All posts by Ross Barrett
This week the fitting of our windows and external doors has been completed and, although they took a little longer to fit than first expected, they do look fantastic and mean that our envelope is now wind and watertight.
In terms of our Passive House standard, the windows and external doors play an extremely important role in the overall envelope, maintaining a fine balance of contributing to the high performance envelope (windows and doors have U-Values of 0.8w/m2K) but also importantly allowing solar gains into the spaces which help reduce space heating demand.
The units we chose to use are Internorm ‘Edition’ windows and doors from Austria (supplied through Dynamight Internorm in Rosyth) with the glass-to-glass corner windows made to the same specification from Bohler Fenster in Germany. They are both high performance composite timber/aluminium windows which are triple glazed (using high performance spacing bars) and are already Passive House certified by the PassivHaus Institute in Germany. The two glass-to-glass jointed corner windows allow some really good views and a nice visual connection back up to the heart of the expo site, the village green.
As the windows were being completed the team was able to begin a very patient and intense final check on wall, floor and window/door junctions with RTC Timber on site again for a few days. Air tightness is crucial to the effectiveness of the Passivhaus. The connections between the various components of the building, such as the floor-to-wall, wall-to-roof or window junctions, are often the areas where air leakage can occur, as movement between the different materials can lead to air loss. The air tightness of the building is also essential for the MVHR unit to run efficiently.
Alan from RTC did a fantastic job with a couple of O’Briens joiners over 3 or 4 days and I think they must have cleaned the local supplier out of EDPM and foil tape!
We used a self adhesive EPDM film to seal wall panels and floors and a self adhesive foil to seal window, door and other small junctions. We also used some polyurethane foam to fill some small awkward joints around timber junctions etc. On a standard project, silicone would normally be used to seal many of these junctions, although this only works for a relatively short period of time, eventually breaking down with the expansion and contraction of materials, whereas an air tightness tape such as Illbruck will accommodate that movement. The tapes and foils we used were all carefully specified using RTC’s own experience and were chosen to last and perform over the lifetime of the building.
Internally the high performance vapour barrier was also carefully taped and sealed. This will be left intact with minimal penetrations - all services will run in a clear 20mm service gap on the inside of the frame. Any staples or nails through the membrane are deemed to also close off and seal the membrane again.
As we arrived on site, final preparations were being made for the air pressure test (or blower door test). Passive House certification requires our building to have an air permeability of 1m3/hr/m2 or less (equivalent to an air tightness of 0.6 air changes) at 50 Pascals (Building Regulations standard is currently 10m3/hr/m2). The air tightness is tested by closing all openings to the outside such as windows, doors, Mechanical Ventilation Heat Recovery (MVHR) intake and extract vents and any other outside penetrations such as waste connections and slab penetrations, and with a variable speed fan fitted to an adjustable frame in the external door opening. By controlling fan speed, the internal pressure is lowered by 50 Pascals from the external pressure which mimics a wind speed against the building of about 20mph.
The fan is then used to pressurise and depressurise the building. The airflow rate that is required to maintain a number of particular pressure differences across the building envelope is recorded and measured – with the leakier the building, the more air flow required to maintain a given pressure differential.
With a bit of tweaking initially with fan speeds etc we got a first reading of just over 1m3/hr/m2 meaning we weren’t far away. By carefully examining junctions around the first house we were quickly able to identify where small areas of leakage occurred and were able to use some additional tape or foam to seal these areas. We were also able to do a smoke test and by going round some small vulnerable areas we could quickly identify where there were very small air leakages some of which can be resolved later by small adjustments in door or window openings etc…
The 3 main areas where we found air leakage were:
- Around 2 of the window frames where it appears the seals may not have been installed as well as they could have between the window unit and the timber frame.
- We found some very slight leakage around the seals on the large sliding doors – maybe a lesson not to specifically use these in passive house however we hope that these can be adjusted slightly to increase air tightness.
- Once the house was pressurised, some of the air seal tape to the upper floor cassettes was coming loose. We corrected this by using some temporary tape but think in future we might use a spray adhesive on the OSB prior to sticking the air seal tape down.
