Spluttering SIPS: Chapter 2

Structural Insulated Panels or SIPS: quick to build, fantastic performance, building system of the future. Or so we hope. But so far the UK experience of SIPS has been checkered, and that is being very polite. There are some very successful SIPS developments, for sure: I visited one in September where everything had gone splendidly. But a good number have run into problems.

Here is an affordable housing scheme currently underway in Bugle in Cornwall. The builders have thoughtfully placed a webcam there so we can monitor progress. Not that there has been a lot. This image was taken off the webcam today (29 November). These 23 apartments have been going up since March and the roof still isn’t on. And the OSB is only just being covered up now. OSB isn’t designed to be left outside to withstand the elements: with SIPS, OSB is an integral part of the structure. Apparently there have been a lot of wranglings going on behind the scenes with building control and warranty providers. It doesn’t look pretty, does it?

My advice remains the same. I don’t want to put people off SIPS but if you do want to go down this route don’t try and do it on the cheap and make sure that your design and erection team know exactly what they are doing. Check their track record and speak to previous clients.

SmartLIFE Green Day, Dec 2nd 2006

Green Day update, complete with timings. We have 50 bookings and there are places for a few more, but bookings close on Thursday Nov 30. It's at the new Smartlife training centre, located at the Cambridge Regional College campus. There will be a full day of lectures and demonstrations plus information on grants available for environmental schemes and renewable technologies. The day features:

• Mark Brinkley at 10.15: I’ll be giving a talk about some of the many interesting projects that have gone on around Cambridge over the past thirty years. It’ll give me the chance to go and photograph a few of them. I might even revisit my first house, a detached Victorian brick structure that we externally insulated back in 1980.

• 11.00: Ralph Carpenter, Suffolk architect and hemp building expert

• 11.45: Eithne Flanagan, Sustainable Construction Co-ordinator for Cambridge Sustainable City

• 1.15: Meredith Bowles, award winning green architect and builder of the Prickwillow Black House

• 2.00: Chris Gooding, of Solar Energy Alliance, a reseller and installer of wind turbines and photovoltaics

• 2.45: Jean Roberts from the Energy Savings Trust with information on low energy building techniques and microgeneration grants

The event will run from 10 till 4 with a buffet lunch provided. Cost is £15 per head, payment by cheque only. Places are limited so please book in advance with Smartlife online or on 01223 712238.

Interview: Ray "Mr U Value" Williams

On the last day of October, I went to the National Physical Laboratory to interview Ray Williams. He runs the department that measures the thermal performance of materials and structures and, as such, he is probably Britain’s leading expert on measuring U-values. Despite having such an important job, at the cutting edge of building science, he had never before been interviewed by a journalist. “It’s a sign of the times,” he joked. I think he was delighted that someone was at last showing an interest in the work he does.

I wanted to talk to him about the multifoil debate, in which he has been deeply involved. But I also wanted to see how they go about their testing work and in particular just what a guarded hot box actually looks like. It is the industry standard equipment, used for measuring U values, and it has played a crucial role in our understanding of how building materials hold onto heat.

The hot box (pictured here with Ray inside) is a much bigger piece of kit than I had imagined. It’s about 3m tall and it weights 3.5 tonnes: it’s also a very expensive. Ray reckoned that it would cost around £300,000 to replicate it. Because of this, there are now very few of them around. He only knows of two others in the UK, both at the BBA test site.

“Anybody can build a simple hot box,” Ray told me, “but the results they get from it will be subject to a huge margin of error, so much so that the results are worth very little. Here we have been refining and developing the apparatus (which complies with BS EN ISO 8990) and the techniques for measuring heat transmission over many years. This is probably amongst the most accurate guarded hot boxes in the world but, even so, our best measurement uncertainty is still only about ± 4.5%. That’s a large measurement uncertainty for scientific testing. It shows just how difficult measuring heat transmission through structures is.”

Thermal performance testing of building products was pioneered in the 40s and 50s when scientists began to systematically study the thermal resistance of all kinds of materials for the first time. However, the evaluation of the insulation properties of building materials and structures was given a boost by the energy crisis that developed in the 70s. The Thermophysical Properties Group at the NPL was established in the late 1970’s, brought about by the need to verify the claims of the manufacturers of low density aerated concrete that the thermal performance of these new materials were actually superior to traditional concrete blocks. A more recent surge in demand for these services came when the 2002 revision to Part L of the Building Regulations set a low U-value criteria for windows, making double-glazing incorporating low-e glass almost mandatory. It was important for manufacturers to have the U-value of their windows measured using the procedures specified in a then new hot box measurement standard known as BS EN ISO 12567-1 and many of them came to the NPL to have these measurements carried out. A hot box measurement at the NPL cost around £2,500 and takes about a week. The NPL hot box can measure element up to 2m wide by 2m high and is fully rotatable, so that it can work vertically, horizontally or at any chosen angle, which is important when the test element contains air cavities.

