General: Insulating at ceiling level

1 to 19 of 19

- CommentAuthorbarney
- CommentTimeNov 22nd 2019
Long story short, some years ago, I acquired circa 4000m2 of land just north of Toulouse on which I have a permit to build a dwelling. The land is currently loaned out to a neighbour who grazes rescued donkeys on the plot, but she's stepping on a bit and I'm increasingly tempted to pack it all in with the UK and build something and move out there.

I've got a rough idea of building a circa 7m x 12m single storey pitched roof building (bit of a bar look alike with 2 beds, kitchen diner and lounge with the principal rooms facing north east to cut down on the summer gains. Initial dialogue suggests that local builders would put up a shell in 200mm blocks or 300mm hollow clay blocks and insulate on the inside(usually 80mm insulated PB) - which seems counterintuitive to me - I'd prefer the blocks on the inside and say 200mm of insulation on the outside - clad over with local oak boards. I was then thinking of putting say 350mm deep manufactured metal web joists over the top and covering the inner and upper surface in say 18mm ply and filling the void with EPS beads - then just dropping trusses over the top and putting a clay tile roof on which is fully ventilated. PB over the bottom skin to give me the finished ceilings (happy for these to be flat rather than vaulted

Is there an obvious flaw in the plan - and whilst unconventional, I could extend the thinking and build a cavity wall and blow that full of beads as well, as part of the same exercise and clad over the outer leaf of blocks

I'm just tracking down a SE and a local architect ready for the new year, but was hoping for opinions on the general idea

Thanks

Barney
- CommentAuthordjh
- CommentTimeNov 22nd 2019 edited
Posted By: barneyI'm increasingly tempted to pack it all in with the UK and build something and move out there.

Some friends of ours just did, although they bought rather than built and intend moving back in a decade or so.

bit of a bar look alike with 2 beds, kitchen diner and lounge with the principal rooms facing north east to cut down on the summer gains

bar look alike?? Only two beds - do you expect many visitors? I don't know what local temperatures are like but north is cold, south has controllable solar gains and east and west are potential nightmares anywhere in the northern hemisphere AIUI.

The local builders sound mad. Do they have any good reasons for what you understand they propose? I'd go with EWI.

Metal web joists are nice (we have them) but sound overkill just to support a ceiling and insulation (they're not cheap), especially if you're planning to duplicate them with trusses. What's the purpose? edit: I'm sure you could add extra horizontal members to a bobtail truss to create the space for insulation.

I'd look for a local PH architect and ask them for ideas.
- CommentAuthorgyrogear
- CommentTimeNov 22nd 2019 edited
With polystyrene you could probably get an R 10 roof but the material does not sound right for those climes - it has very low density and would offer very little summer heat buffering not to mention acoustical attenuation...

A more bioclimatic approach would be for timber roof structure and hemp or wood-fibre boards.

And certainly EWI like you say.

gg
- CommentAuthordjh
- CommentTimeNov 22nd 2019
Posted By: gyrogearA more bioclimatic approach would be for timber roof structure and hemp or wood-fibre boards.

Or blown-in cellulose. Boards are difficult between joists or trusses.
- CommentAuthorPeter_in_Hungary
- CommentTimeNov 23rd 2019
Posted By: barneyI've got a rough idea of building a circa 7m x 12m single storey pitched roof building (bit of a bar look alike with 2 beds, kitchen diner and lounge with the principal rooms facing north east to cut down on the summer gains. Initial dialogue suggests that local builders would put up a shell in 200mm blocks or 300mm hollow clay blocks and insulate on the inside(usually 80mm insulated PB) - which seems counterintuitive to me - I'd prefer the blocks on the inside and say 200mm of insulation on the outside - clad over with local oak boards.

Is the 7m internal or external measurement. If it is internal then do you need the 7m wide? once you go over 6m things get expensive (at least over here). Here 6m between the walls is fairly standard 6.6 is doable but beams are not as easy to get.

By hollow clay blocks do you mean 'porotherm' type honeycombed blocks? If so I would use 25cm wide (20 cm are a bit short on the structural loading and 30cm aren't needed) and then put on EWI to the desired U value. Apart from aesthetics any reason to clad with boards rather than standard EWI render and thin film acrylic render to any colour of your choice? And of course you can get very creative with details around windows etc. and have contrasting colours for highlights.

Oh and I would agree that the local solution of blocks with IWI sounds a bit silly if there is no reason why EWI can't be used.
- CommentAuthorbarney
- CommentTimeNov 25th 2019
Thanks All

For "bar" read "barn" !!