In the end, we achieved an average result of 0.92m3/m2/m2 (on the first house) which we are all really happy with. Whilst we may have all been hoping for something a little more significant given all our hard work, this is what we need to achieve our passive House certification and in that respect we are all delighted and relieved! It took some time to set up the other units and catch some small areas of leakage but all units passed the test! Our tester believes that our units are in the top ten of air tight residential buildings in the UK.
Once plaster boarding and other second fix joinery work and finishing has been completed, we hope that this figure could be significantly bettered although we are not required to do a second test for Passive House certification.
I think it’s fair to say that this result wouldn’t have been achieved without the great working relationship we have had with timber frame supplier RTC and the main contractor O’Brien properties. Throughout the process, all of the team has understood their part in the process and have given their commitment to get the air sealing and envelope right. This was really only brought about by the early inclusion in the process of both RTC and O’Briens. In the end however it has been a learning process for us all and will be easier next time round!
The external cladding works are just about complete with the timber and vertical profiled sheeting looking pretty sharp, although there are a few small niggling issues with the timber cladding and the way it has been set out. Roof cladding and flashings are also complete.
We met recently with Steph Marsden from Craft House Concept who we are talking to about exciting ways of furnishing one of our units for the duration of the expo. Hopefully we can showcase some great contemporary Scottish made furniture and promote some great young furniture designers.
Some other great news recently on the funding of our landscaping, with confirmation that one of our gardens will be completed in line with our original sustainable garden concept.
Look back 10 to 15 years and there was little or no mention of the term sustainability or zero carbon amid the architectural or construction press.
In 2010, it seems we can’t now escape the concepts of ‘low energy’ or ‘sustainability’ and it seems that the industry has come a long way (at least in terms of thinking and awareness) in a relatively short time. Arguably, however, the industry needs to do a lot more to meet the increasing regulations and expectations being forced upon us all.
The climate change agenda and the UK government’s response have fuelled a number of publications, guidance documents and legislative requirements in the last few years climaxing recently with our own Scottish Government’s vote to cut C02 emissions in Scotland by 42 per cent by 2020 (the most ambitious targets in the world).
This leads us to ask whether or not we as an industry have a long term workable solution to respond to much of this guidance or indeed the likes of the Code for Sustainable Homes in England and Wales or the Low Carbon Building Standards Strategy for Scotland (‘the Sullivan Report’), which urges the target of zero carbon homes in Scotland by 2030?
The Sullivan Report certainly encourages some bold responses and makes many sensible suggestions some of which we are beginning to adopt in forthcoming building standards. But how about we just adopt the old adage “build tight and ventilate right”, which must be achievable within the realms of developer house building? We probably need to accept that the zero carbon ambition (or net zero carbon as it more likely will be) may not be readily achievable without expensive renewable add-ons likely to be entirely cost prohibitive to the mass market housing industry.
The issue for us is to try and understand just how the Passive House model (a development of ‘build tight and ventilate right’) might offer us a low carbon solution and look at how we might learn from Germany and adapt its standards for the Scottish climate. We hope that our work on the Passive House project at Scotland’s Housing Expo might inform or even inspire the industry towards a workable and realistic solution for future low energy housing.
Of course, it’s generally accepted that a low energy building, whether a house or a multi-storey office, will have a greater capital cost and Passive House is no different. Although, as yet, we lack specific cost data on any completed Passive House projects in the UK. It’s generally acknowledged that a Passive House construction could cost between 10-20% more than a equivalent conventional new build house. Predominantly, the additional capital expenditure is invested in an upgraded building envelope including additional insulation, higher performing windows and a greater attention to air tightness as well as a basic MVHR with small diameter supply and extract ducting throughout the house.
To consider however that this investment reaps an 80-90% reduction in energy consumption and, in the context of rising energy bills (the average household bill recently cited as £1,000 per annum), the capital costs are eclipsed by the potential energy savings over the lifetime of the Passive House.
Combining this with increased comfort levels and a dramatically improved indoor air quality, it is clear that there are a number of significant benefits to Passive House which you can’t necessarily ‘put a price on’ or calculate the benefits of directly through life cycle analysis.
With most Passive House projects to date seemingly restricted to one-off self build projects (other than at Dunoon built by Fyne Homes Housing Association), it appears that the model is not yet attractive enough to the developer driven residential market in Scotland or indeed the UK.
