I have been toying with the idea of becoming a LEED Accredited Professional and looking at the benefits of the time and money that it requires. This is an illuminating article on the pitfalls of the system which I found very interesting…
LEED works well if you’re a wealthy person building within a Northern city. But that probably includes about 1% of the world’s population. We need a green building rating system for the rest of us.
Furthermore I found the reader’s comments entertaining and illuminating – I love the passionate expression!
I agree that LEED has moved out of the certification business and is focusing on education and accredidation. Like you, I am grossly disappointed. Having processed numerous LEED jobs it has become clear that the reviewers are based in India, have NO design or construction cridentials, and base their “review” on checklists that automatically spit-out comments compiled by lawyers who make their money being obscure. It’s a pitty that LEED went in this direction. I would have preferred a system that was streamlined enough to capture 10% of the market by now instead of a pathetic 0.5%. Fortunately, we have alternatives.
A much needed change. LEED has become the symbol of all that is wrong with sustainable building.
The LEED certification program is a massive, creativity-snuffing bureaucratic boondoggle and the enemy of intelligent & responsible site-specific and client-specific design.
I’ve never understood this rhetoric. No one rating system will be right for all different building types but LEED has helped to transform the industry and continues to do so. The USGBC is a consensus based organisation. If you think it should change, get involved. If you don’t believe in the system, don’t use it. And “gizmo green”??? Most of our highest achieving LEED certified projects have used the most passive of systems. In no way does LEED preference gizmoness. It’s not a secret that it doesn’t make sense for all projects, in all places, at all budgets. Nor does it guarantee performence. That doesn’t mean it’s not a useful system. Can’t we give this argument a rest and put our energy into improving the built environment in measurable ways?
No one likes a leaky building! You may not have thought about it before but I guarantee you have felt the discomfort of being in a draughty room. Much of sustainable building design relies of appropriate building materials and the orientation of windows and openings, these are the obvious aspects that are considered towards energy efficient buildings. However, if the building is not adequately airtight, any effort you might have made for insulation and orientation will be seriously compromised. Think about it – the idea is to keep heating or cooling INSIDE but if the nice warm/cool air is simply escaping out through poorly sealed building envelope, any insulation is rendered mostly useless. So to answer the question in the title – It is all about hot (or cool) air to achieve optimum thermal comfort at minimum cost.
Typical heat-loss pathways
The diagram above shows the common spots that contribute to poor airtightness…Junctions – roofs to walls, walls to floors; and openings – doors and windows and wall penetrations for services.
Regulations and guidelines vary on the level of airtightness required. From the best (Passivhaus) at 0.6 air changes per hour (ach) at 50Pa to British building regs at 10 air changes per hour.
Maximum air permeability
(m3/(h.m2) at 50Pa*
UK Building regulations – poorest acceptable standard
10
Building regulations indicative Part L 2010 target
7
Netherlands
6
Germany
1.8 – 3.8
Energy Saving Trust best practice
3
Super E® (Canada)
1.5
PassivHaus Standard
0.6
* Some values are actually air changes per hour @ 50Pa.
Buildings have to be constructed VERY well to achieve the passivhaus requirement of 0.6 and generally require the use of special membranes and taping to minimise air leakage. Airtightness tests are conducted during construction to check where levels are at and if more work needs to be done to achieve the desired levels (see image below)
Airtightness test carried out during construction
Where a building has less than 4 ach @ 50Pa, artificial ventilation will be required or the air quality will become unhealthy. (See previous blog post on this). Great for heat retention but bad for oxygen levels! The best systems in use are the Mechanical Ventilation Heat Recovery (MVHR) which uses heat from stale air being extracted, to warm incoming fresh air. You might be thinking, whats the point of making a building so airtight if you need energy to regulate air quality. But the energy used to run MVHR is minimal and costs about 50 pence per week and when you compare this to the reduced heating or cooling demand, there is no contest.
So, what kind of design decisions are required to achieve exemplar airtightness?
During my studies, SIGA did a workshop with us to educate us about their many products and how these should be used…
SIGA workshop at Oxford Brookes University
Membranes line out the entire inside of the building and these are fixed in place with tape and double sided sticky strips. Nails or staples should never be used as the piercings would compromise the integrity of the membrane.
All openings and penetrations are taped up:
SIGA product diagram showing where the products are used on a typical house envelope
There are typically two layers of BARRIER MEMBRANES in a good roof and wall design:
(RED LINE) the VAPOUR BARRIER (Airtightness layer) stops warm, moist internal air from getting into through the insulation and causing mould growth.
(BLUE LINE) the BREATHER MEMBRANE (Weather-tight layer) allows moisture OUT but stops weather driven air and moisture INTO the building.
It is important to note that there is a difference between AIRTIGHTNESS and AIR INFILTRATION – the former refers to gaps in the building envelope which allow valuable warm or cool air to escape. Infiltration, however, is affected by wind loads / occupant behavior / natural ventilation strategies.
Energy Savings Trust has produced a document with some good case study information regarding this subject.
Next post I will look at the problems associated with Airtight buildings, namely poor air quality and mould and moisture issues, and how these can be avoided.