The local builders seem to like IWI as a simple way to meet the current thermal regulations (R2012) in that part of the world. It can get hot in summer, so I was minded that mass on the inside, coupled with sensible glazing sizes and an ability to face NE with the principal rooms has to be a better idea to avoid comfort cooling. From 2020, the regulations are likely to need all new dwellings to be net zero carbon - and short periods in winter can get pretty cold. So I was planning about 4kWp of PV and heat pump system to UFH

I'm still not sure about render over EWI, I have this reservation about defective rendering and a direct water path to the inside - possibly unfounded, for sure. The planking, boarding look was to try and resemble slightly more some of the buildings around the plot (which are primarily agricultural in nature) - so something that looks like a local barn converted for habitation

The 7m dimension fits my preferred 2 bed layout - I wont be expecting many visitors, once I leave the UK, then I won't be coming back. There is for the most part a spine wall that would roughly half that dimension on the lattice - so bob tail trusses with extended bottom chords and blown in insulation at ceiling level is certainly feasible

My thinking was simplicity of construction to create a well insulated and "buffered" shell and then a ventilated void above - which could also have some insulation (wood fibre) at rafter level if required to minimise the absolute heat gains to the void above - coupled with good ventilation

For PinH, yes, they are porotherm or similar - the local builder suggested 300mm against 200mm hollow concrete block, with a minor adjustment in IWI thickness. Locally, they tend to machine plaster with lime and red sand finish straight on the block.

Thanks all - I'll try and track down a sensible local architect who understands the basics of "passive" techniques

Cost of initial construction is less of an issue - I'm happy to spend capital to minimise revenue maintenance and running costs - so I don't need to shave good ideas

Regards

Barney
- CommentAuthorRobL
- CommentTimeNov 25th 2019
Most EWI insulation sheets are flammable, and in order to make it use safe a suitable air-tight covering is needed. Generally thin coat renders on EWI adhesive with fibre-glass mesh makes the whole thing pretty fire-safe, while any sort of mechanically attached covering (even if it didn't burn) with air voids won't be as safe.
- CommentAuthorgyrogear
- CommentTimeNov 25th 2019
RT2020 will not come into effect until 1st Jan 2021 *at the earliest*, so perhaps you can get your project in quickly and escape under the radar...

Becos RT2020 means between 5 and 10% more on the construction cost...

gg
- CommentAuthorbarney
- CommentTimeNov 25th 2019
For RobL - agreed, which is why I was considering going as far as 200mm cavity wall construction - I'm just not comfortable with thin coat renders on EWI

For gyrogear - yes, noted - although I'm not overly focussed on capital cost. The land cost me less than a cheap car, and I want a robust, efficient property that will outlast me with minimum intervention in the ensuing period.
I'm happy to get involved in buiding so I'm essentially paying a builder to build what the architect designs - not a project manager so 10% either way isn't that important (to me)

Regards

Barney
- CommentAuthordjh
- CommentTimeNov 25th 2019 edited
Some further thoughts

An alternative to the pitched roof would be to use metal web joists on top as you intended and then put a flat top on and have a green roof.

Plan for external shutters on all windows and doors to keep the heat out.

Main wall structure could be anything: even straw bale if you wanted or hemp-lime for something a bit more traditionally solid. If you did use hollow blocks then you could put Larsen trusses up the outside to fill with whatever insulation you choose, then cover with MgO boards and render in the local traditional way.
- CommentAuthorgyrogear
- CommentTimeNov 25th 2019
Posted By: barneyI'm just not comfortable with thin coat renders on EWI

This one might be OK, though...

https://www.youtube.com/watch?v=Q2cmhK8uex4

Uses pinestraw and hemp for EWI and other uses also.

It seems to be commercialised by SARL PHISO but I cannot find their details, and applied by JM MACONNERIE, but can't find them neither...

gg
- CommentAuthorbarney
- CommentTimeNov 25th 2019
Flat roofs are not currently allowed with the local planning conditions - although that is likely to change soon

I've got louvered swinging shutters planned on all the south west facing windows (1 x bedroom, bathroom, kitchen and doors from the dining area)

With a quick scan of the sun path, the windows on the other side (N-E) don't see the sun beyond mid morning - there are no plans for west facing windows or east facing windows - ie the narrow ends of the building are unfenestrated. Perfectly happy with keeping windows shut during the day.

I did think of putting up Larsen trusses on the walls (or actually metal web joists on end) tied to the horizontal elements with MagOx boards over and blowing the lot full of cellulose. That would allow me to put up say 6 or 7 courses of the local brick from external ground level and then use horizontal cladding above that - with a counter batten to bring the boards out to overlap the plinth.

Which keeps taking me back to "Why not do a Denby Dale" and build a 200mm inner skin and 100mm outer skin which allows any render or cladding to simply and reliably fix to the outer skin which the local guys are used to - quick, cheap (ish) and reliable.

I made a few phone calls over the weekend and a local contractor is perfectly happy to dig out and put in strip founds, 3 courses of blocks to DPC 300mm of polystryrene insulation and 200mm concrete slab and run up to 2700mm in 200mm hollow blocks (filled, and with rebar ties) and a U channel at the top filled with concrete (again rebar tied to the wall bars) to form a ring beam (all openings included) - circa 15K (euros). Whilst he thinks I'm mad, he'll run up the outer skin for about 5k(euros) - so basically 20k gets me a shell and a further 15K would get me a trussed roof with clay tiles. Which I didn't think was unreasonable.