The question I really wanted an answer to was this: “Just how good are hot boxes at indicating what goes on on site?” Ray Williams wasn’t really in a position to answer this, as he doesn’t carry out site tests, but he did point out that there was really no reason why a structure should perform better on site than it would in a hot box. Which brought us on to the subject of multifoils, of which he has tested quite a few. What struck me was that he wasn’t at all dismissive of them, which I had half expected, but was really interested in the whole debate and was keen to devise a test that might show multifoils off in a better light, if at all possible.

“I have had a number of multifoil manufacturers here talking to me and while some are quite prepared to accept that hot box testing is the best way of quantifying the thermal performance of their products, others are not. Some really seem to believe that multifoils behave differently in dynamic temperature situations than when tested with a constant temperature difference across them (as in hot plate and hot box measurements) but they don’t have any data to support those views. I keep getting results that indicate the thermal resistance of an air cavity insulated with a multifoil mounted centrally, is the equivalent of between 50mm and 80mm of mineral wool, but no more.”

It is partly these continuing negative results which have finally persuaded Local Authority Building Control and the NHBC to issue guidance to their members to only use thermal performance values obtained from hot box measurements, at least until further notice. Even so, Ray is still open to carrying out further tests. “Some multifoil manufacturers want me to test dynamically. Thus far, every test I have done in the hot box has been steady state. That is to say that we test for the heat loss of a wall or roof with a steady 20°C temperature drop across it; designed to mimic the difference between internal and external conditions in winter. A dynamic test, in contrast, would look at total heat transmission through an insulated structure over an extended time period whilst the temperature difference is being varied, just as you might expect in the course of a day. The BRE have carried some in situ (hence dynamic) measurements of walls insulated with multifoil insulation and those results were broadly in agreement with hot box results. The DTI have now funded a small project for NPL to look at identifying the best way to evaluate these kinds of products. I have already had extensive contacts with many people involved in this debate and I must soon decide how best I can help to resolve these issues. I am of a mind to include carrying out some dynamic testing, either in a hot box or a hot plate apparatus to see if I can determine if different insulation systems can behave significantly differently in those circumstances. But I am at a loss to explain just how it could give a markedly different result. Dynamic testing takes longer and it’s far harder to interpret the results, but in principle I don’t mind having a go.”

Whatever your feelings about multifoils — if you have any feelings at all that is — I find it reassuring to know that the government’s chief thermal performance tester is open-minded about trying alternative testing regimes. Because if, in the future, we want to address issues such as solar gain, quality of on-site workmanship, building anomalies and dynamic thermal performance, in a truly rigorous way, the guarded hot box apparatus is unlikely to be able to provide all the answers. But in the absence of any widely accepted and validated alternatives, it remains the best testing method for comparing products that we have for now. Whilst it is easy to see why a product might not perform as well on as it does in a lab test, it remains a puzzle as to how exactly it could be persuaded to improve.

Men of Straw

These two young men want to build houses out of straw. David Menell (pictured left) and John Ogle have started a business called Conscious Construction and they have a mission to make straw bale building mainstream. Or at least, a little more mainstream than it is right now. Which wouldn’t be difficult because there are only ten straw bale houses in the UK.

Thus far, if you want to know about straw bale building, you beat a path to the door of Barbara Jones, the diminutive dynamo behind Amazon Nails. Barbara learned about the technique in North America and brought her knowledge back to the UK where she has refined it and almost single-handedly driven it into the public consciousness. But her work is often community-based and is usually at the non-profit end of things. She is more teacher and guru than businesswoman.

John and David are approaching it from a different perspective and are hoping to move straw-bale building onto another level. Not surprisingly, they have learned about straw bale building techniques from Barbara and she is apparently keen to support their new venture. They want to develop straw bale as a viable alternative to rival other non-standard building systems, such as SIPs panels or ICFs (both of which have featured in the blog over the past few months).

I must admit I had never considered this to be a likely development before. Straw bale seemed just too….whacky. For a start, there are a whole bunch of fears to work through. Fire. Rodents. Moisture problems. Asthma. You name it, people worry about stuff like this. When you are investing your life savings into a house, you want to minimise your risk, not take part in some construction experiment. You need a comfort zone and straw bale ain’t there yet. But it’s also fair to say that it’s not that far off either. Amazon Nails’ pioneering work over the past 15 years has addressed all these issues and although the number of straw bale homes in the UK is still tiny, there are enough around to know that, as a technique, it works. And in North America and Denmark, there has been loads more development work carried out which further enhances the credentials of straw as a walling material.