But can the Scottish Futures Trust (SFT) and its newly devised National Housing Trust (NHT) be bold enough to take on the Passive House model? With a recent announcement of over 1,000 homes to be built in conjunction with 10 local councils, is the NHT not best placed to insist on a low energy housing model which meets the Government’s own future energy and emissions targets and which has as built performance at its heart, rather than ‘eco-bling’?
We believe that with increased experience, understanding and potential larger scale Passive House developments (where repetitive elements are increased), it will be possible to reduce the costs of passive house construction within the affordability envelope of developer housing, of course perhaps relying on an increased market value for a better quality, lower energy, cheaper running housing product.
We have begun speaking to local councils, housing associations, care home providers and even forward-looking developers who want to know more and who want to be well placed to deliver Passive House on a bigger scale, perhaps when the market or legislation eventually demands it.
With the Timber frame essentially complete, the joinery team has begun the task of cladding the buildings. Due to the delay with the windows, we’ve had to carefully look at the sequencing of this as normally the windows would have been installed prior to any cladding works. Our detail is for a build up of 50x50mm battens and 50x50mm counter battens which support a locally sourced horizontal larch boarding from Russwood in Newtonmore. Due to the open profiled nature of the boards we specified, we also had to wrap the Soft Wood framing in insect mesh to prevent insect ingress. The boards will eventually conceal an external rain water downpipe as well as the extract and intake vents for the MVHR system. We have broken up the horizontal boards into panels which are defined by the vertical larch boards at the jambs of the window and door openings.
The detailing of the timber cladding took some time to resolve, including numerous discussions with Highland Council to agree on the form of cavity barriers. Building Control unfortunately wouldn’t accept our initial proposals for an intumescent or flexible type barrier, which would have assisted with the drainage, ventilation and drying of the cladding boards, and instead stipulated that all cavity barriers were to be of a solid type.
Dynamight has also been on site to install the first fix of the MVHR ducting layout. We had to coordinate this layout with the structural engineers and timber frame manufacturer to ensure that the holes for the ducting were cored in the correct places within the I-joists and glulam beams. Dynamight has done a neat job and with this in place the first fix electrical and plumbing elements can proceed. The intake and extract vents have also been fitted to the external walls but will require some additional insulation to be replaced around these and fully taped internally to ensure a tight air seal. We also need to fully seal the ducts off prior to the initial air pressure test. When the final test is done however the balanced vent system will be fully operational and connected to the MVHR unit.
All the lead work has been completed on the roof and the bespoke, pressed aluminium gutters are now in place awaiting the fixing of the Marley profiled roof sheeting. Despite wanting to achieve a concealed gutter, we took the decision to keep the gutters and their outlets outwith the airtight envelope – ensuring that if there are any problems in future with leakage/ failure that it will occur outwith the envelope.
Despite some minor problems with the painting of our roof sheets at the Marley Factory, it looks like our roof sheeting is still due to be delivered in the next week. Panic ensued when we realised that the factory was about to shut for a week, but thankfully they did enough to get our sheets through the painting line before the shut down!
We originally wanted to use a recycled aluminium profiled sheet on the roof but struggled with sourcing something of the right appearance and quality. We instead turned to Marley’s profiled fibre cement roof sheeting as we felt it still fitted with the rural aesthetic we were trying to achieve. We have since seen it used on some interesting small scale housing projects in the highlands and islands. Whilst work progresses on site, we are also continuing to push to find some sponsorship in order to realise one of our gardens which will be planted with local species to enhance wildlife habitats and encourage biodiversity, whilst allotting space for food production and composting. The Highland Housing Alliance has appointed Gerardine and Wayne Hemmingway to design a number of other gardens across the expo scheme, however our ‘sustainable’ garden was part of our competition scheme and with our in-house Landscape Architects, we hope it will become a showcase for sustainable landscape design delivered in conjunction with local suppliers and assistance from the Highland Housing Alliance. We now have a definitive date for delivery of the external windows and doors from Austria and have a team of both local and more experienced German fitters lined up to start fitting as soon as possible. As soon as the windows and doors are completed (which we think will take about a week), the team will do a final walk around to inspect every window, wall and floor junction to ensure that everything has been sealed as detailed (and maybe even sealed a bit more)! We then expect the first air test to be carried out – so fingers crossed!
