The second part of our Question and Answer session on key aspects of the Code for Sustainable Homes

Get fully up to speed with the code, as Scott Sanderson answers your questions submitted at the Building webinar held last month. This week Scott, associate director at PRP Architects, fields queries on use of materials, costs, water and skills

Question 1 - Elisa Yon: Suggestions for minimizing cold bridging at steel column, beam locations with external envelope?

Answer: Cold bridging effects need to be avoided where possible by sheathing the steel frame with insulation. An interesting development in this area is the increasing use of fully encapsulated factory assembled light steel framing wall panels.

Question 2 - Elisa: What can be done to minimize cold bridging for metal frame walls with full fill cellulose insulation within cavity - within an airtight construction?

Answer: As above

Question 3 - Elisa Yon: Would you recommend using treated timber within a timber frame/ breathing wall construction - using cellulose insulation within cavity?

Answer: : There is certainly increasing interest in natural and recycled insulation products albeit our experience is that their use is not yet common in volume build delivery. A cellulose product such as Warmcell could certainly be compatible with factory assembled timber framed closed panel walling.

Question 4 - Dawn Archambault: How will considerable reductions in water consumption be achieved and still provide homes that are appealing in the market place?

Answer: : Rainwater harvesting and grey water recycling will play an increasingly significant role alongside efficiency measures such as reduced flow rates to taps, the use of reduced capacity dual flush WCs, smaller baths and water efficient showers. From a marketing perspective it is the performance of showers which is emerging as the most sensitive adjustment. Ultimately all these measures require a positive attitude a lifestyle adjustment and a practical recognition that we need to change how we use our valuable potable water resources.

Question 5 - John Wilde: Other than trendy but very costly and ultimately inefficient ECO-bling such as micro wind turbines and photovoltaics - what simple measures can you take to elevate any code rating?

Answer: The focus should first be towards passive design - improving envelope performance, sensitive consideration of solar access etc - this approach is a basic strategy to be applied at all levels of the Code. At Code level 3 the energy standards will usually require a renewables element, unless perhaps when biomass is specified. At 4 and above the renewables element becomes key to Code compliance and whilst some might consider such equipment 'ECO-bling' as long as the Code continues to focus on energy assessment at a development level, other than perhaps looking at changes to infrastructure supply or remote offsite generation, these product will be essential features.

Question 6 - Leanne Morgan: Is timber a viable material for building homes particularly in light of the recent floods etc.

Answer: Yes, but more detailed consideration is required of flooding risk.

Question 7 - Nicholas Cousins: With the amount of weighting applied, the fact that calculations have to be carried out for each unit; does the team feel these credits are to costly and will promote developers to supply material that are not sustainably/ environmentally procured and gain the required credits elsewhere.

Answer: At the higher levels of the Code it is necessary to score well across all the areas of the assessment so there will be pressure to gather points in the materials section.

Question 8 - Gurpal Johal: What is the difference between the current 'Very Good' Eco Homes rating compared to Code for Sustainable Homes Level 3 in terms of materials and energy consumption/saving?

Answer:The Code imposes a mandatory requirement that a minimum of 3 of the 5 key building elements should achieve at least Green Guide Specification D. Similarly on energy the Code imposes mandatory minimum standards which for most schemes may require consideration of renewables.

Question 9 - Kavita Kumari: Define super insulation?

Answer: There's probably no agreed definition but one might reasonably benchmark standards such as Passivehaus or the Energy Saving Trust's 'Advanced AS1' standard.

Question 10 - May eco homes use a mix of facade materials. Is it possible to achieve a high rating with "standard" brick houses ?

Answer: Yes.

Question 11 - Steve Scott: How is air leakage through electrical sockets dealt with?

Answer: The improved air permeability targets really increase focus on service penetrations which need strong strategies. The Sigma House design, for example, included a battened service zone to the inside of the external walls which enable electrics fitting and wiring distribution without penetration to the vapour/air check barrier membrane.

Question 12 - Declan Hayes: What low or zero carbon technology would you tip for success and why?

Answer: Biomass - which is a cost effective solution particularly on larger developments.

Question 13 - Kate Smith: Where would be a good resource for Architect's details for air tight junctions?

Answer:: The technical guidance associated to the Passivehouse standards is very helpful. The BRE offer detail support on air tightness as do specialist product suppliers such as Dupont.


Question 14 - Elliot Carter: Do you feel that biomass for every new home built is likely to be a problem in terms of national/local fuel supply?

Answer: At present there is adequate supply and it seems reasonable to anticipate that supply capacity might increase with increased demand. Ultimately we anticipate that energy strategy responses will continue to be varied, driven by project specific decisions, context, legislation and the rising price of fossil fuels.

Question 15 - Spencer Back: With PV units at such a high cost, what alternatives exist or are in development to produce electricity?

Answer:In appropriate settings wind turbine are an effective solution.

Question 16 - Helen Raymond: Do you think there is a danger that wood chip fuels rely on heavy transportation?

Answer: Yes, albeit wood chips can generally be sourced more readily that wood pellets. Our energy strategy assessments take local sourcing into account.

Question 17 - Darren Curry: Why should private house developers support the code when it is not mandatory?

Answer: An interesting question. Whilst it is probably correct to anticipate that many private developers will apply a commercial view and will deliver to the minimum standards required our experience at Offsite is that there are real competitive design, process and skills advantages to be gained through the experience of delivering to the Code. Looking forward and considering the 2016 target for the full implementation of the Code at level 6 it might also be the case that developers who hold back are then ill prepared to rise to the challenge later. Ultimately though the right answer is for a clearer, enforced stair cased implementation strategy to 2016.