All up, I was figuring on 1000 Euro/m2 using local tradsmen with me managing things

It must be a personal thing - whilst I fully appreciate EWI systems are robust, reliable etc, I just can't seem to get wedded to the idea yet - and equally, cavity wall construction is a madness - but there we have it

Thanks again, it's helped me distil a few things ready for meeting up with the architect

Regards

Barney
- CommentAuthorPeter_in_Hungary
- CommentTimeNov 26th 2019
Posted By: barneyI'm still not sure about render over EWI, I have this reservation about defective rendering and a direct water path to the inside - possibly unfounded, for sure.

IMO fears unfounded. EPS is resilient stuff and doesn't track water through itself It is also resistant to freeze thaw cycles from any water getting on the surface. The thin coat renders and adhesive with glass mesh are sufficiently flexible to withstand casual impacts. Although I will own up to having one bit of damage from a tennis ball sized hail stone but the same hail storm destroyed several roofs in the area.

Posted By: barneyThe 7m dimension fits my preferred 2 bed layout - I wont be expecting many visitors, once I leave the UK, then I won't be coming back. There is for the most part a spine wall that would roughly half that dimension

If the spine wall is load bearing why not use normal timber joists. for a span of 3.5m a joist of 38x180 at 500mm centres or 50 x 180 at 600 centers would do up to a load of about 48kg/m2. Probably cheaper than prefab. metal joists and I would expect timber to be instantly available locally, known by the locals and easier to attach plaster board.

Posted By: barneyThe local builders seem to like IWI as a simple way to meet the current thermal regulations (R2012) in that part of the world.

For all the reasons in various threads here IWI is not as good as EWI

Posted By: barneyFor RobL - agreed, which is why I was considering going as far as 200mm cavity wall construction

Posted By: barneyand equally, cavity wall construction is a madness

Correct, I would not even consider it.

Posted By: barneyI made a few phone calls over the weekend and a local contractor is perfectly happy to dig out and put in strip founds, 3 courses of blocks to DPC 300mm of polystryrene insulation and 200mm concrete slab and run up to 2700mm in 200mm hollow blocks (filled, and with rebar ties) and a U channel at the top filled with concrete (again rebar tied to the wall bars) to form a ring beam

Over here hollow concrete blocks filled plus rebar (if needed) are used for foundations up to DPC (on top of 30cm concrete as it is cheaper than full fill with concrete and easier than shuttering. (they are called shuttering blocks here) For your proposal 30cm porotherm type are a bit excessive, 25cm would do but if 30cm is what the local store has and if 25 is a special order then go for 30cm. Over here a ring beam on top would be standard practice. I would expect porotherm type construction to be cheaper due to the reduced labour involved.
If I were to build your proposal here then it would be filled concrete blocks to DPC then 25cm porotherm type with ring beam on top plus EPS EWI at 200mm or 250mm thickness joining up with the loft insulation. The roof and ceiling would be an all timber affair, probably cold roof. Over here such a construction would be simple, known by the locals with no surprises and excessive attention to detail by the builders is not needed.
- CommentAuthorbarney
- CommentTimeNov 26th 2019
That's pretty much what I was looking for - with possibly less visible render and more timber cladding - although I guess that wouldn't be a significant problem going on over EPS (with possibly MagOx under the clad sections).

Insulation at ceiling level all good but I'm happy with an extended bottom chord so I can get a reasonable thickness and still "board" out the cold (or very hot) attic and keep squirrel nutkins out of the insulation layer

Thanks all - now to ascertain maximum roof pitch and ridge height allowable. The local roof lines are worryingly shallow for clay tiles !!

Best Regards

Barney
- CommentAuthorPeter_in_Hungary
- CommentTimeNov 26th 2019
Posted By: barneyThe local roof lines are worryingly shallow for clay tiles !!

You can get tiles down to 10 deg or a bit less
- CommentAuthorbarney
- CommentTimeNov 27th 2019
Sure Peter - although I was thinking more along the lines of 25 - 30 degrees for the aesthetic

Regards

Barney
- CommentAuthorPeter_in_Hungary
- CommentTimeNov 27th 2019
25 -30 degrees might be more of a problem for the PV in the winter than for getting tiles to cope with the low angle
- CommentAuthordjh
- CommentTimeNov 27th 2019
Posted By: Peter_in_Hungary25 -30 degrees might be more of a problem for the PV in the winter than for getting tiles to cope with the low angle

Put some on the wall for winter?
- CommentAuthorbarney
- CommentTimeNov 28th 2019
Lots of options for the PV

Most local roofs are pretty shallow (somewhere between 15 and 25 degrees) and to me look horrible

I have options to put PV "off the roof" on frames within the plot

First off, I need to see what's allowable locally as I would prefer a much steeper roof (say 35 degrees)

Thanks for the observations though

Regards

Barney

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