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How to build - so many options

Sue B

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When we first started on this path, we wanted a hands off, almost turnkey project.  I'd heard of SIPS and seen lots of positive stories about energy efficiency so all was set.  Then we spoke with a mortgage advisor and our world started to tumble down.  I am now 56, Peter is 57.  We will need a mortgage to build this house but because of our ages, we know that the mortgage providers will all keep the term of the mortgage down to 15 years max which will make the repayments large.  Drastic action needed to be taken so we have now decided to build using a method where we can do this ourselve.

 

We have no experience of actual building work but let's face it, how hard can it be 😲 - famous last words.

 

Our previous house was built using traditional methods.  We did have underfloor heating and a MVHR system but we struggled to get through the air-tightness test.  We have learnt a lot since then.  We nearly built that time round using ICF but I chickened out.  This time, it looks like it is going to win.

 

We have looked at the various types of ICF.  The majority are of course the polystyrene type blocks and these do have real advantages for self builders.  They are light and easy to manage.  Our main  issue with them is the fixing ability at the end of the build.  Once the plaster is on, finding the fixing lines becomes harder and harder and so other ways of fixing heavy items to walls need to be used. Looking at various websites and you tube videos, it is also apparent that blow outs are more likely using the polystyrene and more bracing is required during the pour.  The concrete is of a stiffer consistency that with the woodcrete ICF.

 

The woodcrete type ICF blocks solve the fixing issues - you can attach anything to it.  We have looked at three types of this type of ICF, Velox, Durisol and Isotex.  Each has pros and cons and we have yet to decide which type to use.  All three appear less likely to blow on pour day without significant bracing but of course it can still happen.  We can't get a price without plans so at the moment the comparisons are being made purely on preference but without the benefit of a cost comparison.  The concrete for this method is of a very runny soup like consistency.

 

VELOX

This method uses two flat panels that are clipped together as you build.  The panels are large - 2000mm x 500mm so will go up quickly.  One panel has the insulation attached to it.  The system comes with a variety of options for the depth of the wall giving different u values.  I have found getting information from the website quite difficult - the website is clunky and parts of it are not in English.  The way the panels fit together, you end up with a completely solid concrete wall inside the formwork.  I believe this gives a better chance of airtightness from the actual structure of the walls. 

The UK supplier seems to be a little difficult to get hold of sometimes - maybe this is the result of too many enquiries but it does ring alarm bells to me.   The system has products for both internal walls and floors.  The internal walls are two panels glued together, this takes the weight to 68kg - we struggled to lift a panel off the floor so raising it above shoulder height would be impossible for us. The size and weight of the panels pretty much rules this system out for us as it is simply too heavy for us to manage ourselves. It is however, my favourite product.

 

DURISOL

Durisol blocks are more like a squarish 8 with the top, middle and bottom bar at less than full height to allow a honeycomb concrete wall to form during the pour.  The blocks are all 500mm x 250mm with the external walls coming is two depths - 300mm with a u value of .23 or 365 mm with a u value of .11.  There are 3 different types of blocks. A standard block with the reduced internal height connectors.  A facing block which has one end at full height - this is also used for lintels.  A corner block for ...... turning corners!  Because of the way the blocks work, the second row and above will all need a cut to ensure that your keep the "brick bond" in place. This is particularly pronounced if you choose the 365mm blocks as it is the width that causes the issues.  QUESTION - couldn't you fix the problem by making the cut on the first row instead and increasing the size slightly so that every other run works properly?  That didn't cross my mind at the training.  The blocks have male and female ends so that they lock togehter prior to the concrete pour

The blocks are rough and gloves are definitely needed.  The blocks do shed while you are working as well so care needs to be taken to butt the blocks up properly as the debris can move things apart a little.  The design of the blocks means that there are the 3 woodcrete bars, each end of the block buts together with only a small amount of concrete bonding the blocks together. 

The blocks are produced in this country so less likely to suffer with issues to do with Brexit.  Lead time is in weeks.  Free training is provided (we have done the one day training course) and they will come to site to help you get the first row laid, ensuring that you get a nice level row.  Purchase of the blocks over £10k gives you one free site visit (need to check if that is the initial row or if you also get the first pour day).  Other visits are by negotiation but they rely heavily on facetime calls to see your site without actually being there.

The anecdotal evidence that I have is that Durisol will discount heavily but they do not talk about a standard price - you only appear able to get a price from the drawing that you provide. 

I believe this will be our third choice of block based on properties but is probably the cheapest of the three.  It is also the one we are most likely to use due to the price.