Our competition design for a bio-diverse landscape
It seems winter in Inverness might just be over and work on our Passive House is gathering pace.
The Spring snow did eventually clear and allow our groundworks team to complete the last of the substructure works. With the underground drainage now in place and a local Building Control inspection complete, the 200mm of under slab insulation was laid and the stepped concrete slabs poured.
In line with our wall and roof constructions, we made sure that our ground floor build up achieved a U-Value of 0.1W/m2K and chose to specify that the 150mm ground bearing concrete slab had a power floated finish. A good smooth finish to the slab edge is key to allow us a good adhesion for our perimeter air seal tape, which will eventually give an air tight joint between our timber frame and ground floor slab. The weather of course still managed to hamper the laying of the slab and the contractor didn’t have the full opportunity to give the slab the finish so we will now need to put a thin layer of screed on top to get the smooth finish needed.
We also put in place a small run of duct from the rear garden of each unit which will eventually carry an insulated pipe from a small Air Source Heat Pump (ASHP). This will help deal with our domestic hot water (DHW) demand within the stringent energy parameters of the Passive House approach. The ASHP will also supply a small heating back up in the form of a wet heated towel rail system in the bathrooms although from our calculations and simulations it is unlikely this will be required to meet any of the primary heating demand. With the number of slab penetrations, we are constantly mindful that each of the penetrations need to be carefully sealed to maintain the high levels of air tightness we are aiming for.
After a short period of the slab curing, the passive wall plates were fixed in place over the Damp Proof Course on top of our aerated concrete block. The O’Brien’s team began to erect the timber panels from the top of the site downwards, with the ground floor panels of each unit lifted into place first followed by the Glulam beam elements, the load bearing spine wall and the 300mm deep first floor cassettes.
The first floor cassettes were orientated to allow for the main 100/125mm diameter duct runs within the floor build ups. They were a key element of the build and were potentially the most time consuming in the timber frame programme. Our Timber Frame Supplier RTC suggested that these may have been the trickiest floor cassettes they have designed and manufactured in the passive wall system but the ease with which they slotted together was a testament to the design team collaboration and the minimal tolerances that RTC manufactured to.
I recall an early design team meeting at Internorm in Dalgety Bay where we asked Alastair at RTC just what tolerances we should be designing to for the timber frame elements. It was met with the response…. “we don’t like tolerances…we like to get it spot on!”
The first floor wall panels were then erected on top of the first floor cassettes, followed by the loft floor Glulam beams and loft floor panels which were similar in design and layout to the first floor panels. The roof panels were the last of the timber frame delivery but slotted in fairly well and fairly quickly, with the whole timber frame erection sequence for the three units taking only nine days.
Next in place were our Fakro triple glazed rooflights which achieve a u-value of 0.9W/m2K and were the best thermally performing rooflights we could get our hands on.
Although the Passive House team at SPHC advised us against the use of rooflights as it’s not the norm for Passive House construction in Germany, we believed it was important for us to stick to the original concept of the top lit double height living space.
Our very first go at reviewing the scheme with the Passive House Planning Package (PHPP) software did show that the rooflights might cause us some problems with compliance due to the heat loss through them.
However, with some small adjustments to the external building fabric in order to increase the envelope U-Values the PHPP software showed that the incremental increase in insulation would allow us to achieve compliance with the roof lights remaining in place. Much like the other glazed elements we had to look carefully at the air seal and thermal bridging details at the roof light but by using an insulated kerb detail and using a similar air seal tape to the windows and timber frame joints we should successfully achieve the correct levels of air tightness with limited thermal bridging.
Stranded for two weeks in the Canary islands thanks to Iceland’s ash cloud, it seems all has gone well in my absence and progress has been swift. The intention now is to make a start on the timber cladding and roof sheeting ready for the arrival of the windows in early June.
Through 11 sets of road works along the A9 we finally made it to site to find that the weather had been a little kinder to our team at O’Brien Properties and, with all of our concrete strip founds in place and two thirds of our sub-structure walls complete, we could start to appreciate the scale of our terrace and its relationship to some of the other units on adjacent plots.
For the sub-structure, we are using an Aerated concrete block to help significantly with our U-Values and thermal bridging. A common concrete block wall would not have provided us with sufficiently low thermal conductivity or indeed a suitable fixing base for the wide prefabricated timber panels which need to be anchored down to resist the significant wind loads experienced on such an exposed site.
