Did you hear the guy from Arups on the news today? They are claiming we are building housing which will be inappropriate for the warmer world we will be inhabiting later this century because it is increasing lightweight timber frame and doesn't have the thermal mass and passive cooling traditional in warmer areas like the Med. He thinks we will all be sat in plasterboard boxes with the aircon on...

I thought they might have produced a report but I can't find anything on their website. What do people think?

Uh-oh another sticky subject - rotten tomatoes at the ready!

I think that he is right to raise this. If the majority view on Global warming comes to fruition then there is indeed a danger that lightweight buildings will require significant energy use for cooling in the summer.

I do not agree with the drive to reduce u-values beyond current building regulation levels as the marginal benefits of doing so are minimal - there are better ways of reducing energy use.

I believe the focus should be on build quality to ensure that installation procedure is actually adhered to and airtightness is at a level which allows heat loss in real life to actually reflect that predicted by out of date steady state predictions.

If the UK is getting warmer then reasonable [current] u-values will be enough in the warmer? winter months to mean that only minimal heating will be required anyway. This could be produced by using 100% efficient electric heaters [and incidental heat gains] powered by off site and/on site carbon free technology.

It also means that petro-chemically derived insulations [which is the only realistic choice for the mass market] can be substituted for natural products which lock up Carbon.

bUT NOT JUST ANY OLD SOLID - IT'S too easy to create something that stores daytime heat and then releases it just as the next day's heat begins, instead of when it's needed, overnight. New knowledge and understanding is needed.

I am happy to store for three days or more.

I think there must be a balance to be struck somewhere. Concrete and stone villas in the Med are are a pleasant refuge in the fierce heat of the summer but I once stayed in one in Crete in April during a poor spell of weather and it was very chilly (although not as chilly as the pool at 2am after a skin full....).

My personal preference is for heavyweight, I just like the solid feel, and I think in the real world you have a better chance of building air tight, but I think this should be combined with good passive solar design and high levels of external insulation. Throw in a nice cosy stove to keep the winter chill off and that should all you need I recon.

I think if you go the lightweight route you are, potentially, buying into the notion that houses need fast response, electronically controlled heating and ventilation systems to maintain themselves at a precise temperatures all year round. I prefer the idea that your building basically moderates temperature and humidity passively and occupants adapt their clothing with the seasons, reconnecting themselves with nature.

I think too much emphasis is placed upon the requirement of high thermal mass to reduce summertime overheating. It is only one of many measures that can be used and is by no means the most important. There are also downsides, for example, at night time when you want to sleep you want a cooler room, thermally massive houses with bedrooms upstairs may actually be hotter at night in the summer when people are most sensitive to higher temperatures. A lightweight house will of course cool much more quickly. Personally I'm quite happy with bedrooms downstairs, it keeps them cooler and makes escape far easier in the event of fire.

Minimising solar gains is the key to preventing overheating, through shading, window sizing/orientation, brise soleils, blinds, shutters, vegetation, etc. Ventilation is the other biggie, in both light and heavyweight construction. High thermal mass without good ventilation will cause more problems than it solves.

Vegetation is somewhat under-rated in its importance, satellite images of Paris during the 2003 heatwave show a strong positive correlation between lower temperatures and vegetation. Vegetation reduces ambient air temperatures and limits the effect of heat islands often created by large urban and surban areas.

Phase change materials provide one possible solution for constructing lightweight yet thermally massive buildings. Plasterboard containing micro-encapsulated paraffins is one way in which these can be used passively, in a similar manner to thermal mass. The cost maybe high at present, but this has a lot of potential as it can be used as a direct replacement for traditional plasterboard and can be used in exactly the same way.

This may read as a somewhat rambling response, but in conclusion, I think high thermal mass should be seen as one of many techniques that can be used to prevent overheating, not a necessity.

Jeff pointed out the use of breeze throughs, my experience of these is that they are very effective.
I spent 5 yrs livng in portakabins in temperatures up to 56 degrees around Meekathara in Western Australia.
Gaps were left between individual units with one large reflective roof (unpainted corrugated iron) covering a group of units.

Caravans/campers are sold with a false roof rased 4/6 inches above.

I think the problem at the moment is that the mass housing that is being constructed is both lightweight and badly designed and is being built in a way that will make it very difficult to improve in the future. I'm thinking of the insulated timber stud frames with brick skins designed to appeal to the conservative tastes of the public.

Gee Tom , lets stay away from sticks and carboard then. I hear a fridge box is the box of choice but they are hard to lay your hands on these days because of repak.
Thankfully our timber is graded and quality checked. I'll keep a look out for those sticks but.
Friends of the family live in a timber house in Sweden that is 350yrs old, it has been in its present local for a mere 150yrs.