 

ISOTEX

Isotex is a very similar produce to Durisol.  The blocks are mainly 500mm x 250mm but there are "pass" blocks to match the block depth that you have chosen.  This gets around the issue of "brick bond" issue.  The blocks come in depths of 300mm with a u value of .23.  330mm with a u value of .19.  380mm with a u value of .15 and 440 with a u value of .11.  There are more options for shape of block - not sure how much that will help on site - will it be more difficult to find the right type of block while doing tricky areas?  

The shape of the blocks is like an H but with 2 horizontal bars not one.  This means that the blocks allow a freer flow of concrete between the blocks than you get with Durisol.  It will still be a honeycomb but less so, there is roughly a third less woodcrete in the way of the concrete wall.  Butting the blocks together mean that they just sit together without the benefit of the locking togethre - this means that there are two short unsupported parts of the block holding the concrete - does this make a blow-out more likely?

Insulb the UK supplier provide similar training to Durisol - we are attending in February half term at Swindon NSBRC.   The blocks are slightly smoother than the Durisol ones and seem less likely to shed.

Jamie has made it quite clear that the price is non-negotiable.  £55m2 for the 300mm block (I think I wrote down the correct block size but not 100% certain) against £62m2 for the 440mm block.

I believe that this will be our second choice block based on properties and probably second choice one price comes into play - time will tell.  

 

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I too am looking at all these systems.

the velox internal wall panels --just don,t use them ,if only non load beating then stud walls?

or use 2 velox panels at thinner size and pour ?

.

where your site  is makes a difference to costings on all  types--due to transport costs --I will be more as in scotland 

Isotex  looks a better made  of block and could be a the one --

I still am looking at one type of poly ICF 

that is ISODOM 2000--looks by far the best poly system and wall blocks are longest,best locking between blocks  --so making straight wall will be easier+ biggest selection of different elements  of any system 

the agent assures me that hire of bracing will not be a probelm ,and inferred it could be included --I may have picked him up wrong

,but same as you 

till I  have a design  I cannot get comparative quote

Isodom agent, ekonect, also build it you wish --they used to be durisol agent -so they are not just salesmen 

 

Edited by scottishjohn

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Thanks for this very informative blog. I wish you luck with your decision and look forward to this project unfolding. If the blog continues in this vein, it will be of much use to others, I'm sure.

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Pat pat, good blog ! Best of luck.

 

>We have no experience of actual building work but let's face it, how hard can it be 😲 - famous last words.

 

There exists a rabbit hole down which - at some point - you will discover that you have fallen !

 

A bit of extra info for Durisol virgins who just surf-on-in:

 

1 - I think Durisol (and the other one) give stronger concrete structures than you may have implied, as done properly the sloppy concrete infiltrates the matrix of the block.

2 - Durisol is cut with a normal power saw (no guarantee on blade life time 😀)

 

Cutting-durisol.jpg

 

Credit: http://endeavourcentre.org/2012/06/a-finished-durisol-block-foundation/olympus-digital-camera-29/

Edited by Ferdinand

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48 minutes ago, Ferdinand said:

There exists a rabbit hole down which - at some point - you will discover that you have fallen !

But I am FANTASTIC at Lego 😂😂

 

49 minutes ago, Ferdinand said:

I think Durisol (and the other one) give stronger concrete structures than you may have implied, as done properly the sloppy concrete infiltrates the matrix of the block.

 

It’s not the strength but the air-tightness that I think will be different.  I know that @JSHarris has previously mentioned that concrete is not necessarily air tight but it has a much better chance than the woodcrete.  The difference between the three products is how complete the concrete wall within the formwork will be.

 

During the Durisol training, they were very keen to talk about the product being breathable.  Passivhaus and air-tightness were almost dismissed as a goal not worth aiming towards.  The MD (a structural engineer) went so far as to state that it made no sense to him as an engineer to make a property air-tight and then introduce an MVHR to bring in ventilation.    They also talked about Thermal Mass and I just smiled sweetly and thought of our Jeremy 😊.

 

We went to a passivhaus seminar at NSBRC in November and cat flaps were mentioned.  IIRC they were mentioned in the hundreds of pounds to much laughter.  During the Durisol PowerPoint, a similar cat flap story had become thousands £s.  We have a similar story in our family.  Peter lost £5 in the sea in Cornwall during our first holiday together when we were mere babes.  (17 &19).  This was way before children came along and before the lottery existed.  That £5 is now referred to by the kids as a winning lottery ticket that would have set them up for life if only their dad hadn’t lost it in the sea - it has taken on a life of it’s own 😂😂.

