Hello All,

First time I've logged onto this site and participated since September 2015 - since then another child, a new job, house renovations, structural alterations and general non-stop pace of life have intervened which means I've done nothing but lurk occasionally.

However, the time has come to bite the bullet and extend my 1960's bungaloid so I come to you seeking pearls of wisdom. Apologies in advance for the length of this missive - lots to cover!

Reality and expediency dictate a rapid build and less regard for natural materials than I'd like (there just isn't enough space to allow for natural insulated stick frames) so the conclusion is that SIPs are the way to go. With a preference for MgO / hybrid SIPs if the quotes are sensible enough and in order to reduce fire risk and make external weatherproofing easier.

However if I am going to use dinosaur paste for insulation then I want to make sure it is used the best way possible and make sure the detailing is up to snuff and it seems excessively difficult to track these down.

For instance; how best to join the sips to the existing cavity walls? Obviously needs a wooden plate attached, but also will have to allow for movement. How do you detail an expansion joint for air tightness and cold bridging?

I would like to use an insulated raft foundation (on chalk) next to the original strip footings so I'm assuming this will bring up its own problems with regard to movement? Advice from Seamus at vikinghouse is to treat them at two boats moored alongside - I don't want them floating apart!

At the rear I am hoping to use sips to create a large dormer - built up from the existing cavity wall. Not yet found a sips supplier who will provide details for how the two are joined, but am assuming cavity closer followed by sole plate - again I'd like to create a thermal break at this point, so assuming something like marmox thermabreak can be used?

The existing cavity walls were filled under green deal but there are lots of thermal bridges that have caused damp inside, mainly around lintels and window reveals. Also the entire front wall of the house faces the fairly extreme winds we get at the top of Dunstable downs and is made up largely of solid brick. External insulation of these parts is therefore a must and it would seem logical to continue this up onto the sips and reduce cold bridging at the junction between the two wall materials.

However; most things I read regarding sips suggest any extra insulation should go inside due to the risks of moving the dew point. This would be even more of a concern if using MgO for the outer surface since this has a reputation for sweating and causing chemical issues with surrounding materials. Any views on this?

Some of the MgO SIPs suppliers are suggesting direct render to the outside face rather than leave a cavity and render board. This worries me somewhat but would allow even more internal space if it could be detailed correctly with regards to the aforementioned sweating.

I also have a preference for adding some internal wood fibre insulation (mainly for the decrement delay) although I'm also investigating weather I can use a Lewis deck and concrete slab for the dormer loft conversion to add some mass instead. Then I could just tape and fill the sips internally, save the cost of plaster finish and get moved in even quicker.

Any comments/ advice / criticism / abuse appreciated :-)

Also any recommendations for builders, architectural designers in the Herts / Beds / Bucks area with experience of this kind of extension and detailing?

Regards, Simon

Thanks djh, I'll check out Good Architecture.

So far I'm finding it hard to get a serious response from SIPs and closed panel suppliers. (Or other product suppliers for that matter...)

Out of 20 emails sent out with requests for indicative costs, only 10 replied.

Of those only 6 gave a proper response - the rest just said my project was 'not a fit for them' which I guess is industry speak for 'too much hassle'.

Of those 6 only 3 can supply (2 with MgO and 1 with wood SIPs)

One of the MgO suppliers seems friendly and forthcoming (fingers crossed) and to quote from his email:

"We have built a number of houses in and around London in our mgo SIP and have had accredited building control and local authority control as well and obtain a warranty when we issue Building Control certificates so as to sell these properties."

So I guess they are confident with the direct render approach.

I remain to be convinced given all the historic problems reported in other countries; although most of the cases seem to be caused by MgO boards used as sheathing without any sign of VCL. As far as I can ascertain it looks like the problems were caused by moisture from within the structure rather than wind driven penetration.

I had thought in the age of Google it would be relatively easy to find standard details online, but have not found any suppliers websites of particular help.

Kingspan have more detail than most, but I don't like the way their panels are connected together, and experience on sites using their products in the past did not give a good impression of their reliability as a supplier.

Even the BRE have nothing that I can find.


P.S. Dinosaur Paste = Oil http://www.greenbuildingforum.co.uk/newforum/extensions/Vanillacons/smilies/standard/bigsmile.gif

Yep, those are the problems I've seen reported in Norway and America amongst others.

The articles I've read are all a bit light on construction details, and details are everything as we know.

I am concerned with the sole plate issue as well, which is why I'm hoping to find an alternative to timber - I have wondered if some of the recycled 'plastic wood' products could be used instead. After all , they are available in similar sizes to conventional timbers and all they have to do is locate the sips securely in the correct location. They shouldn't rot and they will provide some insulation as well.

Not sure how dimensionally stable they are though - when you see plastic wood used in park benches it seems to sag and twist after a few years - but perhaps if they are protected from UV by the SIPs this will not be an issue?

I like the idea of Durisol instead of SIPs (again for speed of construction) but the finished walls will end up considerably thicker and reduce space inside. I'm also not happy with using so much concrete.

Hopefully I will get some answers on this in the next few days... I have sent requests for technical details to a few suppliers of plastic woods.

At least one manufacturer is making plastic roofing battens which would require them to be dimensionally stable unless you want the arts and crafts look?

Also, just found out that in America they have MgO SIPs using expanded cork as the core:

https://innovaecobuildingsystem.com/specialty-custom-laminations-special-use-sip/

Probably hugely expensive (natural insulation always is) but the cork comes from Portugal apparently, so why cant we get the same option in the EU?