This beautiful 14 unit development is affordable, sustainable and built to last.
Passivhaus, or Passive House, is becoming so popular that it is getting hard to keep up with all the fascinating projects being done around the world. Inhabitat points us to this one that I somehow missed in Norfolk, UK that shows how far Passivhaus has come to be almost mainstream. There are a number of unusual aspects to Carrowbreck Meadow.
First, it was developed by Broadland Growth, a private development company put together by the Broadland District Council and the Norfolk County council, so it is sort of but not quite public housing. Some are rented; some are sold on a shared equity basis. The fourteen units were built to Passivhaus standard because "it means reduced need for space heating and higher levels of comfort and wellbeing. The carbon reduction is also good for the environment – which means everyone benefits. And for the local community, our homes both enhance the area and provide an affordable option for people with who live or work in Broadland."
The houses were designed by Hamson Barron Smith, a multidisciplinary 130 person firm of architects, engineers and consultants, not the usual kind of firm one usually sees designing small Passivhaus projects.
Being a sort of social housing, "maintaining the highest public sector values", 43 percent of the site is devoted to affordable housing. They look good too;
The design response is a contemporary rendition of a well-established and local typology, a ‘Norfolk style’ –defined by a number of references to the historic barn vernacular seen throughout the county. A material pallet of white render, black stained timber cladding and either slate or plain red roof tiles also reflects the materials used in the adjacent Carrowbreck House.
Trees and Passivhaus don't always play nice together, since solar gain is often calculated in as a source of heating. However, early Passivhaus designs often overheated because of too much gain in the summer; so in this case, the windows are relatively small (Passivhaus windows are expenisive!) and bigger ones facing south are shaded.
The properties have been carefully grouped so the development sits comfortably in its woodland setting. The positioning and orientation of the homes maximises the access to solar gain in winter and prevents overheating in summer.
There are very good reasons for building social housing to the Passivhaus standard- "The scheme has created comfortable healthy homes which are affordable to run, eliminating fuel poverty, future proofing these homes for the demands of our changing climate."
The project was built on a tight budget and schedule, so the architects have used some interesting innovations including Porotherm clay blocks with a "unique interlocking design rules out the need for mortar in the vertical joints and consistent manufacturing quality allows for true 1mm bed joints. Used successfully for decades across Europe." According to the architects brief, it is faster and comes with a design life of 150 years.
Then the exterior is insulated with another product I have never heard of, Baumit Open expanded polystyrene insulation, which is vapour permeable so that no moisture gets stuck in the clay brick. Lime plaster is used (and a big heat recovery ventilator) to ensure perfect indoor humidity." That is a substantial wall.
The roof design made me a bit nervous at first. It is built up of a Finnjoist I-beam made from oriented strand board (OSB) with flanges made from Kerto LVL, and filled with Warmcel, cellulose insulation made from recycled newspaper. "The airtightness layer was installed as an OSB3 board with taped joints." According to the section, there is also a layer of Pro Clima smart vapor retarder.
I thought it funny that they design such a solid, conservative wall made of clay and designed to last 150 years, and then build a roof that is made of glue, wood chips and newspaper.
Where the wall appears to be designed to breathe, the roof has no air space, nowhere for moisture to go if it gets into the cellulose. I must be missing something here, and look forward to the comments from the experts. UPDATE: There is an air space above the "breathing membrane", battens and counter battens, and I am advised this is considered sufficient. When I practiced Canada, code required 6 inches of vented space so I was nervous but all the experts tell me that it is fine.
But other than my vague and probably uneducated concerns, it is a truly lovely project. A resident says "we all now have amazingly wonderful sleeps at night which we believe is due to the air quality. The consistent temperature of this house is perfect.” Another resident says it costs almost nothing to heat. The architect writes that "Carrowbreck Meadow has delivered an important benchmark for future developments by demonstrating best practice in the design, layout and construction of affordable units within housing developments."
Social and affordable housing doesn't have to be crappy; we can have nice things.