I've not had any experience with stone walling but have with timber frame and block construction. As the timber frame provides all the structural support for the building, the outer skin is only for decorative and weather proofing purposes. With a block skin on the outside we had a 50mm cavity and 150mm timber frame. I dont know how narrow you can build with stone but I guess that 200-300 should be easy to do? This would give you an overall wall thickness 400-500mm. As this is no more than you have at present, but lighter due to timber frame instead of solid stone, your existing foundations should be adequate but you may need to get an engineer to prove it to the satisfaction of building control for what is seen as a new build. Your timber frame can all be built on site from a bundle of structurally graded sawn timber-minimal joinery skills required so it can be DIY once you have the design done.

depending on the type of stone, and coursing requirements, any stonemason worth tuppence will be able to 'back off' the stone and build a wall from 150mm thick

doing it yourself?
get a mason, or a mason's mate to show you the ropes for a day or two.
at least for the backing off.
as for building it yourself? ideally you need an eye generated from experience, so start in a corner that no-one will see!

combination of mallet and chisels and diamond blade angle grinder.

given 150mm, 50mm cavity, then timber kit, job's a good'un.
you are going to need at least a 150mm thick kit to get good insulation levels, so overall wall thickness may be 350mm
He will need to use ties back to the kit, as per any masonry construction.


we re-built a garage opening to its original two windows.
the stone walls are 600 thick, but we built a 150mm skin in front of a well insulated timber infil panel.

allowed us to work inside quickly, and allow the stonework to take its time.


Looks excellent.

Paul... spray foam.....

pah... that is a dirty word and a complete NO NO in this country.

With 140 mm stud, mineral wool, refective breather membrane and vcl should see a U value of below 0.3, which is good, but not 'super insulation'.

Timber

Thank you all,

All taken on board and appreciated.

Doctor, Figured we should be able to do the stonework ourselves, what you say reassures me.

Timber and Paul, forgive my ignorance but what is vcl. Also Paul what is 1x3 strapping

Give the budget constraints, 150mm natural mineral insulation is all we can stretch, Is it worth stretching the 60mm pavotherm to 80mm or even 100mm? Is there a significant gain to preferable U values in doing so ? We may not gain as much internal space as we wanted with 150 stud, 100 Pavotherm, 50 cavity, and 150 stone. But happy to compromise space for warmth.

Also does the fact that the build is in a very damp climate, it sometimes seems to rain 360 days a year, have any bearing on anything...

Posted By: mirabilAlso Paul what is 1x3 strapping

It's probably the same as battens. 1x3 is wood that's 1"x3". Like in the picture below :)

''Give the budget constraints, 150mm natural mineral insulation is all we can stretch, Is it worth stretching the 60mm pavotherm to 80mm or even 100mm? ''Depends what you mean by ''natural mineral insulation''. If you mean rockwool or glass fibre, why have less of that in favour of expensive pavatherm. On the other hand, in environmental terms, why have any mineral wool at all. Even if the frames are 150 you can still use spaced studs to give you whatever depth you want.

Also worth looking in classified ads and freecycle for surplus insulation from building and diy jobs.

If you're set on the Pavatherm then NBT give design assistance.
Given the weather conditions you describe i'd suggest something like xtratherm if you want to wrap the face of the frame as per Paul comment. Their description of insulating frames should help you anyway.
http://www.xtratherm.com/products/thinrtimberframe.php

Main thing to point out is that Pavatherm system is vapour-open (breathable) whereas foil faced rigid boards act as a vcl.
My take on VCL is that VCL is an acronym for Vapour Control Layer which is a catch all term for both 'vapour check' eg oriented strand board (osb), foil backed plasterboard; and a 'vapour barrier' eg properly detailed polythene sheet.

With respect, I dont believe my post refers to vcl on exterior. "as per pauls comment" refers to foil faced-polyisocyanurate on internal face, in his post further up, to act as a barrier to thermal bridging.
Link to xtratherm site gives a brochure showing insulation studwork and masonry to assist visualisation for original post, brochure shows 4 framing systems of differing composition and the effect on u-value.
Xtratherm is the insulation, with foil either side - but you're right one of these faces will be on the cold side hence xtratherm spec is for separate vcl on warm side.

Posted By: TimberRigid foil faced boards have no place in timber framed construction.

I suspect empirical evidence would suggest that they do... ...I see where your going with that, but surely horses for courses and all that...

J

PS look how happy the chap with the tape is... he obviously like foil faced boards....

Take another look at the xtratherm link. at top of the page theres a bba cert and an iba cert for use in timber framing systems.

Thanks everyone for all your suggestions, they've all helped bring our ideas closer to reality .

As you might have sussed we are novices when it comes to house construction and are keen to get it right from the start. Thanks Ali-gill, for the xtratherm link. It looks like that is the route we will go although we will use Ballytherm ( http://www.ballytherm.ie/timber/index.htm ) as the build is in the north west of Ireland and Ballytherm are relatively close. Also take on board the freeads and freecycle. We are already doing that. We've been collecting wood and insulation for 5 years now and have managed to procure all the timber required for the frame,roof trusses and windows as well as 80 sheets of 40mm celotex . It looks like the celotex will go towards insulating the workshop where we are building the frame. (workshop is also timber framed and is 45m2, which has been built entirely from free recycled materials including roof and looks good. Hope the house turns out as good).
So to summarise the wall construction will be 150 stone cladding (secured to frame with s steel wall ties), 50mm cavity, Tyvek (or something similar), 15mm exterior ply, 150mm stud filled with hemp insulation, 40mm Ballytherm (also acts as a vcl) secured with battens,plasterboard.

Does that sound like we will have adequate insulation...? Or more importantly will this design allow the walls to breathe. The windows in each room will all have condensation vents...

One more request for info please regarding the stone wall cladding which is to built using lime mortar, what sort of ventilation is needed for the cavity..?

thanks again for all coments, it really is helpful having access to this forum

Peter

hmmm, laboured my way through the treads and breathing wall seems to be an ambigous term for some. My take on "allow the walls to breathe" is if any moisture does get in to the internal construction (where the timber is ) it has a way to get out..

On the internal side the clay plaster does look like a natural solution to moisture, condensation, humidity issues but also looks unfortunately out of our budget range. Our site is surrounded by clay deposits but unfortunately we don't possess the time or skills to make up and apply the mix and the only prices I can find for board seem to be way over the price of gyproc.

From what I can gather the ballytherm joints are sealed with a metalic tape (their term) to minimise moisture penetration from the room into the internal wall frame . I imagine the fixing holes can also be sealed with tape. I thought that would be enough, do you think I need a seperate polythene barrier..? I'm still not 100% on what people mean by vcl. I thought that with ventilation in the form of condensation ducts in the windows and decent ventilation options for the Bathroom and Kitchen, and of course the semi ancient technique of windows that open, I can prevent high humidity levels internally. I'm also unsure as to what effect using exterior ply will have on the outside of the frame.I thought this would prevent any moisture that did manage to get into the frame from migrating to the outside but have been told this is not so and that it is permeable. I'm a little confused as to how that can be but am running out of time to finalise the design and so am almost decided on that. Please put me straight if that is not so
My reason of using lime mortar in the cladding wall is to give the easiest exit route possible to any moisture build up in the cavity, given the extremely damp climate. Even if it the cavity is well ventilated I can see damp building up as this seems to happen to almost all surfaces exposed to the elements locally.

Opinions appreciated and still been sought....

Peter