And once you get past the fears, there are lots of things going for it as a building method. It’s cheap and abundant – it requires no manufacturing at all. The walls are wide – typically 450mm – but they provide good insulation and they can be easily made into interesting shapes. Covered with flexible lime renders, straw bale walls look fantastic. And they can accommodate all aspects of modern living like double-glazed sealed units and cabling. In many ways, straw bale has similarities with ICF construction but without having to use truck after truck of readymix. I can see that there is real potential here, but I can also see that unlocking that potential is going to be a long hard sell. Thanks to exposure on programmes like Grand Designs, there is an awareness that you can build structures using straw bales, but that’s still not quite the same thing as building your own home out of them. That’s still an option for the brave, but maybe, just maybe, it’ll move mainstream much quicker than might be expected. Maybe, just maybe, Conscious Construction have timing on their side.

Eco Bollocks Award — Jeanette Winterson

Jeanette Winterson is a very good writer. She hit the big time with her first novel, Oranges are not the Only Fruit, which won the Whitbread Prize in 1985 and went on to our TV screens five years later. I remember it. It was compulsive viewing. What does she write about? Wikipedia says her novels explore the boundaries of physicality and the imagination, gender polarities, and sexual identities. I’ll leave it at that.

But Jeanette also writes about other stuff that interests her and, in particular, she sometimes muses on property. An article on extending her thatched cottage which appeared in the Times last week is so bad that I couldn’t let it pass and have decided to award her with my first Eco Bollocks award for A1 rubbish written in the name of greening the planet. So Jeannette, I hope you don’t mind too much in collecting another award — you seem to have quite a few already.

Why has Jeanette been so honoured? She writes:

Any idiot can make a square out of breeze blocks — I know, I’ve done it myself. Yet breeze blocks are not just ugly, they produce huge amounts of carbon dioxide in their manufacture and require heavy cement mortars to hold them together. The things may be faced with stone or brick, but once your inner shell is made of cement blocks you might as well be in a concrete apartment in the former East Germany.

What a load of crap! Breeze blocks don’t produce huge amounts of carbon dioxide in manufacture. They may be ugly but then they are not designed to be seen so what difference does it make. If you are building an extension with a stone facing, as she appears to have done, living as she does in the Cotswolds, then concrete blocks are easily the most sensible way of building a structure. But no, she chose to do her walling in timber frame. Or, as she likes to call it, eco-timber.

Yes, this cost more, but even if you leave out the environmental pluses of using eco-timber and no cement, there were two further advantages: while the kit was being built elsewhere, the men were able to get on with renovating other parts of the house — so the process is economical on time.

Sounds like she has been spoon-fed some spiel by a very good salesman. Yes, timber frame can and sometimes does reduce the critical path. But not on a stone extension. Give us a break.

Just as good, and much to the disbelief of building regulations inspectors, we have achieved four times the required insulation (U-value) by packing the cavities with Tri-Iso Super 10, an insulating material that looks like layers of coloured Kleenex and shiny cooking foil. It is far superior to blown foam, and unlike using sheep’s wool you won’t find your whole house full of moths next spring.

Where does she get this stuff from? Building inspectors have just been told to no longer accept Tri-Iso Super 10 because it doesn’t do what it says on the tin. It only ever claimed to be as good as blown foam, not four times as good. And it has been unable to prove that it’s even half as good. As for the comments about sheeps wool….I am no particular fan of using sheeps wool as insulation because it’s bloody expensive but the comment about moths is bizarre. Especially from a woman who owns an organic food shop in London’s East End.

I have to say that building regulations make anything green or eco as difficult as possible. Most inspectors know little about green building, and mostly don’t seem interested in learning more. In the years and years that I have been renovating property, I have never met a single one who even wanted to talk about what we were trying to do, let alone offer any help or advice.

I wonder why, Jeanette, I wonder why?

Here’s Jeanette on her ground source heat pump. This wonderful, simple idea, developed in Sweden, works like a fridge in reverse, and converts low-grade heat from the ground into high-grade heat for radiators and hot water. For every one kilowatt-hour (kWh) of electricity used to boost the earth-core temperature, 4 kWh are generated; in other words, you cut your carbon dioxide emissions and your heating bills by a whacking 75 per cent.

Actually, that’s fine until you reach the last bit about heating bills and CO2 emissions. Not even the most ebullient heat pump manufacturer (and there are lost of ebullient ones out there) would make such an outlandish claim. The true figures are subject to much debate but essentially there is very little difference between a really efficient gas or oil fired boiler and a ground source heat pump on either heating costs or carbon emissions. Search this blog for ground source heat pumps for a more detailed explanation.

So there you have it. This blog has launched into new territory by starting an award scheme. The Eco Bollocks award may not yet carry quite the cachet of the Whitbread or the Booker, but all awards schemes have to start somewhere. Anyone else fancy trotting out some complete tosh?