when the wattle and daub is left undisturbed and acts as insulation, it is better. It would mean increasing the thickness of the walls by approx on inch, this would interfere, at times, with eaves and gable ends details and may spoil the aesthetic aspect.

These are observations made by myself on a number of buildings when presented with decayed frames.

Timber barns clad with simple lapped boards, with no restriction of air movement, usually last longer than rendered timber
houses.

This may help you make decisions as to what may be best in your situation.

 

[Johneds]

Tread carefully and double check any advice you get on this.

If you introduce insulation you must also include a vapour check as well, otherwise you will create severe condensation within the wall structure. Of course, vapour checks are not beathable.

 

[andrew gayton]

that is only the case if you intend to use a non permeable insulation. I agree that a non permeable insulation material without vapour check will lead to interstitial condensation. there are a number of insulation boards - made from recycled timber and clay etc - which are permeable, can be applied straight to the substrate and lime plastered over with no problem; this will reduce 'intrusion' into the room (and reduce impact on linings etc etc)and retain any existing undulation to the face of the walling.

 

[sue gazzard]

Hey guys, this thread has all gone a bit pear-shaped....I was talking about insulation on the OUTSIDE before application of new lime render - either by stuffing something like sheep's wool where space permitted between the timbers or, just possibly, using one of the "new" breathable boards made of recycled newspapers or summat, thereby creating a skin of boards fixed to the timbers. But at no point have I ever wanted to board over them on the inside - I've just spent months uncovering 'em for goodness sakes! Can we go back to basics? :?

 

[andrew gayton]

simple then - fix cl*ytec or d*ffutherm boards straight to the wall and lime plaster over.