We did consider importing a unique German foundation system called ‘Isoquick’ which uses modular foam blocks to create a foam ‘tub’ into which the concrete slab can then be poured. It was ideal for Passive House construction but we couldn’t satisfy ourselves that it could deal with the stepped profile of our terrace or more importantly the significant wind loads it had to withstand. We have however decided to do some more research into this product for our next Passive House project as it would minimise many of the cold bridging issues we have come across. In the end we went for the best solution available in the wide format Aerated blocks although I don’t think we’ve been the brickie’s best friends!
Given the stringent standards for thermal performance in Passive House construction we have had to accurately model every junction to understand and predict the heat loss of the buildings accurately. This was done in conjunction with the Scottish Passive House Centre using the Passive House Planning Package (PHPP) software, a widely accepted energy design tool for Passive Houses which is frequently updated with numerous years of experience from built Passive House projects. The tool itself is fairly complex but helped us to look at every heat loss and heat gain associated with thermal conductivity, thermal bridging, air-tightness, ventilation, solar gains and internal gains. PHPP very simply establishes a number of rules and conventions against which we can test our design. For us it simplifies the design process and the route towards the eventual Passive House certification. It’s far more advanced and relevant than the current UK norm, the standard assessment procedure (SAP).
RTC have more or less finalised the manufacture of the timber frame panels with only the roof panels to complete, set for delivery soon. Whilst we were on site RTC made the first delivery of their patented Passive Wall Plates which act as wall plates for their Passive Wall system and help achieve significant air tightness in the wall panels. We have talked about the lead in times on the window delivery and have decided that the timber frame openings will need to be covered sufficiently to allow some first fix works internally to proceed. We also think we can get the triple glazed roof lights in, the profiled roof sheeting on and some of the external wall cladding framing commenced before we absolutely need the windows and doors!
The block work is complete this week and the drainage is in place and our insulation and concrete slab is in place awaiting the Passive Wall panels.
Progress varies around the site with most ground works underway and even some timber frames complete.
The snow returned again though and the site looked as though it’s the middle of winter again. We can’t believe the impact the weather has had on this project this year but everyone’s still confident everything will be ready in time! I wonder if there’s some snowmen being built just out of picture?!
Our first visit to site this week made for positive viewing with some plots a hive of activity and, with a number of timber frames in place, the shape of the Expo community is vastly becoming reality. Those who managed to get out of the ground before or between the snow have managed to make some good progress.
There was still no concrete flowing on 11 but the large scale timber formwork for our rather tricky concrete footing and retaining wall detail was in place and awaiting better weather.
The last week has seen final discussions on timber frame prior to going into manufacture in Elgin by RTC and arrived on site at the end of March, although it looks as though the delays caused by bad weather may stretch that slightly. We are using RTCs Passivwall system that was specially created for building to PassivHaus standard and ours will be the 3rd scheme to use the system after Bethania in Dunoon and Midmar in Aberdeenshire. We’ve been working closely with Buro Happold and Alastair Rennie and his team at RTC to get the most out of the timber frame system and resolve some challenging structural issues like the corner cantilevers which will help form the distinctive architecture of the units. Our external walls will achieve a U-Value of 0.1 W/m2K and help us achieve an air tightness 10 times better than current building regs.
Finalising the timber frame manufacturing drawings have also allowed us to do a final check on window sizes and specifications and push through the Window order with Internorm in Rosyth, who are importing the window and door units from Internorm’s manufacturing base in Austria. With external windows and doors so critical to the PassivHaus strategy, it was important for us to use a tried and tested product that was also PassivHaus certified. The windows and external door units achieve a 0.71W/m2K U value. It is unfortunate that we couldn’t source anything with such a good U-Value or indeed PassivHaus certification any closer to home although we have talked with Internorm in Scotland about their plans to hopefully start manufacturing the same system using Scottish materials and Scottish Labour in the future. Windows could be 8-10 weeks so a bit of a risk to programme but isn’t that always the way on Grand Designs?!
The first and most obvious progress arriving on site is on plot 5 by JM being constructed by Robertson Highland where timber roof panels are being put in place and also at plot 4.2 by Andrew Black and William Gray where the timber frame and distinctive curved roof is being completed.