Question 18 - Norman Morrison: How feasible would it be to include a basement and still achieve a high code?

Answer: It would be feasible and in fact some of emerging designs anticipate that basements might offer useful additional space for recycling and cycle storage and control equipment related to renewables.

Question 19 - Ian Mchugh: Any examples of urban windpower? With proper monitoring?

Answer:Yes, most recently some promising results from the Hockerton housing project.


Question 20 - Elliot Carter: Do the team have any comments on the requirements for low water consumption fittings. Do you feel that adequate supply/options for these are available for every new home built if compliance becomes compulsory next year?

Answer: Most of the 'standard' plumbing and sanitary ware is readily available - flow restrictors, reduced dual flush WCs etc. Successful, volume procurement of internal grey water recycling products appears to be a concern.

Question 21 - Noel Barrowclough: Are any developers moving onto built examples in large numbers as opposed to single proto types?

Answer: Yes, we have larger scale developments in detail design for both developers and RSL clients. English Partnerships Carbon Challenge programme is also very high profile and significant.

Question 22 - Robert Clark: In any of the Code 6 example projects described how was 80 l/p/d water use achieved?

Answer:: Through a combination of grey water recycling (ECO play used in both the Sigma House and Light House at BRE), reduced flow fittings, reduced dual flush WCs and small baths.

Question 23 - Declan Hayes: How important are low or zero carbon technology to the creation of zero carbon home?

Answer: As opposed to insulation, they are essential due to the requirement to offset electricity use.

Question 24 - Simon Baugh: From your examples of dwelling type and energy use, are you suggesting that to effectively achieve Code levels to 2016, flats and apartments are the way forward? How does this fit with the need for better communities?

Answer: No we are not suggesting this. Whilst flats offer some efficiencies (perhaps communal heating and improved HLPs for some units) they are not necessarily preferred over houses. In fact flatted developments may struggle to meet the energy requirements of the upper levels of the Code - i.e. how will the energy demands for a flatted development be offset with (probably) reduced roof area for PV relative to no. of units and (in urban locations) the various challenges to the use of wind power technology.

Question 25 - Matt Lucas: What material or product guides or manuals would you recommend to find those appropriate?

Answer: Firstly the Green Guide which is benchmark document to be used with the Code. The Green Building Bible is another useful reference.

Question 26 - David Ranson: Should planning laws be changed to protect new homes that rely on direct sunlight for energy from being 'put in the shade' by newer higher adjacent developments?

Answer: As a first response I think probably not as current consultation processes and protection of amenity and rights of light should probably cover this ground.

Question 27 - Gurpal Johal: Is it true that timber frame houses overheat more than traditional construction?

Answer: Not if solar gain is properly considered in the detail design.

Question 28 - Gurpal Johal: What are the cost implications of achieving Code 6 from Code 3?

Answer: Current thinking suggests approx £6k uplift for Level 3 over and above Eco Homes Very Good. Code 6 is estimated approx plus £35k albeit costs are of course very much dependant on local decisions on energy strategy and the scale of the development. There is very interesting and detailed guidance on this subject available in English Partnerships policy document, A Cost Review of the Code for Sustainable Homes.

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Question 29 - Michael Power: Does design life have any effect on points for the Code?

Answer: Whilst not directly referenced design life (through product Life Cycle Assessment) is part of the consideration of the Green Guide specification which feature in the materials section of the Code.

Question 30 - Adewale Adeyeye: Is there a conflict between the need to make a house to air-tight and the need for fresh air for occupants?

Answer: Potentially yes but most strategies at the upper levels of the Code will include use of mechanical ventilation and heat recovery which will actually improve air quality.

Question 31 - Michael Jenkins: What are the implications of the low air change rates required by the code on Dermatophagoides Pteronyssinus (house dust mites)

Answer: I think the Code will tend to place a positive and welcome emphasis on controlled passive or mechanical ventilation solutions. Ultimately I believe this will deliver improvements to the internal living environment. It's certainly better than living in leaky homes with

Question 32 - Michael Power: Are we learning from the experiences of other countries that are more focused on energy & carbon?

Answer: Yes. For instance PRP has organised study tours to Germany and Scandinavia to visit exemplar schemes.

Question 33 - Brendan Beck: I am amazed with the push for biomass in a country that has very little biomass growth! Where is this biomass expected to come from?

Answer: Many commentators believe that much better use could be made of existing resources - there is also room for the biomass service supply industry to expand to meet rising demand.

Question 34 - Tessa Parnell: Do you believe that we have the correct skills base at trade level to create these houses and turn a theoretical house into a practical house? Will this work on a large development where many houses are built?

Answer: There is definitely a huge skills, process and build quality challenge delivering to the upper levels of the code and there must be real concern that as a whole our industry is not yet geared to deliver to these standards. For this reason we welcome the stair cased implementation of the Code. Events like Offsite and project initiatives like English Partnership's Carbon Challenge will continue to be significant in driving the agenda forward and in providing tangible, accessible examples for others to learn from.

Question 35 - Kenneth Jenn: Are Hydrogen Fuel Cells on the horizon and would they be practical?

Answer: Hopefully the answer is yes on both counts.

Question 36 - Stephen Vaughan: Can you build a code 4 home of 1150ft2 for £60K or is the £60K house now unachievable given the new code?

Answer: I would imagine Level 4 compliance would be a very significant cost challenge (say circa £12k) on any £60k house.