One of the biggest hindrances to the construction of sustainable buildings is the extra cost incurred to achieve the improved performance. Despite the savings that one can experience during the life of the building as a result of lower energy bills, the build costs upfront are a deterrent. As building regulations improve to demand high quality, high performing, low carbon buildings, the gap between national regulations and exemplar standards (eg. Passivhaus and Code for Sustainable home level 6) is diminishing.
The LIGHTHOUSE by Sheppard Robson Architects was the first UK building to achieve zero carbon (Code for Sustainable Homes level 6) status.
The findings are very encouraging. The results show that the additional costs associated with reaching Low Carbon buildings has roughly halved since the previous report in 2011. Additionally costs are expected to continue to fall between 2014 and 2020.
At Today’s prices, the additional cost to build a semi-detached dwelling to zero carbon standard is in the region of £5000.
The elements that contribute to the zero carbon standard are as follows:
Fabric Energy efficiency should contribute the greatest componant and refers to the insulating properties of the building envelope. High performance windows and openings, well insulated roofs, walls, and floors
Low / zero carbon technologies are used to reduce energy demand from non-renewable fuel sources (gas & coal-powered electricity). These typically include solar PV (electricity), wind turbines, Solar hot water systems, and Heat pumps (ground / air-source) etc.
‘Allowable solutions’ refer to a government scheme to offset additional carbon use by investing in projects that aim to improve carbon reduction in various industries.
Continuing drop in costs associated with reach low carbon standard for dwellings. Particular reductions in cost estimates for Solar PV, air-tightness and thermal bridging components.
Reasonable additional costs are found to be:
Detached dwelling = £6700 – £7500
Semi-detached = £3700 – £4700
Apartments (low-rise) = £2200 – £2400
Costs will continue to fall from 2014 to 2020 – resulting in additional costs for detached dwellings = £5700 – £6300; semi-detached = £2900 – £3600; apartments = £1900 – £2000
These costs assume the lowest capital costs associated with zero carbon standard – this requires the use of Solar PV.
The cost of solar PV is expected to fall at a greater rate than the cost of improved building fabric solutions such that the use of PV will achieve a zero carbon solution at lower cost that a Passivhaus solution (to use an example of Advanced energy efficiency scenarios).
Cost of PV has dropped from around £3800 / kWp in 2010 to £1500 / kWp today.
Table below shows a summary of cost breakdown for the 4 different housing types.
Energy targets associated with different dwelling types:
This report is most encouraging as we strive to boost the number of new buildings (and retrofitted buildings) that are zero carbon. Thanks to the Zero Carbon Hub for this report and for making the costs associated with green buildings easier to interpret and therefore entertain.
Image courtesy of Zero Carbon Hub: Cost Analysis Report 2014
When it comes to sustainable building design, a key phrase is FABRIC FIRST. In essence this means that the primary objective when designing a green building should be exemplar wall, window / door openings, roof, floor composition to ensure that the transfer of heat between inside and outside is minimized. The INSULATION value of the building envelope.
Where this is achieved, the energy required to maintain thermal comfort indoors will be dramatically reduced. Hand-in-hand with the insulation levels, is the AIR TIGHTNESS of the building. For it would be of little value if the building had great insulation values but high infiltration such that the hot / cool air merely escaped through gaps in the enclosure.
The PASSIVHAUS standard, developed in Germany in 1990s, is a specific energy performance standard that delivers very high levels of energy efficiency and thermal comfort. With stringent requirements for the U-values of the building fabric and air tightness, Passivhaus buildings have little or no heating / cooling demand. It is widely recognized as the global leader in the fabric first approach to low energy buildings.
Benefits of a Passivhaus building:
ultra low fuel bills and much less exposure to energy price rises
unrivalled indoor comfort – no drafts or cold spots in winter
cooler indoor temperatures in summer
improved indoor air quality bringing many potential health benefits
quieter indoor space when the triple glazed windows are closed
better use of your available floor space – no radiators
lower maintenance costs – less technology to go wrong
greater building fabric durability
huge variety of styles, layouts and materials that can be employed
You will notice for the graph above that there is an energy requirement for ventilation. This is owing to the low infiltration achieved, thus fresh air must be circulated through the building. This a generally achieved by means of an MVHR (Mechanical Ventilation with Heat Recovery).
This system takes heat from outgoing stale air to warm incoming cool air. Air is EXTRACTED from Bathrooms and Kitchens and SUPPLIED to living areas such as bedrooms and lounge. (The heating of the air can be switched off in summer to avoid unwanted heat gains.)
RESOURCES
There are many websites and books that help to understand and apply the Passivhaus principles. If the certification is what you are after, you need to use the Passivhaus Planning Package which will ensure that you have met the requirements. (Buy Here)
Passipedia is a great online resource with details, links and discussion forums.
CASE STUDIES
Crossway Passivhaus, UK (Hawkes Architecture)Camden Passivhaus, London (Bere Architects)Bessancourt, France (Karawitz Architects)Oakmeadow Primary School, Wolverhampton (Architype)
Sustainable Building Design 