Since winning the RIAS competition in May 2007, nearly 30 architectural practices and design teams including ourselves at HLM Architects, have been working immensely hard with the Highland Housing Alliance to make the vision of Scotland’s Housing Expo a reality.
Somewhat against the tide of the recent financial climate and the freezing winter weather, work commenced on site a few weeks ago with a consortium of five local Highland contractors (O’Brien Properties, Robertson Highland, Morrison Construction, William Gray and Tulloch Express) and James McQueen Builders of Skye. Over the next few months, we will be posting regular blogs on the construction progress of the expo project as it advances towards its official opening just five months away in August this year.
The construction of our own three units began on site with O’Brien Properties amid the latest snow blizzards to hit the Inverness area. Whilst the site has been levelled and set out, the holes in the ground have seen more snow than concrete due to the sub-zero temperatures, but then the weather gave us some welcome relief and in turn some more substantial progress.
When complete later this year, our three units will become only the second certified PassivHaus scheme in Scotland and still one of the first few in the UK. Our homes aim to use at least 80% less energy for space heating than the average UK house and will aim to demonstrate the benefits and appropriateness of the PassivHaus concept in the Scottish and UK climate.
Our scheme is one of over 50 homes on the site set within an innovative masterplan by Caddell2, which collectively hopes to truly raise the bar for Scottish and UK housing. We hope that over the next few months we can illustrate the progress of some of these schemes moving towards the public event in August 2010 and more importantly towards the legacy of the expo community beyond.
Work has started on HLM Architects’ competition-winning sustainable housing design, which will form part of the UK’s first sustainable housing fair, Scotland’s Housing Expo. The event, being hosted in Inverness in August 2010, is based on a successful Finnish model, and showcases environmentally friendly innovation in residential design and construction.
HLM has designed a terrace of three-bedroom homes which meet the Passivhaus standard for energy efficiency. Passivhaus is a concept from the late 1980s and the first Passivhaus was built in Darmstadt, Germany, in 1990. The design standard has been taken up across the continent and, as of 2008, 20 per cent of Austria’s new housing stock meets the standard.
HLM’s terrace, one of the first Passivhaus schemes in the UK, will achieve an 80 per cent reduction in energy consumption with the average heating consumption as low as 1,430kWh – less than a tenth of the usage of a comparably sized home under current Building Regulations. This has been achieved by careful orientation, shape and compact form, taking advantage of the climate and solar gains and using a pre-fabricated closed panel timber frame system from RTC to achieve a super insulated building fabric; u-values for walls, roof and floor will achieve 0.1W/m2K with highly efficient Passivhaus certified triple glazed windows from Internorm achieving u-values of 0.71W/m2K.
The units utilise a balanced mechanical ventilation system with 88 per cent efficient heat recovery in place of a conventional heating system – this not only vastly reduces heating bills but also provides cleaner, fresher quality of indoor air free from pollutants.
Careful attention has been paid to achieving airtight design in close conjunction with the timber frame manufacturer; RTC, and the Scottish Passivhaus Centre to achieve a significant reduction in ventilation heat loss, with a target of at least 10 times better than current Scottish Building Regulations. This will be guaranteed by on-site air tightness testing as soon as the envelope is complete with a further test on completion.
Materials, such as the FSC-certified larch timber cladding for the external walls, are being sourced locally, and off-site prefabrication will reduce pollution, waste, transport and construction time significantly. The gardens are being landscaped with local species to enhance wildlife habitats and encourage biodiversity, while allotting space for composting and garden agriculture.
More than 30,000 visitors are expected to attend the SHE in August 2010, which is being billed as ‘The single most important architecture and design event to take place in Scotland over the past decade’. Whilst the individual houses, numbering over 50 in total, will be the core of the expo event, there will be a series of supporting exhibitions, talks, seminars, and themed events, in which HLM will be playing a key role.
HLM’s terrace of Passivhaus eco-homes, along with the expo’s other sustainable homes, will be part of the legacy of a living, breathing, contemporary village which hopes to act as a model for future housing design and development. They will also be available for sale or rent at the end of the housing fair, so three families will soon be enjoying a far cheaper and greener cost of living.
Ross Barrett is project architect at HLM