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1 hour ago, Redoctober said:

Thanks for this very informative blog. I wish you luck with your decision and look forward to this project unfolding. If the blog continues in this vein, it will be of much use to others, I'm sure.

Hopefully others will find it useful, the danger is that it will be too dry as it is my decision making process as opposed to nice action posts - that should, with luck come

along later.

 

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2 minutes ago, Sue B said:

 

 I know that @JSHarris😊 has previously mentioned that concrete is not necessarily air tight but it has a much better chance than the woodcrete. 

 

 

Not quite.  I've mentioned before that block and brickwork won't be very airtight, unless parged or wet plastered, but cast in-situ concrete should be pretty airtight I'd have thought.  It very much depends on the nature of the ties between the inner and outer skins of ICF, as they are about the only places where there is a small risk of air leakage. 

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This is what is was thinking of -  not you @JSHarris but @najem-icf.  “Reminds me of an article I read when I was Stateside some years ago about a Durisol build 22 storey hotel in Canada - built back in the early 1980's - guests complained of "ghosts" in the rooms - later realised it was curtains moving due to air penetration through the structure.”

 

I knew I’d Read something somewhere.

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Just parge coating Durisol should fix that easily enough I'd have thought.  Pretty quick and easy to do, just need a bucket and broom.

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If you chase channels out on  inside  of wall for your electrics

then hard plaster ,that will do the same .

and if cladding outside ,then maybe house wrap it under the batons for the cladding

but if going rendered that will also serve  to do the same

plenty of good options

should be less concrete cost using durisol  or isotex as they are 120mm concrete -

lot of poly types are much thicker 

 

Edited by scottishjohn
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Thanks for sharing your thoughts and research @Sue B really interesting to read. I'm just along the coast from you  I think in Boscombe, building in Parkstone.

 

Also ICF enthusiasts, interested to see your concerns re fixing to the walls. I'd considered that and thought that for internal fixings we'd fix structural ply before fixing plasterboard for key areas in kitchen and bathroom. I am thinking now about exterior fixings as after render that isn't so obvious - thinking initially lighting but even simple things like hose reels in garden or in future who knows what. You can of course go through to the concrete but with ~75mm of EPS that isn't ideal and heavy items I'm a little concerned (maybe unnecessarily) about the pressure applied to the wall so will keep researching this. May even have a look at non-EPS/XPS options - we have rear walls which are below ground so need something that is appropriate (of course with waterproofing solution).

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Not far at all @Adam2.  I was in Poole this morning and took the opportunity to drive round past the Durisol build there.  Window forms are in so I'm sure they will be pouring very shortly.

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in the process of studying dry wall finish  against  chasing wall for electrics + then mechanical spray plastering --

used in europe for years --now plenty of uk companies that do it--will be good for air tightness as well

easy to chase woodcrete --and how often do you REALLY want to add new electric supplies?

ball park figure i,m being told by  an ICF supplier  is around £8 sqm -for spray plastering finished job .

so anyone done a calculation of proper drylining with service void ?

cos with drywall stuck on ,

you might as well go hard plaster 

 

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One of our wish list items is wet plaster (possibly spray) as opposed to dot and dab.  Partly because of the air-tightness but more

because I just prefer the finish.

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The house will have to have a VCL, and that will be on the inside face of the structure, and that should be airtight as well as being vapour tight.  It worries me when we see poor construction allowing cold air in behind dreadful dot'n'dab plasterboard, as it's not the dot'n'dab that's really the problem at all, it's that the builder hasn't ensured there's an effective VCL.  Houses like this are going to have interstitial condensation problems, I'm sure.

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not convinced that an ICF solid wall house where insulation is on outside and keeping solid wall warm ,same temp as room ,or near enough 

and with proper MVHR will ever have the required temp dif of wall and air to get condensation 

 but interested to know how and where you would fit a vcl  on these types of build ?

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52 minutes ago, Sue B said:

One of our wish list items is wet plaster (possibly spray) as opposed to dot and dab.  Partly because of the air-tightness but more

because I just prefer the finish.

 

Do you mean the solid feel of wet plaster ..?? I’ve used the new foam adhesive rather than dot and dab and been surprised how solid it feels - you get the speed benefit of the skim coat and quick drying with the “solid” feel with no hollow sound behind the boards. 

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The VCL is what it says, a Vapour Control Layer.  It can easily be a part of the fabric and doesn't have to be a separate entity that's added on as an afterthought.  Take our build as an example; our VCL is an inner frame racking skin of Spano Durelis.  In an EPS ICF construction the VCL may well be the inner layer of EPS.  With wood/cement fibre ICF construction the VCL could well be a cementitious parge coat on the inner face, before plastering.

