Definitive timber frame constructions

[SimmondsMills]

I am keen to hear members' favourite timber frame constructions (as compatible with the AECB energy standards – both Silver and Gold – see 'technical' section on web site)),. This with a view to the AECB assessing what systems / methods should be ranked as most ecologically successful, practical and economic. These could inform the training materials being developed for the AECB SussEd courses. This may require further development work for which industry or government funding would be sought.

[Eco Design]

I have used a hybrid block & timber system very recently:-

Block int leaf P/B and skim on dabs int finish or 2ct plaster
ex.150×50 stud outer leaf @ 600mm cts with 75mm cavity/thermal break with ss frame cramps fixed to block and cavity fully filled with quilt insulation.
Stud fully filled with 150mm quilt insulation.
Breathable membrane.
ex.25×50 battens
Cedar shingle cladding.

Result: a very stable structure, block mass retains heat and good insulation value, solid internal structure prefered by users which carries floor and roof loads. Simple to carry out and can be improved on with insulation block and thin joint technology. Disadvantage is its width.

[Nick Grant]

Jim Rann (Leominster) did a similar design to Neil's for Steve Wade of Wind and Sun with the addition of exposed timber 'cruck' like roof structure supported on the block walls.

As structure was on inside the spaced studs can carry on up walls and over roof so minimal cold bridging and potentially good airtightness despite the rustic interior.

[SimmondsMills]

i have used similar to petes using rammed earth block as internal wall: external studs wer load bearing to get frame uip quickly although blocks could have been structural (in fact were providing wind vracing). i was unclear if, neill, you have built your construction or is it a proposed design? Are you all up for compiling 'as built' wall constructions, drawings and spec to compile over time with a view to publishing and selling a compendium of them all. i would be  – i think it would be very useful to people, and am sure we can avoid liability issues somejow! what do you think?
andy

….continuing this again : pete what thickness were the block walls, 150mm? how high can a single skin wall like this go for domestic? also what is the impact thermally of using pb on dabs – does this conflict with role of thermal mass on a daily / monthly basis.

Another post by Andy but split to form new topic on airtightness:

Hope David Olivier reads this, he would know! I aim to use similar construction next new house > am getting frustrated with finding builders who can do timber frame without lots of hand holding! this approach seems more robust and provides much needed thermal mass > however an internal lining of 20mm lime plaster is pretty good in this respect I suspect. My favourite at present is structural stud wall (either solid sawn with counterbattens to reduce thermal bridges) or I beams, with 11mm osb sheathing internal. this allows easy domestic fixing, supports the air tightness membrane (warm side osb) but requires electrics to be set within depth of plaster / plaster board finish.

[Eco Design]

Andy

I think an alternative “As built” detail book would be worth investing some time in. I'd be up for it.

As for my as built hybrid: The block was 100mm and tied back to timber frame with SS frame cramps. As it's not conventional I've not seen it in text books but I didn't have a problem eith Building Control for 2 storey construction. I didn't have to prove anything structurally.

Because the p'b on dabs is on block effectively one has created another cavity and insulant layer, so yes it does conflict the the thermal mass to some degree. I would have prefered 2ct lime plaster but I was compromised!! The drying out process is the problem to some. I got a pretty good 'U' value which I can not recall whilst typing and client (who's been in jsut a week or so) says how much warmer it is to the rest of the house already.

Peter

[David Olivier]

Stephen Reyburn, architect built a house in London 20 years ago with a similar wall to this and 175 mm insulation (see cover of GIR 38) The workers said it was easier to insulate than a cavity wall would be and being masonry it was easily made airtight by plastering top to bottom; his 1st and 2nd floors are in situ concrete which is also airtight.

It wasn't a hybrid, as a structural engineer said the house would be self-supporting without the timber (or in places without the brick outer leaf). The house has provided extremely good comfort in heatwaves due to the high thermal capacity.

My own house has 150 mm mass concrete walls, outside which are 50×50 mm timbers on 1200 mm centres, tied back infrequently to the concrete and all sheathed with 18 mm plywood. The 300 mm space is filled with insulation. It's not a hybrid; the amount of structural timber needed for that causes excessive thermal bridging within the timber layer.

David.

[SimmondsMills]

David
I am wondering if it is worth just paying for an hour of your preferred engineer's time to assess what the local engineer says about this design…although the client can't afford to pay for a checking enginer, it might be interesting to see if we can do some last minute 'value engineering' ….(I will check to see how our overdraft is looking!)

Nevertheless it is worth pointng out that this house (awaiting minor cross checks from you at some point) achieves Gold heat loss limits, albeit with more development could do so more affordably and more simply. Whether this project can afford this refinement work remains to be seen.

Also has made me realise that at this stage in the game we should only take on design team members who are suitable, rather than clients local recommendations.