What are the roofs of your houses made of tom?

NZ has many different climates, such as cold(-16) and dry around central otago, humid and extremely wet(annual rainfall of 30-35ft) on the south west coast, to nearly tropical(mangrove swamps) in the far north, European settlement began in earnest in the 1860's, but the Maori were building timber structures long before that.

The valley I come from has an annual rainfall of 7.5m winter mean temp of around 7 and summer of 16. It has a lattitude similar to that of southern france.

I am not aware of a building with a block/brick internal leaf being built in the area, though I would imagine there has been

Yes I completely agree with that Mark and have been regularly advocating it for a while. Nice to hear you say it but why isnt everyone doing it?

I find it strange that people contemplating building new houses are still posting on this forum asking for advice on heating systems. It does not make any sense when a building designer should know that the only way forward is super airtight and super insulation with MVHR, which means no requirement for an installed heating system. This seems to be the conclusive way forward always discussed on this forum.

Anybody building a new "green building" house today who ends up paying out for an heating system and subsequent heating bills should be able to sue the building designer for negligence because the customer has not been advised on the latest energy saving technology. They are professional people giving professional opinions which should make them liable for their advise. Can they be sued? The answer is probably yes? It is the only way to get them up to speed on the latest technology. We need architects giving advice like Mark Siddall.

I am relatively new to the building trade and I talk everyday to professional building designers and I'm staggered by the lack of understanding of the latest building envelope technologies. I gather most of my knowledge from this forum. Some building designers are not even aware of warm flat roofs.

Suing the incompetant designers might be the quickest way forward to greener buildings. Then the building designers will recommend the latest technologies because of this threat and the liability is then transferred to the suppliers/manufacturers because they know exactly how their materials perform in a building envelope and should be able exonerate themselves if their products do exactly what they say on the tin.....

A new house is not fit for purpose if its going to saddle the occupant with a heating requirement which is getting more and more expensive as peak oil approaches.

Cheers

Steve

I dont fully understand the graphs Mike but I am proposing 300mm of cavity insulation and it looks like from your graphs that this equates to a 3 fold benefit?100mm saves 2.3% 300mm saves 7% ?

I agree with Steve's point re the over emphasis on heating systems for new build. Design out the need for a full central heating system and you free up some cash to pay for the higher insulation levels etc.

I think the reason that people feel they have to install central heating systems is that self builders are taking a big financial risk in constructing their own homes and fear that the resale value of their home will suffer for the lack of central heating, even though it may be largely redundant.

The Government doesn't help by declaring that anyone without central heating is suffering from some kind of inhuman deprivation, or "fuel poverty". We never had it until I was 14 and it didn't kill me. You appreciate warmth more when you are occasionally cold.

There is perhaps also an industry developing that has a vested interest in persuading people to install "green" energy technologies when the same capital could be better deployed in good design, high levels of insulation, air tightness etc. It is a lot more profitable to sell a bolt on piece of bolt-on technology than to earn a fee for convincing someone they don't need it.

Mark, I think you would need to read the BSJ article [and subsequent ones to have a full understanding of how I have drawn my conclusions. The original Dissertation had obvious limitations , but these have been ironed out as part of ongoing research in this area.

I don't follow why you think the analysis is flawed as I have indeed compared each model to an uninsulated static base model, with the same conclusions. Other students have come up with similar results for both small scale and large scale buildings.

The methodology used is this: Take a building with a given size, fabric , heating, incidental, occupancy, lighting and solar gains. Simulate this and use it as a control- output results Then take the roof for example, add 10mm mineral wool, re-simulate- Output results. Add a further 10mm mineral wool re-simulate- output results. Repeat this procedure up to say 1000mm. The curve obtained clearly shows the diminishing return by way of percentage annual savings. Finding the optimum is the tricky part as economic and environmental factors need to be considered. I have attempted to find the environmental optimum by utilising a LCA of the embodied energy of mineral wool, but I am not sure that the manufacturers data is sufficient for this purpose. I would agree [and have previously concluded] that the optimum economic [real life] u-value in a roof is around 0.2W/m2K, maybe even as low as 0.16W/m2K given other factors such as ventilation and detrerioration of material.

Walls are more tricky, especially for masonry, increasing cavity widths requires wider foundations, more concrete,more spoil transported off site and consequently less units per plot.

I do not agree with insulating a solid floor [unless there is UFH], other than at the perimeter. I have seen Best practice u-values advocated as low as 0.1W/m2K. The optimum level for floors is nowhere near this and I do not see how it can be justified either economically or environmentally.

All of this is in a UK context