 

A VCL doesn't have to be totally vapour impermeable, it just has to have a permeance that is significantly lower than anything within the build outside it.  The name gives away exactly what it does, control vapour movement, not necessarily completely block it.

 

Finally, as ICF is a sandwich that may well have a significant amount of insulation on the inside as well as the outside (some ICF seems to be almost 50/50) then the concrete core is going to tend to sit at a temperature part way between the inside and outside temperature.  Concrete is a relatively good thermal conductor (around 1.5 to 2 times more conductive than water and around 25 times the thermal conductivity of something like EPS) so it's likely that the core will be at a reasonably even temperature through its thickness with the greatest temperature gradients being through the insulation on either side.

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VCL was mentioned during the Durisol course but I didn’t listen as I was busy making notes about another issue and it was just background noise at the time.  However, I will of course be asking Jamie about it later this month during the Isotex training.  

 

Heads up Jamie - you know one ofnhe questions coming your way 😊

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23 hours ago, JSHarris said:

an inner frame racking skin of Spano Durelis

 

Blimey. That sounds like an STD.

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On 03/02/2019 at 10:30, JSHarris said:

Spano Durelis

so how did that compare with osb+vcl  in price --could end being cheaper maybe?.

providing you comparing 12mm osb and not 9mm 

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I don't know, as it was a closed panel system that was designed to meet the performance spec and be quick to put up.  The inner panels are 12mm thick, and taping the joints after assembly looked to be much quicker and easier than fitting a separate VCL membrane, particularly as the surface of the inner panels is very smooth, because of the vapour sealant on the outer surfaces of the board.

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We have just had the word that the Durisol build near us has the first concrete pour on Tuesday 26th.  Just booked my half day holiday so that we can go there first thing.  Very excited so I can't imagine how they are feeling :)

 

Edited by Sue B

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And the pour has been delayed - sturctural engineers disagreeing over what is required.  

 

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Today we went to the free training day at Swindon NHBRC for the Isotex build system.  The day was a very similar format to the Durisol training day but the whole day felt less formal and went really well.  The actual hand's on part of the day, I thoroughly enjoyed, I felt we learnt much more about how to actually use this product, including how to fix something that we know is likely to happen (putting a block round the wrong way so that the insulation is on the inside and not the outside).  The issue with this is the break it will make in the concrete honeycomb - the wall will have a weak spot so you have to fix it.  We built over a window frame, cut some blocks, talked about door openings and left feeling quite confident about the product.

 

So now I have seen the 2 products that are in contention in a training environment.  My verdict comes down 100% on the side of Isotex, luckily Peter agrees and I didn't even have to tell him what his decision was!  The reasons for this are really a confirmation of my thoughts prior to the training:

  • Less webbing so that the concrete honeycomb is more complete
  • Smoother so that they appear to "shed" less
  • The pass block which keeps your "brick bond" does make life easier as there will be less cutting of blocks on site.  
  • The design of the block increases the air-tightness of the finished wall - Durisol has two woodcrete faces that butt together, Isotex has open ended blocks that fill with concrete, sealing the air gap.
  • I felt that the support during a build would be better - that is purely a gut feeling of course, but there is no way of quantifying this without talking to lots of previous self builders.  It was clear however, if we needed a visit, they said they would come out to us in addition to the visit that they actually schedule in to make sure you are getting on ok at the start of the build.

The choice of build methond is one of the more fundamental of any self build and in addition to the quantifiable benefits that have helped us favour this product is the inevitable personal prejudices that we all have regardless of how much we may try to neutralise them.  For me, having the saleperson talk positively about a foundation system that I have only heard good things about on this forum made me feel that they were on the right page with how builds should be today.  Durisol were quite dismissive of insulated slabs.  MVHR - again, Durisol were dismissive, let the house breath and you don't need an MVHR.  Isotex understood the need for air-tightness and therefore an MVHR to give you the ventilation that is needed to keep the house healthy.

 

Our next steps are to visit a site for both product on pour day.  Hopefully we should be able to do this in March as they both have pours quite locally to us.

 

The BBA certification is still rumbling along, however for me it not a particular concern.  If we can get a mortgage and the 10 year warranty insurance, I really can't see an issue.  That along with the fact that we will not be bulding until next year, when BBA certification (for what it's worth) should be in place means for us it is a minor item.

 

So, for us, we have a product in a clear lead, it will come down to real world usage on a site with people like us and of course price.    

 

Finally, it was lovely to see @Tom's Barn again and to meet Karen who is hopefully a member of Build Hub in the very near future.

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