[Nick Grant]

I took the liberty of splitting Steve's post and renaming it 'Conventional' timber frame to Silver standard.

https://aecb.net/forum/index.php?topic=641.0

Nick

[SimmondsMills]

I have updated the down-loadable drawing ('thermal bridge free' cross section for Gold house design) – see my original post below for the download – on the 13.12.06… a few small changes…

31.01.07: BTW the original downloadable doc has now slipped to the last page of this thread, so click 'page' 2 to find it, way back….

[Mark Siddall]

David,
1) Has the house been completed yet? If so what was the final airtightness and how much work did the constructor have to undertake in order to achieve this (i.e. did the building pass first time or were remedial works required…much or little…any hot tips?).
2) Was the mass concrete insitu or precast? If insitu what technique was employed tunnel form or traditional shuttering? (I am trying to get a handle on which solution you found to be cost effective.)

I look forward to the responses.

Mark

[David Olivier]

Mark

I don't have a main contractor so the house is a slow build by sub-contractors in between all my other tasks and still isn't finished. It has in situ mass concrete walls and reinforced concrete floors. Calcs. were made to minimise the volume of steel. The walls were moderately easy to build (with no skilled labour apart from the carpenter who made the shutters); the floors were very easy.

The final air permeability isn't yet known. When tested in an unfinished state by Paul Jennings (AECB member) well before completion it was about 1.5. Some leaks have since been sealed but other leaks were via holes cast in the walls for incoming services and can't be totally sealed until all services are installed.

I'm writing a book on it all.

Most UK concrete houses use ICF. Over ten companies make blocks for thin ICF walls (100-110 mm insulation) but only two companies sell ICF blocks which are thick enough to meet the Passive House or Gold standards.

I don't think tunnel form is applicable to one house. I don't think prefabricated concrete is cost-effective unless one needs rapid construction or very thin floors or has a huge project.

David.

[SimmondsMills]

Mark
we will certainly share the costs of the hybrid construction on this forum: post tender costs then final costs, if the exact prices can be determined clearly from the builders costings!

One issue I am nervous about is the practicality of the inner skin working to concrete block modules and the outer skin to stud/timber panel co-ordinating dimensions, particulary where the external studs frame a window opening that needs to coincide with the same opening in the blockwork – whilst avoiding excessive noggings/'cripple' studs – and working to a tight tolerance for the structural opening as a whole (at least with our current window in wall detail).

BTW what is 'tilt up' and 'IFCs'?

Andy

[Anonymous]

Hi
Sorry I'd just like to clarify something I'm confused over

In this hybrid construction , is the timber outer frame generally tied in ,though set off, with frame clamps to the blocks and this cavity filled or could it be/is it a seperate self-supporting skin tied only at the ground and wall plate and openings

thanks Jim

[Mark Siddall]

Jim,
I think the original intention was that the two elements block wall and timber frame would be structurally independent; the driving force for this decision was to mitigate thermal bridging.

However this approach raises the issue of the slenderness ratio of the blockwork wall. If it isn't considered appropriately then the wall will be prone to collapse. Three ways of addressing the slenderness ratio have been considered:
1) concrete ring beams. Though this does not address the slenderness ratio in the true sense of the term is does tie the blockwork together in such a manner as to increasing the stiffness of the masonry.
2) increased width of block i.e. 150mm rather than 100mm
3) Tying the timber frame and the blockwork together, be it studs or I beams. (It is recognised that this compromises the structural independence, however with appropriate detailing the thermal bridging issues could be addressed to reflect details built on mainland Europe.) NOTE: This is the closest to traditional timber frame and will probably require the least input from a struct eng.

All the above are subject to input from a struct eng.

Hope this clarifies my interpretation and thus my comments above.

Mark

[David Olivier]

Mark

It's not really a concrete frame as the mass concrete walls are load-bearing; there's no masonry infill. The superstructure cost was somewhat higher than a block house with timber intermediate floors – not surprising since block is the UK standard – and lower than a softwood timber-frame kit.

David.

[Mark Siddall]

Andy,
I'm with you on the build up to the first floor. I can picture how the load from the first floor should help to overcome slenderness issues up to this level. Furthermore I hadn't split the build sequence in quite the same way and your strategy makes the build much easier.
Look forward to hearing the rest.

Mark

[Mark Siddall]

Andy,
Just thought…..the ply 'fish plates' that tie the timber frame and the blockwork together at first floor level could also be used at eaves level. If these 'fish plates', and perhaps those at first floor as well, are fitted with cavity ties improved restraint can be achieved (note: being fitted on the warm side of the insulation, and the ply 'fish plate' acting as a thermal break, cold bridging is minimised.) Hope this is constructive.

Mark

[Mark Siddall]

Andy,
This one is just for you 😉
https://aecb.net/forum/index.php?topic=704.0

Mark

[Author]

Posts