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.
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 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 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.